Protein dynamics and electron transfer: electronic decoherence and non-Condon effects

Area of Science:

• Biophysical Chemistry
• Electron Transfer Dynamics
• Molecular Biophysics

Background:

• Electron transfer (ET) is fundamental in biological and chemical processes.
• Non-Condon effects can significantly influence ET rates, but their extent is system-dependent.
• Ru-azurin derivatives provide a model system to study protein-mediated electron transfer.

Purpose of the Study:

• To quantify the influence of non-Condon effects on electron transfer rates in Ru-azurin derivatives.
• To investigate the structural and dynamical origins of non-Condon effects.
• To compare ET dynamics in Ru-azurin with solvent-mediated ET in small molecules.

Main Methods:

• Computation of the autocorrelation function of the donor-acceptor tunneling matrix element .
• Analysis of as a function of donor-acceptor distance, tunneling pathway structure, tunneling energy, and temperature.
• Comparison with decay times of time-dependent Franck-Condon factors.

Main Results:

• The autocorrelation function for Ru-azurin derivatives is largely insensitive to tunneling pathway structure.
• The decay time of is only slightly shorter than for solvent-mediated ET in small organic molecules.
• The primary contribution to the decay time originates from fluctuations of valence angles, not bond lengths.

Conclusions:

• Non-Condon effects play a minor role in the electron transfer dynamics of Ru-azurin derivatives.
• Valence angle fluctuations are the dominant dynamical factor influencing electron transfer in this system.
• The findings provide insights into the mechanisms of protein-mediated electron transfer.