A coiled-coiled hexamer (ACC-Hex) is a self-assembled helical peptide bundle formed by three coiled dimers of a short α-helix peptide chain. The published low electric resistance of ACC-Hex nanofiber films in experiment motivates a computational investigation into the electronic structure of ACC-Hex. Here, we present an all-atom classical molecular dynamics (MD) and Kohn-Sham density functional theory (DFT) study of the structure and electronic properties of solvated ACC-Hex; without a priori assumption of the atoms and electrons most relevant to conductivity. The classical MD captures the structural distortions of the peptide and aqueous solvent at 303.15K and 1atm. From MD, averaged structures of the entire ACC-Hex with a solvation shell are extracted for DFT, to capture the electronic interaction of nearest-neighbor molecules from first-principles. The DFT electronic structure shows dense, near-degenerate electronic orbitals near the electronic gap. Spanning the peptide bundle, these near-degenerate electronic orbitals have significant density on the phenylalanine residues at the core of ACC-Hex, as well as the peptide backbone and residues on the outer edge of ACC-Hex. These electronic orbitals thus suggest an electron transfer path for conductivity along the length of ACC-Hex, induced by thermal fluctuations; requiring complexity in building predictive peptide conductivity models for ACC-Hex. To further characterize thermal fluctuations for model building, we consider 100 MD snapshots of a solvated dimer unit of ACC-Hex, observing significant oscillations of the DFT electronic structure consistent with a vibration-induced conductivity model. We present our computational protocol and connect our DFT electronic orbitals to conductivity models for bio-inspired materials.

Modelling ACC-Hex: Thermal fluctuations of Kohn-Sham orbitals facilitate electron transfer

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