Search results for "aqueous solution"
showing 10 items of 1610 documents
Molecular recognition processes at functionalized lipid surfaces: a neutron reflectivity study
1992
The specific binding of proteins to functionalized monolayers on aqueous subphases has been characterized by neutron reflectivity measurements. As a model for the investigation of a recognition process on a molecular length scale, streptavidin (SA) and biotin were chosen because of the high specific affinity between them. Reflectivities from the aqueous (NaCl/H2O or NaCl/D2O) surfaces covered with the biotin-lipid monolayers before and after the adsorption of proteins were collected with a novel, fixed wavelength liquid surface neutron reflectometer. In quantitative terms, binding was found to occur at a biotin surface concentration as low as 1 molecule/1250 A2 (compare to ∼ 1 molecule/40 A…
Influence of surface chemistry on the structural organization of monomolecular protein layers adsorbed to functionalized aqueous interfaces.
1993
The molecular organization of streptavidin (SA) bound to aqueous surface monolayers of biotin-functionalized lipids and binary lipid mixtures has been investigated with neutron reflectivity and electron and fluorescence microscopy. The substitution of deuterons (2H) for protons (1H), both in subphase water molecules and in the alkyl chains of the lipid surface monolayer, was utilized to determine the interface structure on the molecular length scale. In all cases studied, the protein forms monomolecular layers underneath the interface with thickness values of approximately 40 A. A systematic dependence of the structural properties of such self-assembled SA monolayers on the surface chemistr…
Specific Protein Binding to Functionalized Interfaces
1992
We report on the characterization of specific binding reactions between streptavidin and biotinylated model membrane surfaces. Self-assembly techniques as well as the Langmuir-Blodgett-Kuhn method were employed to prepare reactive, functionalized surfaces on various solid supports in contact with the aqueous protein solution. Plasmon surface polaritons optical measurements as well as atomic force microscopy and studies with the surface forces apparatus give rather detailed information as to the streptavidin monolayer formation, the kinetics of this process (either binding site- or diffusion limited), the selectivity of the reaction at laterally heterogeneous membranes, and the involved inte…
The effect of elastic strain on the microstructure of free surfaces of stressed minerals in contact with an aqueous solution
2001
The influence of gradients in bulk elastic strain energy on the dissolution and growth behaviour of minerals in rocks is commonly considered negligible. We experimentally observed, however, that regular arrays of macroscopically visible etch grooves may develop on the originally smooth free surfaces of soluble crystals held in an undersaturated aqueous solution if the crystals are only elastically stressed. These grooves are oriented perpendicular to the compressive stress. They disappear soon after the stress is taken off. The formation of the grooves is well explained by recent theories on the instability of the surface of stressed solids. Development of such instabilities could significa…
Purification of recovered phosphoric acid by extracting aluminium with di-2-ethylhexyl phosphoric acid
2021
AbstractThe extraction of aluminium from dilute phosphoric acid with di-2-ethylhexyl phosphoric acid (DEHPA) was optimized using response surface methodology. The optimization was based on the experimental three-level central composite face-centred design (CCF) and was conducted on real-life samples. The three variables included were pH, extractant concentration and aqueous to organic phase ratio (AO). Under the optimized conditions (pH 2.5, 0.6 M DEHPA and AO ratio 1:2), extraction efficiency of 99% for aluminium in four extraction stages is achieved. The purified phosphoric acid solution can then be utilized by the fertilizing industry. Stripping tests for organic phase loaded with alumin…
Rate Effects of AOT-Stabilized Microemulsions on Reactions of Ligand Substitution in Cationic Palladium(II) Complexes
1998
Rate data for the substitution reactions of the coordinated ligand X (=2,2‘-bipyridine or 4,4‘-dimethyl-2,2‘-bipyridine) of the palladium(II) complex [Pd(en)X]2+, where en = ethylenediamine, by en or N,N-dimethylethylenediamine in heptane−AOT−water microemulsions have been obtained at 25.0 °C as a function of the AOT concentration at the constant R (=[H2O]/[AOT]) values of 3, 8, and 20 or 30. The overall second-order rate constants are higher in microemulsions than in bulk water and decrease significantly as both the AOT concentration (at constant R) and the molar ratio R (at a given [AOT]) increase. The quantitative analysis of the kinetic data, made by applying the pseudophase model, lead…
Experimental and theoretical study on the substitution reactions of aryl 2,4-dinitrophenyl carbonates with quinuclidines
2006
Abstract The reactions of quinuclidines with phenyl, 4-methylphenyl, and 4-chlorophenyl 2,4-dinitrophenyl carbonates are kinetically evaluated in aqueous solution. The Bronsted-type plots (log kN vs pKa of quinuclidinium ions) are linear. The magnitude of the slopes and validated theoretical scales of electrophilicity and nucleophilicity confirm the concerted nature of these reactions.
Mechanistic Understanding of Food Effects: Water Diffusivity in Gastrointestinal Tract Is an Important Parameter for the Prediction of Disintegration…
2013
Much interest has been expressed in this work on the role of water diffusivity in the release media as a new parameter for predicting drug release. NMR was used to measure water diffusivity in different media varying in their osmolality and viscosity. Water self-diffusion coefficients in sucrose, sodium chloride, and polymeric hydroxypropyl methylcellulose (HPMC) solutions were correlated with water uptake, disintegration, and drug release rates from trospium chloride immediate release tablets. The water diffusivity in sucrose solutions was significantly reduced compared to polymeric HPMC and molecular sodium chloride solutions. Water diffusivity was found to be a function of sucrose concen…
Ascorbic Acid Oxidation in Sucrose Aqueous Model Systems at Subzero Temperatures
2004
The reduction of Tempol by ascorbic acid in concentrated sucrose solutions was measured by electron paramagnetic resonance (EPR) at temperatures ranging from 16 to −16 °C. This method allowed the determination of the rate constants (k) of this fast reaction, by recording the Tempol reduction as a function of time. The two reactants were initially separated and had to migrate for the reaction to occur. The experimental findings were compared with predicted values according to the equation for diffusion-controlled reaction proposed by Atkins. The experimental reaction rate constants were observed to be lower than the calculated ones. However, the experimental values were found to be controlle…
Thermal Aggregation of Bovine Serum Albumin in Trehalose and Sucrose Aqueous Solutions
2012
We report results of static and dynamic light scattering measurements performed on bovine serum albumin (BSA) in saccharide (trehalose and sucrose) solutions. Our aim is to study the effects of the two disaccharides on the first steps of thermal aggregation of BSA in aqueous solutions at two protein concentrations (1 and 30 mg/mL) at increasing sugar/water ratio. Results show that sugars modify early stages of aggregation mainly by perturbing the thermodynamic behavior of the solvent (i.e., general solvent effects) without involving direct, specific sugar-protein interactions. This agrees with current hypotheses on sugar action in protein solutions. (1-3) The linear correlation detected bet…