Long-Range Electron Transfer in Engineered Azurins Exhibits Marcus Inverted Region Behavior

Area of Science:

• Biophysical Chemistry
• Biochemistry
• Electron Transfer Theory

Background:

• The Marcus theory describes electron transfer (ET) rates influenced by driving force and reorganization energy.
• The Marcus inverted region, where ET rates decrease with increasing driving force, is well-established in many systems.
• Experimental evidence for the inverted region in "protein-only" systems has been lacking.

Purpose of the Study:

• To provide experimental evidence of the Marcus inverted region in nonderivatized protein systems.
• To investigate electron transfer dynamics within proteins without external redox mediators.
• To explore implications for designing novel bio-inspired energy conversion devices.

Main Methods:

• Studied electron transfer rates in a series of nonderivatized proteins.
• Varied the driving force of the electron transfer reactions.
• Analyzed experimental data to identify the Marcus inverted region.

Main Results:

• Demonstrated experimental evidence of the Marcus inverted region in protein-only systems.
• Observed a decrease in electron transfer rate constants at higher driving forces.
• Confirmed the occurrence of the inverted region in the absence of conjugated redox moieties.

Conclusions:

• The Marcus inverted region is observable in intrinsic protein electron transfer.
• These findings validate Marcus theory in biological systems.
• Results pave the way for designing efficient ET centers in proteins for energy applications.