Preliminary X-ray crystallographic and Raman studies on gramicidin S.2HCl

The cyclic decapeptide gramicidin S.2HCl has been crystallized from an aqueous solution containing about 33% (v/v) ethanol. The crystals are suitable for X-ray diffraction studies and are obtained reproducibly. Preliminary X-ray crystallographic studies reveal the crystal to have the orthorhombic space group C222(1), with a = 25.76, b = 35.79, and c = 38.13 A. The asymmetric unit consists of two molecules of gramicidin S.2HCl and several molecules of solvent. This result corresponds closely to that reported by Schmidt et al. (1957, Biochem. J. 65, 744-750). A Raman spectrum of the crystal has been recorded. A strong amide I band at 1670 cm-1 and an amide III band at 1240 cm-1 indicate that gramicidin S has a beta-sheet conformation in its crystal structure. An enhancement of Raman signals from gramicidin S.2HCl adsorbed on Ag sol has been observed.