Fluorescent Organo-Antimony Compounds as Precursors for Syntheses of Redox-Active Trimeric and Dimeric Alkali Metal Antimonides: An Insight into Electron Transfer Reduction Processes

(Tip)2SbCl (1, Tip = 2,4,6-triisopropylphenyl) has been utilized as a precursor for the synthesis of distibane (Tip)4Sb2 (4) by one-electron reduction using KC8. Two-electrons reduction of 1 and 4 afforded...

Photochemical hydrogen production based on HCOOH/CO2 cycle promoted by pentanuclear cobalt complex

The first catalytic cycle for hydrogen production based on the photochemical two-electron reduction of carbon dioxide (CO2) and the dehydrogenation of formic acid at ambient temperature was demonstrated using a...

Balancing high energy density and chemical stability in redox flow batteries with symmetric tetrazines

Nonaqueous redox flow batteries are a promising technology for grid-scale energy storage, however, their commercial success relies on identifying redox active materials that exhibit extreme potentials, high solubilities in all states of charge, and long cycling stabilities. Meeting these requirements has been particularly challenging for molecules capable of storing negative charge. Within this context, the symmetric tetrazines remain unexplored despite their unique structural properties that enable them to meet these challenges. Herein, we prepared s-tetrazines substituted with methyl, methoxy, and thiomethyl substituents and evaluated their electrochemical properties, solubility, and cycling stability. These studies revealed that 3,6-dimethoxy-s-tetrazine undergoes a reversible one-electron reduction to generate a soluble (>0.5 M in electrolyte/solvent) and stable (t1/2 > 1240 h) radical anion. When implemented in a lab-scale flow battery, it exhibited a relatively slow capacity fade of 13% over 100 cycles (38 h). Given their uncommonly high solubility and cycling stability, we believe that s-tetrazine derivatives should be further explored for non-aqueous redox flow batteries.

A Binuclear Cobalt Complex for Molecular CO2 Electrocatalysis

A pyrazole–based ligand substituted with terpyridine groups at the 3 and 5positions has been synthesized to form the dinuclear cobalt complex 1, that electrocatalytically reduces carbon dioxide (CO2) to carbon monoxide (CO) in the presence of Brønsted acids in DMF. Chemical, electrochemical and UV–vis spectro–electrochemical studies under inert atmosphere indicate a single 2 electron reduction process of complex 1 at first, followed by a 1 electron reduction at the ligand. Infrared spectro–electrochemical studies under CO2 and CO atmosphere allowed us to identify a reduced CO–containing dicobalt complex which results from the electroreduction of CO2. In the presence of trifluoroethanol (TFE), electrocatalytic studies revealed single–site mechanism with up to 94 % selectivity towards CO formation when 1.47 M TFE were present, at –1.35 V vs Saturated Calomel Electrode in DMF (0.39 V overpotential). The low faradaic efficiencies obtained (<50%) are attributed to the generation of CO–containing species formed during the electrocatalytic process, which inhibit the reduction of CO2.

The strong interfacial coupling effect of Nafion between LaFeO3/electrolyte for efficient photoelectrochemical water reduction

Insufficient reduction capability and scanty active substance limit the application of LaFeO3 (LFO) in the field of photoelectrochemical (PEC) water splitting. In this work, a judicious combination of LFO/Nafion composite to improve the PEC performance by a special dip-coating method on the FTO is demonstrated. The photocurrent density of the LFO electrode coated with two layers Nafion increased to -23.9 μA/cm2 at 0.47 V vs RHE, which is 4.1 times that of the pristine LFO. Based on the experimental data and theoretical analysis,the improvement of the PECproperties is attributed to the construction of organic/inorganic units, which would enable strong electronic coupling and favor interfacial charge transfer, resulting in a 30mV downward shift of its flat band potential. Thus, conduction band gets closer to the proton reduction potential of H+ to H2 after decoration with Nafion, resulting in stronger photogenerated electron reduction ability. Our study provides insights that organic materials modify semiconductor photoelectrodes for accelerating the charge kinetics.

Restoring Tumour Selectivity of the Bioreductive Prodrug PR-104 by Developing an Analogue Resistant to Aerobic Metabolism by Human Aldo-Keto Reductase 1C3

PR-104 is a phosphate ester pre-prodrug that is converted in vivo to its cognate alcohol, PR-104A, a latent alkylator which forms potent cytotoxins upon bioreduction. Hypoxia selectivity results from one-electron nitro reduction of PR-104A, in which cytochrome P450 oxidoreductase (POR) plays an important role. However, PR-104A also undergoes ‘off-target’ two-electron reduction by human aldo-keto reductase 1C3 (AKR1C3), resulting in activation in oxygenated tissues. AKR1C3 expression in human myeloid progenitor cells probably accounts for the dose-limiting myelotoxicity of PR-104 documented in clinical trials, resulting in human PR-104A plasma exposure levels 3.4- to 9.6-fold lower than can be achieved in murine models. Structure-based design to eliminate AKR1C3 activation thus represents a strategy for restoring the therapeutic window of this class of agent in humans. Here, we identified SN29176, a PR-104A analogue resistant to human AKR1C3 activation. SN29176 retains hypoxia selectivity in vitro with aerobic/hypoxic IC50 ratios of 9 to 145, remains a substrate for POR and triggers γH2AX induction and cell cycle arrest in a comparable manner to PR-104A. SN35141, the soluble phosphate pre-prodrug of SN29176, exhibited superior hypoxic tumour log cell kill (>4.0) to PR-104 (2.5–3.7) in vivo at doses predicted to be achievable in humans. Orthologues of human AKR1C3 from mouse, rat and dog were incapable of reducing PR-104A, thus identifying an underlying cause for the discrepancy in PR-104 tolerance in pre-clinical models versus humans. In contrast, the macaque AKR1C3 gene orthologue was able to metabolise PR-104A, indicating that this species may be suitable for evaluating the toxicokinetics of PR-104 analogues for clinical development. We confirmed that SN29176 was not a substrate for AKR1C3 orthologues across all four pre-clinical species, demonstrating that this prodrug analogue class is suitable for further development. Based on these findings, a prodrug candidate was subsequently identified for clinical trials.

Quinone binding in respiratory complex I: Going through the eye of a needle. The squeeze-in mechanism of passing the narrow entrance of the quinone site

At the joint between the membrane and hydrophilic arms of the enzyme, the structure of the respiratory complex I reveals a tunnel-like Q-chamber for ubiquinone binding and reduction. The narrow entrance of the quinone chamber located in ND1 subunit forms a bottleneck (eye of a needle) which in all resolved structures was shown to be too small for a bulky quinone to pass through, and it was suggested that a conformational change is required to open the channel. The closed bottleneck appears to be a well-established feature of all structures reported so-far, both for the so-called open and closed states of the enzyme, with no indication of a stable open state of the bottleneck. We propose a squeeze-in mechanism of the bottleneck passage, where dynamic thermal conformational fluctuations allow quinone to get in and out. Here, using molecular dynamics simulations of the bacterial enzyme, we have identified collective conformational changes that open the quinone chamber bottleneck. The model predicts a significant reduction—due to a need for a rare opening of the bottleneck—of the effective bi-molecular rate constant, in line with the available kinetic data. We discuss possible reasons for such a tight control of the quinone passage into the binding chamber and mechanistic consequences for the quinone two-electron reduction. Graphic abstract

Hybrids of Reduced Graphene Oxide Aerogel and CNT for Electrochemical O2 Reduction

Carbon nanotubes (CNTs), graphene aerogels (GAs), and their hybrid (CNT-GA) prepared by hydrothermal treatment were tested in the electrocatalytic oxygen reduction reaction (ORR). The importance of porous structure derived from the combination of mesoporosity coming from CNTs with macroporosity stemming from GAs was evidenced because the hybrid carbon material exhibited synergistic performance in terms of kinetic current and onset potential. Different electrocatalysts were prepared based on these hybrids doped with nitrogen using different precursors and also supporting Fe nanoparticles. N-doped carbon hybrids showed higher electrocatalytic activity than their undoped counterparts. Nevertheless, both doped and undoped materials provided a mixed two and four electron reduction. On the other hand, the addition of a Fe precursor and phenanthroline to the CNT-GA allowed preparing an N-doped hybrid containing Fe nanoparticles which favored the 4-electron oxygen reduction to water, thus being an excellent candidate as a structured cathode in fuel cells.