Assessment of cellulose interactions with water by ssNMR: ¹H->¹³C transfer kinetics revisited

To evaluate cellulose interactions with water, ¹H->¹³C polarization transfer kinetics during Variable Contact Time CP-MAS NMR spectroscopy were studied and modelled using cellulose of different origins. The increase in the temporal resolution of the plot relating signal intensity to contact-time made it possible to compare different physical models for use in fitting the kinetic curve. These models involve combinations of variables, such as proton spin diffusions, that require a better understanding of their physicochemical and structural bases. To that end, hydrogen interactions were modulated by adding water, first by varying cellulose water content, second by exchanging hydroxyl protons with D2O, and last by varying the spinning rate. The results demonstrate that this approach makes it possible to probe interactions of polysaccharides with structural water, as well as to follow the evolution of the proton-proton interactions during hydration through spin diffusion times.