Influence of free protein on flocculation stability of beta-lactoglobulin stabilized oil-in-water emulsions at neutral pH and ambient temperature

The influence of protein concentration and order of addition relative to homogenization (before or after) on the extent of droplet flocculation in oil-in-water emulsions stabilized by a globular protein was examined using laser diffraction. n-Hexadecane (10 wt%) oil-in-water emulsions (pH 7, 150 mM NaCl) stabilized by beta-lactoglobulin (beta-Lg) were prepared by three methods: (1) 4 mg/mL beta-Lg added before homogenization; (2)10 mg/mL beta-Lg added before homogenization; (3) 4 mg/mL beta-Lg added before homogenization and 6 mg/mL beta-Lg added after homogenization. Emulsion 1 contained little nonadsorbed protein (<3%) and underwent extremely rapid and extensive droplet flocculation immediately after homogenization. Emulsion 2 contained a significant fraction of nonadsorbed beta-Lg and exhibited relatively slow droplet flocculation for some hours after homogenization. Measurements on Emulsion 3 showed that the extremely rapid particle growth observed in Emulsion 1 could be arrested by adding native beta-Lg immediately after homogenization. The extent of particle growth in the three types of emulsions was highly dependent on the time that the salt was added to the emulsions, i.e., after 0 or 24 h aging. We postulate that the observed differences are due to changes in droplet surface hydrophobicity caused by differences in the packing or conformation of adsorbed proteins. Our data suggest that history effects have a strong influence on the flocculation stability of protein-stabilized emulsions, which has important implications for the formulation and production of protein stabilized oil-in-water emulsions.     

Structure of biodiesel based bicontinuous microemulsions for environmentally compatible decontamination: A small angle neutron scattering and freeze fracture electron microscopy study

Most toxic industrial chemicals and chemical warfare agents are hydrophobic and can only be solubilized in organic solvents. However, most reagents employed for the degradation of these toxic compounds can only be dissolved in water. Hence, microemulsions are auspicious media for the decontamination of a variety of chemical warfare agents and pesticides. They allow for the solubilization of both the lipophilic toxics and the hydrophilic reagent. Alkyl oligoglucosides and plant derived solvents like rapeseed methyl ester enable the formulation of environmentally compatible bicontinuous microemulsions. In the present article the phase behavior of such a microemulsion is studied and the bicontinuous phase is identified. Small angle neutron scattering (SANS) and freeze fracture electron microscopy (FFEM) measurements are used to characterize the structure of the bicontinuous phase and allow for an estimation of the total internal interface. Moreover, also the influence of the co-surfactant (1-pentanol) on the structural parameters of the bicontinuous phase is studied with SANS.     

Interpretation of the magnetic structures of Cu2Te2O5X2 (X = Cl,Br) and Ca3.1Cu0.9RuO6 on the basis of electronic structure considerations: cases for strong super-superexchange interactions involving Cu2+ ions

For super-superexchange interactions between Cu(2+) ions, a qualitative rule was formulated to assess their strengths based on the geometrical parameters of the exchange paths. Spin dimer analysis was carried out for Cu(2)Te(2)O(5)X(2) (X = Cl, Br) and Ca(3.1)Cu(0.9)RuO(6) to evaluate the relative strengths of their superexchange and super-superexchange interactions. The strongest antiferromagnetic interactions in Cu(2)Te(2)O(5)X(2) (X = Cl, Br) are given by the super-superexchange interactions involving the most linear Cu-X.X-Cu paths between tetrahedral clusters Cu(4)O(8)X(4) along the (a +/- b)-directions. The adjacent CuRuO(6) chains of Ca(3.1)Cu(0.9)RuO(6) are antiferromagnetically coupled through the most linear Cu-O.O-Cu paths along the direction perpendicular to the plane of the CuRu zigzag chain. The spin lattices of Cu(2)Te(2)O(5)X(2) and Ca(3.1)Cu(0.9)RuO(6) deduced from our spin dimer analysis are consistent with the available magnetic data. The spin lattice of a magnetic solid should be determined on the basis of appropriate electronic structure considerations.