Some new investigations on the structure of synthetic polypeptides

Abstract

Films of poly- γ -methyl-L-glutamate have been prepared with a high degree of orientation. X-ray photographs show that the least dimensions of the unit cell are a = 11·95 Å, b = 20·70 Å, c = 43·2 Å (fibre axis). One near-meridional reflexion, if produced by the same crystalline phase, requires doubling of the length of the c -axis. If all the observed reflexions arise from a single phase, no structure hitherto proposed for the α -fold will completely explain the intensities. However, the general pattern of intensities of non-meridional reflexions is in at least qualitative agreement with that calculated by Cochran & Crick for the α -helix. The significance of the infra-red dichroism of polypeptides is discussed, and compared with the dichroism observed in the C ═O stretching band in acetanilide. Measurements of the density of poly- γ -methyl-L-glutamate are reported, and compared with the value calculated on the α -helix model.