The trimer 2-acetamido-2-deoxy-D-glucopyranosyl-beta-(1 --> 4)-2-acetamido-2-deoxy-D-glucopyranosyl-beta-(1
--> 4)-2,5-anhydro-D-mannofuranose (A-A-M) was reductively N-alkylated
onto a fully de-N-acetylated chitosan (F-A < 0.001, DPn = 25) to
obtain branched chitosans with degree of substitution (DS) of 0.070,
0.23 and 0.40, as determined by H-1 NMR spectroscopy. The apparent
pK(a) values of the primary and secondary amines of the chitosans
substituted with the trimer A-A-M were determined by monitoring the
chemical shift of the H-2 of GlcN, and were determined as 6.5-6.9
for the primary (unsubstituted) amines and as 5.0-5.2 for the secondary
(substituted) amines. The intrinsic pK(a) values (pK(int)) were found
to be 7.3-7.4 for the substituted and 8.7 for the unsubstituted amines.
The chitosan branched with A-A-M (DS 0.40) was found to be soluble
in aqueous solution over the entire pH range. SEC-MALLS (size-exclusion
chromatography with a multi-angle laser light scattering detector)
further showed that addition of branches did not affect the molar
hydrodynamic volume of the chitosan. (C) 2002 Elsevier Science Ltd.
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