Infra-red spectra of polypeptides with small side chains

Abstract The infra-red spectrum of several synthetic polypeptides with small side chains (polymers of glycine and alanine) have been examined in the region 800 to 1700 cm-1. The observations include measurements with polarized radiation on the α (folded) and β (extended) forms of poly-L-alanine; deductions from these results are compared with those derived from X-ray observations on similar materials. Some observations on the spectrum of deuterated poly-DL-alanine have also been made. The new observations enable a partial classification of bands in the little explored region 800 to 1500 cm-1 to be made. Some observations on silk gut and on water-soluble silk have also been made. They emphasize the difference between these two forms of fibroin. An extension of the complex NH absorption, centred at ca. 3300 cm-1, has been observed; it appears to extend at least to 2800 cm-1. Evidence of steric hindrance in methyl groups is deduced from the spectrum of poly-L-alanine (α and β forms).