NMR STUDY OF WATER IN NANOSCOPIC CONFINEMENT AND AT THE INTERFACE OF BIOMOLECULES

Water in nanoscopic confinement and at the interface of biomolecules plays critical roles in a wide range of biological processes including protein dynamics and functions. For the nanoconfined water, I report a hydrophobic-hydrophilic transition upon cooling from 22 C to 8 C via the observation of water adsorption isotherms in SWNTs measured by NMR. A considerable slowdown in molecular reorientation of such adsorbed water was also detected. Nanoconfined water in slit-shaped wettable pores has a spin-lattice relaxation time similar to that observed in bulk water, suggesting a similar molecular reorientation in both conditions. The dependence of the capillary condensation pressure on the nanoscopic pore size resembles that given by the Kelvin equation, despite the equation's questionable validity on nanoscale. For water at the interfaces of proteins, the most basic property of protein hydration--the water sorption isotherm--remains inadequately understood. Using NMR to measure the isotherms of lysozyme in situ between 18 and 2 C, the present work provides evidence that the part of water uptake above the hydration level at which protein starts to function is significantly reduced below 8 C. Quantitative analysis shows that such reduction is directly related to the reduction of protein flexibility and enhanced cost in elastic energy for accommodating the hydration water at lower temperature. The elastic property derived from the water isotherm agrees with direct mechanical measurements, providing independent support for the solution model, in which protein is treated as a polymer-like solute. The hemoglobin hydration shows similar temperature dependence to that observed in lysozyme. NMR relaxation with paramagnetic centers that are present in those proteins could reveal the dynamics of hydration water within the protein. The role of interfacial water in the action of general anesthesia remains a topic of controversy. Using 1H and 19F NMR, I provide direct experimental evidence that interfacial water in the proximity to proteins is essential for the molecular interaction between anesthetics and proteins. The halothane adsorption isotherms can reveal the molecular nature of general anesthesia.Doctor of Philosoph