Evidence from Infra-Red Spectroscopy on the Structure of Proteins

Abstract

THE infra-red absorption spectra of compounds containing the CO.NH peptide link, as observed by a number of investigators^1–3, frequently exhibit two bands in the region between 3,000 cm.^-1 and 3,400 cm. ¹ where NH-stretching frequencies may be expected. In the spectra of many amides and polyamides, nylon², and of certain proteins^2,4, there is a strong band near 3,280 cm.^-1 and a less intense band near 3,060 cm.¹. The intensity of the latter varies widely among different compounds. It is absent in polyglycine but increases in intensity through the series polyalanine, polyvaline, polyleucine and polyisoleucine, while it is even more intense in the copolymer of D-leucine and DL-phenylalanine². There is no definite maximum near 3,060 cm.^-1 in silk fibroin² ; but in tropomyosin, myosin, fibrinogen and fibrin the absorption coefficient of this band is about one third of that of the 3,280 cm.^-1 band. In specimens of nylon the intensity is variable and may be even higher.