Vibrational spectra of N-acylglycine oligomers and the long N-acyl chain effect

Abstract

Trimers, tetramers and pentamers of N-acylglycine oligomer acid types with various acyl chains, their potassium or sodium salts, and their N-deuterated salts have been prepared. The vibrational spectra of these molecules have been measured and compared with those of polyglycine I (PGI; extended β form) and polyglycine II (PGII; helical form). Only a conformation similar to PGII exists in the solid state for these compounds. The long acyl chains induce a further PGII-like structure in the NH⋯OC and peptide skeletons. This effect is reflected markedly in the NH and ND stretching, amide I and II and low-frequency regions.