HETERONUCLEAR OVERHAUSER EFFECT MEASUREMENTS IN SURFACTANT SYSTEMS .1. THE DIRECT ESTIMATION OF THE DISTANCE BETWEEN WATER AND THE MICELLAR SURFACE

Heteronuclear Overhauser effect (HOE) NMR experiments have been applied to micellized surfactant in water. These experiments include a variant of the HOESY two-dimensional experiment (perturbation of proton and observation of carbon-13) which shows a correlation between water protons and the carboxylate C-13 of sodium alkanoates. Nonselective one-dimensional experiments, concerning essentially aliphatic carbons, are discussed with regard to cross-relaxation terms between proton and carbon-13 and within the proton spin system. A new selective one-dimensional experiment allows quantification of cross-relaxation between water protons and the carboxylate C-13. From these data, an average distance of 2.8 angstrom between water and the micellar surface is found to be nearly constant for the three systems investigated (sodium octanoate at 2 M and 1 M concentrations and sodium decanoate at 1 M concentration).