Electron transfer between biological molecules by thermally activated tunneling

Area of Science:

• Physical Chemistry
• Biophysics
• Quantum Mechanics

Background:

• Electron transfer is crucial in biological systems.
• Previous models did not fully explain temperature-dependent electron transfer rates.

Purpose of the Study:

• Develop a comprehensive theory for electron transfer between fixed sites.
• Incorporate vibronic coupling to explain temperature effects.
• Quantitatively interpret experimental data from biological systems.

Main Methods:

• Developed a theoretical model for electron transfer.
• Incorporated vibronic coupling to account for activation energy.
• Compared model predictions with experimental data for Chromatium and Rhodopseudomonas spheroides.
• Validated model parameters using optical absorption spectra.

Main Results:

• The theory explains temperature-dependent activation energy at high temperatures.
• It describes temperature-independent tunneling at low temperatures.
• The model quantitatively interprets electron transfer data for Chromatium and Rhodopseudomonas spheroides.
• Determined a linking site separation of 8-10 Å in Chromatium.

Conclusions:

• The developed theory provides a robust framework for understanding electron transfer.
• Vibronic coupling is key to explaining temperature effects in electron transfer.
• The model suggests a smaller linking site separation in Chromatium than previously estimated.