Synthesis and Charaterization of Silica-Based Aldehyde Chitosan Hybrid Material for Biodiesel Purification.

This study concerns the development and charaterization of Silica-based aldehyde Chitosan hybrid material as an adsorbent for biodiesel purification. This biocomposite was prepared by sol-gel route and oxidation with periodate, and then characterized. FTIR experiments showed that the hybrid formed presents absorption bands similar to those of Chitosan-Silica, with the exception of the vibrations at 1480 cm-1 and 1570 cm-1 attributed to the symmetrical angular deformation in the N-H plane, and possess large N2 Brunauer-Emmett-Teller (BET) surface areas. Thermogravimetric analysis (TG) and scanning electron microscopy (SEM) was also carried out. Adsorption studies of bioadsorbents involving the analysis of free glycerol, soap, acidity, diglycerides, triglycerides, and fluorescence spectroscopy showed that silica-based aldehyde chitosan has a good affinity for glycerol and a good purification process.

Evaluation of in-channel amperometric detection using a dual-channel microchip electrophoresis device and a two-electrode potentiostat for reverse polarity separations.

In-channel amperometric detection combined with dual-channel microchip electrophoresis is evaluated using a two-electrode isolated potentiostat for reverse polarity separations. The device consists of two separate channels with the working and reference electrodes placed at identical positions relative to the end of the channel, enabling noise subtraction. In previous reports of this configuration, normal polarity and a three-electrode detection system were used. In the two-electrode detection system described here, the electrode in the reference channel acts as both the counter and reference. The effect of electrode placement in the channels on noise and detector response was investigated using nitrite, tyrosine, and hydrogen peroxide as model compounds. The effects of electrode material and size and type of reference electrode on noise and the potential shift of hydrodynamic voltammograms for the model compounds were determined. In addition, the performance of two- and three-electrode configurations using Pt and Ag/AgCl reference electrodes was compared. Although the signal was attenuated with the Pt reference, the noise was also significantly reduced. It was found that lower LOD were obtained for all three compounds with the dual-channel configuration compared to single-channel, in-channel detection. The dual-channel method was then used for the detection of nitrite in a dermal microdialysis sample obtained from a sheep following nitroglycerin administration.

Molecular mechanism of action of 2-ferrocenyl-1,1-diphenylbut-1-ene on HL-60 leukemia cells.

The aim of this work was to investigate the mechanism of action of 2-ferrocenyl-1,1-diphenylbut-1-ene (1) on HL-60 human leukemia cells. While inactive against noncancerous cells, 1 provoked a concentration-dependent decrease in viable tumor cells, primarily via apoptosis, as evidenced by analysis of cell morphology, activation of caspases 3 and 7, increased DNA fragmentation, and externalization of phosphatidylserine. Necrosis was observed only at the highest tested concentration (4 µM). Compound 1 interfered with the cell cycle, causing an accumulation of cells in the G1 /G0 phase. Interaction of 1 with dsDNA and ssDNA was observed by differential pulse voltammetry and confirmed by hyperchromicity in the UV/Vis spectra of dsDNA, with an interaction constant of 2×10(4) M(-1). Both the organic analogue 1,1,2-triphenylbut-1-ene (2) and ferrocene were inactive against cancer and noncancer cell lines and did not react with DNA. These results reinforce the idea that the hybrid strategy of conjugating ferrocene to the structure of tamoxifen derivatives is advantageous in finding new substances with antineoplastic activity.

Nature of electrogenerated intermediates in nitro-substituted nor-ß-lapachones: the structure of radical species during successive electron transfer in multiredox centers.

Electrochemical, spectroelectrochemical, and theoretical studies of the reduction reactions in nor-ß-lapachone derivatives including a nitro redox center showed that reduction of the compounds involves the formation of several radical intermediates, including a biradical dianion resultant from the separate reduction of the quinone and nitro groups in the molecules. Theoretical descriptions of the corresponding Fukui functions f(αα)⁺ and f(ßß)⁺(r) and LUMO densities considering finite differences and frozen core approximations for describing the changes in electron and spin densities of the system allowed us to confirm these results. A description of the potential relationship with the obtained results and biological activity selectivity indexes suggests that both the formation of stable biradical dianion species and the stability of the semiquinone intermediates during further reduction are determining factors in the description of their biological activity.

Synthesis and cytotoxic activity of new acridine-thiazolidine derivatives.

Although their exact role in controlling tumour growth and apoptosis in humans remains undefined, acridine and thiazolidine compounds have been shown to act as tumour suppressors in most cancers. Based on this finding, a series of novel hybrid 5-acridin-9-ylmethylene-3-benzyl-thiazolidine-2,4-diones were synthesised via N-alkylation and Michael reaction. The cell viability was analysed using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and DNA interaction assays were performed using electrochemical techniques.

Preclinical genotoxicology of nor-ß-lapachone in human cultured lymphocytes and Chinese hamster lung fibroblasts.

Nor-ß-lapachone has shown several biological properties. Regarding cytotoxic activity against cancer cell lines, it has been recognized as an important prototype. However, quinonoid drugs present a major challenge because of their toxicity. In this study, we evaluated the cytotoxicity and genetic toxicity of nor-ß-lapachone in human lymphocytes and HL-60 leukemia cells and murine V79 fibroblasts, to shed some light on its selectivity toward cancer cells. As measured by MTT test, exposure of V79 cells to nor-ß-lapachone resulted in a weak cytotoxicity (IC(50) = 13.41 µM), and at a concentration up to 21.9 µM, no cytotoxic effect was observed in lymphocytes, while in HL-60 cells, nor-ß-lapachone elicited significantly greater cytotoxicity (IC(50) = 1.89 µM). Cultures coexposed to GSH-OEt showed an increased viability, which may indicate a neutralization of ROS generated by quinonoid treatment. In fact, only the highest concentrations of nor-ß-lapachone (10 or 20 µM) caused an increase in oxidative stress in nontumor levels cells as measured by TBARS and nitrite/nitrate detection. This was accompanied by an alteration in intracellular thiol content. However, NAC pre-exposure restored the redox equilibrium of the cells and the concentration of thiol levels to control values. Nor-ß-lapachone at 2.5 and 5 µM failed to induce DNA damage in nontumor cells, but at the highest concentrations tested, it induced single and double DNA strand breaks and increased the frequency of chromosomal aberrations. Interestingly, these damages were prevented by NAC pretreatment or exacerbated by prior exposure to the GSH-depleting agent 1-bromoheptane. In electrochemical experiments, nor-ß-lapachone at the same concentrations as those used in genotoxic tests did not damage DNA directly, but at the highest concentration tested (200 µM), it caused a very weak DNA interaction. Corroborating electrochemical data, oxidative modifications of DNA bases were observed, as checked by DNA repair enzymes EndoIII and FPG, which reinforced the indirect actions caused by nor-ß-lapachone through ROS generation and not via DNA intercalation. The DNA repair capacities were higher for nontumor cells than for leukemia cells, which may be related to the selective cytoxicity of nor-ß-lapachone toward cancer cells. Our data suggest that ROS play an important role in nor-ß-lapachone toxicity and that its DNA-damaging effect occurs only at concentrations several times higher than that needed for its antiproliferative effect on cancer cells.

Electroanalytical studies of sulfentrazone in protic medium, its degradation by the electro-Fenton process, and toxicity assessment using ss-DNA.

Sulfentrazone is an herbicide used as a pre-plant incorporated or pre-emergence treatment. The electrochemical oxidation of sulfentrazone was studied, by cyclic, differential and square-wave voltammetry on unmodified and on glassy carbon nanotube-modified electrodes, and by controlled-potential coulometry and electrolysis. The voltammograms of sulfentrazone showed a main irreversible diffusion-controlled pH-dependent oxidation peak. The in situ DNA-damaging capacity of sulfentrazone was also investigated, employing double stranded ds-DNA-modified glassy carbon electrode, without evidence of interaction. On the other hand, in a solution of sulfentrazone and single stranded ss-DNA, the oxidation signals of the respective bases decreased concentration-dependently, indicating binding of sulfentrazone to guanine and adenine. The electro-Fenton method was employed to promote decontamination by eliminating the herbicide, resulting in almost 60% of mineralization.

Inner reorganization during the radical-biradical transition in a nor-beta-lapachone derivative possessing two redox centers.

In this work, the electrochemical behaviour of an antitumoral nitro o-quinone derivative obtained from 3-bromo-nor-beta-lapachone was studied. Cyclic voltammetric experiments, in acetonitrile solution, revealed that both quinone and nitro functions are reduced independently as quasi-reversible one-electron transfer processes in this order. Depending on the reduction potential, a radical anion or a biradical dianion is obtained. The formation of these paramagnetic species was confirmed by performing in situ Electrochemical-Electron Spin Resonance (E-ESR) experiments. Analysis of the kinetics of electron transfer associated to those electron uptake processes, in terms of the Marcus-Hush-Levich model, revealed differences in the reorganization energy (lambda((k))) for both steps (lambda((I)): 1.07-1.11 eV; lambda((II)): 1.21-1.30 eV). By evaluating the conformations of the radical and biradical systems by calculations at the BLYP//TZVP level of theory, it was found that the inner component, for the second reduction process (lambda((II))) was approximately 72% of lambda((II)), reflecting modifications in the molecular structure during the radical anion-biradical dianion transition. This change is also reflected in the differences presented by line widths of the ESR signals of both electrogenerated radical and diradical species.

Novel nitrofurazone derivatives endowed with antimicrobial activity.

The N-alkylated derivatives from nitrofurazone were synthesised and evaluated in vitro for their efficacy as antimicrobial agents against representative strains, including methicillin-resistant Staphylococcus aureus (MRSA). The derivative 2a demonstrated greater activity than the prototype and was comparable to currently used antimicrobial drugs.

The Application of DNA-Biosensors and Differential Scanning Calorimetry to the Study of the DNA-Binding Agent Berenil.

The in situ DNA-damaging capacity of berenil (1) has been investigated usingan electrochemical approach employing double stranded (ds) DNA-modified glassy carbonelectrode biosensors. Electrochemical voltammetric sensing of damage caused by 1 todsDNA was monitored by the appearance of peaks diagnostic of the oxidation of guanineand adenine. When 1 was incorporated directly onto the biosensor surface, DNA damagecould be observed at concentrations of additive as low as 10 µM. In contrast, when thedsDNA-modified biosensor was exposed to 1, in acetate buffer solution, the method wasmuch less sensitive and DNA damage could be detected only in the presence of 100 µMberenil. When mixed solutions of 1 and single stranded (ss) DNA, polyguanylic acid orpolyadenylic acid were submitted to voltammetric study, the oxidation signals of therespective bases decreased in a concentration-dependent manner and the major variation ofthe adenine current peak indicated preferential binding of 1 to adenine. The electrochemical results were in close agreement with those deriving from a differentialscanning calorimetric study of the DNA-berenil complex.