Conformational study on poly[gamma-(alpha-phenethyl)-L-glutamate] using vibrational circular dichroism spectroscopy

Vibrational circular dichroism (VCD) and IR absorption spectra are obtained in a chloroform solution for paly[gamma-((R)-alpha -phenethyl)-L-glutamate ] (PRPLG) and poly[gamma-((S)-alpha -phenethyl)-L-glutamate] (PSPLG), whose only structural difference is an opposite chiral center in the side chain. Their characteristic amide A, I, and II bands show VCD patterns quite simi lar to those of poly[gamma -benzyl-L-glutamate] (PBLG), indicating that the secondary structure of these polypeptides is a right-handed alpha -helix. The VCD spectra in the CH stretching region exhibit different patterns for PRPLG and PSPLG, reflecting the chirality difference in the side chains. Th is difference is interpreted on the basis of the additivity of optical acti vity contributions from the main chain conformation and the chirality diffe rence in the side chains. The results indicate that a VCD difference spectr um of the CPI stretching region is a useful diagnostic tool for elucidating local chirality differences. (C) 2001 John Wiley & Sons, Inc.