Deusanilde de Jesus Silva

Effect of charge asymmetry on adsorption and phase separation of polyampholytes on silica and cellulose surfaces.

The relation between the properties of polyampholytes in aqueous solution and their adsorption behaviors on silica and cellulose surfaces was investigated. Four polyampholytes carrying different charge densities but with the same nominal ratio of positive to negative segments and two structurally similar polyelectrolytes (a polyacid and a polybase) were investigated by using quartz crystal microgravimetry using silica-coated and cellulose-coated quartz resonators. Time-resolved mass and rigidity (or viscoelasticity) of the adsorbed layer was determined from the shifts in frequency (Deltaf) and energy dissipation (DeltaD) of the respective resonator. Therefore, elucidation of the dynamics and extent of adsorption, as well as the conformational changes of the adsorbed macromolecules, were possible. The charge properties of the solid surface played a crucial role in the adsorption of the studied polyampholytes, which was explained by the capability of the surface to polarize the polyampholyte at the interface. Under the same experimental conditions, the polyampholytes had a higher nominal charge density phase-separated near the interface, producing a soft, dissipative, and loosely bound layer. In the case of cellulose substrates, where adsorption was limited, electrostatic and polarization effects were concluded to be less significant.

Application of PCDA/SPH/CHO/Lysine vesicles to detect pathogenic bacteria in chicken

During the course of infection, Salmonella must successively survive the harsh acid stress of the stomach and multiply into a mild acidic compartment within macrophages. Inducible amino acid decarboxylases are known to promote adaptation to acidic environments, as lysine decarboxylation to cadaverine. The idea of Salmonella defenses responses could be employed in systems as polydiacetylene (PDA) to detect this pathogen so important to public health system. Beside that PDA is an important substance because of the unique optical property; that undergoes a colorimetric transitions by various external stimuli. Therefore 10,12-pentacosadyinoic acid (PCDA)/Sphingomyelin(SPH)/Cholesterol(CHO)/Lysine system was tested to determine the colorimetric response induced by Salmonella choleraesuis. PCDA/SPH/CHO/Lysine vesicles showed a colour change even in low S. choleraesuis concentration present in laboratory conditions and in chicken meat. Thus, this work showed a PCDA/SPH/CHO/Lysine vesicle application to simplify routine analyses in food industry, as chicken meat industry.

Evaluation of Adsorbed Polyampholyte Layers by Using Quartz Crystal Microbalance

Abstract Viscoelastic properties of layers of polyampholytes adsorbed on charged surfaces were studied by quartz microgravimetry. By applying the Voigt viscoelastic model the effective mass and thickness of layers after adsorption from solution at different salt concentrations were calculated. The obtained results were compared with the Sauerbrey equation, which applies to the case of thin, rigid adsorbed layers. The estimates of mass and thickness from the Voigt model were typically larger, and were more strongly affected by variations in the ionic strength of adsorbing solution. Since the Voigt model uses multiple frequencies and dissipation overtones, it was found that the calculated adsorbed layer mass was closer to the actual values, while the Sauerbrey approach resulted in underestimation. This observation was explained by the fact that adsorbed layers of polyampholytes were soft and highly dissipative. It was noted that the observed changes in dissipation of the adsorbed polyampholyte layers were comparatively large, which suggests a large amount of coupled water.