SECONDARY STRUCTURE CONFORMATIONS AND LONG-RANGE ELECTRONIC INTERACTIONS IN OLIGOPEPTIDES

Combined quantum mechanical coupling calculations and molecular dynami cs simulations were performed to examine the role of modest geometrica l fluctuations of peptide secondary structures on long range electroni c interactions in oligopeptides. Molecular dynamics simulations were p erformed to obtain typical relevant conformations of oligopeptides, an d self-consistent Hartree-Fock calculations at the semiempirical quant um theory level were performed to extract the long range electronic pr opagation. Initial a-helical oligopeptides show dominant hole-mediated coupling over a large tunneling energy range, while the initial exten ded conformation oligopeptides have more nearly equal contributions fr om both hole and electron mechanisms. Modest geometrical fluctuations lead to changes in the character of long range electronic interactions . The computations highlight the danger of drawing conclusions from el ectronic structure calculations of electronic coupling in peptide mode l systems on the basis of computations on single geometries.