Thiourea-Based Receptors for Anion Recognition and Signaling

This work reports on two thiourea-based receptors with pyridine and amine units including 1-naphthyl (MT1N) and 4-nytrophenyl (MT4N) as signaling units. For both compounds, their affinity and signaling ability toward various anions of different geometry and basicity in DMSO were studied using UV–vis, fluorescence, and 1H NMR techniques. Anion recognition studies revealed that both MT1N and MT4N have, in general, high affinities toward basic anions. In this regard, a higher acidity of the MT4N receptor was demonstrated. Furthermore, MT4N has a higher affinity for fluoride (log K1 = 5.98) than for the other anions and can effectively detect it through colorimetric changes that can be monitored by the UV–vis technique. The interaction between receptors and anions mainly involves the hydrogens of the amino and thiourea groups of the former. Complementary single-crystal X-ray diffraction studies and molecular modeling at the DFT level were also performed.


Figure S10 .
Figure S10.Absorption spectra of MT1N at several concentrations (1-8x10 -5 M).The inset is a linear regression at 331 nm to determine the molar extinction coefficient.

Figure S12 .
Figure S12.Absorption spectra of MT1N (3×10 -5 M) in the presence of increasing concentrations of Cl -(0-4.39×10-3 M) in DMSO at 298 K.The upper right inset shows the relative abundance of the different species during the titration, where H = receptor and G = anion guest.The dashed lines represent the theoretical profiles obtained from data fitting.

Figure S13 .
Figure S13.Absorption spectra of MT1N (3×10 -5 M) in the presence of increasing concentrations of NO3 -(0-4.72×10 - M) in DMSO at 298 K.The upper right inset shows the relative abundance of the different species during the titration, where H = receptor and G = anion guest.The dashed lines represent the theoretical profiles obtained from data fitting.

Figure S14 .
Figure S14.Absorption spectra of MT1N (3×10 -5 M) in the presence of increasing concentrations of HSO4 -(0-5.91×10 - M) in DMSO at 298 K.The upper right inset shows the relative abundance of the different species during the titration, where H = receptor and G = anion guest.The dashed lines represent the theoretical profiles obtained from data fitting.

Figure S15 .
Figure S15.Absorption spectra of MT1N (3×10 -5 M) in the presence of increasing concentrations of H2PO4 -(0-1.9×10 - M) in DMSO at 298 K.The upper right inset shows the relative abundance of the different species during the titration, where H = receptor and G = anion guest.The dashed lines represent the theoretical profiles obtained from data fitting.(Non-reproducible experiment).

Figure S16 .
Figure S16.Absorption spectra of MT1N (3×10 -5 M) in the presence of increasing concentrations of CH3CO2 -(0-2.19×10 - M) in DMSO at 298 K.The upper right inset shows the relative abundance of the different species during the titration, where H = receptor.The dashed lines represent the theoretical profiles obtained from data fitting.

Figure S17 .
Figure S17.Absorption spectra of MT4N (3.6×10 -5 M) in the presence of increasing concentrations of Cl -(0-5.25×10 - M) in DMSO at 298 K.The upper right inset shows the relative abundance of the different species during the titration, where H = receptor and G = anion guest.The dashed lines represent the theoretical profiles obtained from data fitting.

Figure S18 .
Figure S18.Absorption spectra of MT4N (3.6×10 -5 M) in the presence of increasing concentrations of NO3 -(0-3.52×10-2 M) in DMSO at 298 K.The upper right inset shows the relative abundance of the different species during the titration, where H = receptor and G = anion guest.The dashed lines represent the theoretical profiles obtained from data fitting.

Figure S20 .
Figure S20.Absorption spectra of MT4N (3.6×10 -5 M) in the presence of increasing concentrations of H2PO4 -(0-1.36×10-3 M) in DMSO at 298 K.The upper right inset shows the relative abundance of the different species during the titration, where H = receptor.The dashed lines represent the theoretical profiles obtained from data fitting.

Figure S21 .
Figure S21.Absorption spectra of MT4N (3.6×10 -5 M) in the presence of increasing concentrations of CH3CO2 -(0-3.88×10 - M) in DMSO at 298 K.The upper right inset shows the relative abundance of the different species during the titration, where H = receptor and G = anion guest.The dashed lines represent the theoretical profiles obtained from data fitting.

Figure
Figure S24.a) Selected spectra from the titration of MT4N (3 mM) with C6H5CO2 -(0-1.20x10 - M) in DMSO-d6 at 298 K. b) Theoretical fit of experimentally measured chemical shift using a 1:1 model by least squares regression.c) Abundance of the different species during the titration, where H = receptor and G = anion guest.

Figure S28 .Figure S31 .
Figure S28.a) Selected spectra from the titration of MT1N (3 mM) with C6H5CO2 -(0-2.25x10 - M) in DMSO-d6 at 298 K. b) Theoretical fit of experimentally measured chemical shift using a 1:2 model by least squares regression.c) Abundance of the different species during the titration, where H = receptor and G = anion guest.

Figure S32 .FluorescenceFigure S33 .
Figure S32.a) Selected spectra from the titration of MT1N (3 mM) with Cl -(0-0.06M) in DMSO-d6 at 298 K. b) Theoretical fit of experimentally measured chemical shift using a 1:2 model by least squares regression.c) Abundance of the different species during the titration, where H = receptor and G = anion guest.

Figure S37 .
Figure S37.A perspective view of the calculated molecular structure of MT1N−CH3CO2 - with the B3LYP/6-31G* level of theory, in DMSO.