Determination of the degree of quaternization of N,N,N-trimethylchitosan by CP-MAS 13C NMR

Abstract

Chitosan is used in several fields such as medicine, environment and advanced functional materials. The N-alkylation of chitosan into N,N,N-trimethylchitosan (TMC) allows to improve some properties. The current quantification methods of the degree of quaternization (DQ) like titration and ¹H NMR spectroscopy require the solubilization of TMC. In this study, a solid-state ¹³C NMR quantification method was developed for insoluble TMCs. For this purpose, four TMC derivatives acting as reference were synthesized and their degrees of quaternization, N,N-dimethylation (DD) and acetylation (DA) were determined in solution by ¹H NMR. CP-MAS ¹³C NMR spectra of those derivatives were deconvolved with Lorentz functions. Several ratios of the ¹³C NMR peak areas were correlated with the degrees of substitution obtained in ¹H NMR. The best quantification method of DQ involved the correlation of the carbon signal of methyl groups. The method was also applied for the determination of the DD and DA of TMCs.

Keywords: Chitosan; Degree of substitution; Polysaccharide; Quantitative method; Solid-state NMR; TMC.