Fourier transform-IR and H-1 NMR studies on the structure of water solubilized by reverse aggregates of calcium bis(2-ethylhexyl) sulfosuccinate in organic solvents

The structure of water solubilized by reverse aggregates of calcium bis(2-e thylhexyl) sulfosuccinate in deuterobenzene and toluene has been probed by Fourier transform-IR and H-1 NMR spectroscopies. The v(OD) band of solubili zed HOD (4% D2O in H2O) has been recorded as a function of the [water]/[sur factant] molar ratio, W/S. Curve fitting of this band showed the presence o f a main peak at 2550 +/- 13 cm(-1) and a small one at 2405 +/- 15 cm(-1). As a function of increasing W/S, the frequency of the main peak decreases, its full width at half-height increases, and its area increases linearly. T he H-1 NMR chemical shift of solubilized H2O-D2O mixtures at W/S = 18.1 has been measured as a function of the deuterium content of the aqueous nanodr oplet. These data were used to calculate the so-called "fractionation facto r" of the aggregate-solubilized water, the value of which was found to be u nity. The results of both techniques show that reverse aggregate-solubilize d water, although different from bulk water, does not seem to coexist in "l ayers" of different degrees of structure, as suggested, for example by the two-state water-solubilization model.