RAMAN-SCATTERING STUDY OF N-ACYL-L-ALANINE OLIGOMER SALTS - STABILIZATION OF THE ALPHA-HELICAL STRUCTURE PROMOTED BY MICELLIZATION

N-acyl-L-alanine oligomer potassium salts (CH3(CH2)(n)CO(NHCH(CH3)CO)( m)O-K+, n = 0, 2, 4, 6 and 8, m = 3 and 4) have been synthesized. Rama n spectroscopic evidence for a conformational change of the oligomer a nions in aqueous solution is reported. The Raman scattering spectra of sample solutions diluted below the critical micelle concentration (cm c) are accounted for by postulating the coexistence of several conform ations containing the alpha-helix, beta-sheet, and beta-turn structure s. Above the cmc, the Raman bands for the amide I, III and skeletal st retch modes which are characteristic of an alpha-helix become more int ense and this result is ascribed to preferential stabilization of the helical structure, promoted by intermolecular association of oligomer anions.