Аннотация
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.
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