Biomedical subjects

de las Nieves FJ

Publications and source records attributed to de las Nieves FJ.

5 recordsLinked to original sources

PubMed2000

Adsorption and Desorption of Triton X-100 in Polystyrene Particles with Different Functionality.

A complete adsorption study of Triton X-100 onto latexes with different functionality is presented. Three surfactant-free polystyrene latices with different chemical surface groups (sulfate, carboxyl, and amidine) were prepared. The pH of the liquid phase controls the surface charge, and hence this factor can be considered an important variable in this study. The adsorption isotherms show that an increase in the surface charge yields a decrease in the amount of adsorbed surfactant. A descriptive mechanism of the adsorption process which considers the presence of holes in the layer of adsorbed surfactant is presented for explaining the experimental results. On the other hand, the adsorption isotherms have been analyzed with two classical adsorption theories, those of Langmuir and Kronberg et al. Both theories give a good description of the results, but the latter offers more information on the adsorption phenomena. Copyright 2000 Academic Press.

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PubMed2000

Adsorption and Desorption of Triton X-100 in Polystyrene Particles with Different Functionality.

An experimental desorption study of Triton X-100 from latices with different functionality is presented. Two different strategies to follow the desorption experiment have been used: first, a discontinuous method based on the wash step (centrifugation-removal-redispersion); and second, a continuous method based on the replacement of the disperse media. The desorption results show that in all cases a residual amount of Triton X-100 remains adsorbed, indicating irreversibility of the surfactant adsorption. Finally, the effect of desorption on the colloidal stability of one type of latex-surfactant complex has been analyzed. Copyright 2000 Academic Press.

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PubMed2000

Titanium Dioxide/Electrolyte Solution Interface: Electron Transfer Phenomena.

Electron transfer between a titanium dioxide/electrolyte solution interface has been studied. As found by other researchers of similar interfaces (TiO(2)- and ZnO-electrolyte solution), a slow consumption of OH(-) ions takes place in this type of interface. A theoretical model has been developed for calculating the change in the Fermi energy of both electrolyte solution and semiconductor, showing that ion consumption from the solution is favoured by the decrease of the difference between their Fermi energies. A kinetic constant (upsilon) is found to characterise the consumption process, its value increasing with electrolyte and semiconductor mass concentrations. Furthermore, this process may be used to estimate the point of zero charge of a titanium dioxide colloidal dispersion. Copyright 2000 Academic Press.

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PubMed1999

Colloidal Stability of Polymer Colloids with Variable Surface Charge.

Colloidal stability of two latexes with variable charge surface groups has been studied at a range of pH. Experimental log W vs log[electrolyte] plots were fitted using the DLVO theory, and values for the diffuse potential, psi(d), and the Hamaker constant, A, were obtained. Reasonable tendency was found for the diffuse potential of both latexes, decreasing when the surface charge decreased. However, the Hamaker constant, which was expected to be constant over the range of pH covered, also showed a decreasing behavior with decreasing charge. Several theories for the electric repulsive potential have been used to try to explain this paradoxing trend, although none of them was successful. Finally, two explanations are proposed, one based on coion adsorption and the other on the hairy layer model, although the first one seems to be the most probable on the basis of thermodynamics considerations. Copyright 1999 Academic Press.

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PubMed1998

Characterization of Immunoglobulin G Bound to Latex Particles Using Surface Plasmon Resonance and Electrophoretic Mobility.

The main objective of this work was the investigation of passive adsorption and covalent coupling of a polyclonal IgG and a monoclonal preparation of IgG against HSA, to a carboxyl latex particle. The functional activity of the coupled protein was then assessed by quantitative immunoassays for the antigen. Sensitized particles, with different protein coverage, were fully characterized using a range of different technologies, including electrophoretic mobility (µe), photon correlation spectroscopy, and surface plasmon resonance (SPR). The antibody-labeled particles were studied with respect to electrokinetic behavior in pH and ionic strength titration, stability, antibody functionality, and their perfomance in immunoaggregation reactions. Important differences were observed between the two sets of particle preparations throughout the series of experiments. The differences could be attributed to the coupling of the IgG molecules to the particles by the two different adsorption protocols. When proteins were chemically bound to the polymer surface it was necessary to activate the carboxyl groups with a carbodiimide (CDI) moiety that in our case was positively charged. The differences in characteristics between the adsorbed and the coupled antibody particles are thought to be due to the fact that in the covalent coupling protocol some CDI molecules remained linked to the particles, which altered the average electrical state of the outer layer in comparison with those samples where antibodies were physically adsorbed. On the other hand, the isoelectric point of the monoclonal antibody was lower (5.4 +/- 0.1) than the pI of the polyclonal antisera (6.9 +/- 0.9), which could explain why the IgG-latex complexes created with monoclonal molecules were colloidally more stable at neutral pH than those created with the polyclonal antisera. However, no immunoaggregation of antibody particles by the presence of antigen was found with the former. The use of SPR demonstrated that the equilibrium constants for the antibody-antigen recognition of the two antibody preparations were quite similar (KA polyclonal IgG = 2.8 10(8) M-1; KA monoclonal IgG = 9.5 10(7) M-1). These observations suggest that the lack of aggregation mediated by antigen demonstrated by the monoclonal antibody coupled to the latex particles may be due to this protein recognizing only one epitope in the HSA molecule. However, as the repulsive charge between antibody-latex particles counteracts the attractive forces between the antigen epitope and the antibody paratope, the greatest immunoaggregation was obtained when using latex particle-antibody complex with a low charge density (N) in the external layer. Copyright 1998 Academic Press.

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