NMR and FT Raman characterisation of regioselectively sulfated chitosan regarding the distribution of sulfate groups and the degree of substitution

Chitosan sulfates (CHS) were prepared with chlorosulfonic acid homogeneously and non-homogeneously. The total degrees of substitution (DS) ascribed to sulfate groups (DS_S) were determined with elemental analysis and the partial DS at 6-O-position was estimated via ¹³C NMR. CHS with diverse total DS_S and sulfation patterns were obtained according to the analysis. The effects of selected reaction parameters that can influence the distribution of sulfate groups were examined. The structure of CHS was then characterized with various NMR techniques, i.e. one- (1D-) and two-dimensional (2D-) NMR, and FT Raman spectroscopy. It was found that the primary hydroxyl groups were always predominantly sulfated for CHS prepared under homogeneous or non-homogeneous conditions and no sulfate groups at 2-N-position could be detected. Finally, the feasibility of using FT Raman spectroscopy as another alternative for determining the total DS_S of CHS was presented.