Optical activity of small peptide chains with right-handed α-helix structure

The optical activity of oligopeptides in the conformation of the right-handed α-helix was calculated by the direct semiempirical quantum chemical CNDO /OPTIC method. The oligomers of glycine and alanine from dimer up to pentamer were considered. The comparison with results obtained using the model of interacting groups (MIG ) based on the perturbation approach was carried out. The calculational results show that the circular dichroism (CD ) of oligopeptide α-helices is essentially different from the CD of the peptide polymers in the same conformation. The comparison between results obtained by the CNDO /OPTIC method and by the MIG leads to doubts about the reliability of the use of the MIG to calculate rotatory strengths of nπ* transitions of oligopeptides in α-helix conformation.