Multi-nuclear Solid-state NMR as a Tool to Assess Hydration Properties of Polysaccharides – Regioselectively Etherified Celluloses

The hydration properties of 2,3-O-hydroxypropylcellulose (HPC) and 2,3-O-hydroxyethylcellulose (HEC) were analyzed by multi-nuclear solid-state MAS NMR spectroscopy. By ¹³C single-pulse (SP) MAS and cross-polarization (CP) MAS NMR, differences between the immobile regions and all parts of the polysaccharides were detected as a function of hydration. Complementary information about the water environments was observed by ²H MAS NMR. Previously this strategy was successfully used for assessment of the hydration properties of the pectin rhamnogalacturonan-I from potato pulp. By the multi-nuclear MAS NMR approach it was demonstrated that side chains in 2,3-O-HPC and 2,3-O-HEC were easier to hydrate than the cellulose backbone. Furthermore the motion of water was more restricted (slower) in 2,3-O-HPC than in 2,3-O-HEC. For both polysaccharides the hydration could be explained by a two-step process: in step one increased ordering of the immobile regions occurs after which the entire polymer is hydrated in step two. It is foreseen that this analytical approach will be a strong and general tool for assessment of hydration properties of polysaccharides.