Distribution of d-glucosamine moieties in heterogeneously deacetylated cuttlefish chitin

The distribution of d-glucosamine moieties was investigated in partially deacetylated chitins prepared under various conditions but with nearly the same degree of deacetylation in the range of 30–65%. The presence of adjacently located (blocked) d-glucosamine moieties was demonstrated by the formation of 2,5-anhydro-d-mannose using the nitrous acid deamination method. Both the alkali concentration and the deacetylation temperature affected the distribution of the d-glucosamine moieties. Within the range of deacetylation mentioned, the amount of released 2,5-anhydrous-d-mannose may vary up to 6-fold, highly depending on the conditions applied during the deacetylation. The effect of reaction conditions on other characteristics, swelling indices, crystallinity, thermal properties and the formation of acid insoluble material, supports the hypothesis that external conditions during thermochemical deacetylation can control the distribution of d-glucosamine in partially deacetylated chitin.