The hydration of sodium bis(2-ethyl-l-hexyl) sulfosuccinate (AOT) reversed micelles has been studied by three independent methods: differential scanning calorimetry, ESR spin labeling, and 2H NMR. A consistent picture is evolving although the actual hydration numbers differ from method to method. This difference is most likely due to differences in the principles underlying these methods. From both calorimetry and 2H NMR it is concluded that two water molecules are tightly bound to one AOT-Na+ molecule whereas ESR spin labeling identifies four strongly bound water molecules. Our calorimetric study benefited greatly from a comparison of the thermal behavior of AOT reversed micelles and AOT smectic (lamellar) phases. Calorimetry reveals that six water molecules are unfreezable in AOT reversed micelles. This is also the case for AOT smectic (lamellar) phases; however, these six water molecules can be frozen by cooling the sample to -40 °C. The difference in the two AOT systems is attributed to supercooling that takes place in the submicroscopic droplets of AOT reversed micelles. 2H NMR gives further insight into AOT hydration. A total number of 13 water molecules are affected and structurally perturbed by 1 AOT molecule. These 13 water molecules consist of three types of water differing in the affinity for AOT-Na+. Two out of these 13 water molecules are more strongly bound; the remaining 11 water molecules appear to be weakly associated with AOT-Na+.

A new family of organogels is described. They originate from water-in-oil microemulsions, from which the name microemulsion gels or microemulsion-based gels is derived. Two different types of such gels are presented here, referred to as gelatine gels and lecithin gels, respectively. In the case of gelatine gels, the initial ternary system typically consists of isooctane, AOT (bis 2-ethylhexyl sodiurnsuccinate) and water; gelation is induced by solubilization of gelatine in the water microphase above a critical concentration. In the case of lecithin gels no polymeric material is needed. Starting from a reverse micellar solution of lecithin (50-200 mM) in an organic solvent, gelation is induced by the addition of a small amount of water. The molar ratio of water to lecithin typically varies between 1 and 12 for the 50 different solvents investigated to date. These gels are isotropic, thermoreversible and optically transparent.For both microemulsion gels the influence of the concentration of the components on gelation is presented in the form of preliminary phase diagrams.The physico-chemical properties of these organogels were characterized using a variety of techniques such as NMR, DSC, dynamic shear viscosity measurements, and light scattering. Based on these measurements, preliminary models for the structure of these novel systems were developed.It is possible to co-solubilize a variety of reactive molecules in these gels. Therefore, it may be possible to use these organogels for a number of chemical, pharmaceutical, and cosmetic applications.

A procedure is described that permits the transformation of hydrocarbon microemulsions into gels. This is obtained by cooling a previously heated isooctane solution of bis(2-ethylhexyl) sodium sulfosuccinate containing 10-20% of an aqueous gelatin solution. The final system is a homogeneous gel, whose consistency and physical properties vary depending upon the relative concentration of water and gelatin. These new hydrocarbon gels have been investigated with 'H NMR, circular dichroism, differential scanning calorimetry, and electron microscopy. Enzymes and bacteria can be entrapped in apolar gels without loss of activity. IntroductionSeveral papers have appeared describing the properties of proteins hosted in reverse micelles.'-5 The system of choice is bis(Zethylhexy1) sodium sulfosuccinate (AOT)/isooctane/water, due mostly to the fact that this system permits water solubilization over a wide range of w, (w, = [HzO]/[AOT]) values6g7 (at high w, values the term water-in-oil microemulsions is more accurate than reverse micelles).As a result of the micellar environment, proteins acquire novel physical and conformational properties, which has lead to an interesting research perspective from both the biophysical and the biotechnological points of In this paper, we will describe a particular effect caused by the solubilization of gelatin in water-in-oil microemulsions. As is well-known, gelatin is able to form gels in water.15 This is generally obtained by cooling concentrated solutions from above 40 "C to approximately 35 "C or below, a phenomenon that is the basis of an industrially important process and one that is very interesting from the point of view of structural protein chemistry. Since gelatin can be solubilized in reverse micelles,I0 it appeared interesting to investigate how the micellar environment affects this protein gelling behavior. Our expectation was that gel formation would take place within the water pools of the reverse micelles, eventually bringing about a clouding of the hydrocarbon micellar solution and possibly phase separation of the aqueous gel. Something completely different takes place: the whole micellar solution becomes a gel. This paper describes the preparation of these novel materials and their basic physical properties and gives indications of some possible application in the area of applied biochemistry.

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