Elsevier

Carbohydrate Polymers

Volume 29, Issue 1, January 1996, Pages 17-24
Carbohydrate Polymers

Compositional heterogeneity of heterogeneously deacetylated chitosans

https://doi.org/10.1016/0144-8617(95)00154-9Get rights and content

Abstract

Commercial chitosans prepared by heterogeneous alkaline deacetylation with different FA values were fractionated into acid-soluble and acid-insoluble fractions. The amount of acid-soluble fractions increased with increasing time of deacetylation. The acid-soluble fractions were characterized with respect to fraction of acetylated units (FA), diad frequencies, intrinsic viscosities, molecular weights and molecular weight distributions. FA values for the acid-insoluble fractions were obtained using CPMAS 13C NMR spectroscopy. As a control, the FA values for the acid-soluble fractions determined from CPMAS 13C NMR spectroscopy were compared and found to be consistent with the FA values from 1H NMR spectroscopy. The diad frequencies indicated that the acetyl groups in the acid-soluble fractions of the commercially heterogeneously deacetylated chitosans were randomly distributed. Determination of [η], Mw and Mw/Mn indicated negligible depolymerization of the acid-soluble fractions when deacetylation was performed under a nitrogen purge at 75 °C. Chemical characterization revealed compositional heterogeneity in the chitosans, with chitin-like acid-insoluble fractions with FA values between 0.88 and 0.95, and acid-soluble fractions with FA values from 0.20 to 0.52.

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