13C and 2H NMR studies of N-acetylglycine oligomer ethyl esters (residue number, n=3–9) and selectively C-deuteriated oligomer acid types (n=3, 4): Intermolecular hydrogen-bonding distance and segmental mobility

Abstract

N-Acetylglycine oligomer ethyl esters (residue number, n=3–9) and selectively C-deuteriated oligomer acid types (n=3, 4) have been synthesized. Two crystalline modifications, the A- and B-series [which correspond to polyglycine (PG) II and I in structure, respectively] have been prepared. For the two series of oligomers, the intermolecular hydrogen-bond distance (R _N···O ) and segmental mobility were evaluated using ¹³ C CP MAS and ² H NMR spectra. The results showed that the R _N···O values for the A- and B-series of oligomer ethyl esters closely correspond to those of PGII and PGI, respectively, and that for the two series of C-deuteriated oligomers segmental mobilities of the CH ₂ groups of both the N- and C-terminal residues are more restricted than those of the methylenes sandwiched between the terminal residues.