NOE Studies of Solvent-Solute Interactions

Intermolecular Overhauser effects resulting from interactions of solvent molecules with a solute are readily detected with modern instrumentation. After a discussion of how these effects arise, applications of intermolecular Overhauser effects in studies of solute.. solvent and other interactions in solution are reviewed. Observed effects may reflect (a) a local concentration of solvent molecules near the solute that is different from the concentration of the bulk. (b) kinematic behavior of solvent molecules near the solute that is different from that characteristic of the bulk solvent, or (c) formation of solute solvent complexes that are long-lived relative to the time associated with diffusive encounters of solute and solvent. In mixed solvents, a solute solvent Overhauser effect may indicate preferential association of one solvent component with the solute: such interactions may be regiospecific. Determination of solvent solute intermolecular Overhauser effects have been done in systems that range from solutions of monoatomic gases to proteins. It is shown that additional experimental developments are needed to enable unambiguous interpretation of observed effects.