HETERONUCLEAR OVERHAUSER EFFECT MEASUREMENTS IN SURFACTANT SYSTEMS .4. DIRECT AND REMOTE CORRELATIONS WITHIN ALKYL CHAINS

This paper deals with the complete interpretation of the heteronuclear Overhauser effect spectroscopy (HOESY) two dimensional nuclear magnet ic resonance (NMR) experiment. This experiment aims at the determinati on of cross relaxation rates (having their origin in dipolar interacti ons) between two different nuclear species, here proton and carbon-13. Extra correlation peaks observed in the 2D map of the system under in vestigation (micellized sodium octanoate) are shown to arise from remo te dipolar interactions and not from strong (J) coupling effects. Seve ral experiments have been performed at different mixing times (during which the nuclear Overhauser effect builds up), allowing the observati on of the whole carbon-13 magnetization evolution. Their analysis yiel ds cross-relaxation rates, refined with respect to those derived from initial behavior. However, this requires inclusion of the effect of sp in diffusion, within the proton spin system, in the data treatment. A novel approach is proposed which models the multiexponential character by means of effective proton relaxation parameters. All the results o f this study are consistent with data obtained by other methods [nucle ar Overhauser effect (NOE) factor determinations and frequency depende nt longitudinal C-13 relaxation times).