Abstract
The trimer 2-acetamido-2-deoxy- d-glucopyranosyl-β-(1→4)-2-acetamido-2-deoxy- d-glucopyranosyl-β-(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, DP n =25) to obtain branched chitosans with degree of substitution (DS) of 0.070, 0.23 and 0.40, as determined by 1H NMR spectroscopy. The apparent p K 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 p K a values (p K 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.
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