A 2ND POLYMORPH OF A HELICAL DECAPEPTIDE

A crystal-state structural analysis of the terminally blocked apolar d ecapeptide pBrBz-(Aib-L-Ala)(5)-OMe bis-dimethylsulfoxide solvate was performed by x-ray diffraction. The peptide molecules are basically al pha-helical with five 1<--5 C=O...H-N intramolecular H bonds. Near the C terminus the regularity of the alpha-helix is disrupted in favor of the formation of intramolecular H bonds of the 1<--4 (beta-bend) and 1<--6 (pi-bend) types. Differences in conformation, solvation and asso ciation with the published structure of the tetrahydrate decapeptide p olymorph are discussed.