HIGH-FIELD NMR-SPECTROSCOPY OF PARTIALLY N-DEACETYLATED CHITINS (CHITOSANS) .1. DETERMINATION OF THE DEGREE OF N-ACETYLATION AND THE DISTRIBUTION OF N-ACETYL GROUPS IN PARTIALLY N-DEACETYLATED CHITINS (CHITOSANS) BY HIGH-FIELD NMR-SPECTROSCOPY

The composition and sequence of 2-acetamido-2-deoxy-beta-D-glucose (GlcNAc) and 2-amino-2-deoxy-beta-D-glucose (GlcN) residues in partially N-deacetylated chitosans, prepared under homogeneous and heterogeneous conditions, have been determined by H-1-n.m.r. spectroscopy. It was necessary to depolymerise the chitosan slightly by treatment with nitrous acid before spectroscopy. A sequence-dependent deshielding of H-1 of the GlcNAc residues made it possible to determine the proportions of the four possible diads. Chitosan prepared by N-deacetylation under homogeneous conditions gave values for the diad frequencies that were roughly consistent with a random distribution of the N-acetyl groups. Samples prepared under heterogeneous conditions have a frequency of the GlcNAc-GlcNc diad slightly higher than for a random (Bernoullian) distribution. The chitosans, prepared under both homogeneous and heterogeneous conditions, with a degree of acetylation of 50% were soluble at neutral pH.