Reaction of Thiosulfate Dehydrogenase with a Substrate Mimic Induces Dissociation of the Cysteine Heme Ligand Giving Insights into the Mechanism of Oxidative Catalysis.

Thiosulfate dehydrogenases are bacterial cytochromes that contribute to the oxidation of inorganic sulfur. The active sites of these enzymes contain low-spin -type heme with Cys/His axial ligation. However, the reduction potentials of these hemes are several hundred mV more negative than that of the thiosulfate/tetrathionate couple (, +198 mV), making it difficult to rationalize the thiosulfate oxidizing capability.

His/Met heme ligation in the PioA outer membrane cytochrome enabling light-driven extracellular electron transfer by Rhodopseudomonas palustris TIE-1.

A growing number of bacterial species are known to move electrons across their cell envelopes. Naturally this occurs in support of energy conservation and carbon-fixation. For biotechnology it allows electron exchange between bacteria and electrodes in microbial fuel cells and during microbial electrosynthesis.

Reversible and Selective Interconversion of Hydrogen and Carbon Dioxide into Formate by a Semiartificial Formate Hydrogenlyase Mimic.

The biological formate hydrogenlyase (FHL) complex links a formate dehydrogenase (FDH) to a hydrogenase (Hase) and produces H and CO from formate via mixed-acid fermentation in . Here, we describe an electrochemical and a colloidal semiartificial FHL system that consists of an FDH and a Hase immobilized on conductive indium tin oxide (ITO) as an electron relay. These systems benefit from the efficient wiring of a highly active enzyme pair and allow for the reversible conversion of formate to H and CO under ambient temperature and pressure.

Heme ligation and redox chemistry in two bacterial thiosulfate dehydrogenase (TsdA) enzymes.

Thiosulfate dehydrogenases (TsdAs) are bidirectional bacterial di-heme enzymes that catalyze the interconversion of tetrathionate and thiosulfate at measurable rates in both directions. In contrast to our knowledge of TsdA activities, information on the redox properties in the absence of substrates is rather scant. To address this deficit, we combined magnetic CD (MCD) spectroscopy and protein film electrochemistry (PFE) in a study to resolve heme ligation and redox chemistry in two representative TsdAs.

Protein film electrochemical EPR spectroscopy as a technique to investigate redox reactions in biomolecules.

Redox reactions and paramagnetic intermediates are ubiquitous in biological chemistry. We report a new method, protein film electrochemical electron paramagnetic resonance spectroscopy (PFE-EPR), that enables the direct and accurate potential control of proteins on the electrode surface for both electrochemical and EPR spectroscopic characterisation of their redox centres.

Structure-Activity Relationships of Hierarchical Three-Dimensional Electrodes with Photosystem II for Semiartificial Photosynthesis.

Semiartificial photosynthesis integrates photosynthetic enzymes with artificial electronics, which is an emerging approach to reroute the natural photoelectrogenetic pathways for sustainable fuel and chemical synthesis. However, the reduced catalytic activity of enzymes in bioelectrodes limits the overall performance and further applications in fuel production. Here, we show new insights into factors that affect the photoelectrogenesis in a model system consisting of photosystem II and three-dimensional indium tin oxide and graphene electrodes.

Photoreduction of CO with a Formate Dehydrogenase Driven by Photosystem II Using a Semi-artificial Z-Scheme Architecture.

Solar-driven coupling of water oxidation with CO reduction sustains life on our planet and is of high priority in contemporary energy research. Here, we report a photoelectrochemical tandem device that performs photocatalytic reduction of CO to formate. We employ a semi-artificial design, which wires a W-dependent formate dehydrogenase (FDH) cathode to a photoanode containing the photosynthetic water oxidation enzyme, Photosystem II, via a synthetic dye with complementary light absorption.

Oxygenic Photoreactivity in Photosystem II Studied by Rotating Ring Disk Electrochemistry.

Protein film photoelectrochemistry has previously been used to monitor the activity of photosystem II, the water-plastoquinone photooxidoreductase, but the mechanistic information attainable from a three-electrode setup has remained limited. Here we introduce the four-electrode rotating ring disk electrode technique for quantifying light-driven reaction kinetics and mechanistic pathways in real time at the enzyme-electrode interface. This setup allows us to study photochemical HO oxidation in photosystem II and to gain an in-depth understanding of pathways that generate reactive oxygen species.

Solar Water Splitting with a Hydrogenase Integrated in Photoelectrochemical Tandem Cells.

Hydrogenases (H ases) are benchmark electrocatalysts for H production, both in biology and (photo)catalysis in vitro. We report the tailoring of a p-type Si photocathode for optimal loading and wiring of H ase through the introduction of a hierarchical inverse opal (IO) TiO interlayer. This proton-reducing Si|IO-TiO |H ase photocathode is capable of driving overall water splitting in combination with a photoanode.

Catechol-TiO hybrids for photocatalytic H production and photocathode assembly.

Visible-light driven H evolution in water is achieved using catechol-photosensitised TiO nanoparticles with a molecular nickel catalyst. Layer-by-layer immobilisation of catechol-TiO onto tin-doped indium oxide electrodes generates photocathodic currents in the presence of an electron acceptor. This approach represents a new strategy for controlling photocurrent direction in dye-sensitised photoelectrochemical applications.

Photoelectrochemistry of Photosystem II in Vitro vs in Vivo.

Factors governing the photoelectrochemical output of photosynthetic microorganisms are poorly understood, and energy loss may occur due to inefficient electron transfer (ET) processes. Here, we systematically compare the photoelectrochemistry of photosystem II (PSII) protein-films to cyanobacteria biofilms to derive: (i) the losses in light-to-charge conversion efficiencies, (ii) gains in photocatalytic longevity, and (iii) insights into the ET mechanism at the biofilm interface. This study was enabled by the use of hierarchically structured electrodes, which could be tailored for high/stable loadings of PSII core complexes and Synechocystis sp.

Competing charge transfer pathways at the photosystem II-electrode interface.

The integration of the water-oxidation enzyme photosystem II (PSII) into electrodes allows the electrons extracted from water oxidation to be harnessed for enzyme characterization and to drive novel endergonic reactions. However, PSII continues to underperform in integrated photoelectrochemical systems despite extensive optimization efforts. Here we carried out protein-film photoelectrochemistry using spinach and Thermosynechococcus elongatus PSII, and we identified a competing charge transfer pathway at the enzyme-electrode interface that short-circuits the known water-oxidation pathway.

A decahaem cytochrome as an electron conduit in protein-enzyme redox processes.

The decahaem cytochrome MtrC from Shewanella oneidensis MR-1 was employed as a protein electron conduit between a porous indium tin oxide electrode and redox enzymes. Using a hydrogenase and a fumarate reductase, MtrC was shown as a suitable and efficient diode to shuttle electrons to and from the electrode with the MtrC redox activity regulating the direction of the enzymatic reactions.

Relative Photoionization Cross Sections of Super-Atom Molecular Orbitals (SAMOs) in C60.

The electronic structure and photoinduced dynamics of fullerenes, especially C60, is of great interest because these molecules are model systems for more complex molecules and nanomaterials. In this work we have used Rydberg Fingerprint Spectroscopy to determine the relative ionization intensities from excited SAMO (Rydberg-like) states in C60 as a function of laser wavelength. The relative ionization intensities are then compared to the ratio of the photoionization widths of the Rydberg-like states, computed in time-dependent density functional theory (TD-DFT).