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2. Extracellular electron transfer explained

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   Bose, Arpita; Wang, Aiden (January 2024, Open Access Government)

   Extracellular electron transfer explainedArpita Bose, PhD from Washington University in St. Louis, guides us through host-associated impacts and biotechnological applications of extracellular electron transfer in electrochemically active bacteria. Electron flow and oxidative and reductive reactions, referred to as “redox reactions,” collectively impact the outcomes of biochemical pathways essential for cell growth, energy conservation, and stress response throughout various organisms. An example of these organisms is electrochemically active bacteria (EAB), which can link internal redox reactions with external electron acceptors or donors via a process known as extracellular electron transfer (EET). 

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3. Electrochemistry of Protein Electron Transfer

   https://doi.org/10.1149/1945-7111/ac60f1  

   Matyushov, Dmitry V. (June 2022, Journal of The Electrochemical Society)

   Protein fold and slow relaxation times impose constraints on configurations sampled by the protein. Incomplete sampling leads to the violation of fluctuation-dissipation relations underlying the traditional theories of electron transfer. The effective reorganization energy of electron transfer is strongly reduced thus leading to lower barriers and faster rates (catalytic effect). Electrochemical kinetic measurements support low activation barriers for protein electron transfer. The distance dependence of the rate constant displays a crossover from a plateau at short distances to a long-distance exponential decay. The transition between these two regimes is controlled by the protein dynamics. 

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4. Reorganization Energy of Electron Transfer

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   Matyushov, Dmitry (February 2023, Physical Chemistry Chemical Physics)

   The theory of electron transfer reactions establishes the conceptual foundation for redox solution chemistry, electrochemistry, and bioenergetics. Electron and proton transfer across the cellular membrane provide all energy of life gained through natural photosynthesis and mitochondrial respiration. Rates of biological charge transfer set kinetic bottlenecks for biological energy storage. The main system-specific parameter determining the activation barrier for a single electron-transfer hop is the reorganization energy of the medium. Both harvesting of light energy in natural and artificial photosynthesis and efficient electron transport in biological energy chains require reduction of the reorganization energy to allow fast transitions. This review article discusses the mechanisms of how small values of the reorganization energy are achieved in protein electron transfer and how similar mechanisms can operate in other media, such as nonpolar and ionic liquids. One of the major mechanisms of reorganization energy reduction is through non-Gibbsian (nonergodic) sampling of the medium configurations on the reaction time. A number of alternative mechanisms, such as electrowetting of active sites of proteins, give rise to non-parabolic free energy surfaces of electron transfer. These mechanisms and nonequilibrium population of donor-acceptor vibrations lead to a universal phenomenology of separation between the Stokes-shift and variance reorganization energies of electron transfer. 

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5. Conformational dynamics modulating electron transfer

   https://doi.org/10.1063/5.0102707  

   Matyushov, Dmitry V. (September 2022, The Journal of Chemical Physics)

   Diffusional dynamics of the donor–acceptor distance are responsible for the appearance of a new time scale of diffusion over the distance of electronic tunneling in electron-transfer reactions. The distance dynamics compete with the medium polarization dynamics in the dynamics-controlled electron-transfer kinetics. The pre-exponential factor of the electron-transfer rate constant switches, at the crossover distance, between a distance-independent, dynamics-controlled plateau and exponential distance decay. The crossover between two regimes is controlled by an effective relaxation time slowed down by a factor exponentially depending on the variance of the donor–acceptor displacement. Flexible donor–acceptor complexes must show a greater tendency for dynamics-controlled electron transfer. Energy chains based on electron transport are best designed by placing the redox cofactors near the crossover distance. 

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