Photophysics and Electrochemistry of Biomimetic Pyranoflavyliums: What Can Bioinspiration from Red Wines Offer?

Natural dyes and pigments offer incomparable diversity of structures and functionalities, making them an excellent source of inspiration for the design and development of synthetic chromophores with a myriad of emerging properties. Formed during maturation of red wines, pyranoanthocyanins are electron-deficient cationic pyranoflavylium dyes with broad absorption in the visible spectral region and pronounced chemical and photostability. Herein, we survey the optical and electrochemical properties of synthetic pyranoflavylium dyes functionalized with different electron-donating and electron-withdrawing groups, which vary their reduction potentials over a range of about 400 mV. Despite their highly electron-deficient cores, the exploration of pyranoflavyliums as photosensitizers has been limited to the “classical” n-type dye-sensitized solar cells (DSSCs) where they act as electron donors. In light of their electrochemical and spectroscopic properties, however, these biomimetic synthetic dyes should prove to be immensely beneficial as chromophores in p-type DSSCs, where their ability to act as photooxidants, along with their pronounced photostability, can benefit key advances in solar-energy science and engineering.

Oxygen Stable Electrochemical CO2 Capture and Concentration through Alcohol Additives

Current methods for CO2 capture and concentration (CCC) are energy intensive due to their reliance on thermal cycles, which are intrinsically Carnot limited in efficiency. In contrast, electrochemically driven CCC (eCCC) can operate at much higher theoretical efficiencies. However, most reported systems are sensitive to O2, precluding their practical use. In order to achieve O2 stable eCCC, we pursued the development of molecular redox carriers with reduction potentials positive of the O2/O2- redox couple. Prior efforts to chemically modify redox carriers to operate at milder potentials resulted in a loss in CO2 binding. To overcome these limitations, we used common alcohols additives to anodically shift the reduction potential of a quinone redox carrier, 2,3,5,6-tetrachloro-p-benzoquinone (TCQ), by up to 350 mV, conferring O2 stability. Intermolecular hydrogen-bonding interactions to the dianion and CO2-bound forms of TCQ were correlated to alcohol pKa to identify ethanol as the optimal additive, as it imparts beneficial changes to both the reduction potential and CO2 binding constant, the two key properties for eCCC redox carriers. We demonstrate a full cycle of eCCC in aerobic simulated flue gas using TCQ and ethanol, two commercially available compounds. Based on the system properties, an estimated minimum of 21 kJ/mol is required to concentrate CO2 from 10% to 100%, or twice as efficient as state-of-the-art thermal amine capture systems and other reported redox carrier-based systems. Furthermore, this approach of using hydrogen-bond donor additives is general and can be used to tailor the redox properties of other quinones/alcohol combinations for specific CO2 capture applications.

Partial synthetic models of FeMoco with sulfide and carbyne ligands: Effect of interstitial atom in nitrogenase active site

Nitrogen-fixing organisms perform dinitrogen reduction to ammonia at an Fe-M (M = Mo, Fe, or V) cofactor (FeMco) of nitrogenase. FeMco displays eight metal centers bridged by sulfides and a carbide having the MFe7S8C cluster composition. The role of the carbide ligand, a unique motif in protein active sites, remains poorly understood. Toward addressing how the carbon bridge affects the physical and chemical properties of the cluster, we isolated synthetic models of subsite MFe3S3C displaying sulfides and a chelating carbyne ligand. We developed synthetic protocols for structurally related clusters, [Tp*M’Fe3S3X]n−, where M’ = Mo or W, the bridging ligand X = CR, N, NR, S, and Tp* = Tris(3,5-dimethyl-1-pyrazolyl)hydroborate, to study the effects of the identity of the heterometal and the bridging X group on structure and electrochemistry. While the nature of M’ results in minor changes, the chelating, μ3-bridging carbyne has a large impact on reduction potentials, being up to 1 V more reducing compared to nonchelating N and S analogs.

Electrochemical Studies of Chlorine Containing Silanes

The reduction potentials of a series of mono-, di- and trichloro alkyl and aryl substituted silanes was investigated by cyclic voltammetry. It was shown that chlorosilanes can be reduced in two one electron steps at potentials more positive than -1V vs SCE. The solvent type (THF, MeCN), silane type and polymerization and electrolyte concentration were varied and found to greatly impact the reduction potential.

PEGylated Doxorubicin Prodrug-Forming Reduction-Sensitive Micelles With High Drug Loading and Improved Anticancer Therapy

Significant efforts on the design and development of advanced drug delivery systems for targeted cancer chemotherapy continue to be a major challenge. Here, we reported a kind of reduction-responsive PEGylated doxorubicin (DOX) prodrug via the simple esterification and amidation reactions, which self-assembled into the biodegradable micelles in solutions. Since there was an obvious difference in the reduction potentials between the oxidizing extracellular milieu and the reducing intracellular fluids, these PEG–disulfide–DOX micelles were localized intracellularly and degraded rapidly by the stimulus to release the drugs once reaching the targeted tumors, which obviously enhanced the therapeutic efficacy with low side effects. Moreover, these reduction-sensitive micelles could also physically encapsulate the free DOX drug into the polymeric cargo, exhibiting a two-phase programmed drug release behavior. Consequently, it showed a potential to develop an intelligent and multifunctional chemotherapeutic payload transporter for the effective tumor therapy.

Selective cobalt and nickel electrodeposition for lithium-ion battery recycling through integrated electrolyte and interface control

Molecularly-selective metal separations are key to sustainable recycling of Li-ion battery electrodes. However, metals with close reduction potentials present a fundamental challenge for selective electrodeposition, especially for critical elements such as cobalt and nickel. Here, we demonstrate the synergistic combination of electrolyte control and interfacial design to achieve molecular selectivity for cobalt and nickel during potential-dependent electrodeposition. Concentrated chloride allows for the speciation control via distinct formation of anionic cobalt chloride complex (CoCl42-), while maintaining nickel in the cationic form ([Ni(H2O)5Cl]+). Furthermore, functionalizing electrodes with a positively charged polyelectrolyte (i.e., poly(diallyldimethylammonium) chloride) changes the mobility of CoCl42- by electrostatic stabilization, which tunes cobalt selectivity depending on the polyelectrolyte loading. This strategy is applied for the multicomponent metal recovery from commercially-sourced lithium nickel manganese cobalt oxide electrodes. We report a final purity of 96.4 ± 3.1% and 94.1 ± 2.3% for cobalt and nickel, respectively. Based on a technoeconomic analysis, we identify the limiting costs arising from the background electrolyte, and provide a promising outlook of selective electrodeposition as an efficient separation approach for battery recycling.

An Assessment of Long-Range Corrected Density Functional Approximations in the Calculation of the Reduction Potentials of Ni(S2C2H2)2, Ni(Se2C2H2)2, Ni(S2C2H2)(N2C2H4), and Ni(Se2C2H2)(N2C2H4) Complexes

Herein an assessment of several Long Range Corrected (LRC) Density Functional Theory (DFT) methods for the calculation of reduction potentials of the ([Ni(X2C2H2)2]n/[Ni(X2C2H2)2]n-1), and ([Ni(X2C2H2)(N2C2H4)]n/[Ni(X2C2H2)(N2C2H4)]n-1) and (where X= S or Se and n = 0, or -1) redox couples was done. From the results the values of ω that provide best agreement with CCSD(T) for the tested LRC DFT methods are 0.05 bohr-1, 0.15 bohr-1, 0.05 bohr-1, and 0.20 bohr-1 for ω-B97XD, LC-BLYP, CAM-B3LYP, and ω-B97, respectively. With these values the unsigned average in error was 0.12 V with a standard deviation of 0.13 V for ω-B97XD. For LC-BLYP, CAM-B3LYP, and ω-B97 the unsigned averages in relative errors were 0.12 V, 0.11 V, and 0.13 V, respectively, with respective standard deviations of 0.11 V, 0.12 V and 0.13 V.