Proton, deuteron and oxygen 17 nuclear magnetic relaxation and water reorientation in a lyotropic lamellar phase

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Abstract
The orientation and dynamical behaviour of water molecules in the sodium dibutylphosphate/H2O lamellar mesophase have been investigated by 1H, 2H and 17O N.M.R. The molecular order parameters have been obtained from the dipolar or quadrupolar splittings of these nuclei and several models have been proposed for their interpretation in terms of a quasi-axial reorientation. The selection between these models has been performed by means of 1H and 2H longitudinal relaxation as well as 17O linewidth measurements on oriented samples. The order parameters and the relaxation data appear to be consistent with a strongly anisotropic reorientation of water about an axis located in the bisector plane and making an angle of ca. 60° with the molecular plane. This axis is therefore directed along an oxygen lone pair orbital and seems likely to correspond to the direction of binding of water to a cationic site. In addition, the proton exchange rate was determined from the temperature dependence of the linewidth and splitting of the doublet spectra and the anisotropy of the 1H or 2H chemical shift tensor measured in this particular system was found to be of the order of 60–70 p.p.m.