Abstract:

As a basis for crystn. studies, the solubilization of amino acids (glycine, l-histidine, and l-phenylalanine) in H2O-in-isooctane microemulsions stabilized by AOT (Na di-2-ethylhexyl sulfosuccinate) was studied. The max. amt. of amino acid that could be solubilized was detd. by the solid-liq. extn. method, and the effect of the guest mols. (amino acids) on the size and shape of the microemulsion droplets and their thermal properties were detd. using SAXS and DSC measurements, resp. The solubilization of glycine mols., which primarily dissolve in the H2O pool, was slightly lower than their soly. in pure H2O, decreasing with increasing concn. of AOT and increasing with increasing H2O content in the microemulsion. But the solubilization of phenylalanine, which is primarily located at the H2O/oil interface, exceeded several times the soly. in H2O, the solubilized amt. increasing with increasing AOT and/or H2O concns. Histidine had characteristics intermediate between these 2 extremes. Solubilization of those mols. effected an increase in droplet size. The thermal anal. showed that loading of the microemulsion droplets with glycine has a much stronger effect on the thermal behavior of the emulsified H2O than has loading with phenylalanine. The low solubilization of glycine as compared to its soly. in pure H2O can be explained by the state of H2O within the microemulsion droplets, i.e., part of it is present as free H2O and part as H2O bound to the AOT headgroups. The loading of phenylalanine changed the shape of the microemulsion droplets from spherical to ellipsoidal, and with increasing droplet sizes, the [phenylalanine]/[AOT] molar ratio at the interface increased. [on SciFinder(R)]