Josealdo Tonholo

Trypanocidal activity and redox potential of heterocyclic- and 2-hydroxy-naphthoquinones

Abstract With the aim of understanding the influence of redox potentials on the trypanocidal activity, a series of quinones were tested in vitro with trypomastigotes of Trypanosoma cruzi and their first cathodic potentials (Epcl) measured by cyclic voltammetry. All quinones with Epcl > −0.72V were active, while most of those with Epcl

Effects of UV irradiation on the wettability of chitosan films containing dansyl derivatives

The morphological and wetting properties of chitosan films containing dansyl derivatives have been investigated. By means of dynamic contact angle measurements, we study the modification of surface properties of chitosan-based films due to UV irradiation. The results were analyzed in the light of the molecular-kinetic theory which describes the wetting phenomena in terms of the statistical dynamics for the displacement of liquid molecules in a solid substrate. Our results show that the immobilization of dansyl groups in the chitosan backbone leads to a pronounced enhancement of the UV sensitivity of polymeric films.

A voltammetric study of α- and β-hydroxides over nickel alloys

The hydrogen evolution reaction (HER) is one of the most studied electrochemical process due to the alternative energy conversion and the importance in some chemical process. The search for new electrocatalytic materials lead to investigate metals and alloys with particular characteristics/properties. This paper describes aspects of hydrogen adsorption and Ni-hydroxide formation over nickel alloys (SAF2205, INCONEL625 and MONEL400) utilizing cyclic voltammetry. The SAF2205 (6.4% Ni) alloy present behavior analogue to pure Ni electrodes to hydroxide species, and can bring some advantages to HER compared with the carbon steel (SAE1020) electrode commonly utilized in industrial process.

Analysis of Roughness and Surface Hardness of a Dental Composite Using Atomic Force Microscopy and Microhardness Testing

The objective of this study was to evaluate the influence of a cola soft drink (CSD) and coffee on the microhardness and surface roughness of composite resin. Fifty cavities were prepared on the vestibular surface of bovine incisors and restored with nanoparticulate resin. The teeth were divided into five groups (n = 10): group A (control), immersion in artificial saliva (AS) for 14 days; group B, immersion in coffee for 15 min (3×/day) for 7 days followed by immersion in AS for another 7 days; group C, immersion in CSD for 15 min (3×/day) for 7 days followed by immersion in AS for another 7 days; group D, immersion in AS for 7 days, immersion in coffee for 15 min (3×/day) for 7 days; group E, immersion in AS for 7 days, immersion in CSD for 15 min (3×/day) for 7 days. After the immersion periods the specimens were analyzed for their microhardness and surface roughness. The data were subjected to analysis of variance (ANOVA) followed by t-test with 5% significance. Group A presented the highest average microhardness and lowest surface roughness, so it was possible to conclude that the consumption of CSD and coffee alters the microhardness and surface roughness of new restorations.

Atomic Force Microscopy of Removal of Dentin Smear Layers

The regular periodontal practice of scaling and root planing produces a smear layer on the root surface that is detrimental to the readhesion of tissues during subsequent regeneration therapy. Although it has been demonstrated that gels containing the chelating agent ethylenediaminetetraacetic acid (EDTA) can assist in the removal of this contaminating layer, no quantitative method is yet available by which to evaluate the efficiency of the treatment. In this article, the power of atomic force microscopy (AFM) as a technique for monitoring and mapping the surfaces of dentinal roots is demonstrated. Roughness parameters of teeth that had been scaled and root planed were determined from AFM images acquired both before and after treatment with EDTA. The results confirmed that EDTA is an efficient cleaning agent and that dentinal samples free from a smear layer are significantly rougher than the same samples covered by a contaminating layer. AFM analysis is superior to alternative methods involving scanning electron microscopy because the same sample section can be analyzed many times, thus permitting it to be used as both the control and the treatment surface.

Preliminary investigation of some commercial alloys for hydrogen evolution in alkaline water electrolysis

Abstract The electrolytical behavior of 16 commercial alloys was investigated as cathodic material to hydrogen evolution. The results were compared with SAE1020 and NI200, used as standards. The electrolytic experiments were carried out in controlled current (240 and 345 mA cm −2 ), intercalated by polarization at undercurrent condition. The analysis of the potential stability during the electrolytic process shows that the following alloys are advantageous to substitute the mild steel currently used: 2RK65, SAF2304, SAF2507, C22 and MONELK500. Surprisingly, SAF2205 alloy showed as far as 250 mV less cathodic to hydrogen evolution reaction, becoming a very promising material for hydrogen evolution.

Cathodic reduction of 2-nitronaphthothiophen-4,9-quinone: evidence of catalysis by proton donors and its simulation

Abstract 2-Nitronaphtho[2,3- b ]thiophen-4,9-quinone (1) is biologically active. The reducible groups have conjugate interaction. Electrochemical experiments (cyclic voltammetry and electrolysis) were performed in order to verify possible intramolecular electron transfer or secondary redox systems and to gain insight into the redox behaviour to help in the understanding of its trypanocidal mechanism of action. Cyclic voltammograms of 1 at the Hg electrode, in DMF+TBAP or DMF+TEAP showed the presence of at least three waves, the two first related to quinone reduction and the third one relative to a catalytic process. After cathodic reduction, at potentials close to the third electron uptake, protons from adventitious water or ammonium quaternary salts can be reduced. Hydrogen formation, with the regeneration of the quinone dianion could be the cause of its catalytic nature. This effect is more pronounced with TEAP. Macroscale electrolyses reinforce the findings. This reaction can be hampered by addition of electrophiles to the medium. Simulated curves fit the experimental ones well. The fourth wave, present at fast scan rates, where the catalysis is not effective, is related to further reduction of the nitro radical anion to the hydroxylamino derivative. At the time scale of cyclic voltammetry, no intramolecular electron transfer was observed. The biological activity of 1 is, possibly, related to the very electrophilic quinone group, generating reactive radical oxygen species through redox cycling.

Electrochemical behavior of metribuzin on a glassy carbon electrode in an aqueous medium including quantitative studies by anodic stripping voltammetry

The electrochemical behavior of the herbicide metribuzin was studied in an aqueous solution on glassy carbon, carbon paste/Nujol oil and carbon paste/castor oil using cyclic voltammetry, square-wave voltammetry, differential pulse voltammetry, controlled-potential coulometry and electrolysis, for quantification and decontamination purposes. The main electrolytic products obtained from the reduction of metribuzin, after consumption of 8.26 mol electron mol-1, were deaminometribuzin and diketometribuzin. The anodic wave observed after electroreduction is associated with the oxidation of the methylthiolate generated in the electrolytic process. This wave was used to quantitatively determine metribuzin in a commercial sample by anodic stripping voltammetry. The electro-Fenton method was employed to promote decontamination by eliminating the herbicide, resulting in 80% of mineralization of the metribuzin.

Synthesis and spectroscopic characterization of a fluorescent pyrrole derivative containing electron acceptor and donor groups.

The synthesis and fluorescence characterization of a new pyrrole derivative (PyPDG) containing the electron donor-acceptor dansyl substituent is reported. The effects of temperature and solvent polarity on the steady-state fluorescence of this compound are investigated. Our results show that PyPDG exhibits desirable fluorescent properties which makes it a promising candidate to be used as the photoactive material in optical thermometry and thermography applications. Further, the electrochemical and emission properties of polymeric films obtained from the oxidation polymerization of PyPDG are also analyzed.

Self-protonation mechanism in the electrochemical reduction of Jatropholone

Abstract The electrochemical reduction mechanism of jatropholone (JOH) and derivatives (JOAc) was investigated by cyclic voltammetry, polarography, coulometry and controlled potential electrolysis. It involves at the first wave potential, a self-protonation mechanism, whereby the two-electron reduction product (JOHH − ), an aromatic ketone, is formed together with the conjugate base of the former compound, JO − . The unusual stoichiometry of the cathodic process at the first wave, 1 mol electron mol −1 , indicates that JOHH − is not further protonated. The decreased basicity of the anion is due to resonance stabilisation. The second wave is related to the reduction of JO − and further reduction of JOHH − , that has a reminiscent electroactive group. In the latter case, the background electrolyte is liable to be the proton donor, through Hoffman elimination. The complete reduction involves 4 e − and 4 protons. Electrolysis performed near the first wave potential led to the almost exclusive reduction of the exocyclic double bond, without dimerization.