On the band gap in peptide alpha-helices

The variation in the band gap of a (Gly)(30) alpha-helix with position in t he peptide sequence has been investigated using AM1 semiempirical molecular orbital (MO) theory within an extensive singles configuration interaction (CI) treatment. The dipole-charge interaction along the length of the helix results in the highest local electron affinity near the N-terminus and the lowest local ionization potential near the C-terminus. The calculations su ggest that the band gap, measured as the difference between the local ioniz ation potential and electron affinity decreases from the C-terminus to the N-terminus for the model (Gly)(30) alpha-helix in vacuo. (C) 2000 John Wile y & Sons, Inc.