Electron Charge Transfer in Linear and Cyclic Structures of Polypeptides

Density functional theory has been used to investigate the intramolecular charge transfer, hole and electron, in linear and cyclic structures of [L-Ala-L-Val (AV)]₃ and [L-Val-L-Ala(VA)]₃ based on the Tight binding Hamiltonian approach. The linear and cyclic structures of (AV)₃ and (VA)₃ have been optimized at B3LYP/6-311G(d, p) level of theory. After the geometry optimization, the fragment calculations have been performed in order to calculate the values of the charge transfer integrals, spatial overlap integrals and site-energies involved in the transport of both positive and negative charges through the peptide bonds of polypeptide. The calculations show that the conductivity property in peptides varies considerably with conformations of linear or cyclic structures and intramolecular interactions like H-bonding.