Browsing by Author "Henderson, MJ"

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    Human serum albumin binding to silica nanoparticles - effect of protein fatty acid ligand
    (Royal Society of Chemistry, 2014-02-19) Ang, JC; Henderson, MJ; Campbell, RA; Lin, JM; Yaron, PN; Nelson, A; White, JW
    Neutron reflectivity shows that fatted (F-HSA) and defatted (DF-HSA) versions of human serum albumin behave differently in their interaction with silica nanoparticles premixed in buffer solutions although these proteins have close to the same surface excess when the silica is absent. In both cases a silica containing film is quickly established at the air-water interface. This film is stable for F-HSA at all relative protein-silica concentrations measured. This behaviour has been verified for two small silica nanoparticle radii (42 Å and 48 Å). Contrast variation and co-refinement have been used to find the film composition for the F-HSA-silica system. The film structure changes with protein concentration only for the DF-HSA-silica system. The different behaviour of the two proteins is interpreted as a combination of three factors: increased structural stability of F-HSA induced by the fatty acid ligand, differences in the electrostatic interactions, and the higher propensity of defatted albumin to self-aggregate. The interfacial structures of the proteins alone in buffer are also reported and discussed. © 2015, Royal Society of Chemistry.
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    Structure of high internal phase aqueous-in-oil emulsions and related inverse micelle solutions. 3. Variation of surfactant
    (American Chemical Society, 2009-09-10) Reynolds, PA; Gilbert, EP; Henderson, MJ; White, JW
    The small angle neutron scattering from high internal phase water-in-hexadecane and saturated ammonium nitrate-in-hexadecane emulsions is compared with that from related hexadecane-based inverse micellar solutions. Three molecular weights of the monodisperse polyisobutylene acid amide (PIBSA) surfactant 750, 1200, and 1700 were studied over a range of surfactant concentrations. As an additional comparison, emulsions based on sorbitan monooleate and isostearate surfactants were investigated. The scattering from molecular weight 1200 water-based PIBSA emulsions can be fitted at all concentrations to a model with a surfactant coated aqueous droplet-oil interface together with the majority of the surfactant in the oil phase of the emulsion in the form of inverse micelles. Variation of the molecular weight shows a variety of phases of increasing curvature: lamellar, sponge, and, most commonly, the emulsion structure described above. In addition, the molecular weight affects the oil component in the emulsions, which can contain either cylindrical micelles or spherical micelles of varying water but constant hexadecane content. Increased phase curvature is favored by both increased PIBSA molecular weight and ammonium nitrate dissolved in the water. These observations are consistent with "Wedge theory". The structures observed in the emulsions are close to those observed in related inverse micellar solutions made from hexadecane, the surfactant, and water. Lower concentrations of surfactant in the micellar solutions decrease micelle curvature, except where the inverse micelles are spherical and small; here, there is little effect of dilution. Substitution of sorbitan surfactants for PIBSAs produces slightly less organized but similar structures, with smaller spherical micelles containing proportionally more water. The aqueous-oil droplet interface has a relatively invariant monolayer of adsorbed surfactant. For all emulsions, we can infer from the mass balance that micelle concentrations are depressed in the inverse micellar solutions because up to half the added surfactant is present as individually dissolved molecules. © 2009, American Chemical Society
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    Structure of high internal phase aqueous-in-oil emulsions and related inverse micelle solutions. 4.Surfactant mixtures
    (American Chemical Society, 2009-09-10) Reynolds, PA; Gilbert, EP; Henderson, MJ; White, JW
    The effects of combinations of surfactants on the structure and stability of high internal phase water-in-hexadecane and saturated ammonium nitrate-in-hexadecane oil-based emulsions and oil-based inverse micellar solutions are reported, The combinations were 750, 1200, and 1700 molecular weight monodisperse and 450 and 1000 molecular weight polydisperse polyisobutylene acid amides, and sorbitan monooleate. The samples made from mixtures have qualitatively similar nanostructures to emulsions made from single surfactants. Again, for the emulsions, micrometer-scale aqueous droplets are dispersed in a continuous oil phase, which contains inverse spherical micelles composed of surfactant, hexadecane, and water. In quantitative terms, lower average surfactant molecular weight, lower ammonium nitrate content, and lower surfactant content increased the swelling of micelles, their water content, and the tendency of the emulsion to be unstable and form a sponge phase. This instability also allows micelle plasticity such that their geometry and content in mixed surfactant systems are not simply predictable by interpolation from single surfactant systems. An example was found of a mixed micelle 3 times larger than either single component micelle. The observed behavior suggests that mixing surfactant molecules of very different molecular weights destabilizes the emulsions, while mixing surfactants close in molecular weight has the opposite effect. The synergistic effects of surfactant molecular weight polydispersity and binary mixing are most marked for 1:1 molecular mixtures of surfactant. © 2009, American Chemical Society