Direct simulation of proton-coupled electron transfer across multiple regimes

Area of Science:

• Chemical Physics
• Computational Chemistry
• Reaction Dynamics

Background:

• Proton-coupled electron transfer (PCET) is vital in biological and molecular catalysis.
• Fundamental aspects of PCET mechanisms remain poorly understood.
• Current theoretical models often require a priori assumptions about reaction pathways.

Purpose of the Study:

• To extend the ring polymer molecular dynamics (RPMD) method for direct simulation of PCET reactions.
• To investigate PCET kinetics and mechanisms across various coupling regimes.
• To provide a unifying framework for understanding PCET driving forces.

Main Methods:

• Developed and applied the ring polymer molecular dynamics (RPMD) method for PCET simulations.
• Modeled symmetric, co-linear PCET in a system-bath model.
• Studied PCET in fully non-adiabatic, partially adiabatic, and fully adiabatic regimes.
• Compared RPMD results with established PCET rate theories and semiclassical instanton theory.

Main Results:

• RPMD identified distinct pathways for sequential and concerted PCET.
• Concerted PCET was shown to proceed via a solvent-gating mechanism.
• The method accurately predicted crossover in thermal reaction rates between coupling regimes.
• A novel 'transient-proton-bridge' mechanism for concerted PCET was revealed.

Conclusions:

• The extended RPMD method provides a powerful tool for simulating PCET reactions without prior mechanistic assumptions.
• The study offers a unified understanding of PCET mechanisms and driving forces.
• New PCET mechanisms may exist, expanding the scope of known catalytic processes.