Stimulus-responsive molecular imaging is a way of detecting interesting ions, enzyme activity, and other biochemical targets. It works by covering the target tissue with a dye that reacts to incoming light by fluorescing, or emitting radiation at a different, easy-to-detect wavelength. But those methods only work within 1.5 mm of the surface. Dyes that emit ultrasonic acoustic waves instead could work up to 10 cm deep and allow for non-invasive imaging of living animals. Now, Effie Y. Zhou and co-authors report improving such dyes and new clues about how the dye’s structure affects their photoacoustic performance (DOI: 10.1021/jacs.9b06694).
The team explored different configurations of restraining molecular rings on an existing dye called aza-BODIPY. Guided by computational models and previous studies, they simulated how six different structural modifications might trap rotating phenyl groups that interfered with absorptivity. The team then made the three most promising dyes based on their simulations for testing in vitro, which revealed photoacoustic responses between 2 and 8 times those of the original dye. In a living tumor model, one of the new dyes outperformed an existing dye by around 20%.
The study hints that an understandable relationship exists between dye structure and photoacoustic performance. Future workers could use it to develop better-performing and targeted dyes.
Disentangling the Effects of Oxygen Vacancies with a Multi-Method Approach
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Christie L. C. Ellis
Across a wide variety of photoelectrochemical and photocatalytic device materials, oxygen vacancies are one of the most common—yet least understood—features. They have been hypothesized to both improve and worsen device performance, as they can affect structure, optical properties, bulk charge carriers, interfacial properties, reactivity, and more. The effect of oxygen vacancies is commonly assessed using changes in overall device performance. This has led to conflicting conclusions, since it is difficult to separate their myriad possible structural, optical, and electrochemical effects, which might simultaneously cause gains and losses in performance.
Durrant and co-workers have devised a method to address this which uses a suite of in situ techniques to separately assess the optical, thermal, and electrochemical properties of a material (DOI: 10.1021/jacs.9b09056). Then, they found ways to correlate results across these techniques to determine the contributions of different properties to the system as a whole. They demonstrated the power of this technique on the common photoanode material BiVO4. They found that its oxygen vacancies created both shallow electron traps, leading to a thermally dependent device performance, and deep hole traps, decreasing bulk electrical conductivity. This suite of methods could lead to a more holistic understanding of one of the most common phenomena in functional materials.
Not So Boron: Discovering Metallaboron Analogs of Benzene
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Matthew P. McLaughlin (Ph.D.)
By selectively connecting nearly any molecular fragments, boron analogs have gained a reputation as the most powerful tool in synthesis. But for boron analogs to reach their full potential, new complexes and approaches will be needed. Ling Fung Cheung and co-workers provide just such an approach, preparing the first metallaboron analogs of benzene, where, by changing the metal used, the electronic structure can be tailored toward new reactivities (DOI: 10.1021/jacs.9b09110).
The researchers prepared two boron analogs of benzene, ReB6– and AlB6–, and used advanced photoelectron spectroscopy and theoretical calculations to characterize their electronic structures. By attaching two different metals, the authors regulated the electronic structure, changing the complex from aromatic to anti-aromatic. These changes are achieved by each metal providing a different number and type of electrons to the benzene analog, shifting not only the aromaticity but also the σ and π character. In sum, these results provide a path to preparing a new class of analogs with an even greater capacity for tailored reactivity. By providing a new handle for controlling the electronic structure of boron-substituted benzenes, this work provides new avenues for the rapid synthesis of complex molecules, with relevance ranging from natural product targets for drug screening to supramolecular structures for material science.
Pushing the Triple-Phase Boundary for Fuel Cells
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Lucka Bibic
Coupled electron- and phase-transfer (CEPhT) reactions are the key processes in many electrochemical systems, including fuel cells and lithium-ion batteries. However, deciphering the electron-transfer mechanisms that occur across phase boundaries is tricky due to a lack of suitable experimental tools that hinder attempts to probe the kinetics, mechanism and energetics behind these reactions. Now Henry S. White and co-workers have devised a straightforward approach to study CEPhT reactions at the triple-phase interface (DOI: 10.1021/jacs.9b07283).
The team employed a solid Pt–Ir wire placed across the interface between two immiscible liquid phases (water/1,2-dichloroethane), creating a triple-phase (Pt–Ir/water/1,2-dichloroethane) boundary. By investigating the oxidation of ferrocene (Fc) in 1,2-dichloroethane and the transfer of its charged product Fc+ across this interface into the aqueous phase, the researchers demonstrate that CEPhT reactions take place at the boundary itself. Furthermore, using finite-element simulations, they show that the rate of transfer of Fc+ is dependent on factors such as the geometry of the triple-phase interface and the salt concentration of electrolyte.
Their results add to the current understanding of the CEPhT mechanism and might result in the applications of CEPhT reactions to other systems, where proton- and electron-transfer steps play key roles in energy conversion.
Cited By
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This article is cited by 1 publications.
Chao Liu, Yihe Zhang, Qi An. Functional Material Systems Based on Soft Cages. Chemistry – An Asian Journal2021, 16
(10)
, 1198-1215. https://doi.org/10.1002/asia.202100178
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