Infra-red spectra and structure of fibrous proteins

Abstract

The spectra of silk suture, porcupine quill, elephant hair, swan quill, gelatine and rat-tail tendon have been observed with polarized infra-red radiation. The first four materials give spectra which show that they contain both extended ($\beta $) and folded ($\alpha $) peptide chains. A band at about 4600 cm.$^{-1}$ is assigned to a C$\chembond{2,0} $O combination frequency, whose dichroism indicates the direction of the transition moment for a C$\chembond{2,0} $O deformation mode. Gelatine and collagen give similar spectra, and are different from either $\alpha $ or $\beta $ proteins or polypeptides. A method of folding a peptide chain, based on a suggestion of Huggins, is given which accounts for the known infra-red and X-ray spectra of collagen and gelatine.