Vibrational spectroscopic study of N-acylglycine monomeric and dimeric salts: the long acyl chain effect on the NH (ND) stretch, amide I, amide II and CH2-wag modes

Abstract

The vibrational spectra of N-acylglycine monomeric and dimeric salts and their N-deuteriated derivatives have been investigated in order to elucidate the long N-acyl chain effect, which promotes the polyglycine II (PGII)-like structure of N-acylglycine oligomers (n= 3–5). The results are summarized as follows. For these very simple oligomers, the long acyl chain induces a large upward shift of the NH-stretch mode and a downward shift of the amide I and II modes. This long acyl chain effect is pronounced for the monomeric salts, indicating that it occurs predominantly at the peptide linkage adjacent to the acyl terminal. For the monomeric and dimeric salts, the Raman spectral patterns of the glycine-CH₂ characteristic modes, which are similar to those for the PGII-like structure of N-acylglycine oligomers (n= 3–5) and to those for PGII, are promoted by the long acyl chain.