Evaluation of the hydration state of saccharides using terahertz time-domain attenuated total reflection spectroscopy.

Despite intensive studies regarding the hydration state, experimental investigations have not fully explained the global hydration state. Terahertz (THz) spectroscopy is an emerging technology that has the potential to evaluate global hydration. This is because THz waves are very sensitive to picosecond water dynamics and, as such, effectively measures the state of water that is weakly bound to solute molecules by observing slowed down water dynamics. THz time-domain attenuated total reflection (THz TD-ATR) spectroscopy allowed to determine the complex refractive index of saccharide solutions and to experimentally characterize the global hydration state. Our result indicates the global hydration state is closely related to the number of hydrophilic groups and steric configuration of hydroxyl groups in saccharide molecules. This new tool to investigate the global hydration state will provide new knowledge about water dynamics around solutes that couldn't have been elucidated with the conventional techniques.