A proton nuclear magnetic resonance study on the release of bound water by inhalation anesthetic in water-in-oil emulsion.

Water-in-oil emulsion was prepared from glycerol-alpha-monooleate, n-decane and water, and was used to analyze the behavior of bound water molecules in response to the addition of an inhalation anesthetic, enflurane. The motion of water molecules is monitored by proton nuclear magnetic resonance spectroscopy. To the first approximation, the half-height width of the proton signal of dispersed water is related to the spin-spin relaxation time and represents the motion of the water molecule. It appears that one of the two OH moieties of glycerol-alpha-monooleate forms a hydrogen bond with the water molecule in average. The half-height width of the dispersed water proton showed a maximal value when the glycerol alpha-monooleate/n-decane mole ratio was 4 X 10(-2). The cause of this maximum is not immediately clear, but it is suggested that the assembly mode of glycerol-alpha-monooleate may be different between the lower and higher concentration range. Enflurane decreased the half-height width of the dispersed water, indicating an increase in the motion of water molecules. This results demonstrates that the anesthetic weakened the hydrogen bond between water and glycerol-alpha-monooleate molecules, and released bound interfacial water. It is postulated that dehydration of the interface, as shown by the release of bound water, would interfere with the transport of current-carrying hydrated ions through membranes and may constitute a molecular mechanism of anesthesia.