A crystallographic study of some derivatives of gramicidin S

Abstract

Single crystals of a series of derivatives of gramicidin S were prepared and examined by X-ray methods. Their morphology, unit cells and space groups were determined, and a comparison between crystals in the wet and dry states was made. The weights of the crystal asymmetric units of the hydrochloride and N-acetyl, N-chloroacetyl and N-iodo-acetyl derivatives were determined by X-ray methods and the results compared with the molecular weights determined by chemical analysis. It is concluded that the gramicidin S molecule is probably a decapeptide in which 2 halves of the molecule are related by a twofold axis of symmetry. Some conclusions about the size and shape of the molecules are drawn.