COMPOSITIONAL HETEROGENEITY OF HETEROGENEOUSLY DEACETYLATED CHITOSANS

Commercial chitosans prepared by heterogeneous alkaline deacetylation with different F-A values were fractionated into acid-soluble and acid -insoluble fractions. The amount of acid-soluble fractions increased w ith increasing time of deacetylation. The acid-soluble fractions were characterized with respect to fraction of acetylated units (F-A), diad frequencies, intrinsic viscosities, molecular weights and molecular w eight distributions. F-A values for the acid-insoluble fractions were obtained using CPMAS C-13 NMR spectroscopy. As a control, the F-A valu es for the acid-soluble fractions determined from CPMAS C-13 NMR spect roscopy were compared and found to be consistent with the F-A values f rom H-1 NMR spectroscopy. The diad frequencies indicated that the acet yl groups in the acid-soluble fractions of the commercially heterogene ously deacetylated chitosans were randomly distributed. Determination of [eta], M(w) and M(w)/M(n) indicated negligible depolymerization of the acid-soluble fractions when deacetylation was performed under a ni trogen purge at 75 degrees C. Chemical characterization revealed compo sitional heterogeneity in the chitosans, with chitin-like acid-insolub le fractions with F-A values between 0.88 and 0.95, and acid-soluble f ractions with F-A values from 0.20 to 0.52. Copyright (C) 1996 Elsevie r Science Ltd