Theoretical π-π* circular dichroic spectra of helical poly(glycine) and poly(L-alanine) as functions of backbone torsion angles.

Circular dichroic spectra and oscillator strengths of the π-π transition near 190 nm are calculated for helical (Gly) and (Ala) at 30° intervals of the backbone torsion angles (ϕ,ψ) over the range -180° ≤ ϕ ≤ -60°, -60° ≤ ψ ≤ 180°, using the partially dispersive normal mode treatment of the dipole interaction model. Polarizabilities of atoms and the NC'O group are those determined semiempirically in previous studies. Calculations for (Ala) at (ϕ,ψ) angles corresponding to the α-helix, the poly(Pro) II helix, a collagen single helix, a poly-(MeAla) helix, and single β-helices are found to agree well with most of the available experimental data.