ABSTRACT In this work, the decomposition of the solvent tetraethylene glycol dimethyl ether (TEGDME) was studied under conditions that simulate the charge of a Li-O2 cell in the presence and absence of hydrogen peroxide and lithium peroxide by means of electron spin resonance spectroscopy (ESR). We detected the formation of radical species, although in low concentrations, originating from solvent decomposition reactions during the oxidation process, in the absence of peroxides. On the other hand, by introducing H2O2 and H2O into the system, oxygen-centered superoxide and hydroxyl radical species were detected. Furthermore, in the presence of Li-O2, carbon-centered radical species were detected which clearly show the decomposition of the solvent. Finally, the results show that it is very important that the charging process of a Li-O2 cell is carried out by direct oxidation via 2 e– to Li2O2 to avoid the formation of radical species that the decomposition of the solvent.

ABSTRACT The bioorganometallic compounds 2-cyrhetrenyl-5-nitro-benzimidazole (Bzn-1) and 2-ferrocenyl-5-nitro-benzimidazole (Bzn-2) have been proposed as potential anti-Trypanosoma cruzi agents. In this regard, electrochemical, electron spin resonance and biological studies were carried out. Cyclic voltammetry experiments showed the generation of nitro anion radical derivatives and a self-protonation process was observed. Nitro anion radicals generated were characterized and analyzed using electron spin resonance spectroscopy. The compounds were tested in vitro against Trypanosoma cruzi (Dm28c strain). Biological evaluation display that 2-cyrhetrenyl-5-nitro-benzimidazole (Bzn-1) was more active than its ferrocene analogue (Bzn-2) and purely organic derivate (Bzn-3), associated with the electron-withdrawing properties of the (η5-C5H4)Re(CO)3 moiety. Finally, theoretical studies were carried out in order to elucidate the correlation between organometallic fragment, nitro-reduction potentials and trypanocidal activity.

Abstract The production of high quality natural Antioxidants from olive pruning wood extracts and their application to prevent the oxidation of vegetable oils were evaluated. The production of antioxidants from branches of olive pruning wood (OPW) using Soxhlet extraction and ethanol was optimized, evaluating the use of dry and fresh OPW, with extraction of an initial mass of 1 and 3 g and extraction times of 2, 4 and 8 h. For the evaluation of the antioxidant properties of the OPW extracts (OPWEs), the 2.2-diphenyl-1-picrylhydrazyl (DPPH) radical bleaching and ORAC-FL assays were performed. Additionally, the phenolic profile of the OPWEs was obtained by using HPLC-DAD, and the total phenolic composition was quantified by the Folin-Ciocalteu assay. The OPWE obtained from dry OPW using 1 g of initial mass showed the highest content of phenolic compounds and better antioxidant capacity compared to the OPWE obtained from fresh OPW. Both extracts showed the same profiles, but the OPWE obtained from dry OPW showed twice the concentrations of catechin (1.00 g 100 g−1 OPWE) and oleuropein (12.59 g 100 g−1 OPWE). Low concentrations of optimized OPWE showed activity against lipid oxidation of sunflower oil, measured by the peroxide value obtained by microwave and forced air oven heating. Under high temperature conditions and concentrations, the results suggest that OPWE may present the opposite effect.

Resumen Se evaluó la producción de antioxidantes naturales de alta calidad desde extractos de madera de poda de olivo y su aplicación para prevenir la oxidación de aceites vegetales. La extracción de antioxidantes desde las ramas de poda de olivo (OPW), fue optimizada usando extractor Soxhlet y etanol, evaluando el empleo de OPW seca y fresca, masas iniciales de extracción de 1 y 3 g y tiempos de extracción de 2, 4 y 8 h. Para la evaluación antioxidante de los extractos de OPW (OPWE) se realizaron los ensayos de Inhibición del radical DPPH y ORAC-FL. Adicionalmente, el perfil fenólico de los OPWE fue obtenido por HPLC-DAD y el contenido total de fenoles fue cuantificado a través del ensayo de Folin-Ciocalteau. El OPWE obtenido desde OPW seca y usando 1 g de masa inicial mostró el más alto contenido de compuestos fenólicos y la mejor capacidad antioxidante, comparado con los obtenidos desde OPW fresca. Ambos extractos mostraron perfiles similares, pero el OPWE obtenido de OPW seca mostro dos veces la concentración de catequina (1.00 g 100 g−1 OPWE) y oleuropeína (12.59 g 100 g−1 OPWE). Bajas concentraciones del OPWE optimizado mostraron actividad contra la oxidación lipídica del aceite de girasol, medida a través del índice de peróxidos durante el calentamiento en microondas y en estufa de aire forzado. En condiciones de mayores temperaturas y concentraciones, los resultados sugieren que el OPWE puede presentar el efecto contrario.

The antioxidant capacity has been determined for a number of flavonoid compounds from Heliotropium sinuatum, a plant that grows in arid areas in the north of Chile. The methodologies used were: ORAC FL (oxygen radical absorbance capacity - fluorescein), DPPH (2,2-diphenyl-2-picrylhydrazyl) bleaching and electron spin resonance (ESR). These compounds were studied in homogeneous and heterogeneous media. The results showed that the 7-o-methyleriodictiol and 3-o-methylisorhamnetin are those with the highest antioxidant capacity

A formação de espécies paramagnéticas a partir da oncocalixona A em meio aprótico foi confirmada pela realização de experimentos eletroquímicos in situ em conjunto com ressonância de spin eletrônico (E-ESR). A alta deslocalização do radical gerado no primeiro potencial de redução está claramente evidenciada pelo acoplamento hiperfino do H-9 com a maior constante de acoplamento, além dos acoplamentos nas posições H-3 (próximo à quinona) e H-7 (distante do núcleo quinônico). Em meio prótico, além dos experimentos de dependência com o pH, oncocalixona A mostrou-se DNA-reativa por meio de experimentos eletroquímicos com sensores de DNA. Sua reação com N-acetilcisteína, com caracterização estrutural dos produtos de adição, evidencia sua habilidade como aceptor de Michael. Ambos os aspectos são importantes em termos de atividades biológicas/farmacológicas e indicam os presentes modelos como ferramentas importantes na avaliação de compostos biologicamente ativos.

The formation of paramagnetic species from oncocalyxone A in aprotic medium was confirmed by performing in situ electrochemical-electron spin resonance (E-ESR) experiments. The high delocalization of the radical generated at the first reduction potential is clearly evidenced by the hyperfine coupling of H-9 with the larger coupling constant, besides the couplings at the H-3 (close to quinone) and H-7 (far from the quinone nucleus) positions. In protic medium, together with pH dependence experiments, oncocalyxone A showed to be DNA-reactive through experiments with DNA sensors. Its reaction with N-acetylcysteine, with structural characterization of the addition products, proved its ability as Michael acceptor. Both aspects are important in terms of biological/pharmacological activities and indicate the present models as important tools in the screening of biologically active compounds.

Cyclic Voltammetry (CV) and electrón spin resonance (ESR) techniques were used in the investigation of several potentially antiprotozoal nitro derivatives of dihydroquinoxaline and indazole. A self-protonation process involving protonation of the nitro group due to the presence of an acidic protón in the structure of the nitro compound was observed in the first step of an ECErev reduction mechanism. ESR spectra of the free radicals obtained by electrochemical reduction in situ were characterized and analyzed. The ESR spectra showed three different hyperfine patterns for both families of compounds. In order to evaluate the free radical scavenger properties of these nitrocompounds we carried out ORAC-Fl (Oxygen Radical Antioxidant Capacity) assay. These derivatives showed a low antioxidant capacity.

Um estudo de DFT em derivados 5-NI foi realizado em diferentes níveis de teoria, a fim procurar a melhor metodologia para calcular constantes de acoplamento hiperfinas (hfccs), distribuições da densidade da rotação e propriedades eletrônicas, sabendo-se que é difícil obter boa concordância entre os valores de hfccs calculados e experimentais para compostos radicais centrados no nitrogênio. Os híbridos funcionais diferentes B1LYP, B3LYP e PBE0 foram usados conjuntamente com vários meios para aumentar o tamanho da base estudada. O modelo de C-PCM foi considerado para interações do soluto-solvente. As comparações de nossos cálculos com os dados experimentais precedentes obtidos por meio de medidas de EPR e raios-X confirmaram que esta aproximação computacional representa importante avanço. Nossos resultados indicaram que os efeitos solventes e a consideração de funções difusas são os fatores mais importantes no cálculo de constantes hiperfinas de acoplamento para este sistema nitro-heterocíclico. Foi verificado também que algumas propriedades eletrônicas calculadas como orbital de LUMO, funções condensadas de Fukui para ataques nucleofílico e afinidade de elétron não são correlacionadas como esperado com a atividade biológica.

A DFT study on 5-NI derivatives was carried out at different levels of theory, in order to seek for the best methodology that helps us to calculate hyperfine coupling constants (hfccs), spin density distributions and electronic properties, since it is difficult to obtain a good agreement between calculated and experimental hfccs for nitrogen center radical compounds. Different functional hybrids namely B1LYP, B3LYP and PBE0 were used in conjunction with various medium to large size basis sets. C-PCM model was considered for solute-solvent interactions. Comparisons of our calculations with previous experimental data obtained from EPR and X-ray techniques confirmed that this computational approach represents an important aid. Our results indicated that solvent effects and consideration of diffuse functions are the most important factors on the calculation of hyperfine coupling constants for this nitro-heterocyclic system. Also, we found that some electronic properties calculated (LUMO orbital, condensed Fukui functions for nucleophilic attacks and electron affinity) do not correlate as expected with the biological activity.

The Electron Spin Resonance (ESR) spectra of radicals obtained from two new potential antitrypanosomal drugs by Trypanosoma cruzi reduction were analyzed. DMPO Spin Trapping was used to investigate the possible formation of free radicals in the trypanosome microsomal system. The Nitro 2 (4-(n-butyl)-1-(5-nitrofurfurylidene)semicarbazide) analogue of Nifurtimox showed better antiparasitic activity than N-oxide 1 (4-(n-butyl)-1-[(7-bromo-N1-oxidebenzo[1,2-c]1,2,5-oxadiazole-5-yl)methylidene]semicarbazide). Only Nitro 2 could produce oxygen redox cycling in T. cruzi epimastigotes. The ESR signal intensities were consistent with the trapping of hydroxyl radical. These results are in agreement with the biological observation that Nitro 2 showed antichagasic activity by an oxidative stress mechanism

The electrochemical behavior of two representative 2,3-dihydro-7H-dibenzo[de,h]quinolin-7-ones was determined using cyclic voltammetry in DMSO as solvent and rationalized by quantum chemical calculations using ab initio and DFT methods. The ESR spectra of the radicals obtained by electrolytic reduction were characterized and analyzed. Calculations at the HF/3-21G and DFT-B3LYP/6-311++G** levels were carried out to obtain the optimized structure, hyperfine coupling constants and to determine the values and to visualize the LUMO and SOMO energy levels, respectively. The calculated electron affinities are in agreement with the reduction potentials measured for both heterocyclic compounds