Structural, Solvent, and Temperature Effects on Protein Junction Conductance.

Area of Science:

• Biophysics
• Computational Chemistry
• Materials Science

Background:

• Cytochrome b562 is a model redox-active heme protein crucial for studying biological electron transfer.
• Understanding electron transport in protein-metal junctions is key for molecular electronics.

Purpose of the Study:

• To theoretically investigate electron transport mechanisms in protein-metal junctions featuring cytochrome b562.
• To compare coherent tunneling and incoherent hopping transport models using computational methods.

Main Methods:

• Multi-scale computational approach combining molecular dynamics (MD) simulations and density functional theory (DFT).
• Analysis of junction geometries under vacuum-dried and solvated conditions with protein covalently bound to gold contacts.
• Application of Landauer-Buttiker formalism for coherent tunneling and Marcus theory for incoherent hopping.

Main Results:

• Coherent tunneling identified as the dominant charge transport mechanism in cytochrome b562 junctions, aligning with experimental data.
• Tunneling exhibited a very shallow distance dependence, characteristic of the coherent mechanism.
• Protein structure and electrode contacts significantly influenced conductance; solvation effects were minor.
• Temperature dependence was strong for hopping but negligible for tunneling, confirming tunneling as the dominant pathway.

Conclusions:

• Coherent tunneling is the primary mechanism for electron transport in cytochrome b562-based protein-metal junctions.
• The study provides theoretical insights into the factors governing junction conductance, including structural and environmental effects.
• Tunneling current magnitude serves as a reliable indicator of the coherent transport mechanism.