Vibrational analysis of peptides, polypeptides, and proteins. XVII. Normal modes of crystalline Pro-Leu-Gly-NH2, a type II beta-turn.

A normal mode calculation has been done for Pro-Leu-Gly-NH2 in its crystalline type II beta-turn structure, and assignments have been made to infrared and Raman bands of this molecule and its N-deuterated derivative. Observed and calculated frequencies below 1700 cm-1 agree to within about 6 cm-1. This analysis provides a sound basis for studying the conformation dependence of the vibrational spectrum.