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Water-solubility Of Partially N-acetylated Chitosans As A Function Of PH: Effect Of Chemical Composition And Depolymerisation
Published 1994 · Chemistry
Abstract The solubility of four partially N -acetylated chitosans with fraction of acetylated units ( F A ) of 0.01, 0.17, 0.37 and 0.60 as a function of pH was investigated. The chitosan with F A =0.60 was soluble at all pH-values between 4 and 9. The solubility versus pH curve of the other chitosans, showed that all chitosans precipitated between pH 6 and 7.5, but with increasing solubility at higher pH-values with increasing F A . Such solubility differences may have profound effects on enzyme accessability and biological effects of chitosans. The three chitosans with the lowest F A values were depolymerised by treatment with nitrous acid, and the fraction of water-soluble material at pH 7.5 was determined. The almost fully deacetylated chitosan was completely insoluble at pH 7.5 in the depolymerisation range investigated, while the most acetylated chitosan ( F A =0.60) was fully soluble at all pH-values. However, the two chitosans with F A =0.17 and 0.37 could be fractionated into a neutral-soluble and a neutral-insoluble fraction. The amount of neutral-soluble material increased with decreasing depolymerisation. The neutral-soluble and the neutral-insoluble fraction differed in both chemical composition and degree of polymerisation. Generally, the neutral-soluble fraction had a higher fraction of acetylated units and a lower degree of depolymerisation than the neutral-insoluble fraction. This compositional heterogeneity of the degraded chitosans was shown to be consistent with what is expected from the theoretical random degradation of chitosans with a Bernoullian (random) distribution of acetylated and deacetylated units.