Flamarion B. Diniz

Chitosan effect on dental enamel de-remineralization: An in vitro evaluation

OBJECTIVES The aim of this work was to evaluate the in vitro effect of chitosan (concentration and time of action) treatment on enamel de-remineralization behavior upon a pH cycling assay. METHODS Different group of human tooth samples were exposed to de-remineralizing solutions of controlled pH using a random experimental design. Microhardness and phosphorus chemical analysis were employed to evaluate the loss of phosphorus from the samples. Optical coherence tomography (OCT) images were obtained for selected specimens in order to evaluate the degree of penetration of chitosan into enamel. RESULTS Vickers microhardness results were higher for samples treated with chitosan for concentration between 2.5mg/mL and 5.0mg/mL and time of action between 60s and 90 s. A maximum inhibition of mineral loss of 81% was obtained. Chemical analysis indicated lower net pohosphorus loss (net P loss) for samples treated with chitosan. Best results were obtained in the same conditions found out with microhardness measurements. Chitosan had little effect on the remineralization process. OCT results indicated a correlation of chitosan penetration with chitosan concentration. For chitosan concentrations of 2.5 g/mL and 5.0 g/mL the penetration was up to the dentin-enamel junction. CONCLUSIONS Chitosan interferes with the process of demineralization of the tooth enamel inhibiting the release of phosphorus in this laboratory study. Demineralization is influenced by the concentration and exposure time of the biopolymer to the enamel. Microhardness measurements may be used as an indication of mineral loss from tooth enamel. Additionally, OCT images support the idea that chitosan may act as a barrier against acid penetration, contributing to its demineralization inhibition.

Concanavalin A and polyvinyl butyral use as a potential dengue electrochemical biosensor.

Immobilization of concanavalin A on gold electrode by means of gold nanoparticles and polyvinyl butyral was carried out and investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The system was tested with sera from patients infected by dengue fever (DF) and dengue hemorrhagic fever (DHF). Electrochemical impedance spectroscopy (in the frequency range from 100mHz to 100KHz), and cyclic voltammetry (from -0.2 to 0.7V vs. Ag/AgCl), was performed in phosphate buffer solution containing 10mM K(3)[Fe(CN)(6)]/K(4)[Fe(CN)(6)] (1:1) mixture as a redox probe. As biomolecules accumulated on the electrode surface the voltammetric response changed from a clear diffusional to an irreversible behavior. Impedance spectroscopy showed a clear increase of the electron-transfer resistance when the sensor is exposed to contaminated sera (DF or DHF) as compared to exposure to uncontaminated serum (NDF). The results were analyzed through an equivalent circuit and values of charge transfer resistance and capacitance were obtained. Variations in charge transfer resistance were used to distinguish the sensor response for the different sera investigated (DF, DHF and NDF). Alternatively, a three-dimensional graph gave the best response for differentiation of all three blood sera. The distinctive patterns of impedimetric responses observed were ascribed to different glycoprotein patterns in the sera investigated. Therefore, the lectin immobilization on electrode surface with gold nanoparticles and polyvinyl butyral, combined with the three-dimensional impedance analysis introduced herein are valuable tools in the development of a biosensor for immunological response to diseases.

Electrochemical evaluation of lectin–sugar interaction on gold electrode modified with colloidal gold and polyvinyl butyral

In this work, ConA and CramoLL lectins were immobilized on gold nanoparticles (AuNp) with polyvinyl butyral (PVB), and adsorbed on the surface of gold (Au) electrodes. Electrochemical impedance spectroscopy (EIS), in the frequency range from 100mHz to 100KHz, and cyclic voltammetry (CV), from -0.2 to 0.7V, were performed on these electrodes, in phosphate buffer (PBS) solution containing 10mM K(3)[Fe(CN)(6)]/K(4)[Fe(CN)(6)] (1:1) mixture as a redox probe. EIS and CV measurements showed that redox probe reactions on the modified Au electrodes were partially blocked due to the adsorption of AuNp-ConA-PVB and AuNp-CramoLL-PVB. SEM images showed the presence of aggregates of AuNp-ConA on PVB spherules in a tridimensional structure on the surface of the Au electrode. Bovine serum albumin (BSA) was adsorbed on the AuNp-Lectin-PVB modified electrode in order to block the remaining free gold sites. Both EIS and CV techniques yielded results that confirm positive responses of the lectins to ovalbumin agglutination. These results indicate an improvement of the sensitivity for detection of sugars that can be applicable to construction of a biosensor sensitive to glycoproteins in solution.

A comparative study of pulsed current formation for positive plates of automotive lead acid batteries

Abstract Positive plate formation with pulsed current is investigated under a wide range of pulse characteristics and compared with continuous current formation. The results indicate that pulsed current formation has a higher faradaic efficiency for conversion into lead dioxide than formation with continuous current. On the other hand, with pulsed current, there is always some residual tetrabasic lead sulfate, not observed on plates formed with continuous current. Pulsed current formation yields higher β-PbO 2 /α-PbO 2 ratio than continuous current formation, and is more efficient at longer times of formation.

Metal-free electrochemical Reformatsky reaction in water: further evidence for a radical mechanism

Abstract The first report of an electrochemical Reformatsky reaction in aqueous medium and in the absence of metal is presented. Ethyl bromoisobutyrate ( 1 ) and benzaldehyde ( 2 ) were electrolyzed in a divided cell at a potential of −1.2 V versus Ag/AgCl, corresponding to the reduction wave of 1 . Several types of carbon cathodes and a platinum anode were used in a 0.1 M KBr solution in either water+methanol (5:1) or water. The Reformatsky adduct ethyl 2,2-dimethyl-3-hydroxy-3-phenyl propionate ( 5 ) was obtained with yields up to 46% (relative to consumed 2 ) together with varying amounts of ethyl isobutyrate ( 3 ) and diethyl 2,2,3,3-tetramethylsuccinate ( 4 ). The probable mechanism starts with a radical species generated from 1 which adds to benzaldehyde giving a radical intermediate, which is further reduced to the final product 5 . A radical chain through bromine abstraction from 1 is also possible. No products resulting from reduction of benzaldehyde were observed. On zinc electrodes, in an undivided cell, an organometallic reaction producing the same coupling product 5 becomes more important. The results represent a strong additional support for a radical mechanism postulated in previous work for the Zn-promoted chemical Reformatsky reaction in water.

A chemometric evaluation of battery performance under overcharge conditions

Abstract The results of overcharge tests performed on seventy automotive batteries from several manufacturers were analyzed by means of a principal component analysis. Two parameters, derived from the analysis, are proposed as convenient measures of overall battery performance and stability, allowing a bidimensional graphical representation of the original fourteen-dimensional data matrix.