REVERSE MICELLE SYSTEMS COMPOSED OF WATER, TRITON X-100, AND PHOSPHOLIPIDS IN ORGANIC-SOLVENTS - 1 - PHASE-BOUNDARY TITRATIONS AND DYNAMIC LIGHT-SCATTERING ANALYSIS

Enzymes entrapped in systems formed with water, phospholipids, toluene , and Triton X-100 show a catalytic activity that is much lower and a thermostability that is much higher than that observed in totally aque ous systems or in other types of reverse micelles. By phase boundary t itrations and dynamic light scattering, this work characterizes revers e micelle systems formed in either toluene or propylbenzene with Trito n X-100 and water. Four regions with distinct structural features were encountered. Up to one molecule of water per one Triton X-100 molecul e, the system was transparent; light scattering measurements of this r egion indicated that water hydrated Triton X-100 monomers. A turbid re gion was formed as water content was increased to water:Triton X-100 r atios of 7.6 in toluene and 4.2 in propylbenzene. This thermodynamical ly unstable region was formed by large polydisperse structures. Transp arent systems containing small size (27-150 Angstrom) thermodynamicall y stable reverse micelles were formed when the ratio of water to Trito n X-100 molecules in the reverse micelle was in the range of 7.6 to 26 .8 in toluene and 4.2 to 15.1 in propylbenzene. In this region, micell ar size increased with water content. Water concentrations higher than the latter values resulted in phase separation. A similar titration o f the aforementioned systems in the presence of phospholipids revealed that in the first region of transparency up to 10 molecules of water hydrated a phospholipid molecule. The inclusion of phospholipids to th e Triton X-100 systems caused a displacement of the boundaries of the second region of transparency toward higher water contents. (C) 1998 A cademic Press.