Detection of fibrinogen monolayers on mica by the colloid enhancement

Physicochemical properties of bovine plasma fibrinogen (Fb) in electrolyte solutions were characterised, comprising the diffusion coefficient (hydrodynamic radius), electrophoretic mobility (zeta potential) and the isoelectric point, found to be at pH=5.8. Similar electrokinetic measurements were performed for the mica substrate using the streaming potential cell. The kinetics of Fb adsorption on mica under diffusion-controlled transport was also studied. The surface concentration of Fb on mica was determined directly by AFM counting. By adjusting the time of adsorption, and bulk Fb concentration, monolayers of desired coverage were produced. It was confirmed that Fb adsorbed irreversibly on mica both at pH=3.5 and pH=7.4 (physiological value). It was postulated that in the latter case, where both the substrate and fibrinogen molecules were negatively charged, adsorption was due to heterogeneous charge distribution over the protein molecule. In order to check this hypothesis, monolayers of Fb on mica were studied using the colloid enhancement (CE) method, in which negatively and positively charged latex particles were used. Results of these experiments were quantitatively interpreted in terms of the fluctuation theory assuming that adsorption sites consisted of two and three Fb molecules, for pH=3.5 and 7.4, respectively. This allowed one to determine limits of applicability of the classical DLVO theory and confirm a heterogeneous charge distribution over the Fb molecule. It was also concluded that the CE method can be used for a sensitive determination of the Fb bulk concentration for the range inaccessible for other methods, i.e., for 0.1ppm and below. Another effect of vital significance confirmed in this work was that for some range of fibrinogen coverage both the negative and positive latexes efficiently adsorbed. This indicates the formation of superadsorbing surfaces having potential significance for various filtration processes

PDDA-Montmorillonite Composites Loaded with Ru Nanoparticles: Synthesis, Characterization, and Catalytic Properties in Hydrogenation of 2-Butanone

The effect of synthesis parameters on the physicochemical properties of clay/ polydiallyldimethylammonium (PDDA)/Ru composites and their applicability in hydrogenation of 2-butanone under very mild conditions (room temperature, atmospheric pressure, and aqueous solution) was studied. Three synthetic procedures were employed, differing in the order of addition of components and the stage at which metallic Ru species were generated. The materials were characterized with XRD (X-ray diffraction), XRF (X-ray fluorescence), EDS (energy-dispersive spectroscopy), AFM (atomic force microscopy), TEM/HRTEM (transmission electron microscopy/high resolution transmission electron microscopy), and TG/DSC (thermal gravimetry/differential scanning microscopy techniques. The study revealed that the method of composite preparation affects its structural and thermal properties, and controls the distribution and size of Ru particles. All catalysts are active in hydrogenation of 2-butanone. For best catalytic performance (100% conversion within 30 min) both the size of Ru particles and the load of polymer had to be optimized. Superior catalytic properties were obtained over the composite with intermediate crystal size and intermediate PDDA load, prepared by generation of metallic Ru species in the polymer solution prior to intercalation. This method offers an easy way of controlling the crystal size by modification of Ru/PDDA ratio