Properties of saccharides and saccharide derivatives in the dry and partially hydrated states

This study investigates the correlation (if any) between the surface properties of dry mannitol, sorbitol and glucose, as determined using inverse gas chromatography (IGC) and other techniques, with microwave dielectric analysis of the molecular polarisability of water in the hydrated material. Microwave dielectric analysis of the hydrated material (using a circular resonant cavity) showed a transition (ht) in the gradient of imaginary permittivity (ε″ at 2.2 GHz) vs. water content for all materials. This transition reflects the appearance of another population of water with enhanced mobility. The gradient below ht (m1) reflects the reorientation mobility of water close to the surface of the solid, and therefore provides one measure of the strength of interaction with each material. Estimates for ht and m1 parallel the IGC data by giving a rank order of affinity as glucose ≥ mannitol ≥ sorbitol. This link suggests that the molecular properties of water and the strength of interaction with the hydrated material are most certainly governed by the acceptor/donor properties of the surface (as determined by IGC). Moreover, it can be inferred that the presence of mobile water (up to the relatively high levels defined by ht) does not change the surface energy of the material.