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Green Synthesis of Gold Nanoparticles Coupled with Nucleic Acid Oxidation

Tatsuki Kunoh^†^‡

Minoru Takeda^§

Syuji Matsumoto^†^‡

Ichiro Suzuki^§

Mikio Takano^†^‡

Hitoshi Kunoh^†^‡

, and

Jun Takada^*^†^‡

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^†Core Research for Evolutionary Science and Technology (CREST), Japan Science and Technology Agency (JST), and ^‡Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530, Japan

§ Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan

*Phone/Fax: +81-86-251-8106. E-mail: [email protected]

Cite this: ACS Sustainable Chem. Eng. 2018, 6, 1, 364–373

Publication Date (Web):October 5, 2017

https://doi.org/10.1021/acssuschemeng.7b02610

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Abstract

Green synthesis of metal nanoparticles, especially gold nanoparticles (AuNPs), has attracted the great interest of scientists and engineers in the medical and pharmaceutical fields; thus, a variety of ecofriendly, energy- and cost-saving techniques have been developed. In this study, we found that cells of Leptothrix (iron-oxidizing bacteria) released extracellular RNA some of which could exist as a constituent of the cell-enclosing sheaths. As a part of studies of metal encrustation in the sheaths, here we show that RNA prepared from the Leptothrix cells can reduce Au(III) and spherical AuNPs eventually form when an aqueous HAuCl₄ solution is added under ambient conditions. RNA and DNA of other organismal origins have the same ability. Of the nucleosides and nucleobases, only guanosine and guanine can form AuNPs. The DNA moiety, 2′-deoxyguanosine (dG) (used as a reference material), forms AuNPs when mixed with HAuCl₄ solution, but 8-hydroxy-2′-deoxyguanosine (8-OHdG) does not, indicating that AuNP formation evidently depends on the reduction potential of the guanine moiety, not the sugar moiety. This finding is the first demonstration that spherical AuNPs of ca. 5 nm diameter can be obtained by simply adding guanine to HAuCl₄ solution at ambient temperature; no other chemicals or physical treatments are needed.

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Synopsis

Here we report Au(III) reduction to form gold nanoparticles (AuNPs) coupling with oxidation of the guanine moiety of nucleic acids (RNA and DNA).

Introduction

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In recent years, metal nanoparticles such as gold, silver, platinum, and copper have attracted the attention and interest of engineers and scientists for specific physical and chemical properties such as their size-dependent surface-plasmon response.(1, 2) Gold nanoparticles [actually, nanoclusters of gold nanoparticles (hereafter referred to as AuNPs)] and nanorods have promising applications particularly in fields such as biology,(1) biomedicine,(3-7) and catalysis.(8) Diverse physical techniques such as thermolysis and irradiation with ultrasound, microwaves, γ-rays, or electron beams(9-14) are often used to synthesize AuNPs, but they can also be produced chemically through the reduction of cationic Au(III) by a reducing agent such as sodium citrate, ascorbic acid, or sodium boron hydride.(15-17) During these processes, undesirable aggregation of AuNPs is prevented by additives such as thiolate surfactants for dispersion in liquid and metal oxides as solid supports.(18-23) Since such chemicals may contaminate the finished AuNPs through infiltration and/or capping and are often toxic to organisms including humans, the use of toxic chemicals to produce AuNPs greatly limits applications in biomedical fields, especially for clinical purposes.(1, 3, 18)

To avoid such risky and costly processes to synthesize AuNPs, scientists and engineers are focusing on green chemistry to harness the biological potential of physicochemical interactions of organisms with surrounding inorganics, such as redox interactions. For example, extracts from organisms (lemongrass, tea, and brown algae),(24-26) human and microbial living cells,(27-31) and biomolecules such as proteins, sugars, and adenine(32-34) have been reported to be beneficial for producing AuNPs through the reduction of cationic Au(III). To take one instance, Zhang et al.(4) biosynthesized nanoscale Au–Ag alloy using chloroplasts as reducers and found that chloroplast proteins attached to the alloy surfaces through free amino groups (NH₂). However, the detailed mechanisms for Au(III) reduction by these biological materials in the context of redox reactions remain largely elusive: which molecules are responsible for interaction with Au(III) and its reduction to Au(0)?

Among the organisms with promise for “green chemistry”, Leptothrix species, which are aquatic iron-oxidizing bacteria, produce microtubular organic–inorganic sheaths that encase their cells. The skeleton of an immature sheath, consisting of organic exopolymer fibrils of bacterial origin, is formed first, then the sheath becomes encrusted with aquatic-phase inorganic materials.(35) Recently, we found that the expolymer fibrils excreted from L. cholodnii SP-6 (hereafter SP-6) can sorb Au(III), although the detailed mechanism remains elusive.(36) Among the glycoconjugates (with uronic acids, amino acids, amino sugars) and lipids that comprise these fibrils,(37, 38) the amino sugars participate in sorption reactions with metallic cations through chelation with the functional groups NH₂ and OH.(11, 39) We have also had an interest in metal sorption by nucleic acids, because the carbonyl group of the nucleobases guanine and thymine are binding sites for the formation of metal–DNA complexes.(40-44) In most earlier methodologies concerning AuNP formation using biomolecules, irradiation with an electron beam or use of a reducing agents was required to reduce Au cations.(11, 41)

Recently, we found that the sheath remnants of SP-6(45) contain RNA and that SP-6 cells release a remarkable amount of extracellular RNA into the culture medium (see Supporting Information Figure S1). This finding led us to postulate that, if RNA is one of the constituents of immature sheaths, extracellular RNA could be involved in metal encrustation of sheaths. Here, we first examined the ability of RNA prepared from Leptothrix cells to chelate Au(III), then searched for critical factor(s) in the RNA moiety that may be involved in the reduction of Au(III) and formation of AuNPs. Our findings have helped us to understand more deeply the process of AuNP formation by the moiety of nucleic acids and their related molecules.

Experimental Section

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Preparation of RNA from Leptothrix Cells

Cells of Leptothrix cholodnii SP-6 (ATCC 51168) (hereafter SP-6) from frozen stock cultures were streaked onto MSVP agar plates(46) and incubated at 20 °C for 7 days. Single colonies were transferred separately to 25 mL of MSVP and precultured on a rotary shaker at 20 °C and 70 rpm. After 2 days, 1–5 mL of the cell suspension (adjusted to 10 cfu/mL by densitometry) was added to 500 mL of MSVP in each of four 1 L flasks, followed by shake culture for 2–3 days. Cells were then harvested by centrifugation at 3400g for 5 min and washed with ultrapure water (hereafter UPW) at least 4 times. The resultant cell pellets were added to a mixture of 25 mL UPW and 25 mL of Isogen-LS (composed of acid guanidinium thiocyanate and phenol; Nippon Gene, Tokyo, Japan), vigorously mixed by a vortex mixer (Scientific Industries, Bohemia, NY, U.S.A.), then rested for 5 min at room temperature. After 1 mL of chloroform (Nacalai Tesque, Kyoto, Japan) was added, the cell suspension was again mixed and rested, then centrifuged at 14 000g for 30 min. The resultant supernatant was carefully collected, dialyzed against 2 L of UPW at least four times using a Slide-A-lyzer dialysis cassette (Thermo Scientific, Waltham, MA, U.S.A.), and then freeze-dried. Because the combination of Isogen-LS and chloroform is the commercial reagent for RNA extraction, the final freeze-dried sample was expected to consist of RNA (tentatively referred to as the GTPC fraction).

Analysis of Sugar Composition in the GTPC Fraction

To examine the purity of RNA in the GTPC fraction, we analyzed the sugar composition (target: ribose) using gas chromatography (GC) as follows. The freeze-dried GTPC fraction (1 mg) was hydrolyzed in 1 mL of 2 M trifluoroacetic acid at 100 °C for 4 h, followed by evaporation. The sugars in the hydrolysate were derivatized to their corresponding alditol acetates as previously described.(47, 48) Alditol acetates were identified using a GC-2010 Plus (Shimadzu, Kyoto, Japan) equipped with flame ionization detector under the following conditions: column, DB-1 (ID 0.25 mm, L 30 m, SUPELCO, Sigma-Aldrich); carrier gas, He; temperature program, from 180 to 250 °C at a rate of 3 °C/min, and then kept at 250 °C for 10 min.

Hydrolysis of RNA Prepared from SP-6

As mentioned already, the GTPC fraction was composed of ribose, a subunit of RNA, and thus, we refer to this fraction as bacterial RNA (bRNA). When necessary, bRNA was hydrolyzed by RNase A. For this purpose, 100 μg of RNase A (Nacalai Tesque, Kyoto, Japan) was added to 3 mL of the bRNA solution in UPW and incubated for 12 h at 37 °C. For assessing the efficacy of the RNase treatment, 20 μL of the solution was separated in 1% agarose, and the gel was then stained using GelRed Nucleic Acid Gel Stain (Biotium Inc., Hayward, CA, USA). RNA bands were visualized using the UV illuminator Dolphin-View2 (Kurabo, Osaka, Japan).

Test Compounds

Baker’s yeast RNA, calf thymus DNA, nucleosides, and DNA-related analogues 2′-deoxyguanosine (dG) and 8-hydroxy-2′-deoxyguanosine (8-OHdG), and a nucleotide, guanine, were purchased from Sigma-Aldrich (St. Louis, MO, U.S.A.). The poly G-DNA primer (45-mer) was synthesized by GeneDesign (Osaka, Japan).

Formation of AuNPs Using Nucleic Acids and Analogues Mixed with HAuCl₄ Solution

To test the ability of the respective test nucleic acids and related analogues to form AuNPs, 0.5 mL of 100 mM Au(III) chloride solution (pH 2.0) (hereafter HAuCl₄ solution), which was prepared by suspending HAuCl₄ (Sigma-Aldrich) in UPW, was added to 3.5 mL of a solution of the respective nucleic acids (final concentrations of 2.5–7.5 mg/mL), nucleosides, or guanine (final concentrations of 5–15 mg/mL) in 15 mL conical tubes wrapped with an aluminum foil to avoid the photochemical reactions and incubated at room temperature on a shaking mixer (SHM-2002, LMS, Tokyo, Japan) for 16 h. Then, specimens were centrifuged at 14 000g for 5–30 min (Model 3750, Kubota, Tokyo, Japan) to collect the precipitates. When necessary, the supernatants were used to test AuNP formation.

Electron Microscopy and ED Analysis

For STEM and TEM observations and XRD analysis of RNA and DNA solutions, the resultant precipitates were washed with UPW at least four times, then in 99.5% ethanol at least 4 times, then freeze-dried (EYELA FDU-1200, Tokyo Rikakikai, Tokyo, Japan). For TEM observation of suspensions of other nucleic acid-related chemicals, the supernatants after a 30 min-centrifugation at 14 000g were transferred to new tubes and diluted 200–1000-fold with 99.5% ethanol. The ethanol suspensions were dropped onto Cu grids and air-dried before placement in the TEM column.

For XRD analysis, the supernatants were freeze-dried. For reference, the nucleic acids, nucleosides and related analogues were suspended in UPW instead of HAuCl₄ solution, then freeze-dried and used as negative controls for XRD analysis.

The air-dried precipitates or freeze-dried supernatants were suspended in 99.5% ethanol using an ultrasonicator (Ultrasonic cleaner USK-3R, AS ONE, Osaka, Japan) and dropped onto a carbon-coated Cu grid, then air-dried. Images were obtained with a TEM (JEOL 2100F, Tokyo, Japan). ED patterns were obtained using the electron diffraction mode of the same TEM.

XRD Analysis

XRD patterns were obtained using an X-ray diffractometer (RINT-2500HF, Rigaku, Tokyo, Japan) with Cu Kα radiation (voltage: 40 kV; current: 200 mA) to examine the crystallinity of the air-dried precipitates or freeze-dried supernatants as described previously.(39) Test nucleic acids, nucleosides and nucleobases were dissolved in UPW instead of HAuCl₄ solution and treated similarly to the test materials and used as mock samples for the XRD analysis. The specimens were fixed on a zero background sample holder and scanned continuously from 10° to 90° (2θ value) at 3°/min. The XRD pattern of the zero background sample holder was also measured.

Detection of Chemical Modification of dG as a Reference to Monitor Modification of Chemical Properties of DNA

To examine whether dG was chemically modified in HAuCl₄ solution, we detected the dG peak using HPLC and the following conditions: column, 5C18-PAQ (4.6 × 150 mm, Nacalai Tesque); mobile phase, 22 mM phosphate buffer (pH 7.0); flow rate, 1 mL/min; column temperature, 30 °C; detection, absorbance at 260 nm. For the redox reaction of Au(III) with dG, 0.1 mL of 10 mM HAuCl₄ solution was added to 0.7 mL of 0.6 mM dG solution followed by incubation at 25 °C. The reaction was monitored by sampling 0.1 mL of the suspended solution at intervals of 30–120 min; the sample was passed through a 0.45 μm-membrane filter (DISMIC-03CP, Advantec, Tokyo, Japan) and analyzed with HPLC.

Colorimetric Assay for 8-OHdG, a Marker of Oxidative DNA Damage

For this purpose, an EpiQuik 8-OHdG DNA damage quantification direct kit (colorimetric) (Epigentek, Farmingdale, NY, U.S.A.) was used. Briefly, 1–400 μg of calf thymus DNA in 400 μL of Tris-EDTA (TE) buffer (pH 8.0) was added to 50 μL of 100 mM HAuCl₄ solution and incubated at room temperature for the indicated times, then ethanol-precipitated and air-dried (Figure 3b, c). After the air-dried DNA precipitates were dissolved completely in 50 μL of TE buffer by sonication for 5 min, 8 μL of the resultant DNA solution was used to detect 8-OHdG according to the manufacturer’s protocol. For colorimetric detection of the specimens, absorbance at 450 nm was measured by a Nanodrop 2000C spectrophotometer (Thermo Scientific).

XRF Analysis

For determining the atomic percentage (hereafter atomic %) of Au in test specimens, freeze-dried precipitates were packed into small aluminum pans for elemental analysis using an Orbis micro X-ray fluorescence (XRF) analyzer (Ametek, Berwyn, PA, USA). Quantitative data for the target element in specimens were expressed as atomic %, defined as the percentage of the theoretical intensity of characteristic X-ray fluorescence from Au per a total characteristic X-ray fluorescence from all constitutive elements, which is calculated using physical constants and instrumental parameters by the fundamental parameter method.(49) Atomic % of Au was expressed as the mean (±SE) of 10 spots.

Results and Discusion

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Formation of AuNPs by Incubation of Leptothrix RNA in Au(III) Chloride Solution

To examine whether the fraction prepared from SP-6 cells by the acid guanidinium thiocyanate-phenol-chloroform method (hereafter GTPC fraction) can interact with Au(III) cations, the fraction was mixed with an Au(III) chloride solution (hereafter HAuCl₄ solution). Within 4 h, the mixture turned brown and turbid (Figure 1a middle). After four washes with ultrapure water (hereafter UPW), the brown precipitate was obtained from the mixture (Figure 1a right), suggesting that the GTPC fraction and Au cations most likely converted to an insoluble GTPC–Au(III) complex. Although the GTPC method is frequently used to extract RNA from a variety of cells, the GTPC fraction is often contaminated with diverse saccharides of cell origin.(50) We therefore examined the purity of the RNA in the fraction by targeting ribose in the GTPC fraction by gas chromatography (GC). A single prominent peak corresponding to ribose was detected at a retention time of 13–14 min (Figure 1b left). When the GTPC fraction was then treated with RNase A, an endonuclease of RNA, the flow pattern on the agarose gel, the bands in the mock disappeared almost completely after the RNase treatment (Figure 1b right). Based on these results, we concluded that the GTPC fraction was primarily RNA and thus refer to it as bacterial RNA (bRNA) hereafter.

Figure 1. Formation of Au-nanoparticles (AuNPs) by the acid guanidinium thiocyanate–phenol–chloroform (GTPC) fraction (= bRNA) in Au(III) chloride (HAuCl₄) solution. (a) The clear yellow HAuCl₄ solution (left) changed to turbid brown (middle) within 4 h after mixing with the GTPC fraction; a brown precipitate formed (right) after 16 h. (b) GC spectrum of sugar composition of GTPC fraction shows a prominent ribose peak. Based on this result, the fraction was regarded as bacterial RNA (bRNA) (left). Electrophoretic patterns of RNase A-treated (right lane) and -untreated bRNA (left lane, Mock) in agarose gel, indicating that bRNA was degraded but not completely (right). (c) STEM images (left) and ED patterns (right) of freeze-dried precipitates obtained from mixture of bRNA and HAuCl₄ solution. Electron-dense particles scattered on the aggregated bRNA (left upper). The particles are nearly spherical in the enlarged image (left, lower). Scale bar = 10nm, upper; 5 nm, lower. ED patterns obtained from the particles (P1 and P2 in left upper image). From calculations using diffraction indices, Au(200) and Au(020) crystal faces were present in P1 and Au(200) in P2 (right upper and lower). (d) Histogram of AuNP diameters measured in STEM images (average 6.1 ± 1.4 nm). (e) XRD patterns of precipitates from bRNA-mixed HAuCl₄ solution and UPW (Mock) after 16 h incubation, showing the presence of Au(111), Au(200), Au(220), Au(311), and Au(222) crystal faces in the former precipitate but not in the latter.

Scanning transmission electron microscopy (STEM) of the precipitate formed in the mixture of bRNA and HAuCl₄ solution revealed abundant electron-dense, spherical, monodisperse particles on the surface of the aggregated bRNA (Figure 1c left). The diameter of over 300 particles, estimated from STEM images, ranged between 2 and 10 nm (average 6.1 ± 1.4 nm), and 86.7% of the particles were 4–8 nm in diameter (Figure 1d). The electron diffraction (ED) patterns obtained individually from arbitrarily selected particles P1 and P2 (Figure 1c left) showed well-defined spots indicating good crystallinity, which were assigned to Au(200) and Au(020) with d₂₀₀ = 0.203 nm and d₀₂₀ = 0.181 nm (Figure 1c right). Consistent with this ED outcome, X-ray diffraction (XRD) analyses showed Au(111), Au(200), Au(220), Au(311), and Au(222) peaks at 2θ values of 38.1°, 44.3°, 64.5°, 77.5°, and 81.6°, respectively (Figure 1e). Therefore, we considered that the bRNA had the potential to reduce Au(III) to Au(0) and eventually to form AuNPs.

To confirm this potential, we tested the ability of baker’s yeast (hereafter yRNA) to reduce Au cations to metal forms for reference (see Supporting Information Figure S2). Results similar to those in Figure 1 were obtained: brown precipitates formed within 5 min when yRNA was mixed with HAuCl₄ solution; electron-dense particles were observed on the aggregated yRNA with transmission electron microscopy (TEM); particle diameters were 3–8 nm (average 5.6 ± 0.9 nm); XRD peaks were ascribed to Au(111), Au(200), Au(220), Au(311), and Au(222). Results apparently showed that yRNA was able to reduce Au(III) to Au(0) as found for bRNA.

Next, we examined the Au(III)-reducing ability of DNA by mixing calf thymus DNA with HAuCl₄ solution. As illustrated in Supporting Information Figure S3, results very similar to those for the RNAs (Figures 1 and Supporting Information Figure S2) were obtained by TEM, ED, and XRD. Here we also examined the possible interference of pH with reduction of Au(III) to Au(0) by DNA, because an earlier paper(41) reported that, in a mixture of salmon sperm DNA in HAuCl₄ solution at pH 5.6, an Au(III)–DNA complex was generated by chelating Au(III) at the sites of O6 and N7 in the guanine moiety and that they needed a reducing agent, hydrazine, to obtain AuNPs. Results similar to Supporting Information Figure S3 were obtained again by TEM and XRD when HAuCl₄ solution was adjusted from its original pH 2.0 to 7.0 (see Supporting Information Figure S4), indicating that as for RNA, DNA could reduce Au(III) to Au(0) without needing a reducing agent, even at neutral pH.

Potential of Guanosine and Guanine to Form AuNPs

Subsequently, we examined which nucleoside(s) of RNA were responsible for reducing Au(III) to Au(0). After mixing each of the nucleosides (adenosine, guanosine, uridine, and cytidine) with HAuCl₄ solution, the yellow mixture of guanosine and adenosine turned brown within 1 min and 1 h, respectively, while that of uridine and cytidine did not change for 16 h (Figure 2a). A small amount of precipitate was obtained from the guanosine mixture by 16 h (Figure 2a, arrow). Unexpectedly, electron-dense particles were not found in this precipitate by TEM (see Supporting Information Figure S5a left), and the subsequent XRD did not detect any peaks corresponding to metallic Au (Figure 2e). Nevertheless, X-ray fluorescence (XRF) analysis detected the peaks of Au and approximately 90 atomic % of Au in this precipitate (see Supporting Information Figure S5b left). Based on these data, we suspected that AuNP-holding guanosine might be in the colloidal state whereby it could not precipitate under the present centrifugation conditions. To be certain, we diluted the supernatant with ethanol, then air-dried it for TEM and ED or freeze-dried it without the ethanol dilution for XRD. As expected, the electron-dense particles 2–6 nm in diameter (average 3.5 ± 0.8 nm) were observed on the surface of the aggregated guanosine by TEM (Figure 2b upper, c), similar to the cases for the RNAs and DNA (Figure 1c and see Supporting Information Figures S2c and S3b). The ED patterns showed several spots indicating metallic Au: Au(111), Au(220), and Au(311) crystal faces (Figure 2b lower). Consistently, XRD analysis detected peaks derived from metallic Au: Au(111), Au(200), Au(220), Au(222), and Au(311) (Figure 2e). These results showed that guanosine can reduce Au(III) and eventually form AuNPs, but the AuNP-holding guanosine was suspended in the mixture.

Figure 2. Formation of Au-nanoparticles (AuNPs) by incubation of RNA nucleosides with Au(III) chloride (HAuCl₄) solution. (a) Colors of HAuCl₄ solution after mixing with either of four RNA nucleosides (adenosine, uridine, guanosine, or cytidine). The mixture started to change color within 1 min after mixing with guanosine and after 1 h with adenosine, but remained unchanged until 1 h after mixing with uridine and cytidine. The precipitate (bottom, arrowheads) and supernatant were obtained by centrifugation at 16 h. (b) TEM image of electron-dense spherical particles on surface of aggregated guanosine obtained from supernatant after 16 h incubation (upper). Scale bar = 5 nm. The ED pattern obtained from an electron-dense particle shows several spots (arrows) reflecting the presence of metallic Au (lower). (c) Histogram of AuNP diameters measured from the TEM images (average 3.5 ± 0.8 nm). (d) TEM image showing absence of electron-dense particles on surface of aggregated adenosine obtained from supernatant (left). Scale bar = 5 nm. The ED pattern obtained from the aggregated adenosine lacked signals for metallic Au (right). (e) XRD patterns from supernatant and precipitate from guanosine-mixed HAuCl₄ solution after 16 h incubation: only the supernatant showed the presence of Au(111), Au(200), Au(220), Au(311), and Au(222) crystal faces. □: unidentified peaks. (f) XRD patterns from supernatant and precipitate from adenosine-mixed HAuCl₄ solution after 16 h incubation. Note lack of signal for Au in both specimens. Mock = guanosine or adenosine mixed with UPW.

Why are the AuNPs holders found in the supernatant but not in the precipitate? We assumed that the polymeric structure of the holders may be necessary for precipitation of AuNPs holders under the present centrifugation conditions. This assumption was supported when poly G DNA-primer (= a polymer of 2′-deoxyguanosine [dG]; hereafter poly dG) was incubated with HAuCl₄ solution, then centrifuged (see Supporting Information Figure S6). In a TEM image, electron-dense AuNPs of 3–9 nm diameter (average 4.9 ± 1.0 nm) were scattered on the aggregated poly dG in the precipitate (see Supporting Information Figures S6b–d). These results strongly suggest that polymerization of dG through a phosphate group might be important for precipitation with AuNPs. In a study on the formation of ATP-mediated capping of the surface of AuNPs, negatively charged phosphate groups were proposed as the mode of interaction between ATP and AuNPs.(18)

Interestingly, no electron-dense particles were observed even on the amorphous-looking aggregated adenosine prepared from either supernatant (Figure 2d left) or precipitate (see Supporting Information Figure S5a middle). Accordingly, neither ED (Figure 2d right) nor XRD (Figure 2f) analyses showed any spots, rings, or peaks that would indicate the existence of metallic Au on both specimens. Nevertheless, XRF analysis detected approximately 92 atomic % of Au in the precipitate (see Supporting Information Figure S5b middle), suggesting that unlike guanosine, adenosine could not form AuNPs, although it interacted with Au cations. Wei et al.(34) reported that the adenine–HAuCl₄ solution hybrid colloidal particles were in a mixed-valence Au(I)/Au(III) state. At present, we infer that their evidence probably accounts for the detection of Au by XRF but lack of detection of metallic Au in the present adenosine-mediated precipitate by XRD and ED.

Considering the difference in molecular structure between guanosine and adenosine, we speculated that the guanine moiety could be significant for formation of AuNPs. To verify this speculation, we mixed guanine with HAuCl₄ solution. The mixture became turbid within 1 min and turned brown within 6 h (see Supporting Information Figure S7a). The precipitate and supernatant obtained from the 16 h specimens were then analyzed further. TEM showed that the electron-dense particles were not found on the surface of the precipitate (see Supporting Information Figure S5a right) but were evidently present on the surface of aggregated guanine prepared from the supernatant (see Supporting Information Figure S7b upper two). These particles were 3–10 nm in diameter (average 5.7 ± 1.4 nm; see Supporting Information Figure S7c). The ED pattern showed rings and spots corresponding to Au(111), Au(200), Au(220), and Au(311) (see Supporting Information Figure S7b lower). Consistent with the case of guanosine (Figure 2e), XRD analysis also detected peaks of Au(111), Au(220), Au(222), and Au(311) in the supernatant but not in the precipitate specimen (see Supporting Information Figure S7d). However, as for guanosine, XRF analysis detected approximately 94 atomic % of Au in the precipitate (see Supporting Information Figure S5b right). Based on these data, among the nucleobases, guanine was considered to be responsible for reducing Au(III) to Au(0) and eventually forming AuNPs in the suspension.

Failure of AuNP Formation by Hydroxylated Guanine Molecule

We suspected that structurally modified guanine analogues might lack the potential to reduce Au(III) and eventually form AuNPs. To check this possibility, we focused on commercially available 8-hydroxy-2′-deoxyguanosine (8-OHdG), because the generation of 8-OHdG from dG is often used as a marker of oxidative damage of DNA and is readily detected by a specific antibody-based enzyme-linked immunosorbent assay.(51) At first, we mixed dG with HAuCl₄ solution and then monitored generation of the byproducts over time using high performance liquid chromatography (HPLC) (Figure 3a). Immediately after mixing (0 min), a prominent peak corresponding to dG was detected at a retention time of approximately 18 min. Intriguingly, at 30 min and later, the peak of dG reduced drastically and an additional peak appeared at a retention time of approximately 19.5 min (Figure 3a, indicated as unidentified), suggesting that HAuCl₄ solution could modify the chemical property of dG and eventually generate an unidentified byproduct. What is the origin of this peak? At present, we infer that the peak could correspond to 8-OHdG because 8-OHdG was detected when calf thymus DNA having dG as one of the nucleoside moieties was mixed with HAuCl₄ solution (Figure 3b, c) as explained below, and, in addition, the retention time of 8-OHdG in HPLC analysis was reported to be longer than that of dG,(52) although further studies are certainly needed before making a conclusion.

Figure 3. Detection of chemical modification of 2′-deoxy guanosine (dG) and generation of 8-hydroxy-2′-deoxyguanosine (8-OHdG) from calf thymus DNA during incubation in Au(III) chloride (HAuCl₄) solution. (a) HPLC analysis of dG after 0 to 240 min in HAuCl₄ solution. One dG peak was detected at a retention time of approximately 18 min at each time. Note that its absorbance level was quite high at time 0 but was much lower from 30 to 240 min and that an additional unidentified peak appeared at a retention time of approximately 19.5 min (arrows). (b) Specific antibody-based colorimetric detection of 8-OHdG production from various concentrations of DNA incubated in HAuCl₄ solution for 12 h. DNA dissolved in UPW was used as the mock sample. (c) Time-course analysis of 8-OHdG production after incubation of 40 ng of DNA in HAuCl₄ solution.

If dG is chemically modified after mixing with HAuCl₄ solution, theoretically, 8-OHdG is supposed to be generated. To verify such a possibility, various quantities of calf thymus DNA (2, 40, and 80 ng/mL) were incubated in HAuCl₄ solution for 12 h, and the production of 8-OHdG was monitored using a colorimetric assay with an 8-OHdG-recognizing antibody. Absorbance at 450 nm remained low (ca. 0.5) when calf thymus DNA was dissolved in UPW (Mock) but the absorbance increased when increasing quantities of DNA were dissolved in HAuCl₄ solution (Figure 3b), indicating the generation of 8-OHdG within DNA in HAuCl₄ solution (pH 2.0). In addition, 8-OHdG was detectable within 0.5 min and continued to increase for 1 h after a fixed amount of DNA (40 ng/mL) was added to HAuCl₄ solution (Figure 3c). These results strongly indicated that DNA was oxidatively damaged in HAuCl₄ solution, resulting in the production of 8-OHdG (see Scheme 1).

Scheme 1. Construable Mechanism of 8-OHdG Generation Coupled with Au(III) Reduction Based on Earlier Proposals for Formation of an Au(III)–DNA Complex and for Oxidative DNA Damage to the Guanine Moiety^a

Keeping these basic outcomes in mind, we separately mixed dG and 8-OHdG in HAuCl₄ solution. Expectedly, the dG mixture turned brown within 5 min, while the 8-OHdG mixture did not change for 16 h (Figure 4a). After centrifugation of each mixture after 16 h, the supernatants were viewed with TEM. As illustrated in Figure 4b (upper left), electron-dense particles 2–7 nm in diameter (mean 4.4 ± 0.9 nm) (Figure 4c) were scattered on the aggregated dG, but no particles were seen on the aggregated 8-OHdG (Figure 4b upper right). The ED analysis detected rings and spots corresponding to Au(111), Au(200), Au(220), and Au(311) in the dG sample but not in the 8-OHdG (Figure 4b). The XRD analysis also detected Au(111), Au(200), Au(220), Au(222), and Au(311) peaks in the supernatant but not in the precipitate of dG (Figure 4d), similar to the case of guanosine (Figure 2e) and guanine (see Supporting Information Figure S7d). All these data evidently show that the guanine moiety hydroxylated at C8 cannot reduce Au(III) and thus cannot form AuNPs.

Figure 4. Potential of Au-nanoparticle (AuNP) formation by 8-hydroxy-2′-deoxyguanosine (8-OHdG) and 2′-deoxy guanosine (dG) in HAuCl₄ solution. (a) The visual appearance of samples after dG (middle) or 8-OHdG (right) was mixed with HAuCl₄ solution. Only the mixture with dG turned brown within 5 min. The supernatant was obtained by centrifugation of the 16-h sample. (b) TEM images (upper) and ED pattern (lower) of the supernatant collected from dG– or 8-OHdG–HAuCl₄ solution at 16 h. Electron-dense particles were observed on the aggregated dG (upper left) but not on the aggregated 8-OHdG (upper right). Scale bar = 5 nm, left; 2 nm, right. Consistently, spots indicating the presence of metallic Au were detected on the aggregated dG (lower left, arrows) but not on the aggregated 8-OHdG (lower right). (c) Histogram of AuNP diameters measured from the TEM images (mean 4.4 ± 0.9 nm). (d) XRD analyses of supernatant and precipitate obtained from dG-suspended HAuCl₄ solution. A suspension of dG in UPW was used as a negative control (Mock). The presence of metallic Au was indicated only in the HAuCl₄ supernatant. □: unidentified peaks.

According to earlier reports for the formation of an Au(III)–DNA complex(40-42) and oxidative DNA damage of guanine moiety,(53, 54) either a chelating adduct is initially generated by the binding of Au(III) to the guanine moiety through N7 and O6, or a radical adduct is generated by interaction through guanine C8 [see Scheme 1a and b]. As the second step, the encounter of the former adduct with HO• or the latter adduct with Au(III) leads to the formation of a chelating and radical adduct [see see Scheme 1c]. Then, the electron abstraction from guanine N7 to Au(III) [see see Scheme 1d] eventually reduces Au(III) to Au(II) and leads to 8-OHdG generation. The generated Au(II) then likely accepts an electron in a similar manner and is converted to Au(I) and thereby to Au(0). Therefore, it seems most likely that electron transfer from guanine C8 to binding Au cations adjacent to guanine C6 and N7 holds a key for reduction of Au cations to metallic Au. The most important oxygen-free radical causing damage to basic biomolecules is the hydroxyl radical (HO•), which can be generated by diverse mechanisms, especially by the Fenton reaction involving hydrogen peroxide and by metals, and other endogenous and exogenous reactive oxygen species.(53) However, in this proposed model, how and when initial HO• generation occurs in HAuCl₄ solution are still unknown. Accordingly, further studies are certainly required to validate this model.

As mentioned already, a variety of chemical, physical, and biological techniques have been used to produce AuNPs. However, the size and shape of the particles were quite variable, and sometimes the particles readily coagulated, especially those synthesized biologically or chemically. For example, irregular shapes and a range of sizes (20–85 nm in diameter) were synthesized using lemongrass extract,(55) relatively large particles (ca. 310 nm in diameter) were generated in an adenine–HAuCl₄ solution mixture,(34) and near-spherical AuNPs with 45–80 nm diameter were produced using DNA/hydrazine.(41) Such variations often slow the development of techniques and eventual applications. In contrast, the nucleic acid-, nucleoside-, or nucleobase-mediated spherical AuNPs in this study were very close in size (mean diameter: 3.5–6.2 nm). Although small nanocrystals tend to aggregate because of van der Waals attraction,(18, 34) the AuNPs formed by the present methods did not, judging from a series of TEM images. These properties are critical for medical and/or pharmaceutical purposes. As far as we know, this is the first report concerning AuNP formation using a guanine moiety without any additional reducing reagents or physical stresses. To date, broad technological strategies have been studied toward developing AuNPs in the fields of optical sensing and imaging, drug delivery, cancer therapy, and so on.(3, 56) To exploit the homologous shape and size, dispersibility, and easy production of the AuNPs generated for the medical and pharmaceutical fields, we also need to develop methods to recover AuNPs from the carrier and modify their surfaces to provide affinitive and reactive properties to AuNPs and study their toxicity to target animal cells(57) and other essential basic issues such as the stability of AuNPs in various salt solutions that are used routinely for biological applications.

The present findings on the potential of bRNA to attract and reduce Au cations may open a new approach to harness the mechanisms of metal encrustation of Leptothrix sheaths in aquatic environments, because RNA is detected in sheaths (see Supporting Information Figure S1).

Conclusions

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Based on the experimental outcomes, we propose that the structural modification from C–H to C–OH at guanine C8 plays a critical role for Au(III) reduction and formation of AuNPs: (i) Mixing bRNA, yRNA, or DNA solutions with HAuCl₄ solution results in AuNP formation in the precipitates of the respective aggregated nucleic acids (Figure 1 and see Supporting Information Figures S2, S3). (ii) Guanosine and guanine cause AuNP formation, but sugar components of nucleic acids do not (Figure 2 and see Supporting Information Figure S7). (iii) Polymeric RNA, DNA, and DNA primer carrying AuNPs can be precipitated in HAuCl₄ solution using the present centrifugation conditions, but monomers such as guanosine and guanine are not sufficient (Figures 1 and 2 and see Supporting Information Figures S2, S3, S5–7). (iv) A chemical property of dG is modified when dG is mixed with HAuCl₄ solution, which could be related to production of 8-OHdG (Figure 3). (v) The C8-hydroxylated dG (= 8-OHdG) fails to form AuNPs when mixed with HAuCl₄ solution (Figure 4). The results indicate that fine spherical AuNPs are produced through the oxidation of the guanine moiety at C8 without the need for any reducing agents or physical stresses.

Supporting Information

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.7b02610.

Figure S1. Presence of RNA in the SP-6 sheath remnants and extracellular release of remarkable amount of RNA from SP-6 cells in MSVP culture medium. Figure S2. Formation of AuNPs after incubation of yRNA with HAuCl₄ solution. Figure S3. Formation of AuNPs by incubation of calf thymus DNA with HAuCl₄ solution. Figure S4. AuNP formation by DNA in buffered HAuCl₄ solution. Figure S5. AuNPs were not detected on the surfaces of precipitates collected from guanosine–, adenosine–, or guanine–HAuCl₄ solution. Figure S6. AuNPs precipitated with poly G DNA primer in HAuCl₄ solution. Figure S7. Formation of AuNPs by incubation of guanine with HAuCl₄ solution (PDF)

sc7b02610_si_001.pdf (1.28 MB)

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Author Information

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Corresponding Author
- Jun Takada - †Core Research for Evolutionary Science and Technology (CREST), Japan Science and Technology Agency (JST), and ‡Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530, Japan; Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan; Email: [email protected]
Authors
- Tatsuki Kunoh - †Core Research for Evolutionary Science and Technology (CREST), Japan Science and Technology Agency (JST), and ‡Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530, Japan; Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan; http://orcid.org/0000-0002-8423-2903
- Minoru Takeda - Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan
- Syuji Matsumoto - †Core Research for Evolutionary Science and Technology (CREST), Japan Science and Technology Agency (JST), and ‡Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530, Japan; Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan
- Ichiro Suzuki - Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan
- Mikio Takano - †Core Research for Evolutionary Science and Technology (CREST), Japan Science and Technology Agency (JST), and ‡Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530, Japan; Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan
- Hitoshi Kunoh - †Core Research for Evolutionary Science and Technology (CREST), Japan Science and Technology Agency (JST), and ‡Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530, Japan; Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan
Author Contributions
T.K. and M.Takeda conceived the overall experimental strategy, performed all physiological and microscopic experiments, and wrote the manuscript. S.M. did the TEM imaging and ED analyses. STEM imaging and some ED analyses were performed by the Kobelco Research Institute (Kobe, Japan). I.S., M.Takano., H.K., and J.T. developed the original concept of the project and/or provided technical advice.
Funding
This study was financially supported by JST-CREST (2012–2017) (J.T.) and a Grant-in-Aid for Scientific Research (C) 16K07714 of JSPS (M.Takeda).
Notes
The authors declare no competing financial interest.

Acknowledgment

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We appreciate professors Yoshihiro Kusano, Tomoki Shiraishi, and Kazuhiro Toyoda for valuable comments. We also thank Drs. Makoto Nakanishi, Tomonari Kasai, and Katsunori Tamura and Ms. Mika Yoneda and Keiko Toyoda for technical supports. We acknowledge Dr. Beth E. Hazen for reviewing and editing the manuscript.

References

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Ji, Xiaohui; Song, Xiangning; Li, Jun; Bai, Yubai; Yang, Wensheng; Peng, Xiaogang
Journal of the American Chemical Society (2007), 129 (45), 13939-13948CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Growth kinetics and temporal size/shape evolution of gold nanocrystals by citrate redn. in boiling water were studied systematically and quant. Results reveal that the size variation and overall reaction mechanism were mostly detd. by the soln. pH that was in turn controlled by the concn. of sodium citrate (Na3Ct) in the traditional Frens's synthesis. This conclusion was further confirmed by the reactions with variable pH but fixed concns. of the two reactants, HAuCl4 and Na3Ct. Two substantially different reaction pathways were identified, with the switching point at pH = 6.2-6.5. The first pathway is for the low pH range and consists of three overlapping steps: nucleation, random attachment to polycryst. nanowires, and smoothing of the nanowires via intra-particle ripening to dots. The second pathway that occurred above the pH switching point is consistent with the commonly known nucleation-growth route. Using the second pathway, we demonstrated a new synthetic route for the synthesis of nearly monodisperse gold nanocrystals in the size range from 20 to 40 nm by simply varying the soln. pH with fixed concns. of HAuCl4 and Na3Ct. The switching of the reaction pathways is likely due to the integration nature of water as a reaction medium. In the citrate redn., the soln. pH was varied by changing the initial HAuCl4/Na3Ct ratio. Consequently, when pH was higher than about 6.2, the very reactive [AuCl3(OH)]- would be converted to less reactive [AuCl2(OH)2]- and [AuCl(OH)3]-.
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Tyagi, H.; Kushwaha, A.; Kumar, A.; Aslam, M. pH-dependent synthesis of stabilized gold nanoparticles using ascorbic acid Int. J. Nanosci. 2011, 10, 857– 860 DOI: 10.1142/S0219581X11009301
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pH-DEPENDENT SYNTHESIS OF STABILIZED GOLD NANOPARTICLES USING ASCORBIC ACID
Tyagi, Himanshu; Kushwaha, Ajay; Kumar, Anshuman; Aslam, M.
International Journal of Nanoscience (2011), 10 (4 & 5), 857-860CODEN: IJNNAJ; ISSN:0219-581X. (World Scientific Publishing Co. Pte. Ltd.)
The stabilization of gold nanoparticles soln. synthesized using ascorbic acid at room temp. is examd. in detail. It is found that gold nanoparticles (AuNPs) synthesized using ascorbic acid have a narrow size distribution (31 ± 5, 36 ± 6, and 40 ± 5 nm) and can be readily stabilized just by adjusting the initial pH conditions of the reaction solns. While the initial pH strongly affects the stability of particles, it has no effect on the size of stabilized particles. The particles are nearly spherical having size distribution effectively in the range of 30 nm to 40 nm. Through time dependent UV-Vis spectra studies we also hypothesize the pH dependent stabilization mechanism wherein a layer of adsorbed ionic complex over AuNPs slows down the aggregation of AuNPs. The information obtained in this study can be used to design in-situ controlled nanoparticle synthesis system esp. within the biol. cells. Moreover, the method is green and biol. acceptable as well.
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Deraedt, C.; Salmon, L.; Gatard, S.; Ciganda, R.; Hernandez, R.; Ruiz, J.; Astruc, D. Sodium borohydride stabilizes very active gold nanoparticle catalysts Chem. Commun. 2014, 50, 14194– 14196 DOI: 10.1039/C4CC05946H
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Sodium borohydride stabilizes very active gold nanoparticle catalysts
Deraedt, Christophe; Salmon, Lionel; Gatard, Sylvain; Ciganda, Roberto; Hernandez, Ricardo; Ruiz, Jaime; Astruc, Didier
Chemical Communications (Cambridge, United Kingdom) (2014), 50 (91), 14194-14196CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
Long-term stable 3 nm gold nanoparticles are prepd. by a simple reaction between HAuCl4 and sodium borohydride in water under ambient conditions which very efficiently catalyze 4-nitrophenol redn. to 4-nitroaniline.
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Zhao, W.; Gonzaga, F.; Li, Y.; Brook, M. A. Highly stabilized nucleotide-capped small gold nanoparticles with tunable size Adv. Mater. 2007, 19, 1766– 1771 DOI: 10.1002/adma.200602449
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Highly stabilized nucleotide-capped small gold nanoparticles with tunable size
Zhao, Weian; Gonzaga, Ferdinand; Li, Yingfu; Brook, Michael A.
Advanced Materials (Weinheim, Germany) (2007), 19 (13), 1766-1771CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
Improved stability of gold nanoparticles in water is achieved by capping the particles. Such stability improvements are significant because of the potential applications of the nanoparticles in various biol. relevant areas. The highly stabilized water-sol. Au nanoparticles have precisely tunable sizes ranging from 2 to 5 nm with a narrow monodispersity, and are prepd. by using nucleotides as capping ligands.
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Hostetler, M. J.; Wingate, J. E.; Zhong, C.-J.; Harris, J. E.; Vachet, R. W.; Clark, M. R.; Londono, J. D.; Green, S. J.; Stokes, J. J.; Wignall, G. D.; Glish, G. L.; Porter, M. D.; Evans, N. D.; Murray, R. W. Alkanethiolate gold cluster molecules with core diameters from 1.5 to 5.2 nm: core and monolayer properties as a function of core size Langmuir 1998, 14, 17– 30 DOI: 10.1021/la970588w
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Alkanethiolate Gold Cluster Molecules with Core Diameters from 1.4 to 5.2 Nanometers: Core and Monolayer Properties as a Function of Core Size
Hostetler, Michael J.; Wingate, Julia E.; Zhong, Chuan-Jian; Harris, Jay E.; Vachet, Richard W.; Clark, Michael R.; Londono, J. David; Green, Stephen J.; Stokes, Jennifer J.; Wignall, George D.; Glish, Gary L.; Porter, Marc D.; Evans, Neal D.; Murray, Royce W.
Langmuir (1998), 14 (1), 17-30CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
The mean size of the gold (Au) core in the synthesis of dodecanethiolate-stabilized Au cluster compds. can be finely adjusted by choice of the Au:dodecanethiolate ratio and the temp. and rate at which the redn. is conducted. The Au clusters have been examd. with a large no. of independent anal. tools, producing a remarkably consistent picture of these materials. Av. cluster and core dimensions, as ascertained by 1H NMR line broadening, high-resoln. transmission electron microscopy, small-angle X-ray scattering, and thermogravimetric anal., vary between diams. of 1.4 and 5.2 nm (∼110-4800 Au atoms/core). The electronic properties of the Au core were examd. by UV/vis and XPS; the core appears to remain largely metallic in nature even at the smallest core sizes examd. The alkanethiolate monolayer stabilizing the Au core ranges with core size from ∼53 to nearly 520 ligands/core, and was probed by Fourier transform IR spectroscopy, differential scanning calorimetry, contact-angle measurements, and thermal desorption mass spectrometry. The dodecanethiolate monolayer on small and large core clusters exhibits discernable differences; the line dividing "3-dimensional" monolayers and those resembling self-assembled monolayers on flat Au (2-dimensional monolayers) occurs at clusters with ∼4.4 nm core diams.
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Weare, W. W.; Reed, S. M.; Warner, M. G.; Hutchison, J. E. Improved synthesis of small (d_CORE ≈ 1.5 nm) phosphine-stabilized gold nanoparticles J. Am. Chem. Soc. 2000, 122, 12890– 12891 DOI: 10.1021/ja002673n
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Improved synthesis of small (dCORE ≈ 1.5 nm) phosphine-stabilized gold nanoparticles
Weare, Walter W.; Reed, Scott M.; Warner, Marvin G.; Hutchison, James E.
Journal of the American Chemical Society (2000), 122 (51), 12890-12891CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
A safer, more convenient, and more versatile synthesis of phosphine-stabilized Au nanoparticles is given which eliminates the use of diborane or borane and can be carried out quickly under ambient conditions. The nanoparticles are prepd. in a single step with NaBH4 instead of diborane which should permit the use of this material in a wider range of applications. The synthesis allows control over the particle core size and is tolerant of a variety of phosphine ligands to provide access to previously unknown phosphine-stabilized nanoparticles.
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Raveendran, P.; Fu, J.; Wallen, S. L. Completely “green” synthesis and stabilization of metal nanoparticles J. Am. Chem. Soc. 2003, 125, 13940– 13941 DOI: 10.1021/ja029267j
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Completely green synthesis and stabilization of metal nanoparticles
Raveendran, Poovathinthodiyil; Fu, Jie; Wallen, Scott L.
Journal of the American Chemical Society (2003), 125 (46), 13940-13941CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
A completely green synthetic method for producing silver nanoparticles is introduced. The process is simple, environmentally benign and quite efficient. By gentle heating of an aq. starch soln. contg. silver nitrate and glucose, relatively monodisperse, starched silver nanoparticles are produced. β-D-Glucose serves as the green reducing agent, while starch serves as the stabilization agent.
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Ulman, A. Formation and Structure of Self-Assembled Monolayers Chem. Rev. 1996, 96, 1533– 1554 DOI: 10.1021/cr9502357
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22
Formation and Structure of Self-Assembled Monolayers
Ulman, Abraham
Chemical Reviews (Washington, D. C.) (1996), 96 (4), 1533-1554CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
A review on the organization of complex, semiflexible org. mols. within quasi-2-D assemblies due to the delicate interplay between substrate-adsorbate interactions, nonbonded interactions between adsorbates, electrostatic and VDW forces, and intramol. interactions (e.g., bond stretches, angle bends, and torsions). Surface reorganization contributes to the final equil. structure of the assembly. Structural factors controlling the formation of self-assembled monolayers (SAMs) are discussed. Different SAMs with unique properties and potential applications are considered. An attempt is made to provide a general picture of self-assembly on solid surfaces as it emerges from a consideration of the interplay of different forces that control this process. 273 Refs.
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Ishida, Y.; Akita, I.; Sumi, T.; Matsubara, M.; Yonezawa, T. Thiolate-protected gold nanoparticles via physical approach: unusual structural and photophysical characteristics Sci. Rep. 2016, 6, 29928 DOI: 10.1038/srep29928
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23
Thiolate-Protected Gold Nanoparticles Via Physical Approach: Unusual Structural and Photophysical Characteristics
Ishida, Yohei; Akita, Ikumi; Sumi, Taiki; Matsubara, Masaki; Yonezawa, Tetsu
Scientific Reports (2016), 6 (), 29928CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
Here we report a novel phys. approach for thiolate-protected fluorescent gold nanoparticles with a controlled size of the order of a few nanometers. This approach is based on a sputtering of gold into a liq. matrix contg. thiolate ligand as a stabilizer at various concns., thus no reductant was used. The size of the gold nanoparticles was successfully controlled to range from 1.6 to 7.4 nm by adjusting the thiol concns. Surface plasmon absorption was obsd. in larger nanoparticles, but it was not obsd. in smaller ones. Such smaller nanoparticles fluoresced at around 670 nm with a small spectral shift according to their size, however, the diam. (1.6-2.7 nm) was very strange to show such red emission compared with photophys. characteristics of reported gold cluster or nanoparticles synthesized by chem. method. By detailed investigations using TEM, HAADF-STEM, XPS, and TGA, and size fractionation by size exclusion chromatog., we finally arrived at the plausible mechanism for the origin of unusual fluorescence property; the obtained gold nanoparticles are not single-crystal and are composed of aggregates of very small components such as multinuclear gold clusters or complexes.
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Shankar, S. S.; Rai, A.; Ankamwar, B.; Singh, A.; Ahmad, A.; Sastry, M. Biological synthesis of triangular gold nanoprisms Nat. Mater. 2004, 3, 482– 488 DOI: 10.1038/nmat1152
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24
Biological synthesis of triangular gold nanoprisms
Shankar, S. Shiv; Rai, Akhilesh; Ankamwar, Balaprasad; Singh, Amit; Ahmad, Absar; Sastry, Murali
Nature Materials (2004), 3 (7), 482-488CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
The optoelectronic and physicochem. properties of nanoscale matter are a strong function of particle size. Nanoparticle shape also contributes significantly to modulating their electronic properties. Several shapes ranging from rods to wires to plates to teardrop structures may be obtained by chem. methods; triangular nanoparticles have been synthesized by using a seeded growth process. Here, we report the discovery that the ext. from the lemongrass plant, when reacted with aq. chloroaurate ions, yields a high percentage of thin, flat, single-cryst. gold nanotriangles. The nanotriangles seem to grow by a process involving rapid redn., assembly and room-temp. sintering of 'liq.-like' spherical gold nanoparticles. The anisotropy in nanoparticle shape results in large near-IR absorption by the particles, and highly anisotropic electron transport in films of the nanotriangles.
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Nune, S. K.; Chanda, N.; Shukla, R.; Katti, K.; Kulkarni, R. R.; Thilakavathy, S.; Mekapothula, S.; Kannan, R.; Katti, K. V. Green nanotechnology from tea: phytochemicals in tea as building blocks for production of biocompatible gold nanoparticles J. Mater. Chem. 2009, 19, 2912– 2920 DOI: 10.1039/b822015h
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25
Green nanotechnology from tea: phytochemicals in tea as building blocks for production of biocompatible gold nanoparticles
Nune, Satish K.; Chanda, Nripen; Shukla, Ravi; Katti, Kavita; Kulkarni, Rajesh R.; Thilakavathy, Subramanian; Mekapothula, Swapna; Kannan, Raghuraman; Katti, Kattesh V.
Journal of Materials Chemistry (2009), 19 (19), 2912-2920CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)
Phytochems. occluded in tea have been extensively used as dietary supplements and as natural pharmaceuticals in the treatment of various diseases including human cancer. Results on the redn. capabilities of phytochems. present in tea to reduce gold salts to the corresponding gold nanoparticles are presented in this paper. The phytochems. present in tea serve a dual role as effective reducing agents to reduce gold and also as stabilizers to provide a robust coating on the gold nanoparticles in a single step. The tea-generated gold nanoparticles (T-AuNPs) have demonstrated remarkable in vitro stability in various buffers including saline, histidine, HSA, and cysteine solns. T-AuNPs with phytochem. coatings have shown significant affinity toward prostate (PC-3) and breast (MCF-7) cancer cells. Results on the cellular internalization of T-AuNPs through endocytosis into the PC-3 and MCF-7 cells are presented. The generation of T-AuNPs follows all principles of green chem. and T-AuNPs have been found to be non toxic as assessed through MTT assays. No man made' chems., other than gold salts, are used in this truly biogenic, green nanotechnol. process thus paving the way for excellent opportunities for their application in mol. imaging and therapy.
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Liu, B.; Xie, J.; Lee, J. Y.; Ting, Y. P.; Chen, J. P. Optimization of high-yield biological synthesis of single-crystalline gold nanoplates J. Phys. Chem. B 2005, 109, 15256– 15263 DOI: 10.1021/jp051449n
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Optimization of high-yield biological synthesis of single-crystalline gold nanoplates
Liu, B.; Xie, J.; Lee, J. Y.; Ting, Y. P.; Chen, J. Paul
Journal of Physical Chemistry B (2005), 109 (32), 15256-15263CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
Single-cryst. gold nanoplates were obtained by reducing an aq. chloroauric acid soln. with the ext. of Sargassum sp. (brown seaweed) at room temp. The resulting gold nanoplates were characterized by UV-visible spectroscopy, x-ray diffraction, at. force microscopy, and TEM. The formation of gold nanoplates depended on a no. of environmental factors, such as the time taken to age the seaweed ext., pH of the reaction medium, reaction temp., reaction time, and initial reactant concns. The size of the gold nanoplates can be controlled to between 200 and 800 nm by manipulating the initial reactant concns. The yield of the flat gold nanocrystals relative to the total no. of nanoparticles formed was as high as ∼80-90%.
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Anshup, A.; Venkataraman, J. S.; Subramaniam, C.; Kumar, R. R.; Priya, S.; Kumar, T. R.; Omkumar, R. V.; John, A.; Pradeep, T. Growth of gold nanoparticles in human cells Langmuir 2005, 21, 11562– 11567 DOI: 10.1021/la0519249
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Growth of Gold Nanoparticles in Human Cells
Anshup; Venkataraman, J. Sai; Subramaniam, Chandramouli; Kumar, R. Rajeev; Priya, Suma; Kumar, T. R. Santhosh; Omkumar, R. V.; John, Annie; Pradeep, T.
Langmuir (2005), 21 (25), 11562-11567CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
Gold nanoparticles of 20-100 nm diam. were synthesized within HEK-293 (human embryonic kidney), HeLa (human cervical cancer), SiHa (human cervical cancer), and SKNSH (human neuroblastoma) cells. Incubation of 1 mM tetrachloroaurate soln., prepd. in phosphate buffered saline (PBS), pH 7.4, with human cells grown to ∼80% confluency yielded systematic growth of nanoparticles over a period of 96 h. The cells, stained due to nanoparticle growth, were adherent to the bottom of the wells of the tissue culture plates, with their morphol. preserved, indicating that the cell membrane was intact. Transmission electron microscopy of ultrathin sections showed the presence of nanoparticles within the cytoplasm and in the nucleus, the latter being much smaller in dimension. Scanning near field microscopic images confirmed the growth of large particles within the cytoplasm. Normal cells gave UV-visible signatures of higher intensity than the cancer cells. Differences in the cellular metab. of cancer and noncancer cells were manifested, presumably in their ability to carry out the redn. process.
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Reith, F.; Etschmann, B.; Grosse, C.; Moors, H.; Benotmane, M. A.; Monsieurs, P.; Grass, G.; Doonan, C.; Vogt, S.; Lai, B.; Martinez-Criado, G.; George, G. N.; Nies, D. H.; Mergeay, M.; Pring, A.; Southam, G.; Brugger, J. Mechanisms of gold biomineralization in the bacterium Cupriavidus metallidurans Proc. Natl. Acad. Sci. U. S. A. 2009, 106, 17757– 17762 DOI: 10.1073/pnas.0904583106
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Mechanisms of gold biomineralization in the bacterium Cupriavidus metallidurans
Reith, Frank; Etschmann, Barbara; Grosse, Cornelia; Moors, Hugh; Benotmane, Mohammed A.; Monsieurs, Pieter; Grass, Gregor; Doonan, Christian; Vogt, Stefan; Lai, Barry; Martinez-Criado, Gema; George, Graham N.; Nies, Diestrich H.; Mergeay, Max; Pring, Allan; Southam, Gordon; Brugger, Joel
Proceedings of the National Academy of Sciences of the United States of America (2009), 106 (42), 17757-17762, S17757/1-S17757/31CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
While the role of microorganisms as main drivers of metal mobility and mineral formation under Earth surface conditions is now widely accepted, the formation of secondary gold (Au) is commonly attributed to abiotic processes. Here, the authors report that the biomineralization of Au nanoparticles in the metallophillic bacterium Cupriavidus metallidurans CH34 is the result of Au-regulated gene expression leading to the energy-dependent reductive pptn. of toxic Au(III)-complexes. C. metallidurans, which forms biofilms on Au grains, rapidly accumulates Au(III)-complexes from soln. Bulk and microbeam synchrotron X-ray analyses revealed that cellular Au accumulation is coupled to the formation of Au(I)-S complexes. This process promotes Au toxicity and C. metallidurans reacts by inducing oxidative stress and metal resistances gene clusters (including a Au-specific operon) to promote cellular defense. As a result, Au detoxification is mediated by a combination of efflux, redn., and possibly methylation of Au-complexes, leading to the formation of Au(I)-C-compds. and nanoparticulate Au0. Similar particles were obsd. in bacterial biofilms on Au grains, suggesting that bacteria actively contribute to the formation of Au grains in surface environments. The recognition of specific genetic responses to Au opens the way for the development of bioexploration and bioprocessing tools.
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Reith, F.; Lengke, M. F.; Falconer, D.; Craw, D.; Southam, G. The geomicrobiology of gold ISME J. 2007, 1, 567– 584 DOI: 10.1038/ismej.2007.75
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30
Johnston, C. W.; Wyatt, M. A.; Li, X.; Ibrahim, A.; Shuster, J.; Southam, G.; Magarvey, N. A. Gold biomineralization by a metallophore from a gold-associated microbe Nat. Chem. Biol. 2013, 9, 241– 243 DOI: 10.1038/nchembio.1179
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30
Gold biomineralization by a metallophore from a gold-associated microbe
Johnston, Chad W.; Wyatt, Morgan A.; Li, Xiang; Ibrahim, Ashraf; Shuster, Jeremiah; Southam, Gordon; Magarvey, Nathan A.
Nature Chemical Biology (2013), 9 (4), 241-243CODEN: NCBABT; ISSN:1552-4450. (Nature Publishing Group)
Microorganisms produce and secrete secondary metabolites to assist in their survival. The authors report that the gold resident bacterium Delftia acidovorans produces a secondary metabolite that protects from sol. gold through the generation of solid gold forms. This finding is the first demonstration that a secreted metabolite can protect against toxic gold and cause gold biomineralization.
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Mandal, D.; Bolander, M. E.; Mukhopadhyay, D.; Sarkar, G.; Mukherjee, P. The use of microorganisms for the formation of metal nanoparticles and their application Appl. Microbiol. Biotechnol. 2006, 69, 485– 492 DOI: 10.1007/s00253-005-0179-3
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32
Leng, Y.; Fu, L.; Ye, L.; Li, B.; Xu, X.; Xing, X.; He, J.; Song, Y.; Leng, C.; Guo, Y.; Ji, X.; Lu, Z. Protein-directed synthesis of highly monodispersed, spherical gold nanoparticles and their applications in multidimensional sensing Sci. Rep. 2016, 6, 28900 DOI: 10.1038/srep28900
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Protein-directed synthesis of highly monodispersed, spherical gold nanoparticles and their applications in multidimensional sensing
Leng, Yumin; Fu, Ling; Ye, Liqun; Li, Bo; Xu, Xiumei; Xing, Xiaojing; He, Junbao; Song, Yuling; Leng, Chaoliang; Guo, Yongming; Ji, Xiaoxu; Lu, Zhiwen
Scientific Reports (2016), 6 (), 28900pp.CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
An in-situ redn. method has been reported to prep. gold nanoparticles (GNPs) of 40-110 nm by using the green reducing agents of proteins, which are activated by H2O2 and the superoxide anion ([Formula Omitted]). The protein of collagen turns HAuCl4 to the aq. Au(I) ainions, which are further reduced by other proteins to be highly monodispersed and spherical GNPs of different sizes. The GNPs reduced by different proteins are found to be with the exposed {100} facets, the distinctive UV-vis absorption spectra and various colors (See Fig. 1). By means of extg. the color responses, such as red, green and blue (RGB) alterations, an in-situ redn. method-based multidimensional sensing platform is fabricated in the process of GNPs synthesis. Without further modification of GNPs, nine common proteins are found to be well detected and discriminated at different concns. Moreover, this sensing platform also demonstrates great potentials in qual. and semiquant. anal. on the individuals of these proteins with high sensitivity. Furthermore, the validation of this multidimensional sensing platform has been carried out by anal. on the spiked proteins in human urine and the target proteins in complex matrix (e.g. lysozyme in human tear).
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Engelbrekt, C.; Sørensen, K. H.; Zhang, J.; Welinder, A. C.; Jensen, P. S.; Ulstrup, J. Green synthesis of gold nanoparticles with starch–glucose and application in bioelectrochemistry J. Mater. Chem. 2009, 19, 7839– 7847 DOI: 10.1039/b911111e
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33
Green synthesis of gold nanoparticles with starch-glucose and application in bioelectrochemistry
Engelbrekt, Christian; Sorensen, Karsten H.; Zhang, Jingdong; Welinder, Anna C.; Jensen, Palle S.; Ulstrup, Jens
Journal of Materials Chemistry (2009), 19 (42), 7839-7847CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)
A method for gold nanoparticle (AuNP) synthesis from buffered glucose and starch soln. has been developed and the particles investigated by UV-Vis spectroscopy, TEM, at. force microscopy (AFM) and electrochem. The synthesis proceeds smoothly in neutral and basic soln. The starch concn., temp. and chem. nature of the buffers are key factors in the AuNP formation. Glucose and starch are reducing and protecting agents, resp. Among several inorg. and biol. Good's buffers, phosphate and MES buffers give the best results with quite uniform AuNPs. Other buffers do not result in well-defined nanoparticle structures. Typical AuNP diams. from MES and phosphate buffers (PB) are 4±1 nm and 13±2 nm with plasmon band peaks at 521 nm and 523 nm, resp. The role of the phosphate buffer is mainly to control the pH, while MES is also a synergist with more composite function. AuNPs prepd. by this method are stable in soln. even after 17 mo at room temp. TEM confirms the cryst. structure of the AuNPs, meaning that the AuNP surfaces are low-index single-crystal facets such as (100), (110) and (111). Electrochem. of the buffers at such single-crystal gold electrode surfaces has offered a more detailed understanding of the buffer effect. The AuNPs have been successfully used in bioelectrochem., and found to efficiently enhance interfacial electrochem. electron transfer of the metalloprotein yeast cytochrome c in homogeneous soln. The synthesis has been extended successfully to direct use of starch-rich foods such as potato, carrot and onion to synthesize AuNPs. The present work thus offers a gentle and nontoxic procedure for the synthesis of monodisperse AuNPs in neutral medium with promising potential for pH sensitive biol. or medically related applications.
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Wei, H.; Li, B.; Du, Y.; Dong, S.; Wang, E. Nucleobase–metal hybrid materials: Preparation of submicrometer-scale, spherical colloidal particles of adenine–gold(III) via a supramolecular hierarchical self-assembly approach Chem. Mater. 2007, 19, 2987– 2993 DOI: 10.1021/cm070028a
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Nucleobase-Metal Hybrid Materials: Preparation of Submicrometer-Scale, Spherical Colloidal Particles of Adenine-Gold(III) via a Supramolecular Hierarchical Self-Assembly Approach
Wei, Hui; Li, Bingling; Du, Yan; Dong, Shaojun; Wang, Erkang
Chemistry of Materials (2007), 19 (12), 2987-2993CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
The authors report a simple and effective supramol. route for facile synthesis of submicrometer-scale, hierarchically self-assembled spherical colloidal particles of adenine-Au(III) hybrid materials at room temp. Simple mixt. of the precursor aq. solns. of adenine and HAuCl4 at room temp. could result in spontaneous formation of the hybrid colloidal particles. Optimization of the exptl. conditions could yield uniform-sized, self-assembled products at 1:4 molar ration of adenine to HAuCl4. TEM results reveal the formation of hierarchical self-assembled structure of the as-prepd. colloidal particles. Concn. dependence, ratio dependence, time dependence, and kinetic measurements were studied. Also, spectroscopic evidence [i.e., FTIR and UV-visible spectra and wide-angle x-ray scattering data] of the interaction motives causing the formation of the colloidal particles is also presented. The as-prepd. nucleobase-metal hybrid materials exhibited hierarchical assembly as follows: the coordination interactions of Au(III) and N atoms in adenine could produce 2-3 nm small particles, these small particles could evolve into submicrometer spherical colloidal particles via noncovalent interaction (i.e., arom. π-π stacking of adenine), and finally the submicrometer particles could be connected together through fusion of the fringes of every independent particle. Work here may open up new possibilities for the fabrication of noncovalent interaction colloidal particles and for the prepn. of decomposable colloidal templates.
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Kunoh, T.; Kunoh, H.; Takada, J. Perspectives on the biogenesis of iron oxide complexes produced by Leptothrix, an iron-oxidizing bacterium and promising industrial applications for their functions J. Microb. Biochem. Technol. 2015, 7, 419– 426 DOI: 10.4172/1948-5948.1000249
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Perspectives on the biogenesis of iron oxide complexes produced by leptothrix, an iron-oxidizing bacterium and promising industrial applications for their functions
Kunoh, Tatsuki; Kunoh, Hitoshi; Takada, Jun
Journal of Microbial & Biochemical Technology (2015), 7 (6), 419-426CODEN: JMBTA9; ISSN:1948-5948. (OMICS Publishing Group)
Leptothrix species, one of the Fe-/Mn-oxidizing bacteria, are ubiquitous in aq. environments, esp. at sites characterized by a circumneutral pH, an oxygen gradient and a source of reduced Fe and Mn minerals. Characteristic traits that distinguish the genus Leptothrix from other phylogenetically related species are its filamentous growth and ability to form uniquely shaped microtubular sheaths through the pptn. of copious amts. of oxidized Fe or Mn. The sheath is an ingenious hybrid of org. and inorg. materials produced through the interaction of bacterial exopolymers with aq.-phase inorgs. Intriguingly, we discovered that Leptothrix sheaths have a variety of unexpected functions that are suitable for industrial applications such as material for lithium battery electrode, a catalyst enhancer, pottery pigment among others. This review focuses on the structural and chem. properties of the Leptothrix sheaths and their noteworthy functions that show promise for development of cost-effective, eco-friendly industrial applications.
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Kunoh, T.; Nakanishi, M.; Kusano, Y.; Itadani, A.; Ando, K.; Matsumoto, S.; Tamura, K.; Kunoh, H.; Takada, J. Biosorption of metal elements by exopolymer nanofibrils excreted from Leptothrix cells Water Res. 2017, 122, 139– 147 DOI: 10.1016/j.watres.2017.05.003
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Biosorption of metal elements by exopolymer nanofibrils excreted from Leptothrix cells
Kunoh, Tatsuki; Nakanishi, Makoto; Kusano, Yoshihiro; Itadani, Atsushi; Ando, Kota; Matsumoto, Syuji; Tamura, Katsunori; Kunoh, Hitoshi; Takada, Jun
Water Research (2017), 122 (), 139-147CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.)
Leptothrix species, aquatic Fe-oxidizing bacteria, excrete nano-scaled exopolymer fibrils. Once excreted, the fibrils weave together and coalesce to form extracellular, microtubular, immature sheaths encasing catenulate cells of Leptothrix. The immature sheaths, composed of aggregated nanofibrils with a homogeneous-looking matrix, attract and bind aq.-phase inorgs., esp. Fe, P, and Si, to form seemingly solid, mature sheaths of a hybrid org.-inorg. nature. To verify our assumption that the org. skeleton of the sheaths might sorb a broad range of other metallic and nonmetallic elements, we examd. the sorption potential of chem. and enzymically prepd. protein-free org. sheath remnants for 47 available elements. The sheath remnants were found by XRF to sorb each of the 47 elements, although their sorption degree varied among the elements: >35% at. percentages for Ti, Y, Zr, Ru, Rh, Ag, and Au. Electron microscopy, energy dispersive x-ray spectroscopy, electron and x-ray diffractions, and Fourier transform IR spectroscopy analyses of sheath remnants that had sorbed Ag, Cu, and Pt revealed that (i) the sheath remnants comprised a 5-10 nm thick aggregation of fibrils, (ii) the test elements were distributed almost homogeneously throughout the fibrillar aggregate, (iii) the nanofibril matrix sorbing the elements was nearly amorphous, and (iv) these elements plausibly were bound to the matrix by ionic binding, esp. via OH. The present results show that the constitutive protein-free exopolymer nanofibrils of the sheaths can contribute to creating novel filtering materials for recovering and recycling useful and/or hazardous elements from the environment.
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Emerson, D.; Ghiorse, W. C. Ultrastructure and chemical composition of the sheath of Leptothrix discophora SP-6 J. Bacteriol. 1993, 175, 7808– 7818 DOI: 10.1128/jb.175.24.7808-7818.1993
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Ultrastructure and chemical composition of sheath of Leptothrix discophora SP-6
Emerson, David; Ghiorse, William C.
Journal of Bacteriology (1993), 175 (24), 7808-18CODEN: JOBAAY; ISSN:0021-9193.
Light microscopy and transmission electron microscopy of thin sections and metal-shadowed specimens showed that the sheath of Leptothrix discophora SP-6 (ATCC 51168) is a tube-like extracellular polymeric structure consisting of a condensed fabric of 6.5-nm-diam. fibrils underlying a more diffuse outer capsular layer. In thin sections, outer membrane bridges seen to contact the inner sheath layer suggested that the sheath fabric was attached to the outer layer of the gram-neg. cell wall. The capsular polymers showed an affinity for cationic colloidal iron and polycationic ferritin, indicating that they carry a neg. charge. Cell-free sheaths were isolated by treatment with a mixt. of lysozyme, EDTA, and N-lauroylsarcosine (Sarkosyl) or sodium dodecyl sulfate (SDS). Both Sarkosyl- and SDS-isolated sheaths were indistinguishable in microscopic appearance. However, the Mn-oxidizing activity of Sarkosyl-isolated sheaths was more stable than that of SDS-isolated sheaths. The Sarkosyl-isolated sheaths also contained more 2-keto-3-deoxyoctanoic acid and more outer membrane protein than SDS-isolated sheaths. The oven-dried mass of detergent-isolated sheaths represented approx. 9% of the total oven-dried biomass of SP-6 cultures; the oven-dried sheaths contained 38% C, 6.9% N, 6% H, and 2.1% S and approx. 34 to 35% carbohydrte (polysaccharide), 23 to 25% protein, 8% lipid, and 4% inorg. ash. Gas-liq. chromatog. showed that the polysaccharide was an approx. 1:1 mixt. of uronic acids (glucuronic, galacturonic, and mannuronic acids and at least one other unidentified uronic acid) and an amino sugar (galactosamine). Neutral sugars were not detected. Amino acid anal. showed that sheath proteins were enriched in cysteine (6 mol%). The cysteine residues in the sheath proteins probably provide sulfhydryls for disulfide bonds that play an important role in maintaining the structural integrity of the sheath.
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Takeda, M.; Makita, H.; Ohno, K.; Nakahara, Y.; Koizumi, J. Structural analysis of the sheath of a sheathed bacterium Int. J. Biol. Macromol. 2005, 37, 92– 98 DOI: 10.1016/j.ijbiomac.2005.09.002
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Structural analysis of the sheath of a sheathed bacterium, Leptothrix cholodnii
Takeda, Minoru; Makita, Hiroko; Ohno, Katsutoshi; Nakahara, Yuichi; Koizumi, Jun-ichi
International Journal of Biological Macromolecules (2005), 37 (1-2), 92-98CODEN: IJBMDR; ISSN:0141-8130. (Elsevier B.V.)
L. cholodnii is an aerobic sheath-forming bacterium often found in oligotrophic and metal-rich aquatic environments. The sheath of this bacterium was isolated by selectively lysing the cells. Glycine and cysteine were the major amino acids of the sheath. The sheath was readily dissolved in hydrazine, and a polysaccharide substituted with cysteine was recovered from the soln. Galactosamine, glucosamine and galacturonic acid were detected in the hydrazinolyzate by gas liq. chromatog. anal. FAB-MS anal. of the hydrazinolyzate suggested a sugar sequence of HexN-GalA-HexN-HexN. Methylation linkage anal. revealed the presence of 4-linked GalA, 3-linked HexN and 4-linked HexN. The sulfhydryl groups of the sheath were used for labeling with the fluorogenic reagent 4-(aminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (ABD-F). The labeled sheath (ABD-sheath) was partially hydrolyzed and 3 fluorescent fragments were purified by HPLC. One of them was identified as ABD-cysteine. The 2nd was the ABD-cysteine tetramer. Another fragment was indicated to be a pentasaccharide substituted with ABD-cysteine by NMR anal. It can be assumed that the polysaccharide and peptide moieties of the sheath are connected by a cysteine residue. NMR anal. of the hydrazinolyzate revealed that the polysaccharide moiety of the sheath was constructed from a pentasaccharide repeating unit contg. 2-amino-2-deoxygalacturonic acid (GalNA): →4)-α-GalNA-(1→4)-α-D-GalN(p)-(1→4)-α-D-GalA(p)-(1→4)-β-D-GlcN(p)-(1→3)-β-D-GalN(p)-(1→.
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Kunoh, T.; Matsumoto, S.; Nagaoka, N.; Kanashima, S.; Hino, K.; Uchida, T.; Tamura, K.; Kunoh, H.; Takada, J. Amino group in Leptothrix sheath skeleton is responsible for direct deposition of Fe(III) particles onto the sheaths Sci. Rep. 2017, 7, 6498 DOI: 10.1038/s41598-017-06644-8
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Amino group in Leptothrix sheath skeleton is responsible for direct deposition of Fe(III) minerals onto the sheaths
Kunoh Tatsuki; Matsumoto Syuji; Tamura Katsunori; Kunoh Hitoshi; Takada Jun; Kunoh Tatsuki; Matsumoto Syuji; Uchida Tetsuya; Tamura Katsunori; Kunoh Hitoshi; Takada Jun; Nagaoka Noriyuki; Kanashima Shoko; Hino Katsuhiko
Scientific reports (2017), 7 (1), 6498 ISSN:.
Leptothrix species produce microtubular organic-inorganic materials that encase the bacterial cells. The skeleton of an immature sheath, consisting of organic exopolymer fibrils of bacterial origin, is formed first, then the sheath becomes encrusted with inorganic material. Functional carboxyl groups of polysaccharides in these fibrils are considered to attract and bind metal cations, including Fe(III) and Fe(III)-mineral phases onto the fibrils, but the detailed mechanism remains elusive. Here we show that NH2 of the amino-sugar-enriched exopolymer fibrils is involved in interactions with abiotically generated Fe(III) minerals. NH2-specific staining of L. cholodnii OUMS1 detected a terminal NH2 on its sheath skeleton. Masking NH2 with specific reagents abrogated deposition of Fe(III) minerals onto fibrils. Fe(III) minerals were adsorbed on chitosan and NH2-coated polystyrene beads but not on cellulose and beads coated with an acetamide group. X-ray photoelectron spectroscopy at the N1s edge revealed that the terminal NH2 of OUMS1 sheaths, chitosan and NH2-coated beads binds to Fe(III)-mineral phases, indicating interaction between the Fe(III) minerals and terminal NH2. Thus, the terminal NH2 in the exopolymer fibrils seems critical for Fe encrustation of Leptothrix sheaths. These insights should inform artificial synthesis of highly reactive NH2-rich polymers for use as absorbents, catalysts and so on.
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Pneumatikkais, G.; Hadjiliadis, N.; Theophanides, T. Complexes of inosine, cytidine, and guanosine with palladium(II) Inorg. Chem. 1978, 17, 915– 922 DOI: 10.1021/ic50182a024
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41
Sohn, J. S.; Kwon, Y. W.; Jin, J. I.; Jo, B. W. DNA-templated preparation of gold nanoparticles Molecules 2011, 16, 8143– 8151 DOI: 10.3390/molecules16108143
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42
Pillai, C. K. S.; Nandi, U. S. Binding of gold(III) with DNA Biopolymers 1973, 12, 1431– 1435 DOI: 10.1002/bip.1973.360120617
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42
Binding of gold(III) with DNA
Pillai, C. K. S.; Nandi, U. S.
Biopolymers (1973), 12 (6), 1431-5CODEN: BIPMAA; ISSN:0006-3525.
Calf thymus DNA reacted with HAuCl4 to form a series of complexes depending on the ratio of constituents. There was a shift in the max. of uv spectra of DNA at 258 nm, a drastic decrease in viscosity, an initial increase in pH, and a change in Tm of DNA. The DNA-Au3+ complex pptd. with EtOH had a max. of 1.85 moles Au/mole DNA-P. Results indicate that Au was bound to phosphate and to bases in DNA.
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Aich, P.; Labiuk, S. L.; Tari, L. W.; Delbaere, L. J.; Roesler, W. J.; Falk, K. J.; Steer, R. P.; Lee, J. S. M-DNA: A complex between divalent metal ions and DNA which behaves as a molecular wire J. Mol. Biol. 1999, 294, 477– 485 DOI: 10.1006/jmbi.1999.3234
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44
Mandal, C.; Nandi, U. S. Kinetic studies on the interaction of gold (III) with nucleic acids. IV. RNA-Au (III) system Chem.-Biol. Interact. 1978, 21, 125– 134 DOI: 10.1016/0009-2797(78)90073-X
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44
Kinetic studies on the interaction of gold(III) with nucleic acids. IV. RNA-gold(III) system
Mandal, Chhabinath; Nandi, Uma Sankar
Chemico-Biological Interactions (1978), 21 (1), 125-34CODEN: CBINA8; ISSN:0009-2797.
The kinetics of the interaction of Au(III) with whole yeast RNA was studied using UV-spectrophotometry. The reaction was 2nd order with respect to the nucleotide unit of RNA and 1st order with respect to Au(III) in the resp. stoichiometry of 2:1. The effects of initial compn., temp., ionic strength, pH, and Cl- on the kinetics were studied. The activation energy was 11.5 kcal/mol. The effect of ionic strength indicated that both the pos. charged and neutral species of Au(III) take part in the rate-limiting step, the former being dominant at low ionic strength. A plausible mechanism is proposed which involves the interaction of 2 nucleotide units of RNA with 1 species of Au(III) in the rate-limiting step.
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Kunoh, T.; Hashimoto, H.; McFarlane, I. R.; Hayashi, N.; Suzuki, T.; Taketa, E.; Tamura, K.; Takano, M.; El-Naggar, M. Y.; Kunoh, H.; Takada, J. Abiotic deposition of Fe complexes onto Leptothrix sheaths Biology (Basel, Switz.) 2016, 5, 26– 42 DOI: 10.3390/biology5020026
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46
Emerson, D.; Garen, R. E.; Ghiorse, W. C. Formation of Metallogenium-like structures by a manganese-oxiding fungus Arch. Microbiol. 1989, 151, 223– 231 DOI: 10.1007/BF00413134
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47
Takeda, M.; Nakamori, T.; Hatta, M.; Yamada, H.; Koizumi, J. Structure of the polysaccharide isolated from the sheath of Sphaerotilus natans Int. J. Biol. Macromol. 2003, 33, 245– 250 DOI: 10.1016/j.ijbiomac.2003.08.008
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47
Structure of the polysaccharide isolated from the sheath of Sphaerotilus natans
Takeda, Minoru; Nakamori, Tomonari; Hatta, Miwa; Yamada, Hiroki; Koizumi, Jun-ichi
International Journal of Biological Macromolecules (2003), 33 (4-5), 245-250CODEN: IJBMDR; ISSN:0141-8130. (Elsevier Science B.V.)
A polysaccharide was isolated from the sheath of a sheathed bacterium, Sphaerotilus natans. The sheath polysaccharide (SPS) was composed of D-glucose and D-(N-acetyl)galactosamine in molar ratios of 1:4. Methylation linkage anal. revealed the presence of the residues of 4-linked glucose, 4-linked (N-acetyl)galactosamine, and 3-linked (N-acetyl)galactosamine in molar ratios of 1:3:1. The oligomer of SPS was prepd. with an SPS-specific degrading enzyme from a sheath-degrading bacterium, Paenibacillus koleovorans. The oligomer was derivatized and subjected to fast atom bombardment-mass spectrometry to investigate the monosaccharide sequence of SPS. The structure of SPS was confirmed by NMR. The resulting data showed that SPS is a straight-chained basic polysaccharide constructed of a pentasaccharide repeating unit.
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Takeda, M.; Nomoto, S.; Koizumi, J. Structural analysis of the extracellular polysaccharide produced by Sphaerotilus natans Biosci., Biotechnol., Biochem. 2002, 66, 1546– 1551 DOI: 10.1271/bbb.66.1546
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49
Kataoka, Y. Standardless x-ray fluorescence spectrometry (fundamental parameter method using sensitive library) Rigaku J. 1989, 6, 33– 40
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50
Meisel, L.; Fonseca, B.; González, S.; Baeza-Yates, R.; Cambiazo, V.; Campos, R.; Gonzalez, M.; Orellana, A.; Retamales, J.; Silva, H. A rapid and efficient method for purifying high quality total RNA from peaches (Prunus persica) for functional genomics analyses Biol. Res. 2005, 38, 83– 88 DOI: 10.4067/S0716-97602005000100010
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50
A rapid and efficient method for purifying high quality total RNA from peaches (Prunus persica) for functional genomics analyses
Meisel, Lee; Fonseca, Beatriz; Gonzalez, Susana; Baeza-Yates, Ricardo; Cambiazo, Veronica; Campos, Reinaldo; Gonzalez, Mauricio; Orellana, Ariel; Retamales, Julio; Silva, Herman
Biological Research (2005), 38 (1), 83-88CODEN: BESEEB; ISSN:0716-9760. (Society of Biology of Chile)
Prunus persica has been proposed as a genomic model for deciduous trees and the Rosaceae family. Optimized protocols for RNA isolation are necessary to further advance studies in this model species such that functional genomics analyses may be performed. Here we present an optimized protocol to rapidly and efficiently purify high quality total RNA from peach fruits (Prunus persica). Isolating high-quality RNA from fruit tissue is often difficult due to large quantities of polysaccharides and polyphenolic compds. that accumulate in this tissue and co-purify with the RNA. Here we demonstrate that a modified version of the method used to isolate RNA from pine trees and the woody plant Cinnamomun tenuipilum is ideal for isolating high quality RNA from the fruits of Prunus persica. This RNA may be used for many functional genomic based expts. such as RT-PCR and the construction of large-insert cDNA libraries.
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Yin, B.; Whyatt, R. M. Determination of 8-hydroxydeoxyguanosine by an immunoaffinity chromatography-monoclonal antibody-based ELISA Free Radi. Biol. Med. 1995, 18, 1023– 1032 DOI: 10.1016/0891-5849(95)00003-G
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51
Determination of 8-hydroxydeoxyguanosine by an immunoaffinity chromatography-monoclonal antibody-based ELISA
Yin, Baoyun; Whyatt, Robin M.; Perera, Frederica P.; Randall, Mary C.; Cooper, Thomas B.; Santella, Regina M.
Free Radical Biology & Medicine (1995), 18 (6), 1023-32CODEN: FRBMEH; ISSN:0891-5849. (Elsevier)
The postulated importance of oxidative damage to DNA in aging and age-related degenerative pathologies such as cancer has prompted efforts to develop sensitive quantitation methods. 8-Hydroxy-2'-deoxyguanosine (8-OHdG) is a widely used marker for oxidative damage to DNA. To develop an immunoassay for quantitation of 8-OHdG, two monoclonal antibodies have been developed and characterized by competitive ELISA. Antibody IF7 has 50% inhibition at 5 pmol 8-OHdG and 1×105 pmol dG, while antibody IF11 has 50% inhibition at 2.5 pmol 8-OHdG and 2000 pmol dG. Both antisera cross-react with guanosine and several structurally related derivs., including 6- and 8-mercaptoguanosine, 8-bromoguanosine, 8-methylguanine, and 7-methylguanosine. Immunoaffinity columns were prepd. with antibody IF7, which exhibits higher selectivity than IF11, to isolate 8-OHdG from DNA hydrolyzates followed by ELISA quantitation with antibody 1F11. This method allows the anal. of approx. one 8-OHdG/105 dG using 100 μg DNA. To validate the assay, DNA extd. from human placental tissues were assayed by both ELISA and HPLC with electrochem. detection. Values by both methods correlated well (r = 0.87), but the levels detd. by ELISA were approx. 6-fold higher than those detd. by HPLC. This may be due to oligonucleotides detected by the ELISA but not the HPLC method or cross-reactivity with other damaged bases present in the immunoaffinity-purified material. Placental samples from current smokers had significantly higher 8-OHdG by ELISA than those from nonsmokers. The method of immunoaffinity purifn. combined with ELISA quantitation has sufficient sensitivity for detecting 8-OHdG in human DNA samples. Although abs. values are higher than those detd. by HPLC, the method provides a good alternative to the HPLC-EC method for monitoring relative oxidative damage in mol. epidemiol. studies.
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Yue, J.; Wang, P.; Liu, Y. H.; Wu, J. Y.; Chen, J.; Peng, R. X. Fast evaluation of oxidative DNA damage by liquid chromatography-electrospray tandem mass spectrometry coupled with precision-cut rat liver slices Biomed. Environ. Sci. 2007, 20, 386– 391
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53
Valavanidis, A.; Vlachogianni, T.; Fiotakis, C. 8-hydroxy-2′-deoxyguanosine (8-OHdG): A critical biomarker of oxidative stress and carcinogenesis J. Environ. Sci. Health C Environ. Carcinog. Ecotoxicol. Rev. 2009, 27, 120– 139 DOI: 10.1080/10590500902885684
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8-hydroxy-2' -deoxyguanosine (8-OHdG): A Critical Biomarker of Oxidative Stress and Carcinogenesis
Valavanidis, Athanasios; Vlachogianni, Thomais; Fiotakis, Constantinos
Journal of Environmental Science and Health, Part C: Environmental Carcinogenesis & Ecotoxicology Reviews (2009), 27 (2), 120-139CODEN: JESHA2 ISSN:. (Taylor & Francis, Inc.)
A review. There is extensive exptl. evidence that oxidative damage permanently occurs to lipids of cellular membranes, proteins, and DNA. In nuclear and mitochondrial DNA, 8-hydroxy-2' -deoxyguanosine (8-OHdG) or 8-oxo-7,8-dihydro-2' -deoxyguanosine (8-oxodG) is one of the predominant forms of free radical-induced oxidative lesions, and has therefore been widely used as a biomarker for oxidative stress and carcinogenesis. Studies showed that urinary 8-OHdG is a good biomarker for risk assessment of various cancers and degenerative diseases. The most widely used method of quant. anal. is high-performance liq. chromatog. (HPLC) with electrochem. detection (EC), gas chromatog.-mass spectrometry (GC-MS), and HPLC tandem mass spectrometry. In order to resolve the methodol. problems encountered in measuring quant. 8-OHdG, the European Stds. Committee for Oxidative DNA Damage was set up in 1997 to resolve the artifactual oxidn. problems during the procedures of isolation and purifn. of oxidative DNA products. The biomarker 8-OHdG or 8-oxodG has been a pivotal marker for measuring the effect of endogenous oxidative damage to DNA and as a factor of initiation and promotion of carcinogenesis. The biomarker has been used to est. the DNA damage in humans after exposure to cancer-causing agents, such as tobacco smoke, asbestos fibers, heavy metals, and polycyclic arom. hydrocarbons. In recent years, 8-OHdG has been used widely in many studies not only as a biomarker for the measurement of endogenous oxidative DNA damage but also as a risk factor for many diseases including cancer.
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Steenken, S.; Jovanovic, S. V. How easily oxidizable is DNA? One-electron reduction potentials of adenosine and guanosine radicals in aqueous solution J. Am. Chem. Soc. 1997, 119, 617– 618 DOI: 10.1021/ja962255b
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How Easily Oxidizable Is DNA? One-Electron Reduction Potentials of Adenosine and Guanosine Radicals in Aqueous Solution
Steenken, Steen; Jovanovic, Slobodan V.
Journal of the American Chemical Society (1997), 119 (3), 617-618CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Redn. potentials (vs. NHE) of the purine nucleosides, adenosine and guanosine, were detd. by pulse radiolysis in aq. solns. The value for the guanosine radical at pH 7, E7 = 1.29±0.03 V (E0 = 1.58 V), was obtained from the electron transfer equil. in both directions, with thioanisole (E7 = 1.44 V) and with 1,2,4-trimethoxybenzene (E7 = 1.13 V) radical cations, resp., as ref. couples. For adenosine radical, the electron transfer equil. with thioanisole were measured at pH 5 and 3, to be E5 = 1.56±0.02 V and E3 = 1.64±0.04 V, to evaluate the pH dependence of the redn. potential. From the pH dependence the value in neutral media is E7 = 1.42 V (E0 = 2.03 V). The values of the redn. potentials of guanosine and adenosine radicals are considerably higher than the previously published ones. Because the redn. potential of guanosine radical (the lowest of all the DNA base radicals) is lower than the E7 = 1.05 V of alkylperoxyl radicals, the oxidative damage of DNA by, e.g., lipid peroxyl radicals via electron transfer is not thermodynamically feasible. The redn. potential of guanosine radical is considerably higher than those of arom. and sulfur amino acid radicals, e.g., E7 (Trp) = 1.01 V, which means that the "hole" in (oxidized) DNA can migrate to a histone protein provided it contains these amino acids.
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A review. Gold nanoparticles (AuNPs) provide non-toxic carriers for drug and gene delivery applications. With these systems, the gold core imparts stability to the assembly, while the monolayer allows tuning of surface properties such as charge and hydrophobicity. An addnl. attractive feature of AuNPs is their interaction with thiols, providing an effective and selective means of controlled intracellular release.
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Gamal-Eldeen, A. M.; Abo-Zeid, M. A. M.; El-Daly, S. M.; Abo-Elfadl, M. T.; Fahmy, C. A.; Ali, M. R. K.; El-Sayed, M. A. In vivo genotoxicity of gold nanorods in mouse bone marrow compared with cyclophosphamide Nano Biomed. Eng. 2016, 8, 306– 314 DOI: 10.5101/nbe.v8i4.p306-314
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Abstract
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Figure 1
Figure 1. Formation of Au-nanoparticles (AuNPs) by the acid guanidinium thiocyanate–phenol–chloroform (GTPC) fraction (= bRNA) in Au(III) chloride (HAuCl₄) solution. (a) The clear yellow HAuCl₄ solution (left) changed to turbid brown (middle) within 4 h after mixing with the GTPC fraction; a brown precipitate formed (right) after 16 h. (b) GC spectrum of sugar composition of GTPC fraction shows a prominent ribose peak. Based on this result, the fraction was regarded as bacterial RNA (bRNA) (left). Electrophoretic patterns of RNase A-treated (right lane) and -untreated bRNA (left lane, Mock) in agarose gel, indicating that bRNA was degraded but not completely (right). (c) STEM images (left) and ED patterns (right) of freeze-dried precipitates obtained from mixture of bRNA and HAuCl₄ solution. Electron-dense particles scattered on the aggregated bRNA (left upper). The particles are nearly spherical in the enlarged image (left, lower). Scale bar = 10nm, upper; 5 nm, lower. ED patterns obtained from the particles (P1 and P2 in left upper image). From calculations using diffraction indices, Au(200) and Au(020) crystal faces were present in P1 and Au(200) in P2 (right upper and lower). (d) Histogram of AuNP diameters measured in STEM images (average 6.1 ± 1.4 nm). (e) XRD patterns of precipitates from bRNA-mixed HAuCl₄ solution and UPW (Mock) after 16 h incubation, showing the presence of Au(111), Au(200), Au(220), Au(311), and Au(222) crystal faces in the former precipitate but not in the latter.
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Figure 2
Figure 2. Formation of Au-nanoparticles (AuNPs) by incubation of RNA nucleosides with Au(III) chloride (HAuCl₄) solution. (a) Colors of HAuCl₄ solution after mixing with either of four RNA nucleosides (adenosine, uridine, guanosine, or cytidine). The mixture started to change color within 1 min after mixing with guanosine and after 1 h with adenosine, but remained unchanged until 1 h after mixing with uridine and cytidine. The precipitate (bottom, arrowheads) and supernatant were obtained by centrifugation at 16 h. (b) TEM image of electron-dense spherical particles on surface of aggregated guanosine obtained from supernatant after 16 h incubation (upper). Scale bar = 5 nm. The ED pattern obtained from an electron-dense particle shows several spots (arrows) reflecting the presence of metallic Au (lower). (c) Histogram of AuNP diameters measured from the TEM images (average 3.5 ± 0.8 nm). (d) TEM image showing absence of electron-dense particles on surface of aggregated adenosine obtained from supernatant (left). Scale bar = 5 nm. The ED pattern obtained from the aggregated adenosine lacked signals for metallic Au (right). (e) XRD patterns from supernatant and precipitate from guanosine-mixed HAuCl₄ solution after 16 h incubation: only the supernatant showed the presence of Au(111), Au(200), Au(220), Au(311), and Au(222) crystal faces. □: unidentified peaks. (f) XRD patterns from supernatant and precipitate from adenosine-mixed HAuCl₄ solution after 16 h incubation. Note lack of signal for Au in both specimens. Mock = guanosine or adenosine mixed with UPW.
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Figure 3
Figure 3. Detection of chemical modification of 2′-deoxy guanosine (dG) and generation of 8-hydroxy-2′-deoxyguanosine (8-OHdG) from calf thymus DNA during incubation in Au(III) chloride (HAuCl₄) solution. (a) HPLC analysis of dG after 0 to 240 min in HAuCl₄ solution. One dG peak was detected at a retention time of approximately 18 min at each time. Note that its absorbance level was quite high at time 0 but was much lower from 30 to 240 min and that an additional unidentified peak appeared at a retention time of approximately 19.5 min (arrows). (b) Specific antibody-based colorimetric detection of 8-OHdG production from various concentrations of DNA incubated in HAuCl₄ solution for 12 h. DNA dissolved in UPW was used as the mock sample. (c) Time-course analysis of 8-OHdG production after incubation of 40 ng of DNA in HAuCl₄ solution.
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Scheme 1
Scheme 1. Construable Mechanism of 8-OHdG Generation Coupled with Au(III) Reduction Based on Earlier Proposals for Formation of an Au(III)–DNA Complex and for Oxidative DNA Damage to the Guanine Moiety^a
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Scheme aInitially, a chelating adduct by binding Au(III) to guanine moiety through N7 and O6 (a), or a radical adduct by interacting of through guanine C8 (b) is generated. Secondly, the encounter of (a) with HO• or (b) with Au(III) leads to form a chelating and radical adduct (c). Then, the electron abstraction occurs from guanine N7 to Au(III) and eventually reduces Au(III) to lead 8-OHdG generation (d).
Figure 4
Figure 4. Potential of Au-nanoparticle (AuNP) formation by 8-hydroxy-2′-deoxyguanosine (8-OHdG) and 2′-deoxy guanosine (dG) in HAuCl₄ solution. (a) The visual appearance of samples after dG (middle) or 8-OHdG (right) was mixed with HAuCl₄ solution. Only the mixture with dG turned brown within 5 min. The supernatant was obtained by centrifugation of the 16-h sample. (b) TEM images (upper) and ED pattern (lower) of the supernatant collected from dG– or 8-OHdG–HAuCl₄ solution at 16 h. Electron-dense particles were observed on the aggregated dG (upper left) but not on the aggregated 8-OHdG (upper right). Scale bar = 5 nm, left; 2 nm, right. Consistently, spots indicating the presence of metallic Au were detected on the aggregated dG (lower left, arrows) but not on the aggregated 8-OHdG (lower right). (c) Histogram of AuNP diameters measured from the TEM images (mean 4.4 ± 0.9 nm). (d) XRD analyses of supernatant and precipitate obtained from dG-suspended HAuCl₄ solution. A suspension of dG in UPW was used as a negative control (Mock). The presence of metallic Au was indicated only in the HAuCl₄ supernatant. □: unidentified peaks.
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7. 7
  Cui, D.; Ma, L.; Zhi, X.; Zhang, C. Advance and prospects of nanotheranostic tchnology for gastric cancer Nano Biomed. Eng. 2016, 8, 219– 239 DOI: 10.5101/nbe.v8i4.p219-239
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8. 8
  Takale, B. S.; Bao, M.; Yamamoto, Y. Gold nanoparticle (AuNPs) and gold nanopore (AuNPore) catalysts in organic synthesis Org. Biomol. Chem. 2014, 12, 2005– 2027 DOI: 10.1039/c3ob42207k
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  8
  Gold nanoparticle (AuNPs) and gold nanopore (AuNPore) catalysts in organic synthesis
  Takale, Balaram S.; Bao, Ming; Yamamoto, Yoshinori
  Organic & Biomolecular Chemistry (2014), 12 (13), 2005-2027CODEN: OBCRAK; ISSN:1477-0520. (Royal Society of Chemistry)
  A review. Org. synthesis using gold has gained tremendous attention in last few years, esp. heterogeneous gold catalysis based on gold nanoparticles has made its place in almost all org. reactions, because of the robust and green nature of gold catalysts. In this context, gold nanopore (AuNPore) with a 3D metal framework is giving a new dimension to heterogeneous gold catalysts. Interestingly, AuNPore chem. is proving better than gold nanoparticles based chem. In this review, along with recent advances, major discoveries in heterogeneous gold catalysis are discussed.
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9. 9
  Yamamoto, M.; Kashiwagi, Y.; Nakamoto, M. Size-controlled synthesis of gold nanoparticles by thermolysis of a gold(I)-sulfide complex in the presence of alkylamines Z. Naturforsch., B: J. Chem. Sci. 2009, 64, 1305– 1311 DOI: 10.1515/znb-2009-11-1208
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  9
  Size-controlled synthesis of gold nanoparticles by thermolysis of a gold(I)-sulfide complex in the presence of alkylamines
  Yamamoto, Mari; Kashiwagi, Yukiyasu; Nakamoto, Masami
  Zeitschrift fuer Naturforschung, B: A Journal of Chemical Sciences (2009), 64 (11/12), 1305-1311CODEN: ZNBSEN; ISSN:0932-0776. (Verlag der Zeitschrift fuer Naturforschung)
  A size-controlled synthesis of gold nanoparticles has been developed by the thermolysis of AuCl(SMe2) in the presence of alkylamines at 120 °C. In the procedure, the key intermediate was [Au(NH2R)2]Cl, detected by electrospray ionization (ESI) mass spectrometry. This thermally unstable intermediate was reduced by alkylamines under mild conditions to produce alkylamine-capped gold nanoparticles. The av. diams. of the gold nanoparticles could be regulated in a range from 4.3 to 6.1 nm by applying primary alkylamines with alkyl chains of different lengths. Larger gold nanoparticles with diams. from 10 to 22 nm were prepd. by a combination of alkylamines and alkylcarboxylic acids with various lengths of the alkyl chains. The gold nanoparticles were characterized by transmission electron microscopy (TEM), UV/Vis absorption spectroscopy, powder X-ray diffraction (PXRD), XPS, gas chromatog./mass spectroscopy (GC/MS), and thermogravimetric and differencial thermal analyses (TG/DTA).
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10. 10
  Kumar, B.; Smita, K.; Sánchez, E.; Guerra, S.; Cumbal, L. Ecofriendly ultrasound-assisted rapid synthesis of gold nanoparticles using Calothrix algae Adv. Nat. Sci.: Nanosci. Nanotechnol. 2016, 7, 025013 DOI: 10.1088/2043-6262/7/2/025013
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11. 11
  Vo, K. D. N.; Guillon, E.; Dupont, L.; Kowandy, C.; Coqueret, X. Influence of Au(III) interactions with chitosan on gold nanoparticle formation J. Phys. Chem. C 2014, 118, 4465– 4474 DOI: 10.1021/jp4112316
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  11
  Influence of Au(III) Interactions with Chitosan on Gold Nanoparticle Formation
  Vo, Khoa Dang Nguyen; Guillon, Emmanuel; Dupont, Laurent; Kowandy, Christelle; Coqueret, Xavier
  Journal of Physical Chemistry C (2014), 118 (8), 4465-4474CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
  Potentiometry, electronic spectroscopy, and X-ray absorption (XAS) expts. were carried out to monitor the course of the complexation reaction between AuCl4- and glucosamine moieties (GLA) of chitosan mols. The disappearance of the ligand (π)-metal (σ*) charge transfer (LMCT) band at 313 nm, characteristic of the AuCl4- ion, upon the addn. of chitosan evidenced the complexation of Au(III) with glucosamine moieties at pH 4. The coordination sphere of Au(III) was detd. from the results of XAS expts. in the case of a [GLA]/[Au(III)] ratio equal to 1/4. The Au-Cl and Au-O(N) bond lengths were detd. Finally, preliminary results of gold nanoparticle synthesis by Au(III) redn. under electron beam in the presence of chitosan were presented. The influence of gold speciation on the size of preformed Au(0) clusters was evidenced.
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12. 12
  Augustine, A. K.; Nampoori, V. P.N.; Kailasnath, M. Rapid synthesize of gold nanoparticles by microwave irradiation method and its application as an optical limiting material Optik 2014, 125, 6696– 6699 DOI: 10.1016/j.ijleo.2014.08.075
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  12
  Rapid synthesize of gold nanoparticles by microwave irradiation method and its application as an optical limiting material
  Augustine, Anju K.; Nampoori, V. P. N.; Kailasnath, M.
  Optik (Munich, Germany) (2014), 125 (22), 6696-6699CODEN: OTIKAJ; ISSN:0030-4026. (Elsevier GmbH)
  We present rapid synthesis of gold nanoparticles by microwave irradn. method. Sample with av. particle size 7.7 nm is obtained from TEM. Linear and nonlinear optical studies of the prepd. samples are discussed. Reverse saturable absorption (RSA) at longitudinal surface plasmon resonance (SPR) in gold nanoparticles (Au NPs) have been obsd. using Z-scan and transient absorption techniques with 532 nm laser pulses. Such RSA behavior makes Au NPs an ideal candidate for optical limiting applications.
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13. 13
  Tue Anh, N.; Phu, D. V.; Duy, N. N.; Du, B. D.; Hien, N. Q. Synthesis of alginate stabilized gold nanoparticles by gamma-irradiation with controllable size using different Au³⁺ concentration and seed particles enlargement Radiat. Phys. Chem. 2010, 79, 405– 408 DOI: 10.1016/j.radphyschem.2009.11.013
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14. 14
  Hermannsdörfer, J.; de Jonge, N.; Verch, A. Electron beam induced chemistry of gold nanoparticles in saline solution Chem. Commun. 2015, 51, 16393– 16396 DOI: 10.1039/C5CC06812F
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  14
  Electron beam induced chemistry of gold nanoparticles in saline solution
  Hermannsdorfer J; de Jonge N; Verch A
  Chemical communications (Cambridge, England) (2015), 51 (91), 16393-6 ISSN:.
  It was studied how the chemistry of gold nanoparticles in water is influenced by solution parameters such as the pH or the NaCl concentration under electron beam irradiation. We found that depending on these parameters the gold nanoparticles either dissolved, merged or remained unchanged.
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15. 15
  Ji, X.; Song, X.; Li, J.; Bai, Y.; Yang, W.; Peng, X. Size control of gold nanocrystals in citrate reduction: the third role of citrate J. Am. Chem. Soc. 2007, 129, 13939– 13948 DOI: 10.1021/ja074447k
  [ACS Full Text ], [CAS], Google Scholar
  15
  Size Control of Gold Nanocrystals in Citrate Reduction: The Third Role of Citrate
  Ji, Xiaohui; Song, Xiangning; Li, Jun; Bai, Yubai; Yang, Wensheng; Peng, Xiaogang
  Journal of the American Chemical Society (2007), 129 (45), 13939-13948CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Growth kinetics and temporal size/shape evolution of gold nanocrystals by citrate redn. in boiling water were studied systematically and quant. Results reveal that the size variation and overall reaction mechanism were mostly detd. by the soln. pH that was in turn controlled by the concn. of sodium citrate (Na3Ct) in the traditional Frens's synthesis. This conclusion was further confirmed by the reactions with variable pH but fixed concns. of the two reactants, HAuCl4 and Na3Ct. Two substantially different reaction pathways were identified, with the switching point at pH = 6.2-6.5. The first pathway is for the low pH range and consists of three overlapping steps: nucleation, random attachment to polycryst. nanowires, and smoothing of the nanowires via intra-particle ripening to dots. The second pathway that occurred above the pH switching point is consistent with the commonly known nucleation-growth route. Using the second pathway, we demonstrated a new synthetic route for the synthesis of nearly monodisperse gold nanocrystals in the size range from 20 to 40 nm by simply varying the soln. pH with fixed concns. of HAuCl4 and Na3Ct. The switching of the reaction pathways is likely due to the integration nature of water as a reaction medium. In the citrate redn., the soln. pH was varied by changing the initial HAuCl4/Na3Ct ratio. Consequently, when pH was higher than about 6.2, the very reactive [AuCl3(OH)]- would be converted to less reactive [AuCl2(OH)2]- and [AuCl(OH)3]-.
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16. 16
  Tyagi, H.; Kushwaha, A.; Kumar, A.; Aslam, M. pH-dependent synthesis of stabilized gold nanoparticles using ascorbic acid Int. J. Nanosci. 2011, 10, 857– 860 DOI: 10.1142/S0219581X11009301
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  16
  pH-DEPENDENT SYNTHESIS OF STABILIZED GOLD NANOPARTICLES USING ASCORBIC ACID
  Tyagi, Himanshu; Kushwaha, Ajay; Kumar, Anshuman; Aslam, M.
  International Journal of Nanoscience (2011), 10 (4 & 5), 857-860CODEN: IJNNAJ; ISSN:0219-581X. (World Scientific Publishing Co. Pte. Ltd.)
  The stabilization of gold nanoparticles soln. synthesized using ascorbic acid at room temp. is examd. in detail. It is found that gold nanoparticles (AuNPs) synthesized using ascorbic acid have a narrow size distribution (31 ± 5, 36 ± 6, and 40 ± 5 nm) and can be readily stabilized just by adjusting the initial pH conditions of the reaction solns. While the initial pH strongly affects the stability of particles, it has no effect on the size of stabilized particles. The particles are nearly spherical having size distribution effectively in the range of 30 nm to 40 nm. Through time dependent UV-Vis spectra studies we also hypothesize the pH dependent stabilization mechanism wherein a layer of adsorbed ionic complex over AuNPs slows down the aggregation of AuNPs. The information obtained in this study can be used to design in-situ controlled nanoparticle synthesis system esp. within the biol. cells. Moreover, the method is green and biol. acceptable as well.
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17. 17
  Deraedt, C.; Salmon, L.; Gatard, S.; Ciganda, R.; Hernandez, R.; Ruiz, J.; Astruc, D. Sodium borohydride stabilizes very active gold nanoparticle catalysts Chem. Commun. 2014, 50, 14194– 14196 DOI: 10.1039/C4CC05946H
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  17
  Sodium borohydride stabilizes very active gold nanoparticle catalysts
  Deraedt, Christophe; Salmon, Lionel; Gatard, Sylvain; Ciganda, Roberto; Hernandez, Ricardo; Ruiz, Jaime; Astruc, Didier
  Chemical Communications (Cambridge, United Kingdom) (2014), 50 (91), 14194-14196CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
  Long-term stable 3 nm gold nanoparticles are prepd. by a simple reaction between HAuCl4 and sodium borohydride in water under ambient conditions which very efficiently catalyze 4-nitrophenol redn. to 4-nitroaniline.
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18. 18
  Zhao, W.; Gonzaga, F.; Li, Y.; Brook, M. A. Highly stabilized nucleotide-capped small gold nanoparticles with tunable size Adv. Mater. 2007, 19, 1766– 1771 DOI: 10.1002/adma.200602449
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  18
  Highly stabilized nucleotide-capped small gold nanoparticles with tunable size
  Zhao, Weian; Gonzaga, Ferdinand; Li, Yingfu; Brook, Michael A.
  Advanced Materials (Weinheim, Germany) (2007), 19 (13), 1766-1771CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Improved stability of gold nanoparticles in water is achieved by capping the particles. Such stability improvements are significant because of the potential applications of the nanoparticles in various biol. relevant areas. The highly stabilized water-sol. Au nanoparticles have precisely tunable sizes ranging from 2 to 5 nm with a narrow monodispersity, and are prepd. by using nucleotides as capping ligands.
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19. 19
  Hostetler, M. J.; Wingate, J. E.; Zhong, C.-J.; Harris, J. E.; Vachet, R. W.; Clark, M. R.; Londono, J. D.; Green, S. J.; Stokes, J. J.; Wignall, G. D.; Glish, G. L.; Porter, M. D.; Evans, N. D.; Murray, R. W. Alkanethiolate gold cluster molecules with core diameters from 1.5 to 5.2 nm: core and monolayer properties as a function of core size Langmuir 1998, 14, 17– 30 DOI: 10.1021/la970588w
  [ACS Full Text ], [CAS], Google Scholar
  19
  Alkanethiolate Gold Cluster Molecules with Core Diameters from 1.4 to 5.2 Nanometers: Core and Monolayer Properties as a Function of Core Size
  Hostetler, Michael J.; Wingate, Julia E.; Zhong, Chuan-Jian; Harris, Jay E.; Vachet, Richard W.; Clark, Michael R.; Londono, J. David; Green, Stephen J.; Stokes, Jennifer J.; Wignall, George D.; Glish, Gary L.; Porter, Marc D.; Evans, Neal D.; Murray, Royce W.
  Langmuir (1998), 14 (1), 17-30CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
  The mean size of the gold (Au) core in the synthesis of dodecanethiolate-stabilized Au cluster compds. can be finely adjusted by choice of the Au:dodecanethiolate ratio and the temp. and rate at which the redn. is conducted. The Au clusters have been examd. with a large no. of independent anal. tools, producing a remarkably consistent picture of these materials. Av. cluster and core dimensions, as ascertained by 1H NMR line broadening, high-resoln. transmission electron microscopy, small-angle X-ray scattering, and thermogravimetric anal., vary between diams. of 1.4 and 5.2 nm (∼110-4800 Au atoms/core). The electronic properties of the Au core were examd. by UV/vis and XPS; the core appears to remain largely metallic in nature even at the smallest core sizes examd. The alkanethiolate monolayer stabilizing the Au core ranges with core size from ∼53 to nearly 520 ligands/core, and was probed by Fourier transform IR spectroscopy, differential scanning calorimetry, contact-angle measurements, and thermal desorption mass spectrometry. The dodecanethiolate monolayer on small and large core clusters exhibits discernable differences; the line dividing "3-dimensional" monolayers and those resembling self-assembled monolayers on flat Au (2-dimensional monolayers) occurs at clusters with ∼4.4 nm core diams.
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20. 20
  Weare, W. W.; Reed, S. M.; Warner, M. G.; Hutchison, J. E. Improved synthesis of small (d_CORE ≈ 1.5 nm) phosphine-stabilized gold nanoparticles J. Am. Chem. Soc. 2000, 122, 12890– 12891 DOI: 10.1021/ja002673n
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  20
  Improved synthesis of small (dCORE ≈ 1.5 nm) phosphine-stabilized gold nanoparticles
  Weare, Walter W.; Reed, Scott M.; Warner, Marvin G.; Hutchison, James E.
  Journal of the American Chemical Society (2000), 122 (51), 12890-12891CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  A safer, more convenient, and more versatile synthesis of phosphine-stabilized Au nanoparticles is given which eliminates the use of diborane or borane and can be carried out quickly under ambient conditions. The nanoparticles are prepd. in a single step with NaBH4 instead of diborane which should permit the use of this material in a wider range of applications. The synthesis allows control over the particle core size and is tolerant of a variety of phosphine ligands to provide access to previously unknown phosphine-stabilized nanoparticles.
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21. 21
  Raveendran, P.; Fu, J.; Wallen, S. L. Completely “green” synthesis and stabilization of metal nanoparticles J. Am. Chem. Soc. 2003, 125, 13940– 13941 DOI: 10.1021/ja029267j
  [ACS Full Text ], [CAS], Google Scholar
  21
  Completely green synthesis and stabilization of metal nanoparticles
  Raveendran, Poovathinthodiyil; Fu, Jie; Wallen, Scott L.
  Journal of the American Chemical Society (2003), 125 (46), 13940-13941CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  A completely green synthetic method for producing silver nanoparticles is introduced. The process is simple, environmentally benign and quite efficient. By gentle heating of an aq. starch soln. contg. silver nitrate and glucose, relatively monodisperse, starched silver nanoparticles are produced. β-D-Glucose serves as the green reducing agent, while starch serves as the stabilization agent.
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22. 22
  Ulman, A. Formation and Structure of Self-Assembled Monolayers Chem. Rev. 1996, 96, 1533– 1554 DOI: 10.1021/cr9502357
  [ACS Full Text ], [CAS], Google Scholar
  22
  Formation and Structure of Self-Assembled Monolayers
  Ulman, Abraham
  Chemical Reviews (Washington, D. C.) (1996), 96 (4), 1533-1554CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
  A review on the organization of complex, semiflexible org. mols. within quasi-2-D assemblies due to the delicate interplay between substrate-adsorbate interactions, nonbonded interactions between adsorbates, electrostatic and VDW forces, and intramol. interactions (e.g., bond stretches, angle bends, and torsions). Surface reorganization contributes to the final equil. structure of the assembly. Structural factors controlling the formation of self-assembled monolayers (SAMs) are discussed. Different SAMs with unique properties and potential applications are considered. An attempt is made to provide a general picture of self-assembly on solid surfaces as it emerges from a consideration of the interplay of different forces that control this process. 273 Refs.
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23. 23
  Ishida, Y.; Akita, I.; Sumi, T.; Matsubara, M.; Yonezawa, T. Thiolate-protected gold nanoparticles via physical approach: unusual structural and photophysical characteristics Sci. Rep. 2016, 6, 29928 DOI: 10.1038/srep29928
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  23
  Thiolate-Protected Gold Nanoparticles Via Physical Approach: Unusual Structural and Photophysical Characteristics
  Ishida, Yohei; Akita, Ikumi; Sumi, Taiki; Matsubara, Masaki; Yonezawa, Tetsu
  Scientific Reports (2016), 6 (), 29928CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
  Here we report a novel phys. approach for thiolate-protected fluorescent gold nanoparticles with a controlled size of the order of a few nanometers. This approach is based on a sputtering of gold into a liq. matrix contg. thiolate ligand as a stabilizer at various concns., thus no reductant was used. The size of the gold nanoparticles was successfully controlled to range from 1.6 to 7.4 nm by adjusting the thiol concns. Surface plasmon absorption was obsd. in larger nanoparticles, but it was not obsd. in smaller ones. Such smaller nanoparticles fluoresced at around 670 nm with a small spectral shift according to their size, however, the diam. (1.6-2.7 nm) was very strange to show such red emission compared with photophys. characteristics of reported gold cluster or nanoparticles synthesized by chem. method. By detailed investigations using TEM, HAADF-STEM, XPS, and TGA, and size fractionation by size exclusion chromatog., we finally arrived at the plausible mechanism for the origin of unusual fluorescence property; the obtained gold nanoparticles are not single-crystal and are composed of aggregates of very small components such as multinuclear gold clusters or complexes.
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24. 24
  Shankar, S. S.; Rai, A.; Ankamwar, B.; Singh, A.; Ahmad, A.; Sastry, M. Biological synthesis of triangular gold nanoprisms Nat. Mater. 2004, 3, 482– 488 DOI: 10.1038/nmat1152
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  24
  Biological synthesis of triangular gold nanoprisms
  Shankar, S. Shiv; Rai, Akhilesh; Ankamwar, Balaprasad; Singh, Amit; Ahmad, Absar; Sastry, Murali
  Nature Materials (2004), 3 (7), 482-488CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
  The optoelectronic and physicochem. properties of nanoscale matter are a strong function of particle size. Nanoparticle shape also contributes significantly to modulating their electronic properties. Several shapes ranging from rods to wires to plates to teardrop structures may be obtained by chem. methods; triangular nanoparticles have been synthesized by using a seeded growth process. Here, we report the discovery that the ext. from the lemongrass plant, when reacted with aq. chloroaurate ions, yields a high percentage of thin, flat, single-cryst. gold nanotriangles. The nanotriangles seem to grow by a process involving rapid redn., assembly and room-temp. sintering of 'liq.-like' spherical gold nanoparticles. The anisotropy in nanoparticle shape results in large near-IR absorption by the particles, and highly anisotropic electron transport in films of the nanotriangles.
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25. 25
  Nune, S. K.; Chanda, N.; Shukla, R.; Katti, K.; Kulkarni, R. R.; Thilakavathy, S.; Mekapothula, S.; Kannan, R.; Katti, K. V. Green nanotechnology from tea: phytochemicals in tea as building blocks for production of biocompatible gold nanoparticles J. Mater. Chem. 2009, 19, 2912– 2920 DOI: 10.1039/b822015h
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  25
  Green nanotechnology from tea: phytochemicals in tea as building blocks for production of biocompatible gold nanoparticles
  Nune, Satish K.; Chanda, Nripen; Shukla, Ravi; Katti, Kavita; Kulkarni, Rajesh R.; Thilakavathy, Subramanian; Mekapothula, Swapna; Kannan, Raghuraman; Katti, Kattesh V.
  Journal of Materials Chemistry (2009), 19 (19), 2912-2920CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)
  Phytochems. occluded in tea have been extensively used as dietary supplements and as natural pharmaceuticals in the treatment of various diseases including human cancer. Results on the redn. capabilities of phytochems. present in tea to reduce gold salts to the corresponding gold nanoparticles are presented in this paper. The phytochems. present in tea serve a dual role as effective reducing agents to reduce gold and also as stabilizers to provide a robust coating on the gold nanoparticles in a single step. The tea-generated gold nanoparticles (T-AuNPs) have demonstrated remarkable in vitro stability in various buffers including saline, histidine, HSA, and cysteine solns. T-AuNPs with phytochem. coatings have shown significant affinity toward prostate (PC-3) and breast (MCF-7) cancer cells. Results on the cellular internalization of T-AuNPs through endocytosis into the PC-3 and MCF-7 cells are presented. The generation of T-AuNPs follows all principles of green chem. and T-AuNPs have been found to be non toxic as assessed through MTT assays. No man made' chems., other than gold salts, are used in this truly biogenic, green nanotechnol. process thus paving the way for excellent opportunities for their application in mol. imaging and therapy.
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26. 26
  Liu, B.; Xie, J.; Lee, J. Y.; Ting, Y. P.; Chen, J. P. Optimization of high-yield biological synthesis of single-crystalline gold nanoplates J. Phys. Chem. B 2005, 109, 15256– 15263 DOI: 10.1021/jp051449n
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  26
  Optimization of high-yield biological synthesis of single-crystalline gold nanoplates
  Liu, B.; Xie, J.; Lee, J. Y.; Ting, Y. P.; Chen, J. Paul
  Journal of Physical Chemistry B (2005), 109 (32), 15256-15263CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
  Single-cryst. gold nanoplates were obtained by reducing an aq. chloroauric acid soln. with the ext. of Sargassum sp. (brown seaweed) at room temp. The resulting gold nanoplates were characterized by UV-visible spectroscopy, x-ray diffraction, at. force microscopy, and TEM. The formation of gold nanoplates depended on a no. of environmental factors, such as the time taken to age the seaweed ext., pH of the reaction medium, reaction temp., reaction time, and initial reactant concns. The size of the gold nanoplates can be controlled to between 200 and 800 nm by manipulating the initial reactant concns. The yield of the flat gold nanocrystals relative to the total no. of nanoparticles formed was as high as ∼80-90%.
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27. 27
  Anshup, A.; Venkataraman, J. S.; Subramaniam, C.; Kumar, R. R.; Priya, S.; Kumar, T. R.; Omkumar, R. V.; John, A.; Pradeep, T. Growth of gold nanoparticles in human cells Langmuir 2005, 21, 11562– 11567 DOI: 10.1021/la0519249
  [ACS Full Text ], [CAS], Google Scholar
  27
  Growth of Gold Nanoparticles in Human Cells
  Anshup; Venkataraman, J. Sai; Subramaniam, Chandramouli; Kumar, R. Rajeev; Priya, Suma; Kumar, T. R. Santhosh; Omkumar, R. V.; John, Annie; Pradeep, T.
  Langmuir (2005), 21 (25), 11562-11567CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
  Gold nanoparticles of 20-100 nm diam. were synthesized within HEK-293 (human embryonic kidney), HeLa (human cervical cancer), SiHa (human cervical cancer), and SKNSH (human neuroblastoma) cells. Incubation of 1 mM tetrachloroaurate soln., prepd. in phosphate buffered saline (PBS), pH 7.4, with human cells grown to ∼80% confluency yielded systematic growth of nanoparticles over a period of 96 h. The cells, stained due to nanoparticle growth, were adherent to the bottom of the wells of the tissue culture plates, with their morphol. preserved, indicating that the cell membrane was intact. Transmission electron microscopy of ultrathin sections showed the presence of nanoparticles within the cytoplasm and in the nucleus, the latter being much smaller in dimension. Scanning near field microscopic images confirmed the growth of large particles within the cytoplasm. Normal cells gave UV-visible signatures of higher intensity than the cancer cells. Differences in the cellular metab. of cancer and noncancer cells were manifested, presumably in their ability to carry out the redn. process.
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28. 28
  Reith, F.; Etschmann, B.; Grosse, C.; Moors, H.; Benotmane, M. A.; Monsieurs, P.; Grass, G.; Doonan, C.; Vogt, S.; Lai, B.; Martinez-Criado, G.; George, G. N.; Nies, D. H.; Mergeay, M.; Pring, A.; Southam, G.; Brugger, J. Mechanisms of gold biomineralization in the bacterium Cupriavidus metallidurans Proc. Natl. Acad. Sci. U. S. A. 2009, 106, 17757– 17762 DOI: 10.1073/pnas.0904583106
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  28
  Mechanisms of gold biomineralization in the bacterium Cupriavidus metallidurans
  Reith, Frank; Etschmann, Barbara; Grosse, Cornelia; Moors, Hugh; Benotmane, Mohammed A.; Monsieurs, Pieter; Grass, Gregor; Doonan, Christian; Vogt, Stefan; Lai, Barry; Martinez-Criado, Gema; George, Graham N.; Nies, Diestrich H.; Mergeay, Max; Pring, Allan; Southam, Gordon; Brugger, Joel
  Proceedings of the National Academy of Sciences of the United States of America (2009), 106 (42), 17757-17762, S17757/1-S17757/31CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
  While the role of microorganisms as main drivers of metal mobility and mineral formation under Earth surface conditions is now widely accepted, the formation of secondary gold (Au) is commonly attributed to abiotic processes. Here, the authors report that the biomineralization of Au nanoparticles in the metallophillic bacterium Cupriavidus metallidurans CH34 is the result of Au-regulated gene expression leading to the energy-dependent reductive pptn. of toxic Au(III)-complexes. C. metallidurans, which forms biofilms on Au grains, rapidly accumulates Au(III)-complexes from soln. Bulk and microbeam synchrotron X-ray analyses revealed that cellular Au accumulation is coupled to the formation of Au(I)-S complexes. This process promotes Au toxicity and C. metallidurans reacts by inducing oxidative stress and metal resistances gene clusters (including a Au-specific operon) to promote cellular defense. As a result, Au detoxification is mediated by a combination of efflux, redn., and possibly methylation of Au-complexes, leading to the formation of Au(I)-C-compds. and nanoparticulate Au0. Similar particles were obsd. in bacterial biofilms on Au grains, suggesting that bacteria actively contribute to the formation of Au grains in surface environments. The recognition of specific genetic responses to Au opens the way for the development of bioexploration and bioprocessing tools.
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29. 29
  Reith, F.; Lengke, M. F.; Falconer, D.; Craw, D.; Southam, G. The geomicrobiology of gold ISME J. 2007, 1, 567– 584 DOI: 10.1038/ismej.2007.75
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30. 30
  Johnston, C. W.; Wyatt, M. A.; Li, X.; Ibrahim, A.; Shuster, J.; Southam, G.; Magarvey, N. A. Gold biomineralization by a metallophore from a gold-associated microbe Nat. Chem. Biol. 2013, 9, 241– 243 DOI: 10.1038/nchembio.1179
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  Gold biomineralization by a metallophore from a gold-associated microbe
  Johnston, Chad W.; Wyatt, Morgan A.; Li, Xiang; Ibrahim, Ashraf; Shuster, Jeremiah; Southam, Gordon; Magarvey, Nathan A.
  Nature Chemical Biology (2013), 9 (4), 241-243CODEN: NCBABT; ISSN:1552-4450. (Nature Publishing Group)
  Microorganisms produce and secrete secondary metabolites to assist in their survival. The authors report that the gold resident bacterium Delftia acidovorans produces a secondary metabolite that protects from sol. gold through the generation of solid gold forms. This finding is the first demonstration that a secreted metabolite can protect against toxic gold and cause gold biomineralization.
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31. 31
  Mandal, D.; Bolander, M. E.; Mukhopadhyay, D.; Sarkar, G.; Mukherjee, P. The use of microorganisms for the formation of metal nanoparticles and their application Appl. Microbiol. Biotechnol. 2006, 69, 485– 492 DOI: 10.1007/s00253-005-0179-3
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32. 32
  Leng, Y.; Fu, L.; Ye, L.; Li, B.; Xu, X.; Xing, X.; He, J.; Song, Y.; Leng, C.; Guo, Y.; Ji, X.; Lu, Z. Protein-directed synthesis of highly monodispersed, spherical gold nanoparticles and their applications in multidimensional sensing Sci. Rep. 2016, 6, 28900 DOI: 10.1038/srep28900
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  32
  Protein-directed synthesis of highly monodispersed, spherical gold nanoparticles and their applications in multidimensional sensing
  Leng, Yumin; Fu, Ling; Ye, Liqun; Li, Bo; Xu, Xiumei; Xing, Xiaojing; He, Junbao; Song, Yuling; Leng, Chaoliang; Guo, Yongming; Ji, Xiaoxu; Lu, Zhiwen
  Scientific Reports (2016), 6 (), 28900pp.CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
  An in-situ redn. method has been reported to prep. gold nanoparticles (GNPs) of 40-110 nm by using the green reducing agents of proteins, which are activated by H2O2 and the superoxide anion ([Formula Omitted]). The protein of collagen turns HAuCl4 to the aq. Au(I) ainions, which are further reduced by other proteins to be highly monodispersed and spherical GNPs of different sizes. The GNPs reduced by different proteins are found to be with the exposed {100} facets, the distinctive UV-vis absorption spectra and various colors (See Fig. 1). By means of extg. the color responses, such as red, green and blue (RGB) alterations, an in-situ redn. method-based multidimensional sensing platform is fabricated in the process of GNPs synthesis. Without further modification of GNPs, nine common proteins are found to be well detected and discriminated at different concns. Moreover, this sensing platform also demonstrates great potentials in qual. and semiquant. anal. on the individuals of these proteins with high sensitivity. Furthermore, the validation of this multidimensional sensing platform has been carried out by anal. on the spiked proteins in human urine and the target proteins in complex matrix (e.g. lysozyme in human tear).
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33. 33
  Engelbrekt, C.; Sørensen, K. H.; Zhang, J.; Welinder, A. C.; Jensen, P. S.; Ulstrup, J. Green synthesis of gold nanoparticles with starch–glucose and application in bioelectrochemistry J. Mater. Chem. 2009, 19, 7839– 7847 DOI: 10.1039/b911111e
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  33
  Green synthesis of gold nanoparticles with starch-glucose and application in bioelectrochemistry
  Engelbrekt, Christian; Sorensen, Karsten H.; Zhang, Jingdong; Welinder, Anna C.; Jensen, Palle S.; Ulstrup, Jens
  Journal of Materials Chemistry (2009), 19 (42), 7839-7847CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)
  A method for gold nanoparticle (AuNP) synthesis from buffered glucose and starch soln. has been developed and the particles investigated by UV-Vis spectroscopy, TEM, at. force microscopy (AFM) and electrochem. The synthesis proceeds smoothly in neutral and basic soln. The starch concn., temp. and chem. nature of the buffers are key factors in the AuNP formation. Glucose and starch are reducing and protecting agents, resp. Among several inorg. and biol. Good's buffers, phosphate and MES buffers give the best results with quite uniform AuNPs. Other buffers do not result in well-defined nanoparticle structures. Typical AuNP diams. from MES and phosphate buffers (PB) are 4±1 nm and 13±2 nm with plasmon band peaks at 521 nm and 523 nm, resp. The role of the phosphate buffer is mainly to control the pH, while MES is also a synergist with more composite function. AuNPs prepd. by this method are stable in soln. even after 17 mo at room temp. TEM confirms the cryst. structure of the AuNPs, meaning that the AuNP surfaces are low-index single-crystal facets such as (100), (110) and (111). Electrochem. of the buffers at such single-crystal gold electrode surfaces has offered a more detailed understanding of the buffer effect. The AuNPs have been successfully used in bioelectrochem., and found to efficiently enhance interfacial electrochem. electron transfer of the metalloprotein yeast cytochrome c in homogeneous soln. The synthesis has been extended successfully to direct use of starch-rich foods such as potato, carrot and onion to synthesize AuNPs. The present work thus offers a gentle and nontoxic procedure for the synthesis of monodisperse AuNPs in neutral medium with promising potential for pH sensitive biol. or medically related applications.
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34. 34
  Wei, H.; Li, B.; Du, Y.; Dong, S.; Wang, E. Nucleobase–metal hybrid materials: Preparation of submicrometer-scale, spherical colloidal particles of adenine–gold(III) via a supramolecular hierarchical self-assembly approach Chem. Mater. 2007, 19, 2987– 2993 DOI: 10.1021/cm070028a
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  34
  Nucleobase-Metal Hybrid Materials: Preparation of Submicrometer-Scale, Spherical Colloidal Particles of Adenine-Gold(III) via a Supramolecular Hierarchical Self-Assembly Approach
  Wei, Hui; Li, Bingling; Du, Yan; Dong, Shaojun; Wang, Erkang
  Chemistry of Materials (2007), 19 (12), 2987-2993CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
  The authors report a simple and effective supramol. route for facile synthesis of submicrometer-scale, hierarchically self-assembled spherical colloidal particles of adenine-Au(III) hybrid materials at room temp. Simple mixt. of the precursor aq. solns. of adenine and HAuCl4 at room temp. could result in spontaneous formation of the hybrid colloidal particles. Optimization of the exptl. conditions could yield uniform-sized, self-assembled products at 1:4 molar ration of adenine to HAuCl4. TEM results reveal the formation of hierarchical self-assembled structure of the as-prepd. colloidal particles. Concn. dependence, ratio dependence, time dependence, and kinetic measurements were studied. Also, spectroscopic evidence [i.e., FTIR and UV-visible spectra and wide-angle x-ray scattering data] of the interaction motives causing the formation of the colloidal particles is also presented. The as-prepd. nucleobase-metal hybrid materials exhibited hierarchical assembly as follows: the coordination interactions of Au(III) and N atoms in adenine could produce 2-3 nm small particles, these small particles could evolve into submicrometer spherical colloidal particles via noncovalent interaction (i.e., arom. π-π stacking of adenine), and finally the submicrometer particles could be connected together through fusion of the fringes of every independent particle. Work here may open up new possibilities for the fabrication of noncovalent interaction colloidal particles and for the prepn. of decomposable colloidal templates.
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35. 35
  Kunoh, T.; Kunoh, H.; Takada, J. Perspectives on the biogenesis of iron oxide complexes produced by Leptothrix, an iron-oxidizing bacterium and promising industrial applications for their functions J. Microb. Biochem. Technol. 2015, 7, 419– 426 DOI: 10.4172/1948-5948.1000249
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  35
  Perspectives on the biogenesis of iron oxide complexes produced by leptothrix, an iron-oxidizing bacterium and promising industrial applications for their functions
  Kunoh, Tatsuki; Kunoh, Hitoshi; Takada, Jun
  Journal of Microbial & Biochemical Technology (2015), 7 (6), 419-426CODEN: JMBTA9; ISSN:1948-5948. (OMICS Publishing Group)
  Leptothrix species, one of the Fe-/Mn-oxidizing bacteria, are ubiquitous in aq. environments, esp. at sites characterized by a circumneutral pH, an oxygen gradient and a source of reduced Fe and Mn minerals. Characteristic traits that distinguish the genus Leptothrix from other phylogenetically related species are its filamentous growth and ability to form uniquely shaped microtubular sheaths through the pptn. of copious amts. of oxidized Fe or Mn. The sheath is an ingenious hybrid of org. and inorg. materials produced through the interaction of bacterial exopolymers with aq.-phase inorgs. Intriguingly, we discovered that Leptothrix sheaths have a variety of unexpected functions that are suitable for industrial applications such as material for lithium battery electrode, a catalyst enhancer, pottery pigment among others. This review focuses on the structural and chem. properties of the Leptothrix sheaths and their noteworthy functions that show promise for development of cost-effective, eco-friendly industrial applications.
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36. 36
  Kunoh, T.; Nakanishi, M.; Kusano, Y.; Itadani, A.; Ando, K.; Matsumoto, S.; Tamura, K.; Kunoh, H.; Takada, J. Biosorption of metal elements by exopolymer nanofibrils excreted from Leptothrix cells Water Res. 2017, 122, 139– 147 DOI: 10.1016/j.watres.2017.05.003
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  36
  Biosorption of metal elements by exopolymer nanofibrils excreted from Leptothrix cells
  Kunoh, Tatsuki; Nakanishi, Makoto; Kusano, Yoshihiro; Itadani, Atsushi; Ando, Kota; Matsumoto, Syuji; Tamura, Katsunori; Kunoh, Hitoshi; Takada, Jun
  Water Research (2017), 122 (), 139-147CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.)
  Leptothrix species, aquatic Fe-oxidizing bacteria, excrete nano-scaled exopolymer fibrils. Once excreted, the fibrils weave together and coalesce to form extracellular, microtubular, immature sheaths encasing catenulate cells of Leptothrix. The immature sheaths, composed of aggregated nanofibrils with a homogeneous-looking matrix, attract and bind aq.-phase inorgs., esp. Fe, P, and Si, to form seemingly solid, mature sheaths of a hybrid org.-inorg. nature. To verify our assumption that the org. skeleton of the sheaths might sorb a broad range of other metallic and nonmetallic elements, we examd. the sorption potential of chem. and enzymically prepd. protein-free org. sheath remnants for 47 available elements. The sheath remnants were found by XRF to sorb each of the 47 elements, although their sorption degree varied among the elements: >35% at. percentages for Ti, Y, Zr, Ru, Rh, Ag, and Au. Electron microscopy, energy dispersive x-ray spectroscopy, electron and x-ray diffractions, and Fourier transform IR spectroscopy analyses of sheath remnants that had sorbed Ag, Cu, and Pt revealed that (i) the sheath remnants comprised a 5-10 nm thick aggregation of fibrils, (ii) the test elements were distributed almost homogeneously throughout the fibrillar aggregate, (iii) the nanofibril matrix sorbing the elements was nearly amorphous, and (iv) these elements plausibly were bound to the matrix by ionic binding, esp. via OH. The present results show that the constitutive protein-free exopolymer nanofibrils of the sheaths can contribute to creating novel filtering materials for recovering and recycling useful and/or hazardous elements from the environment.
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37. 37
  Emerson, D.; Ghiorse, W. C. Ultrastructure and chemical composition of the sheath of Leptothrix discophora SP-6 J. Bacteriol. 1993, 175, 7808– 7818 DOI: 10.1128/jb.175.24.7808-7818.1993
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  37
  Ultrastructure and chemical composition of sheath of Leptothrix discophora SP-6
  Emerson, David; Ghiorse, William C.
  Journal of Bacteriology (1993), 175 (24), 7808-18CODEN: JOBAAY; ISSN:0021-9193.
  Light microscopy and transmission electron microscopy of thin sections and metal-shadowed specimens showed that the sheath of Leptothrix discophora SP-6 (ATCC 51168) is a tube-like extracellular polymeric structure consisting of a condensed fabric of 6.5-nm-diam. fibrils underlying a more diffuse outer capsular layer. In thin sections, outer membrane bridges seen to contact the inner sheath layer suggested that the sheath fabric was attached to the outer layer of the gram-neg. cell wall. The capsular polymers showed an affinity for cationic colloidal iron and polycationic ferritin, indicating that they carry a neg. charge. Cell-free sheaths were isolated by treatment with a mixt. of lysozyme, EDTA, and N-lauroylsarcosine (Sarkosyl) or sodium dodecyl sulfate (SDS). Both Sarkosyl- and SDS-isolated sheaths were indistinguishable in microscopic appearance. However, the Mn-oxidizing activity of Sarkosyl-isolated sheaths was more stable than that of SDS-isolated sheaths. The Sarkosyl-isolated sheaths also contained more 2-keto-3-deoxyoctanoic acid and more outer membrane protein than SDS-isolated sheaths. The oven-dried mass of detergent-isolated sheaths represented approx. 9% of the total oven-dried biomass of SP-6 cultures; the oven-dried sheaths contained 38% C, 6.9% N, 6% H, and 2.1% S and approx. 34 to 35% carbohydrte (polysaccharide), 23 to 25% protein, 8% lipid, and 4% inorg. ash. Gas-liq. chromatog. showed that the polysaccharide was an approx. 1:1 mixt. of uronic acids (glucuronic, galacturonic, and mannuronic acids and at least one other unidentified uronic acid) and an amino sugar (galactosamine). Neutral sugars were not detected. Amino acid anal. showed that sheath proteins were enriched in cysteine (6 mol%). The cysteine residues in the sheath proteins probably provide sulfhydryls for disulfide bonds that play an important role in maintaining the structural integrity of the sheath.
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38. 38
  Takeda, M.; Makita, H.; Ohno, K.; Nakahara, Y.; Koizumi, J. Structural analysis of the sheath of a sheathed bacterium Int. J. Biol. Macromol. 2005, 37, 92– 98 DOI: 10.1016/j.ijbiomac.2005.09.002
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  38
  Structural analysis of the sheath of a sheathed bacterium, Leptothrix cholodnii
  Takeda, Minoru; Makita, Hiroko; Ohno, Katsutoshi; Nakahara, Yuichi; Koizumi, Jun-ichi
  International Journal of Biological Macromolecules (2005), 37 (1-2), 92-98CODEN: IJBMDR; ISSN:0141-8130. (Elsevier B.V.)
  L. cholodnii is an aerobic sheath-forming bacterium often found in oligotrophic and metal-rich aquatic environments. The sheath of this bacterium was isolated by selectively lysing the cells. Glycine and cysteine were the major amino acids of the sheath. The sheath was readily dissolved in hydrazine, and a polysaccharide substituted with cysteine was recovered from the soln. Galactosamine, glucosamine and galacturonic acid were detected in the hydrazinolyzate by gas liq. chromatog. anal. FAB-MS anal. of the hydrazinolyzate suggested a sugar sequence of HexN-GalA-HexN-HexN. Methylation linkage anal. revealed the presence of 4-linked GalA, 3-linked HexN and 4-linked HexN. The sulfhydryl groups of the sheath were used for labeling with the fluorogenic reagent 4-(aminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (ABD-F). The labeled sheath (ABD-sheath) was partially hydrolyzed and 3 fluorescent fragments were purified by HPLC. One of them was identified as ABD-cysteine. The 2nd was the ABD-cysteine tetramer. Another fragment was indicated to be a pentasaccharide substituted with ABD-cysteine by NMR anal. It can be assumed that the polysaccharide and peptide moieties of the sheath are connected by a cysteine residue. NMR anal. of the hydrazinolyzate revealed that the polysaccharide moiety of the sheath was constructed from a pentasaccharide repeating unit contg. 2-amino-2-deoxygalacturonic acid (GalNA): →4)-α-GalNA-(1→4)-α-D-GalN(p)-(1→4)-α-D-GalA(p)-(1→4)-β-D-GlcN(p)-(1→3)-β-D-GalN(p)-(1→.
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39. 39
  Kunoh, T.; Matsumoto, S.; Nagaoka, N.; Kanashima, S.; Hino, K.; Uchida, T.; Tamura, K.; Kunoh, H.; Takada, J. Amino group in Leptothrix sheath skeleton is responsible for direct deposition of Fe(III) particles onto the sheaths Sci. Rep. 2017, 7, 6498 DOI: 10.1038/s41598-017-06644-8
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  39
  Amino group in Leptothrix sheath skeleton is responsible for direct deposition of Fe(III) minerals onto the sheaths
  Kunoh Tatsuki; Matsumoto Syuji; Tamura Katsunori; Kunoh Hitoshi; Takada Jun; Kunoh Tatsuki; Matsumoto Syuji; Uchida Tetsuya; Tamura Katsunori; Kunoh Hitoshi; Takada Jun; Nagaoka Noriyuki; Kanashima Shoko; Hino Katsuhiko
  Scientific reports (2017), 7 (1), 6498 ISSN:.
  Leptothrix species produce microtubular organic-inorganic materials that encase the bacterial cells. The skeleton of an immature sheath, consisting of organic exopolymer fibrils of bacterial origin, is formed first, then the sheath becomes encrusted with inorganic material. Functional carboxyl groups of polysaccharides in these fibrils are considered to attract and bind metal cations, including Fe(III) and Fe(III)-mineral phases onto the fibrils, but the detailed mechanism remains elusive. Here we show that NH2 of the amino-sugar-enriched exopolymer fibrils is involved in interactions with abiotically generated Fe(III) minerals. NH2-specific staining of L. cholodnii OUMS1 detected a terminal NH2 on its sheath skeleton. Masking NH2 with specific reagents abrogated deposition of Fe(III) minerals onto fibrils. Fe(III) minerals were adsorbed on chitosan and NH2-coated polystyrene beads but not on cellulose and beads coated with an acetamide group. X-ray photoelectron spectroscopy at the N1s edge revealed that the terminal NH2 of OUMS1 sheaths, chitosan and NH2-coated beads binds to Fe(III)-mineral phases, indicating interaction between the Fe(III) minerals and terminal NH2. Thus, the terminal NH2 in the exopolymer fibrils seems critical for Fe encrustation of Leptothrix sheaths. These insights should inform artificial synthesis of highly reactive NH2-rich polymers for use as absorbents, catalysts and so on.
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40. 40
  Pneumatikkais, G.; Hadjiliadis, N.; Theophanides, T. Complexes of inosine, cytidine, and guanosine with palladium(II) Inorg. Chem. 1978, 17, 915– 922 DOI: 10.1021/ic50182a024
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41. 41
  Sohn, J. S.; Kwon, Y. W.; Jin, J. I.; Jo, B. W. DNA-templated preparation of gold nanoparticles Molecules 2011, 16, 8143– 8151 DOI: 10.3390/molecules16108143
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42. 42
  Pillai, C. K. S.; Nandi, U. S. Binding of gold(III) with DNA Biopolymers 1973, 12, 1431– 1435 DOI: 10.1002/bip.1973.360120617
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  Binding of gold(III) with DNA
  Pillai, C. K. S.; Nandi, U. S.
  Biopolymers (1973), 12 (6), 1431-5CODEN: BIPMAA; ISSN:0006-3525.
  Calf thymus DNA reacted with HAuCl4 to form a series of complexes depending on the ratio of constituents. There was a shift in the max. of uv spectra of DNA at 258 nm, a drastic decrease in viscosity, an initial increase in pH, and a change in Tm of DNA. The DNA-Au3+ complex pptd. with EtOH had a max. of 1.85 moles Au/mole DNA-P. Results indicate that Au was bound to phosphate and to bases in DNA.
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43. 43
  Aich, P.; Labiuk, S. L.; Tari, L. W.; Delbaere, L. J.; Roesler, W. J.; Falk, K. J.; Steer, R. P.; Lee, J. S. M-DNA: A complex between divalent metal ions and DNA which behaves as a molecular wire J. Mol. Biol. 1999, 294, 477– 485 DOI: 10.1006/jmbi.1999.3234
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  Mandal, C.; Nandi, U. S. Kinetic studies on the interaction of gold (III) with nucleic acids. IV. RNA-Au (III) system Chem.-Biol. Interact. 1978, 21, 125– 134 DOI: 10.1016/0009-2797(78)90073-X
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  The kinetics of the interaction of Au(III) with whole yeast RNA was studied using UV-spectrophotometry. The reaction was 2nd order with respect to the nucleotide unit of RNA and 1st order with respect to Au(III) in the resp. stoichiometry of 2:1. The effects of initial compn., temp., ionic strength, pH, and Cl- on the kinetics were studied. The activation energy was 11.5 kcal/mol. The effect of ionic strength indicated that both the pos. charged and neutral species of Au(III) take part in the rate-limiting step, the former being dominant at low ionic strength. A plausible mechanism is proposed which involves the interaction of 2 nucleotide units of RNA with 1 species of Au(III) in the rate-limiting step.
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  Structure of the polysaccharide isolated from the sheath of Sphaerotilus natans
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  International Journal of Biological Macromolecules (2003), 33 (4-5), 245-250CODEN: IJBMDR; ISSN:0141-8130. (Elsevier Science B.V.)
  A polysaccharide was isolated from the sheath of a sheathed bacterium, Sphaerotilus natans. The sheath polysaccharide (SPS) was composed of D-glucose and D-(N-acetyl)galactosamine in molar ratios of 1:4. Methylation linkage anal. revealed the presence of the residues of 4-linked glucose, 4-linked (N-acetyl)galactosamine, and 3-linked (N-acetyl)galactosamine in molar ratios of 1:3:1. The oligomer of SPS was prepd. with an SPS-specific degrading enzyme from a sheath-degrading bacterium, Paenibacillus koleovorans. The oligomer was derivatized and subjected to fast atom bombardment-mass spectrometry to investigate the monosaccharide sequence of SPS. The structure of SPS was confirmed by NMR. The resulting data showed that SPS is a straight-chained basic polysaccharide constructed of a pentasaccharide repeating unit.
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  Biological Research (2005), 38 (1), 83-88CODEN: BESEEB; ISSN:0716-9760. (Society of Biology of Chile)
  Prunus persica has been proposed as a genomic model for deciduous trees and the Rosaceae family. Optimized protocols for RNA isolation are necessary to further advance studies in this model species such that functional genomics analyses may be performed. Here we present an optimized protocol to rapidly and efficiently purify high quality total RNA from peach fruits (Prunus persica). Isolating high-quality RNA from fruit tissue is often difficult due to large quantities of polysaccharides and polyphenolic compds. that accumulate in this tissue and co-purify with the RNA. Here we demonstrate that a modified version of the method used to isolate RNA from pine trees and the woody plant Cinnamomun tenuipilum is ideal for isolating high quality RNA from the fruits of Prunus persica. This RNA may be used for many functional genomic based expts. such as RT-PCR and the construction of large-insert cDNA libraries.
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  Free Radical Biology & Medicine (1995), 18 (6), 1023-32CODEN: FRBMEH; ISSN:0891-5849. (Elsevier)
  The postulated importance of oxidative damage to DNA in aging and age-related degenerative pathologies such as cancer has prompted efforts to develop sensitive quantitation methods. 8-Hydroxy-2'-deoxyguanosine (8-OHdG) is a widely used marker for oxidative damage to DNA. To develop an immunoassay for quantitation of 8-OHdG, two monoclonal antibodies have been developed and characterized by competitive ELISA. Antibody IF7 has 50% inhibition at 5 pmol 8-OHdG and 1×105 pmol dG, while antibody IF11 has 50% inhibition at 2.5 pmol 8-OHdG and 2000 pmol dG. Both antisera cross-react with guanosine and several structurally related derivs., including 6- and 8-mercaptoguanosine, 8-bromoguanosine, 8-methylguanine, and 7-methylguanosine. Immunoaffinity columns were prepd. with antibody IF7, which exhibits higher selectivity than IF11, to isolate 8-OHdG from DNA hydrolyzates followed by ELISA quantitation with antibody 1F11. This method allows the anal. of approx. one 8-OHdG/105 dG using 100 μg DNA. To validate the assay, DNA extd. from human placental tissues were assayed by both ELISA and HPLC with electrochem. detection. Values by both methods correlated well (r = 0.87), but the levels detd. by ELISA were approx. 6-fold higher than those detd. by HPLC. This may be due to oligonucleotides detected by the ELISA but not the HPLC method or cross-reactivity with other damaged bases present in the immunoaffinity-purified material. Placental samples from current smokers had significantly higher 8-OHdG by ELISA than those from nonsmokers. The method of immunoaffinity purifn. combined with ELISA quantitation has sufficient sensitivity for detecting 8-OHdG in human DNA samples. Although abs. values are higher than those detd. by HPLC, the method provides a good alternative to the HPLC-EC method for monitoring relative oxidative damage in mol. epidemiol. studies.
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  Journal of Environmental Science and Health, Part C: Environmental Carcinogenesis & Ecotoxicology Reviews (2009), 27 (2), 120-139CODEN: JESHA2 ISSN:. (Taylor & Francis, Inc.)
  A review. There is extensive exptl. evidence that oxidative damage permanently occurs to lipids of cellular membranes, proteins, and DNA. In nuclear and mitochondrial DNA, 8-hydroxy-2' -deoxyguanosine (8-OHdG) or 8-oxo-7,8-dihydro-2' -deoxyguanosine (8-oxodG) is one of the predominant forms of free radical-induced oxidative lesions, and has therefore been widely used as a biomarker for oxidative stress and carcinogenesis. Studies showed that urinary 8-OHdG is a good biomarker for risk assessment of various cancers and degenerative diseases. The most widely used method of quant. anal. is high-performance liq. chromatog. (HPLC) with electrochem. detection (EC), gas chromatog.-mass spectrometry (GC-MS), and HPLC tandem mass spectrometry. In order to resolve the methodol. problems encountered in measuring quant. 8-OHdG, the European Stds. Committee for Oxidative DNA Damage was set up in 1997 to resolve the artifactual oxidn. problems during the procedures of isolation and purifn. of oxidative DNA products. The biomarker 8-OHdG or 8-oxodG has been a pivotal marker for measuring the effect of endogenous oxidative damage to DNA and as a factor of initiation and promotion of carcinogenesis. The biomarker has been used to est. the DNA damage in humans after exposure to cancer-causing agents, such as tobacco smoke, asbestos fibers, heavy metals, and polycyclic arom. hydrocarbons. In recent years, 8-OHdG has been used widely in many studies not only as a biomarker for the measurement of endogenous oxidative DNA damage but also as a risk factor for many diseases including cancer.
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  Steenken, S.; Jovanovic, S. V. How easily oxidizable is DNA? One-electron reduction potentials of adenosine and guanosine radicals in aqueous solution J. Am. Chem. Soc. 1997, 119, 617– 618 DOI: 10.1021/ja962255b
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  How Easily Oxidizable Is DNA? One-Electron Reduction Potentials of Adenosine and Guanosine Radicals in Aqueous Solution
  Steenken, Steen; Jovanovic, Slobodan V.
  Journal of the American Chemical Society (1997), 119 (3), 617-618CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Redn. potentials (vs. NHE) of the purine nucleosides, adenosine and guanosine, were detd. by pulse radiolysis in aq. solns. The value for the guanosine radical at pH 7, E7 = 1.29±0.03 V (E0 = 1.58 V), was obtained from the electron transfer equil. in both directions, with thioanisole (E7 = 1.44 V) and with 1,2,4-trimethoxybenzene (E7 = 1.13 V) radical cations, resp., as ref. couples. For adenosine radical, the electron transfer equil. with thioanisole were measured at pH 5 and 3, to be E5 = 1.56±0.02 V and E3 = 1.64±0.04 V, to evaluate the pH dependence of the redn. potential. From the pH dependence the value in neutral media is E7 = 1.42 V (E0 = 2.03 V). The values of the redn. potentials of guanosine and adenosine radicals are considerably higher than the previously published ones. Because the redn. potential of guanosine radical (the lowest of all the DNA base radicals) is lower than the E7 = 1.05 V of alkylperoxyl radicals, the oxidative damage of DNA by, e.g., lipid peroxyl radicals via electron transfer is not thermodynamically feasible. The redn. potential of guanosine radical is considerably higher than those of arom. and sulfur amino acid radicals, e.g., E7 (Trp) = 1.01 V, which means that the "hole" in (oxidized) DNA can migrate to a histone protein provided it contains these amino acids.
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  Santra, T. S.; Tseng, F.; Barik, T. K. Green biosynthesis of gold nanoparticles and biomedical applications Am. J. Nano Res. Appl. 2014, 2, 5– 12 DOI: 10.11648/j.nano.s.2014020602.12
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  Ghosh, P.; Han, G.; De, M.; Kim, C. K.; Rotello, V. M. Gold nanoparticles in delivery applications Adv. Drug Delivery Rev. 2008, 60, 1307– 1315 DOI: 10.1016/j.addr.2008.03.016
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  Gold nanoparticles in delivery applications
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  Advanced Drug Delivery Reviews (2008), 60 (11), 1307-1315CODEN: ADDREP; ISSN:0169-409X. (Elsevier B.V.)
  A review. Gold nanoparticles (AuNPs) provide non-toxic carriers for drug and gene delivery applications. With these systems, the gold core imparts stability to the assembly, while the monolayer allows tuning of surface properties such as charge and hydrophobicity. An addnl. attractive feature of AuNPs is their interaction with thiols, providing an effective and selective means of controlled intracellular release.
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57. 57
  Gamal-Eldeen, A. M.; Abo-Zeid, M. A. M.; El-Daly, S. M.; Abo-Elfadl, M. T.; Fahmy, C. A.; Ali, M. R. K.; El-Sayed, M. A. In vivo genotoxicity of gold nanorods in mouse bone marrow compared with cyclophosphamide Nano Biomed. Eng. 2016, 8, 306– 314 DOI: 10.5101/nbe.v8i4.p306-314
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Supporting Information
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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.7b02610.
- Figure S1. Presence of RNA in the SP-6 sheath remnants and extracellular release of remarkable amount of RNA from SP-6 cells in MSVP culture medium. Figure S2. Formation of AuNPs after incubation of yRNA with HAuCl₄ solution. Figure S3. Formation of AuNPs by incubation of calf thymus DNA with HAuCl₄ solution. Figure S4. AuNP formation by DNA in buffered HAuCl₄ solution. Figure S5. AuNPs were not detected on the surfaces of precipitates collected from guanosine–, adenosine–, or guanine–HAuCl₄ solution. Figure S6. AuNPs precipitated with poly G DNA primer in HAuCl₄ solution. Figure S7. Formation of AuNPs by incubation of guanine with HAuCl₄ solution (PDF)
- sc7b02610_si_001.pdf (1.28 MB)
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Green Synthesis of Gold Nanoparticles Coupled with Nucleic Acid Oxidation

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Abstract

Synopsis

Introduction

Experimental Section

Preparation of RNA from Leptothrix Cells

Analysis of Sugar Composition in the GTPC Fraction

Hydrolysis of RNA Prepared from SP-6

Test Compounds

Formation of AuNPs Using Nucleic Acids and Analogues Mixed with HAuCl4 Solution

Electron Microscopy and ED Analysis

XRD Analysis

Detection of Chemical Modification of dG as a Reference to Monitor Modification of Chemical Properties of DNA

Colorimetric Assay for 8-OHdG, a Marker of Oxidative DNA Damage

XRF Analysis

Results and Discusion

Formation of AuNPs by Incubation of Leptothrix RNA in Au(III) Chloride Solution

Figure 1

Potential of Guanosine and Guanine to Form AuNPs

Figure 2

Failure of AuNP Formation by Hydroxylated Guanine Molecule

Figure 3

Scheme 1

Figure 4

Conclusions

Supporting Information

Terms & Conditions

Author Information

Acknowledgment

References

Cited By

Abstract

Figure 1

Figure 2

Figure 3

Scheme 1

Figure 4

References

Supporting Information

Supporting Information

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Formation of AuNPs Using Nucleic Acids and Analogues Mixed with HAuCl₄ Solution