Ionization energy and electron affinity of oligoglycines: a CAM-B3LYP density functional theory study

Long-range corrected CAM-B3LYP density functional theory level with the polarized and diffuse 6-31+G* basis set has been used to compute delta self-consistent field (Delta SCF) vertical ionization energies (VIE) and electron affinities (VEA) of single-chain oligoglycines (H2N-(CH2-CO-NH) (n) -CH2COOH, n = 1-9) in the alpha-helix and beta-strand conformations. For all the investigated oligopeptides VIE (alpha-helix) < VIE (beta-strand), whereas VEA (alpha-helix) > VIE (beta-strand), owing to the cooperative effects of the -N-H center dot center dot center dot O=C- intramolecular hydrogen bonds in the alpha-helices. The VIE-VEA band gap for beta-strands is predicted to be greater than that of the corresponding alpha-helices. In the limit of the polymer, the conductivity of the alpha-helix is predicted to be ca. double that of the beta-strand. The alpha-helix-based materials are potentially more efficient single-chain conductors than beta-strands.