Kim Jun Y, Dungan Stephanie R
Department of Food Science and Technology, Department of Chemical Engineering and Materials Science, University of California, Davis, One Shields Avenue, Davis, California 95616, USA.
J Phys Chem B. 2008 May 1;112(17):5381-92. doi: 10.1021/jp7112413. Epub 2008 Apr 15.
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.
水溶性球状蛋白调节表面活性剂/油/水自组装的能力，对于形成生物相容性微乳液具有潜力，并且在生物界面的蛋白质功能中也发挥作用。在这项工作中，我们研究了蛋白质α-乳白蛋白对油与0.1 M盐水等体积混合物中气溶胶-OT（AOT）相结构的影响。在这个伪三元体系中，表面活性剂可以自由移动到油相或水相，以采用接近表面活性剂自发曲率的相结构。使用小角X射线散射，我们观察到添加这种蛋白质会显著改变表面活性剂单层的自发曲率。在没有蛋白质的情况下，AOT呈现负自发曲率以形成球形油包水微乳液滴。当向体系中添加少于1 wt%的α-乳白蛋白时，油包水微滴变得非球形且体积增大，这对应于微滴中吸水量的增加。随着蛋白质与表面活性剂比例的增加，蛋白质、表面活性剂和油越来越多地向水相分配。在水相中，蛋白质引发了具有正自发曲率的水包油微乳液的形成。这些含蛋白质的结构表现出显著的颗粒间吸引力。我们还比较了两种油（异辛烷和环己烷）对蛋白质/表面活性剂相互作用的影响。我们提出，在没有蛋白质的情况下，AOT/环己烷单层的自然曲率更负，这阻止了蛋白质掺入有机相结构中，从而促使体系自组装向水性聚集体形成。
