Anesthetic effect on interfacial water: A 2H-NMR study of water-in-oil reversed micelles

Abstract

Anesthetic effects upon surface-bound water were investigated with 2H 2O NMR spectroscopy in water-in-oil reversed micelles consisting of 2H 2O, n-decane, and glycerol-α-monooleate (GMO). The spin-lattice relaxation rate, R 1 (= 1/T 1), of the 2H 2O molecules, trapped in the reversed micelle, decreased in the presence of a volatile anesthetic, enflurane. The decrease, however, varied according to the ratio of the surfactant, ndecane, and 2H 2O. Analysis of the Arrhenius activation energy indicated that the surface-bound 2H 2O molecules exist in two forms: those directly bound to glycerol-α-monooleate OH moiety (primary-bound 2H 2O), and those making hydrogen bonds to the primary-bound molecules (secondary-bound 2H 2O). The anesthetic increased the mobility of the secondary-bound 2H 2O but not the mobility of the primary-bound 2H 2O.