Determination of the degree of N-acetylation and the distribution of N-acetyl groups in partially N-deacetylated chitins (chitosans)by high-field n.m.r. spectroscopy*

The composition and sequence of 2-acetamido-2-deoxy-B-D-glucose (GlcNAc)and 2-amino-2- deoxy-/?-o-glucose (GlcN)residues in partially N-deacetylated chitosans, prepared under homogeneous and heterogeneous conditions, have been determined by 'H-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-l 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-GlcNAc 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(percent)were soluble at neutral pH.