Biochemistry and Theory of Proton-Coupled Electron Transfer

Abstract

havior in PCET 3400 5.3. Adiabatic and Nonadiabatic PCET Interpreted in the Context of the Schrodinger Equation and the Born−Oppenheimer (Adiabatic) Approximation 3404 5.3.1. Quantum-State Dynamics of PCET Systems and the Underlying Potential (Free) Energy Surfaces 3404 5.3.2. Investigating Coupled Electronic−Nuclear Dynamics and Deviations from the Adiabatic Approximation in PCET Systems via a Simple Model 3408 5.3.3. Formulation and Representations of Electron−Proton States 6. Extension of Marcus Theory to Proton and Atom Transfer Reactions 6.1. Extended Marcus Theory for Electron, Proton, and Atom Transfer Reactions 6.2. Implications of the Extended Marcus Theory: Brønsted Slope, Kinetic Isotope Effect, and Cross-Relation 7. Beyond Marcus Theory: Nuclear Tunneling and Structural Constraints on PCET 8. Proton-Activated Electron Transfer: A Special Case of Separable and Coupled PT and ET 9. Dogonadze−Kuznetsov−Levich (DKL) Model of PT/HAT and Connections with ET and PCET Theories 10. Borgis−Hynes (BH) Theory for PT and HAT 10.1. Dynamical Regimes of the BH Theory 10.2. Splitting and Coupling Fluctuations 10.3. Reaction Rate Constant 10.4. Analytical Rate Constant Expressions in Limiting Regimes 11. Cukier Theory of PCET 11.1. Double-Adiabatic and Two-Dimensional Approaches 11.2. Reorganization and Solvation Free Energy in ET, PT, and EPT 11.3. Generalization of the Theory and Connections between PT, PCET, and HAT 12. Soudackov−Hammes-Schiffer (SHS) Theory of PCET 12.1. Regarding System Coordinates and Interactions: Hamiltonians and Free Energies 12.2. Electron−Proton States, Rate Constants, and Dynamical Effects 12.3. Note on the Kinetic Isotope Effect in PCET 12.4. Distinguishing between HAT and Concerted PCET Reactions 12.5. Electrochemical PCET 13. Conclusions and Prospects Appendix A Appendix B Associated Content Supporting Information

Proton-Coupled Electron Transfer in Organic Synthesis: Fundamentals, Applications, and Opportunities

“…In the former, Brettel has demonstrated that FAD initiates oxidation of Trp382, which engages in a hole-hopping oxidation of Trp359 and finally Trp306, which deprotonates to yield the neutral tryptophan radical [1,[178][179]. For the oxidation of the terminal Trp306 found in E. coli photolyase, Schelvis and coworkers have demonstrated the electron transfer proceeds by concerted PCET below pH = 6.5, but otherwise undergoes stepwise PCET via an initial electron transfer [180].…”

“…'Proton-coupled electron transfer' (PCET) describes any elementary step (or series of elementary steps) in which both a proton and an electron are exchanged [1][2][3][4][5][6][7][8][9]. Within this broad definition, further distinctions may be drawn: if the proton and electron move simultaneously, the elementary step is referred to as a concerted PCET.…”

Hole hopping through tyrosine/tryptophan chains protects proteins from oxidative damage

“…Several decades of experimental investigations (5, 7), guided by a transparent theoretical model (8), have produced a clear understanding of single-step ET in proteins. Biological electron transfers frequently are accompanied by proton transfers, introducing an additional complication (9)(10)(11). Although the details of protein structure and redox thermodynamics must be taken into account when considering individual cases (12), tunneling timetables indicate that 20-25 Å is the maximum distance that an electron (or hole, in the case of high-potential reactions) can transfer on submillisecond timescales (5,7).…”

Direct observation of light-driven, concerted electron–proton transfer

“…light driven | electron | proton | transfer | photoEPT P roton-coupled electron transfer (PCET) reactions, in which both electrons and protons are transferred, play an important role in redox processes in chemistry and biology with examples in water oxidation (1)(2)(3)(4), CO 2 reduction (5), mitochondrial respiration (6), and conversion of nucleotides to 2′-deoxynucleotides (7,8). Mechanistically, PCET occurs by stepwise, electron transfer followed by proton transfer(ET-PT) (9-13) or proton transfer followed by electron transfer (PT-ET), or concerted pathways (EPT) with concerted transfer in a single step.…”