Tulio Matencio

Metal complexes of 2-benzoylpyridine-derived thiosemicarbazones: structural, electrochemical and biological studies

Complexes of 2-benzoylpyridine thiosemicarbazone (H2Bz4DH) as well as of its N(4)-methyl (H2Bz4Me) and N(4)-phenyl (H2Bz4Ph) analogues with iron(II), nickel(II) and zinc(II) were characterized by a variety of spectroscopic techniques. Electrochemical studies revealed that the iron(II) complexes undergo oxidation giving the iron(III) analogues, which could be reduced back by cellular thiols such as thioredoxine, suggesting that this process could occur in biological media. The thiosemicarbazones have antifungal activity against Candida albicans that significantly decreases on coordination. The crystal structure 2-benzoylpyridine-N(4)-methyl thiosemicarbazone (H2Bz4Me) was determined.

Nanostructured δ-FeOOH: a novel photocatalyst for water splitting

We report on the first use of nanostructured δ-FeOOH as a promising photocatalyst for hydrogen production. The high surface area, interparticle mesoporosity, small particle size and band gap energy in the visible region make nanostructured δ-FeOOH a suitable candidate for use as a photocatalyst.

Electrochemical impedance spectroscopy studies for chemically prepared poly(o-methoxyaniline) doped with functionalized acids

Poly(o-methoxyaniline) was prepared by the chemical oxidation of the monomer with ammonium peroxydisulfate in the presence of the following acids: hydrochloric, p-toluenesulfonic, dodecylbenzenosulfonic and dodecylsulfuric. The polymers obtained are soluble in dimethylformamide and this enabled the preparation of films by casting. The electrochemical behavior of the polymers prepared by chemical synthesis is very similar to polyaniline prepared by electrochemical methods. Impedance spectroscopy measurements indicated that the acid affects mainly the potential range where the charge transfer resistance is lower. The diffusion coefficients obtained by impedance spectroscopy are higher for poly(o-methoxyaniline) doped with chloridric and p-toluene sulfonic acids than for those doped with dodecylbenzenosulfonic and dodecylsulfuric acids.

Electrochemical behavior of polyurethane ether electrolytes:carbon black composites and application to double layer capacitor

Abstract The thermal and electrochemical properties of polyurethane electrolyte/carbon black composites have been studied. The material structure presented amorphous features and the electrical response was described in terms of equivalent circuits accounting for the different relaxation processes occurring in the medium. The conductivity behavior did not fit satisfactorily either the effective medium theory or conventional percolation models. Flexible electrochemical capacitors using the composite as active material in association with large area collectors have been built and tested. The performance of the capacitors were characterized by a variety of electrochemical techniques, including impedance spectroscopy, cyclic voltammetry, galvanostatic charge–discharge methods, and long term cycling tests. The device prepared with composite electrodes containing 20 wt% of carbon black exhibited a capacity of 0.7 F cm −3 under 2 V providing an energy density of 0.4 W h l −1 .

Synthesis and characterization of new 3-substituted thiophene copolymers

This work reports the synthesis of three polymers and two new copolymers based on 3-substituted polythiophene derivatives, all of them demonstrated photoluminescent properties. All polymers synthesized, i.e., poly(3-methoxythiophene) (PMOT), poly(3-thiopheneethanol) (PTE), poly(3-thiophenemethanol) (PTM), poly(3-methoxythiophene-co-3-thiopheneethanol) (PMOT-co-TE) and poly(3-methoxythiophene-co-3-thiophenemethanol) (PMOT-co-TM), were characterized by FT IR, UV-Vis, photoluminescence (PL), thermal analysis (TG and DSC) and X-ray diffraction (XRD). All materials emitted light in the orange region of the visible spectrum. Spectrometric analysis in the infrared region demonstrated the successful synthesis of polymers and copolymers by the presence of characteristic bands. Thermal analysis showed that the obtained materials had good thermal stability.

Cross-linking effect on thermal, conducting and electrochemical properties of an elastomeric polymer electrolyte

Abstract Complexing salts, like lithium perchlorate, form interesting polymer electrolytes with terpolymers containing branched ether derivatives, which can be cross-linked, depending on the allyl glycidyl ether group content. Using thermal and electrochemical techniques, the effect of polymer cross-linking upon the properties of the resulting electrolytes has been estimated. It is shown that increasing the salt concentration intensifies the stiffness of the terpolymer network or the linear/branched one and the glass transition temperature consequently rises. Both electrolyte systems investigated in this work present good thermal stabilities up to 270 °C and ionic conductivities of 10 −4 S cm −1 at 30 °C with 8 wt.% of LiClO 4 . Cross-linking does not severely affect the electrolyte conductivity but very significantly enlarges the electroactivity window (from 3 to 5 V) and improves the mechanical stability. The thermal dependence of the conductivity revealed a particular conduction mechanism attributed to the presence of short mobile chains due to the high polydispersity of the terpolymer. Thermal, electrical and special electrochemical properties suggest the inclusion of this material into the available polymer electrolytes for developing new electrochemical applications.

Analysis of hysteresis phenomenon as observed from voltammetric data of conducting polymers: part I

Estudamos o fenomeno de histerese inerente aos processos redox dos polimeros condutores eletronicos (PCE). As histereses foram separadas em duas classes: i) as histereses dinâmicas constituidas por componentes cineticas e ohmicas e ii) as histereses estacionarias ou termodinâmicas. Efetuamos uma analise matematica das histereses dinâmicas observadas nos voltamogramas ciclicos de dois polimeros: a polianilina (PANI) e o poli(3-metiltiofeno) (P3MT). Mostrou-se que no caso do P3MT a histerese e principalmente cinetica devido a velocidade de uma das etapas do processo redox com tambem uma componente ohmica relacionada a existencia de uma impedância eletrica em serie com o sistema eletroquimico. No caso da PANI, observou-se que a histerese e independe da corrente, o que e caracteristico de uma histerese termodinâmica.

Ethanol extract of propolis as a protective coating for mild steel in chloride media

The anticorrosion performance of commercial extract of ethanolic propolis (EP)-coated mild steel samples immersed in a 3.5% w/v NaCl in neutral and near neutral media was evaluated by classical electrochemical and electrochemical probe beam deflection techniques. The functional groups and major components of the extract were identified by Fourier transform infrared spectroscopy and high-performance liquid chromatography, respectively. The extract and the major constituent identified in the extract, 3,5-diprenyl-4-hydroxycinnamic acid (DHCA), are poorly hydro-soluble in a neutral medium. The bare and coated carbon steel surfaces were characterized by scanning electron microscopy and atomic force microscopy before and after a saline immersion. The electrochemical response of the coated electrodes was compared with bare mild steel electrodes and all qualitative and quantitative data obtained supported the hypothesis that EP is a potential mild steel corrosion inhibitor. Although several flavonoids are known to have remarkable antioxidant properties and be effective metal corrosion inhibitors, this work is pioneering in its evaluation of the inhibitory capacity of a natural product whose main constituent is DHCA.

Correlation between morphological properties and ionic conductivity in an electrolyte based on poly(vinylidene fluoride) and poly (2-hydroxyethyl methacrylate)

. MDSC results showed that the transition temperatures of the polymers shifted to higher temperatures for systems containing high concentrations of each polymer. SEM images indicated that there was some miscibility between the polymers especially for the 25 and 75 wt. % compositions. In terms of the electrical performance, the ionic conductivity level of the electrolyte could be controlled by changing the composition of the system.

A New Molecular Magnetic Semiconductor Based on Tetrathiafulvalene (ttf) and Oxamato Ligand (opba): (ttf) 2 (Cu(opba))·H 2 O

An oxamato-based compound of formula (ttf) 2 (Cu(opba))·H 2 O, with ttf = tetrathiafulvalene and opba = ortho-phenylenebis(oxamato), has been prepared and characterized. The complex was obtained by metathesis from (ttf) 3 (BF 4 ) 2 and (Bu 4 N) 2 (Cu(opba)) in acetonitrile at room temperature. The UV-Vis-NIR spectrum reveals the presence of the radical cation in two forms, (ttf •+ ) and (ttf •+ ) 2 dimer. The electronic transport properties of (ttf) 2 (Cu(opba))·H 2 O were studied by impedance spectroscopy (IS) and linear voltammetry (LV), and show a typical semiconductor behavior. The EPR spectra exhibit two superposed lines corresponding to electron spins of Cu II