VIBRATIONAL SPECTROSCOPIC ANALYSIS OF N-ACYL-L-ALANINE OLIGOMERS AND BETA-SHEET STRUCTURE PROMOTED BY THE LONG ACYL CHAINS

Trimers and tetramers of N-acyl-L-alanine oligomer acid types with var ious acyl chains (acetyl, butanoyl, hexanoyl and octanoyl groups), the ir potassium (K) salts and their benzylesters have been synthesized. T he vibrational spectra of these oligomers have been measured and compa red with those of alpha-helical and beta-sheet poly(L-alanine). A conf ormation similar to beta-poly(L-alanine) was found in the solid state for these oligopeptides. The long acyl chains induce a further beta-sh eet structure in the hydrogen bonding of the peptide skeleton. This ef fect is reflected by noticeable changes in the NH stretching, amide-ch aracteristic vibrational modes and low frequency regions.