Changes in Microemulsion and Protein Structure in IgG−AOT−Brine−Isooctane Systems

Gerhardt, Natalia I.; Dungan, Stephanie R.

doi:10.1021/jp040231i

Cited by 11 publications

(6 citation statements)

References 59 publications

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“…A similar size dependency of w/o microemulsion droplets on the AOT concentration was observed previously using photon correlation spectroscopy . At higher AOT concentrations, the radius (and the molar ratio of water-to-surfactant) becomes constant, as expected; , in this region, larger amounts of water in the organic phase are accommodated within an increased number of droplets, whose size remains the same. For the sample with 0.2 M AOT, the SAXS curve could not be fit with a structure factor of hard-sphere interactions alone, and the Yukawa tail structure factor (5) was used to fit the data, with parameters A = 4 k B T and k = 0.27.…”

Section: Resultssupporting

confidence: 84%

“…[9][10][11][12][13][14] We have become interested in a somewhat different phenomenon: the effect of protein on surfactant self-assembly in two-phase systems consisting of both oil and water. [15][16][17][18][19][20] Selfassembly is more unconstrained in such two-phase mixtures, and more far-reaching changes in phase morphology can potentially be observed. Water-in-oil microemulsion droplets can change their size by taking up or releasing water from the coexisting aqueous phase, while oil-in-water droplets can do the same with the adjacent oil phase.…”

Section: Introductionmentioning

confidence: 99%

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Effect of α-Lactalbumin on Aerosol-OT Phase Structures in Oil/Water Mixtures

Kim

Dungan

2008

J. Phys. Chem. B

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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.

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Section: Resultssupporting

confidence: 84%

Section: Introductionmentioning

confidence: 99%

Effect of α-Lactalbumin on Aerosol-OT Phase Structures in Oil/Water Mixtures

Kim

Dungan

2008

J. Phys. Chem. B

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“…Previous research in single-phase organic , or aqueous − surfactant solutions, as well as in aqueous/organic mixtures, − provides evidence that proteins can shift the phase boundaries of such solutions. These effects of proteins on surfactant phase behavior are generally associated with intimate interactioneither peripheral or intrinsicbetween the protein molecule and surfactant, often accompanied by changes in nanostructure morphology.…”

Section: Introductionmentioning

confidence: 99%

Effect of α-Lactalbumin on the Phase Behavior of AOT−Brine−Isooctane Mixtures: Role of Charge Interactions

et al. 2005

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We have found that both electrostatic and hydrophobic interactions are involved in the ability of the protein alpha-lactalbumin (alpha-LA) to affect the self-assembly of the anionic surfactant sodium bis(ethylhexyl) sulfosuccinate (AOT, 3.5 wt %) in equivolume mixtures of organic and aqueous solutions. The composition and size of AOT phase structures that form in the presence of 0.35 wt % protein were evaluated as a function of pH and ionic strength. In the absence of protein, AOT forms water-in-oil microemulsion droplets for all pH and salt concentrations studied here. The presence of the protein in the water-in-oil microemulsion phase boosts water solubilization and droplet size, as the spontaneous curvature of the surfactant interface becomes less negative. Aggregates of protein, surfactant, and oil also form in the water-continuous phase. The size and composition of structures in both phases can be tuned in the presence of protein by varying the pH and ionic strength. alpha-LA induces the appearance of an anisotropic surfactant phase at pH <5.8. At intermediate salt concentrations, a third isotropic, viscous aqueous phase appears that contains 55-60% of the protein, 10-14% of the surfactant, and significant amounts of oil. Circular dichroism and fluorescence spectroscopy indicate that the protein contains enhanced alpha-helical secondary structure when self-assembling with surfactant, and has a loosened tertiary structure. The protein does not interact with the surfactant as an unfolded random coil. Although the conformation of alpha-LA in aqueous salt solutions is known to depend on pH, when self-assembling with AOT the protein adopts a structure whose features are quite pH insensitive, and likely reflect an intrinsic interaction with the interface.

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“…In water and oil mixtures, amphiphilic molecules form monolayer membranes at the oil -water interface, known as microemulsion droplets. Among the various structures formed by amphiphilic molecules, vesicles and microemulsion droplets have closed membrane surfaces formed by the amphiphilic molecules and have important functions as nanometre-and micrometre-sized membrane capsules in biological systems [1,2] and molecular carrier systems. [3,4] When guest molecules are confined in the capsules, their translational motions are restricted and the interaction between the guest molecule and the membrane is enhanced.…”

Section: Introductionmentioning

confidence: 99%

Molecular dynamics simulation for shape change of water-in-oil droplets

Urakami

Takaki

Imai

et al. 2014

Molecular Simulation

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We performed molecular dynamics (MD) simulations of water-in-oil droplet shape transformations induced by the addition of polymer chains. In a prior experiment, transformations of spherical droplets to rod-like, worm-like and network-like droplets were observed. In our previous study, we reproduced rod-like droplets via coarse-grained MD simulations, and the mechanism for the droplet shape change was elucidated by considering the contact area between the chains and the surfactant head groups. However, in that simulation model, we could not reproduce the worm-like and network-like droplets. In this study, we improved the simulation model. For a small number of chains, several spherical droplets were obtained. As the number of chains increased, the spherical droplets were transformed to rod-like, worm-like and networklike shapes by coalescence of the droplets. The calculated and experimental results agreed well, and we verified that the mechanism for the droplet shape transformations observed in the present simulations could be explained by the mechanism suggested in the previous study.

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Changes in Microemulsion and Protein Structure in IgG−AOT−Brine−Isooctane Systems

Cited by 11 publications

References 59 publications

Effect of α-Lactalbumin on Aerosol-OT Phase Structures in Oil/Water Mixtures

Effect of α-Lactalbumin on Aerosol-OT Phase Structures in Oil/Water Mixtures

Effect of α-Lactalbumin on the Phase Behavior of AOT−Brine−Isooctane Mixtures: Role of Charge Interactions

Molecular dynamics simulation for shape change of water-in-oil droplets

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