title: Effect of alpha-lactalbumin on aerosol-OT phase structures in oil/water mixtures.
abstract: The ability of water-soluble, globular proteins to tune surfactant/oil/water self-assemblies has potential for the formation of biocompatible microemulsions and also plays a role in protein function at biological interfaces. In this work, we examined the effect of the protein alpha-lactalbumin on Aerosol-OT (AOT) phase structures in equivolume mixtures of oil and 0.1 M brine. In this pseudo-ternary system, surfactants are free to move to either oil or water phase to adopt phase structures close to the spontaneous curvature of the surfactants. Using small-angle X-ray scattering, we observed that addition of this protein changed the spontaneous curvature of the surfactant monolayer substantially. In the absence of protein, AOT adopted a negative spontaneous curvature to form spherical w/o microemulsion droplets. When less than 1 wt % of alpha-lactalbumin was added into the system, the w/o droplets became nonspherical and larger in volume, corresponding to an increase in water uptake into the droplets. As the protein-to-surfactant ratio increased, protein, surfactant, and oil increasingly partitioned toward the aqueous phase. There the protein triggered the formation of o/w microemulsions with a positive spontaneous curvature. These protein-containing structures exhibited significant interparticle attraction. We also compared the influence of two oil types, isooctane and cyclohexane, on the protein/surfactant interactions. We propose that the more negative natural curvature of the AOT/cyclohexane monolayer in the absence of protein prevented protein incorporation within organic phase structures and consequently pushed the system self-assembly toward aqueous aggregate formation.
authors.affiliation: Department of Food Science and Technology, Department of Chemical Engineering and Materials Science, University of California, Davis, One Shields Avenue, Davis, California 95616, USA.
authors.forename: Jun Y
authors.initials: JY
authors.lastname: Kim
authors.forename: Stephanie R
authors.initials: SR
authors.lastname: Dungan
mesh_terms: D003510:Cyclohexanes / Q000737:chemistry; D004143:Dioctyl Sulfosuccinic Acid / Q000737:chemistry*; D007768:Lactalbumin / Q000737:chemistry*; D009795:Octanes / Q000737:chemistry; D009821:Oils / Q000737:chemistry*; D044367:Phase Transition; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
chemical_list: D003510:Cyclohexanes; D009795:Octanes; D009821:Oils; D014867:Water; D004143:Dioctyl Sulfosuccinic Acid; C506365:Cyclohexane; D007768:Lactalbumin; C045798:2,2,4-trimethylpentane