Inactivation and spike protein denaturation of novel coronavirus variants by CuxO/TiO2 nano-photocatalysts.

In order to reduce infection risk of novel coronavirus (SARS-CoV-2), we developed nano-photocatalysts with nanoscale rutile TiO2 (4-8 nm) and CuxO (1-2 nm or less). Their extraordinarily small size leads to high dispersity and good optical transparency, besides large active surface area. Those photocatalysts can be applied to white and translucent latex paints. Although Cu2O clusters involved in the paint coating undergo gradual aerobic oxidation in the dark, the oxidized clusters are re-reduced under > 380 nm light. The paint coating inactivated the original and alpha variant of novel coronavirus under irradiation with fluorescent light for 3 h. The photocatalysts greatly suppressed binding ability of the receptor binding domain (RBD) of coronavirus (the original, alpha and delta variants) spike protein to the receptor of human cells. The coating also exhibited antivirus effects on influenza A virus, feline calicivirus, bacteriophage Qß and bacteriophage M13. The photocatalysts would be applied to practical coatings and lower the risk of coronavirus infection via solid surfaces.

Whole-cell circular dichroism difference spectroscopy reveals an in vivo-specific deca-heme conformation in bacterial surface cytochromes.

We established whole-cell circular dichroism difference spectroscopy to identify the inter-heme interaction in deca-heme cytochrome protein MtrC in whole cell. Our data showed that the heme alignment of reduced MtrC in whole cell is distinct from that in purified one, suggesting the in vivo specific electron transport kinetics.

Preparation of Polyoxometalate-based Photo-responsive Membranes for the Photo-activation of Manganese Oxide Catalysts.

This paper presents a method to prepare charge-transfer chromophores using polyoxotungstate (PW12O403-), transition metal ions (Ce3+ or Co2+), and organic polymers, with the aim of photo-activating oxygen-evolving manganese oxide catalysts, which are important components in artificial photosynthesis. The cross-linking technique was applied to obtain a self-standing membrane with a high PW12O403- content. Incorporation and structure retention of PW12O403- within the polymer matrix were confirmed by FT-IR and micro-Raman spectroscopy, and optical characteristics were investigated by UV-Vis spectroscopy, which revealed successful construction of the metal-to-metal charge transfer (MMCT) unit. After deposition of MnOx oxygen evolving catalysts, photocurrent measurements under visible light irradiation verified the sequential charge transfer, Mn → MMCT unit → electrode, and the photocurrent intensity was consistent with the redox potential of the donor metal (Ce or Co). This method provides a new strategy for preparing integrated systems involving catalysts and photon-absorption parts for use with photo-functional materials.

Design Strategy of Multi-electron Transfer Catalysts Based on a Bioinformatic Analysis of Oxygen Evolution and Reduction Enzymes.

Understanding the design strategy of photosynthetic and respiratory enzymes is important to develop efficient artificial catalysts for oxygen evolution and reduction reactions. Here, based on a bioinformatic analysis of cyanobacterial oxygen evolution and reduction enzymes (photosystem II: PS II and cytochrome c oxidase: COX, respectively), the gene encoding the catalytic D1 subunit of PS II was found to be expressed individually across 38 phylogenetically diverse strains, which is in contrast to the operon structure of the genes encoding major COX subunits. Selective synthesis of the D1 subunit minimizes the repair cost of PS II, which allows compensation for its instability by lowering the turnover number required to generate a net positive energy yield. The different bioenergetics observed between PS II and COX suggest that in addition to the catalytic activity rationalized by the Sabatier principle, stability factors have also provided a major influence on the design strategy of biological multi-electron transfer enzymes.

Electrochemical Detection of Deuterium Kinetic Isotope Effect on Extracellular Electron Transport in Shewanella oneidensis MR-1.

Direct electrochemical detection of c-type cytochrome complexes embedded in the bacterial outer membrane (outer membrane c-type cytochrome complexes; OM c-Cyts) has recently emerged as a novel whole-cell analytical method to characterize the bacterial electron transport from the respiratory chain to the cell exterior, referred to as the extracellular electron transport (EET). While the pathway and kinetics of the electron flow during the EET reaction have been investigated, a whole-cell electrochemical method to examine the impact of cation transport associated with EET has not yet been established. In the present study, an example of a biochemical technique to examine the deuterium kinetic isotope effect (KIE) on EET through OM c-Cyts using a model microbe, Shewanella oneidensis MR-1, is described. The KIE on the EET process can be obtained if the EET through OM c-Cyts acts as the rate-limiting step in the microbial current production. To that end, before the addition of D2O, the supernatant solution was replaced with fresh media containing a sufficient amount of the electron donor to support the rate of upstream metabolic reactions, and to remove the planktonic cells from a uniform monolayer biofilm on the working electrode. Alternative methods to confirm the rate-limiting step in microbial current production as EET through OM c-Cyts are also described. Our technique of a whole-cell electrochemical assay for investigating proton transport kinetics can be applied to other electroactive microbial strains.

Synthesis of diketopyrrolopyrrole-based polymers with polydimethylsiloxane side chains and their application in organic field-effect transistors.

Linear polydimethylsiloxane (PDMS) was investigated as a solubilizing group for π-conjugated polymers with the aim of combining high solubility in organic solvents with the molecular packing in solid films that is advantageous for charge transport. Diketopyrrolopyrrole-based copolymers with different contents and substitution patterns of the PDMS side chains were synthesized and evaluated for application in organic field-effect transistors. The PDMS side chains greatly increased the solubility of the polymers and led to shorter d-spacings of the π-stacking in the thin films compared with polymers containing conventional branched alkyl side chains.

Anodic and Cathodic Extracellular Electron Transfer by the Filamentous Bacterium Ardenticatena maritima 110S.

Ardenticatena maritima strain 110S is a filamentous bacterium isolated from an iron-rich coastal hydrothermal field, and it is a unique isolate capable of dissimilatory iron or nitrate reduction among the members of the bacterial phylum Chloroflexi. Here, we report the ability of A. maritima strain 110S to utilize electrodes as a sole electron acceptor and donor when coupled with the oxidation of organic compounds and nitrate reduction, respectively. In addition, multicellular filaments with hundreds of cells arranged end-to-end increased the extracellular electron transfer (EET) ability to electrodes by organizing filaments into bundled structures, with the aid of microbially reduced iron oxide minerals on the cell surface of strain 110S. Based on these findings, together with the attempt to detect surface-localized cytochromes in the genome sequence and the demonstration of redox-dependent staining and immunostaining of the cell surface, we propose a model of bidirectional electron transport by A. maritima strain 110S, in which surface-localized multiheme cytochromes and surface-associated iron minerals serve as a conduit of bidirectional EET in multicellular filaments.

Effects of Chain Orientation in Self-Organized Buffer Layers Based on Poly(3-alkylthiophene)s for Organic Photovoltaics.

Surface-segregated monolayers (SSMs) based on two poly(3-alkylthiophene)s with semifluoroalkyl groups at either the side chains (P3DDFT) or one end of the main chain (P3BT-F17) were used as self-organized buffer layers at the electrode interfaces in bulk heterojunction (BHJ) organic photovoltaic devices. Both of the SSMs greatly shifted the vacuum levels of the BHJ films at the surface due to the aligned permanent dipole moments of the semifluoroalkyl chains. Hole extraction in the BHJ of poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61-butyric acid methyl ester (PCBM) became more efficient in the presence of the P3DDFT buffer layer, resulting in an improved power conversion efficiency. In contrast, the SSM of P3BT-F17 induced changes in the chain orientation of P3HT and the morphology of the BHJ films, resulting in decreased performance. These results indicate that the molecular design of polymer-based SSMs can affect not only the energy structure at the interface but also the morphology and the molecular orientations in the BHJs.

Multi-heme cytochromes provide a pathway for survival in energy-limited environments.

Bacterial reduction of oxidized sulfur species (OSS) is critical for energy production in anaerobic marine subsurfaces. In organic-poor sediments, H2 has been considered as a major energy source for bacterial respiration. We identified outer-membrane cytochromes (OMCs) that are broadly conserved in sediment OSS-respiring bacteria and enable cells to directly use electrons from insoluble minerals via extracellular electron transport. Biochemical, transcriptomic, and microscopic analyses revealed that the identified OMCs were highly expressed on the surface of cells and nanofilaments in response to electron donor limitation. This electron uptake mechanism provides sufficient but minimum energy to drive the reduction of sulfate and other OSS. These results suggest a widespread mechanism for survival of OSS-respiring bacteria via electron uptake from solid minerals in energy-poor marine sediments.

Ru atom-modified covalent triazine framework as a robust electrocatalyst for selective alcohol oxidation in aqueous electrolytes.

This work demonstrates that a single Ru atom-modified covalent triazine framework (Ru-CTF) has selectivity for the electrooxidation of benzyl alcohol in water over the oxygen evolution reaction. Additionally, Ru-CTF displayed higher stability than an immobilized Ru-organometallic complex due to the covalently cross-linked structure of CTF.

Proton Transport in the Outer-Membrane Flavocytochrome Complex Limits the Rate of Extracellular Electron Transport.

The microbial transfer of electrons to extracellularly located solid compounds, termed extracellular electron transport (EET), is critical for microbial electrode catalysis. Although the components of the EET pathway in the outer membrane (OM) have been identified, the role of electron/cation coupling in EET kinetics is poorly understood. We studied the dynamics of proton transport associated with EET in an OM flavocytochrome complex in Shewanella oneidensis MR-1. Using a whole-cell electrochemical assay, a significant kinetic isotope effect (KIE) was observed following the addition of deuterated water (D2 O). The removal of a flavin cofactor or key components of the OM flavocytochrome complex significantly increased the KIE in the presence of D2 O to values that were significantly larger than those reported for proton channels and ATP synthase, thus indicating that proton transport by OM flavocytochrome complexes limits the rate of EET.

In situ electrochemical enrichment and isolation of a magnetite-reducing bacterium from a high pH serpentinizing spring.

Serpentinization is a geologic process that produces highly reduced, hydrogen-rich fluids that support microbial communities under high pH conditions. We investigated the activity of microbes capable of extracellular electron transfer in a terrestrial serpentinizing system known as 'The Cedars'. Measuring current generation with an on-site two-electrode system, we observed daily oscillations in current with the current maxima and minima occurring during daylight hours. Distinct members of the microbial community were enriched. Current generation in lab-scale electrochemical reactors did not oscillate, but was correlated with carbohydrate amendment in Cedars-specific minimal media. Gammaproteobacteria and Firmicutes were consistently enriched from lab electrochemical systems on δ-MnO2 and amorphous Fe(OH)3 at pH 11. However, isolation of an electrogenic strain proved difficult as transfer cultures failed to grow after multiple rounds of media transfer. Lowering the bulk pH in the media allowed us to isolate a Firmicutes strain (Paenibacillus sp.). This strain was capable of electrode and mineral reduction (including magnetite) at pH 9. This report provides evidence of the in situ activity of microbes using extracellular substrates as sinks for electrons at The Cedars, but also highlights the potential importance of community dynamics for supporting microbial life through either carbon fixation, and/or moderating pH stress.

Organic Solar Cells with Controlled Nanostructures Based on Microphase Separation of Fullerene-Attached Thiophene-Selenophene Heteroblock Copolymers.

Heteroblock copolymers consisting of poly(3-hexylthiophene) and fullerene-attached poly(3-alkylselenophene) (T-b-Se-PCBP) were synthesized for organic photovoltaic applications by quasi-living catalyst transfer polycondensation and subsequent conversion reactions. Characterization of the polymers confirmed the formation of well-defined diblock structures with high loading of the fullerene at the side chain (∼40 wt %). Heteroblock copolymer cast as a thin film showed a clear microphase-separated nanostructure approximately 30 nm in repeating unit after thermal annealing, which is identical to the microphase-separated nanostructure of diblock copolymer consisting of poly(3-hexylthiophene) and fullerene-attached poly(3-alkylthiophene) (T-b-T-PCBP). These heteroblock copolymers provide an ideal platform for investigating the effects of nanostructures and interfacial energetics on the performance of organic photovoltaic devices.

Molecular design of cytocompatible amphiphilic redox-active polymers for efficient extracellular electron transfer.

For electrochemical regulations of the intracellular metabolisms, lipophilic electron mediators with cell membrane permeability have been conventionally used. We have recently developed amphiphilic, cell-membrane permeable polymer composed of hydrophilic 2-methacryloyloxyethyl phosphorylcholine and hydrophobic redox-active units as a new category of electron mediator. The advantage of the redox active polymer is that we can obtain appropriate molecules in a synthetic bottom-up manner. Here we report that the rate of the extracellular electron transfer (EET) through the redox active polymer can be regulated by sophisticated molecular design of the polymers. It was also shown that the cellular metabolism of yeast Saccharomyces cerevisiae was regulated by using the polymer with the highest EET rate.

Highly Boosted Oxygen Reduction Reaction Activity by Tuning the Underwater Wetting State of the Superhydrophobic Electrode.

By rationally designing superhydrophobic electrodes with different underwater wetting states, it is revealed that only the underwater Wenzel-Cassie coexistent state shows the clearly enhanced ability in catalyzing the oxygen reduction reaction, a typical underwater gas-consuming reaction at electrode. It is proposed that the maximizing and stabilizing the liquid/gas/solid triphase interface, endowed by the underwater Wenzel-Cassie coexistent state, plays a rather crucial role.

Stability of organic compounds on the oxygen-evolving center of photosystem II and manganese oxide water oxidation catalysts.

Surrounding organic residues are indispensable for the high water oxidation activity of the Mn4 cluster in photosystem II. Here, the stability of organic compounds on synthetic Mn oxides was analyzed using inlet electrochemical mass spectroscopy. Carboxyl groups, which are the most abundant residues around the Mn4 cluster, were found to stably facilitate the oxygen evolution reaction.

Oxygen-Tolerant Electrodes with Platinum-Loaded Covalent Triazine Frameworks for the Hydrogen Oxidation Reaction.

Reducing the use of platinum (Pt) on polymer electrolyte fuel cell anodes is critical for the widespread dissemination of these energy conversion systems. Although Pt usage can be minimized by the even dispersion of isolated Pt atoms, no atomically dispersed Pt catalysts that promote hydrogen oxidation at a rate required for practical fuel cells have been reported to date. Covalent triazine frameworks with atomically dispersed Pt atoms (0.29 wt %) are described and it is demonstrated that the material has a high electrocatalytic hydrogen oxidation activity without an overpotential. Importantly, when the loading amount was increased to 2.8 wt %, the electrocatalytic hydrogen oxidation activity of the resulting electrode was comparable to that of commercial carbon supported 20 wt % Pt catalysts, and the catalytic activity for oxygen reduction was markedly reduced. Thus, Pt-modified covalent triazine frameworks selectively catalyze hydrogen oxidation, even in the presence of dissolved oxygen, which is critical for limiting cathode degradation during the start-stop cycles of fuel cells.

Nickel-Nitrogen-Modified Graphene: An Efficient Electrocatalyst for the Reduction of Carbon Dioxide to Carbon Monoxide.

Nickel-nitrogen-modified graphene (Ni-N-Gr) is fabricated and Ni-N coordination sites on Ni-N-Gr as active centers effectively reduce CO2 to CO. The faradaic efficiency for CO formation reaches 90% at -0.7 to -0.9 V versus RHE, and the turnover frequency for CO production comes up to ≈2700 h-1 at -0.7 V versus RHE.

Legitimate intermediates of oxygen evolution on iridium oxide revealed by in situ electrochemical evanescent wave spectroscopy.

Understanding how the four-electron oxidation of water to dioxygen proceeds in different materials is critical to the rational design of efficient catalysts towards artificial photosynthetic systems. Here, using in situ electrochemical evanescent wave spectroscopy under oxygen-evolving conditions, we report two intermediates of iridium oxide (IrOx), which is the most active and stable catalyst characterized to date in acidic medium. The observed potential dependence of the two intermediates indicated that they were associated with different surface sites, and intermediate scavenging experiments using H2O2 provided insight into their role during catalysis. Notably, an Ir(V) species with an absorption maximum at 450 nm was found to mediate the initial two-electron oxidation of water. Inhibition of the Ir(V) species by H2O2, combined with computational modeling, indicates that the accumulation and concurrent spin-state change of the Ir(V) species is a prerequisite for efficient water oxidation by IrOx electrodes.