Interactions of binary liquid mixtures with polysaccharides studied using multi-dimensional NMR relaxation time measurements

Nuclear magnetic resonance transverse T2 relaxation time has proven to be a valuable parameter for characterizing liquid/polymer interactions. This measurement is applicable to many food, personal care, and cosmetic products that contain multi-component liquid mixtures. Here, we investigate the interactions of corn starch with water/glycerol mixtures of different weight compositions and explore liquid exchange dynamics; such a system is relevant to the personal care industry. We use a combination of chemical shift resolved 1H T2 relaxation measurements and corresponding two-dimensional T2 relaxation exchange experiments using both a conventional experimental protocol and a modified method with the addition of NMR chemical shift selectivity. Two relaxation regimes were evident for the hydroxyl 1H (found in both water and glycerol) whilst three relaxation regimes are evident for the aliphatic glycerol 1H associated here with strongly bound, weakly bound, and free (bulk) liquid, respectively. At higher water contents preferential absorption of glycerol was evident. T2-T2 exchange maps with a range of storage times reveal molecular exchange rates between all three regimes due to self-diffusion. Rapid exchange of water between the bulk and bound locations was evident in the case of pure water. Exchange rates for hydroxyl 1H was considerably reduced by the inclusion of glycerol.