Conformational analysis of peptides in oriented polyoxyethylene bye infrared dichroism

A new procedure for the determination of infrared dichroic spectra of oligo- and polypeptides is described. The peptide is incorporated in a polyoxyethylene film and partially oriented by uniaxial stretching. The infrared characteristics of the polyoxyethylene support allow measurement of the dichroic spectra of amide N--H stretching bands between 3500 and 3000 cm-1, of amide I and II bands between 1700 and 1500 cm-1, and of far-infrared bands below 800 cm-1. Procedures for measuring the kinetics of N--H to N--D isotopic exchange reactions of molecules oriented in polyoxyethylene are described. The infrared dichroic spectra of gramicidin S and of several synthetic oligo- and polypeptides are presented. Gramicidin S exhibits a ''cross-β'' dichroic spectrum which could arise from extensive association of the β-sheet conformation of Hodgkin--Oughton and Schwyzer into ribbon-like aggregates. Polypeptides were found to be oriented in the α-helical, β-sheet, and ''cross-β'' conformation in polyoxyethylene films. (U.S.)