Anomalous temperature-isotope dependence in proton-coupled electron transfer

Area of Science:

• Physical Chemistry
• Theoretical Chemistry
• Chemical Physics

Background:

• Experiments reveal anomalous temperature dependence in electron transfer (ET) rates (k(H)/k(D)) across hydrogen-bonding interfaces.
• Existing models for proton-coupled electron transfer (PCET) do not fully explain these observed isotopic effects.

Purpose of the Study:

• To develop a new theoretical model for condensed-phase PCET that accounts for anomalous temperature dependence without invoking real proton transfer.
• To reframe the mechanism as vibrationally assisted ET, driven by bath-induced proton coordinate fluctuations.

Main Methods:

• Development of a novel theoretical framework for PCET.
• Analysis of joint temperature-isotope effects in coupled charge transfer reactions.
• Modeling bath-induced fluctuations in the proton coordinate influencing electron tunneling.

Main Results:

• The proposed model successfully explains the anomalous temperature dependence of k(H)/k(D) observed in experiments.
• Electron tunneling dynamics are modulated by bath-induced proton coordinate fluctuations.
• The mechanism is better described as vibrationally assisted ET rather than traditional PCET.

Conclusions:

• Vibrationally assisted ET provides a viable explanation for coupled charge transfer phenomena with anomalous isotopic effects.
• This mechanism may be applicable to understanding traditional PCET processes with timescale separation.
• The model offers insights into long-range ET in proteins and other systems involving hydrogen-bonded residues.