Felipe S. Semaan

Potentiometric and conductimetric studies of chemical equilibria for pyridoxine hydrochloride in aqueous solutions: simple experimental determination of pKa values and analytical applications to pharmaceutical analysis

The combination of two low-cost classical procedures based on titrimetric techniques is presented for the determination of pyridoxine hydrochloride in pharmaceuticals samples. Initially some experiments were carried out aiming to determine both pKa1 and pKa2 values, being those compared to values of literature and theoretical procedures. Commercial samples containing pyridoxine hydrochloride were electrochemically analysed by exploiting their acid-base and precipitation reactions. Potentiometric titrations accomplished the reaction between the ionizable hydrogens present in pyridoxine hydrochloride, being NaOH used as titrant; while the conductimetric method was based on the chemical precipitation between the chloride of pyridoxine hydrochloride molecule and Ag+ ions from de silver nitrate, changing the conductivity of the solution. Both methods were applied to the same commercial samples leading to concordant results when compared by statistical tests (95 and 98% confidence levels). Recoveries ranging from 99.0 to 108.1% were observed, showing no significant interference on the results.

Synthesis, characterization and biological activities of 3-aryl-1,4-naphthoquinones – green palladium-catalysed Suzuki cross coupling

Quinones are important scaffolds that are present in a variety of natural products or synthetic bioactive molecules. Arylation is an important strategy for accomplishing structural modifications, leading to new potential candidates for use as drugs. In the present work, palladium-catalysed, ligandless and phosphine-free Suzuki coupling reactions between 2-hydroxy-3-iodo-1,4-naphthoquinone and boronic acids were employed to prepare several 2-hydroxy-3-aryl-1,4-naphthoquinones in aqueous conditions using microwave irradiation or conventional heating. Because of the biological activities of quinones, which are related to their ability to accept electrons to form semiquinones and hydroquinones, the electrochemical behaviour of the synthesized molecules was investigated. The Osiris and Molinspiration Cheminformatics programs, utilizing in silico analyses, imply that these naphthoquinones are candidates for use as drugs which was reinforced by the outcomes of the in vitro antifungal and trypanocidal activity tests. Our in vitro data indicated a MIC value of 8 μg mL−1 against Candida albicans ATCC 24433 strains, and an EC50 of 0.67 μM with respect to trypanocidal activity against Trypanosoma cruzi epimastigote strains (Y).

Sensor development exploiting graphite-epoxy composite as electrode material

This study presents some results regarding the development and characterization of graphite-epoxy composites for use as working electrodes in electroanalysis. Such composites were preliminary assessed by TGA-DTA, AFM, XDR and cyclic voltammetry (CV), standing for a suitable stable and low cost material for electroanalytical purposes. The described material was used, in its best proportion (65% graphite m/m), to build a cell electrochemistry.

Graphite-Epoxi Based Composite Electrodes as Substrate for the Electrodeposition of Nickel Films for Determination of Sulfide in Oil Industry Samples

Sulfide derivatives are sulfur compounds mostly found in oil and its presence may cause serious consequences to the pipe in the withdrawal of oil, as well as its refining. For these reasons, its determination and removal are highly relevant to the oil industry. In this work, a graphite-epoxy composite electrode modified by nickel film was developed for the quantification of sulfide in oil industry samples. The composition of 65 % graphite was the one that originates better performance after characterization of electrodes by cyclic voltammetry and thermogravimetric analysis. A methodology was developed for electrodeposition films, and application studies of modified electrodes for monitoring the efficiency of H2S scavengers as a means of sulfide removal.

Paraffin-Graphite Based Composite Electrodes as Substrate for the Electrodeposition of Conductive Films with Analytical Purposes

In order to use composite electrodes as modification platform for analytical purposes, carbon was used as solid and paraffin as liquid phase in the composite preparation. To the electrodes use, first the electroactive area was determined and then the modifications were done. To this purpose, Prussian blue, neutral red and metallic copper were used. The two first depositions were done by cyclic voltammetry technique and the third one, by electroplating with constant potential. As analite, hydrogen peroxide was studied in the two first cases with amperometric detection and, in the third case, ethanol with cyclic voltammetry.

Development and application of a routine robust graphite/poly(lactic acid) composite electrode for the fast simultaneous determination of Pb2+ and Cd2+ in bijou by square wave anodic stripping voltammetry

A handcrafted, low cost sustainable electrochemical sensor based on graphite/PLA was developed and applied for the simultaneous quantification of Pb2+ and Cd2+ in jewelry (metallic ores) on the basis of square-wave anodic stripping voltammetry (SWASV). The proposed electrode was characterized by different complementary strategies such as cyclic voltammetry (CV), thermogravimetric analysis (TGA), Raman spectroscopy, X-ray Micro Computed Tomography (μCT), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Experimental results showed that the developed electrode exhibits excellent electrochemical performance, with accurate and well-resolved voltammetric responses for the analytes assessed. Under optimized conditions, experiments led to linear ranges from 0.9 to 35.0 μg L−1 for Cd2+, and from 1.2 to 35.0 μg L−1 for Pb2+, with detection limits estimated as 0.3 μg L−1 and 0.4 μg L−1, respectively. The fabricated electrode was successfully applied to the fast simultaneous quantification of Pb2+ and Cd2+ in jewelry samples and the findings were in agreement to those reached by graphite furnace atomic absorption spectrometry (GF AAS).

Electrochromic Behavior of Vanadium Oxide Nanostructures Synthesized by Melt Sonoquenching

This paper reports a new procedure for V2O5 synthesis using the combination of two traditional methods, melt quenching and sonochemistry, called melt sonoquenching. The resulting nanomaterial was characterized by several methods in order to verify physical and chemical characteristics, and its possible use as electrochromic electrode material. Scanning electron micrographs revealed V2O5 nanofibers with lengths varying from 140 to 160 nm, and diameters varying from 10 to 15 nm, X-ray diffraction experiments pointed to an amorphous structure with an interlamellar spacing of 13.3 Å. Chemical composition was estimated by TGA, suggesting that the composition for such xerogel oxide was V2O5.1.8H2O. Besides these, spectroelectrochemical characterization showed a transmittance variation of 45 % at 410 nm, with coloration persistence of 91.3 %, response times for the oxidation and reduction were, respectively, 1 s and 3.5 s, being such electrochomic efficiency of 55 cmC in throughout 100 cycles of color changes from blue-green-orange.

Electrochromic Windows: A New Age in Energy Efficiency

In this work an overview regarding smart electrochromic windows as a promising technology capable of providing significant energy savings in buildings is presented. Electrochromic windows are devices able to control of light and acclimatization of indoor spaces. Therefore, these technologies allow energy savings with lighting and HVAC systems of these spaces. These devices are already commercially available and research and development in such field is increasing, due to its technological and financial importance.