Electrochemical determination of nitroaromatic explosives at boron-doped diamond/graphene nanowall electrodes: 2,4,6-trinitrotoluene and 2,4,6-trinitroanisole in liquid effluents.

The study is devoted to the electrochemical detection of trace explosives on boron-doped diamond/graphene nanowall electrodes (B:DGNW). The electrodes were fabricated in a one-step growth process using chemical vapour deposition without any additional modifications. The electrochemical investigations were focused on the determination of the important nitroaromatic explosive compounds, 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitroanisole (TNA). The distinct reduction peaks of both studied compounds were observed regardless of the pH value of the solution. The reduction peak currents were linearly related to the concentration of TNT and TNA in the range from 0.05-15 ppm. Nevertheless, two various linear trends were observed, attributed respectively to the adsorption processes at low concentrations up to the diffusional character of detection for larger contamination levels. The limit of detection of TNT and TNA is equal to 73 ppb and 270 ppb, respectively. Moreover, the proposed detection strategy has been applied under real conditions with a significant concentration of interfering compounds - in landfill leachates. The proposed bare B:DGNW electrodes were revealed to have a high electroactive area towards the voltammetric determination of various nitroaromatic compounds with a high rate of repeatability, thus appearing to be an attractive nanocarbon surface for further applications.

Comparison of the paracetamol electrochemical determination using boron-doped diamond electrode and boron-doped carbon nanowalls.

Two different type of electrodes, boron-doped diamond electrode (BDD) and boron-doped carbon nanowalls (B:CNW) electrode, were used for the electrochemical determination of paracetamol using the cyclic voltammetry and the differential pulse voltammetry in phosphate buffered saline, pH = 7.0. The main advantage of these electrodes is their utilization without any additional modification of the electrode surface. The peak current was linearly related to the concentration of paracetamol in the range from 0.065 µM to 32 µM for BDD electrode and from 0.032 µM to 32 µM for B:CNW electrode. The limit of detection was 0.430 µM and 0.281 µM for BDD and B:CNW electrode, respectively. Additionally, we studied the effect of pH on the redox reaction of paracetamol at the both electrodes in Britton-Robinson buffer solution in the range of pH 3.0-12.0, indicating the pH 7.0 value as the most suitable for the current experiments. The studies also included the various scan rates in range of 50-500 mV/s. Finally, our team selected the B:CNW electrode for the determination of paracetamol in the artificial urine sample using differential pulse voltammetry method, obtaining the calculated limit of detection on the level of 0.08006 µM.

Structure, physicochemical and biological properties of new complex salt of aqua-(nitrilotriacetato-N,O,O',O")-oxidovanadium(IV) anion with 1,10-phenanthrolinium cation.

The crystal structure of new 1,10-phenathrolin-1-ium aqua-(nitrilotriacetato-N,O,O',O")-oxidovanadium(IV) semihydrate of molecular formula (phenH)[VO(NTA)(H2O)]∙1/2H2O was determined. This is the first example of structurally characterized compound that comprises a distinctly separated, monomeric [VO(NTA)(H2O)](-) coordination entity. The crystallographic measurements have subsequently been complemented by the IR spectroscopic characterization and thermal analysis. Furthermore, the electrochemical (cyclic voltammetry) as well as spectrophotometric (UV-vis) studies revealed that the compound is capable of scavenging the superoxide free radicals (O2(-)) as well as stable organic radicals i.e. 2,2'-azinobis(3-ethylbenzothiazoline-6 sulfonic acid) cation radical (ABTS(+)) and 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), but its reactivity towards radicals is lower than that of VOSO4. Finally, biological properties of the complex in the range of 1-100 µM were investigated in relation to its cytoprotective activity against the oxidative damage generated exogenously by using hydrogen peroxide in the hippocampal neuronal HT22 cell line (the MTT and LDH tests). It has been established that in contrast to VOSO4 the title compound protects the HT22 from the oxidative damage. The paper presents a new perspective for oxidovanadium(IV) complexes as candidates for novel, low-molecular mass cytoprotective agents.

Effect of iron additions on intergranular cohesion in chromium.

The structural, cohesive, and magnetic properties of (111) and (210) tilt grain boundaries (GBs) in pure Cr, and in Cr with Fe additions, are studied from first principles. Different concentration and position of solute atoms are considered. Our calculations show that Fe atoms placed in the GB interstice enhance cohesion, whereas Fe substituted for one of the Cr layer atoms, in most cases, has very small (or negligible) effect on the cohesion at GBs in Cr. We have found that Fe additions show a tendency to enrich the boundaries in Cr. In the presence of Fe additions the magnetic moments on the GB host atoms are substantially modified and those on Fe impurities are reduced. In most cases the moments on Fe additions remain much higher than the local moments on the Cr atoms.

Interactions of metal ions with monoaza crown ethers A15C5 and A18C6 carrying dansyl fluorophore as pendant in acetonitrile solution.

The influence of metal cations Li(+), Na(+), K(+), Cs(+), Mg(2+), Ca(2+), Sr(2+), Ba(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Pb(2+) and Al(3+) on the spectroscopic properties of the dansyl (1-dimethylaminonaphthalene-5-sulfonyl) group covalently linked to monoaza crown ethers 1-aza-15-crown-5 (1,4,7,10,-tetraoxa-13-azacyclopentadecane) (A15C5) and 1-aza-crown-6 (1,4,7,10,13-pentaoxa-16-azacyclooctadecane) (A18C6) was investigated by means of absorption and emission spectrophotometry. Interaction of the alkali metal ions with both fluoroionophores is weak, while alkaline earth metal ions interact strongly causing 50 and 85% quenching of dansyl fluorescence of N-(5-dimethylamine-1-naphthalenesulfonylo)-1,4,7,10,-tetraoxa-13-azacyclopentadecane (A15C5-Dns) and N-(5-dimethylamine-1-naphthalenesulfonylo)-1,4,7,10,13-pentaoxa-16-azacyclooctadecane (A18C6-Dns), respectively. The Cu(2+), Pb(2+) and Al(3+) cations interact very strongly with dansyl chromophore, causing a major change in absorption spectrum of the chromophore and forming non-fluorescent complexes. The Co(2+), Ni(2+), Zn(2+), Mg(2+) cations interact moderately with both fluoroionophores causing quenching of dansyl fluorescence by several percent only.

Molecular modeling of singlet-oxygen binding to anthraquinones in relation to the peroxidating activity of antitumor anthraquinone drugs.

Anthraquinone derivatives are important anti-cancer drugs possessing, however, undesirable peroxidating and, in consequence, cardiotoxic properties. This results from the mediation by these compounds of the one-electron reduction processes of the oxygen molecule, which produces the highly toxic superoxide anion radical and other active oxygen species. This article summarizes the results of our studies on the molecular aspects of the mechanism of anthraquinone-mediated peroxidation which were carried out using enzymatic-assay, electrochemical, and quantum-mechanical methods.

Enthalpy of oxygen addition to anthraquinone derivatives determines their ability to mediate NADH oxidation.

Anthraquinone derivatives are important anti-cancer drugs possessing undesirable cardiotoxic properties related to their peroxidating activity. Previous studies have suggested that this activity can be caused by the binding of a singlet oxygen molecule to an anthraquinone, followed by the one-electron reduction of the complex formed, and its further dissociation into anthraquinone and the superoxide anion radical. In this study, we have carried out semi-empirical PM3 calculations of the energetics of the formation of peroxides and hydroperoxides from hydroxy, amino and imino derivatives of 9,10-anthracenedione. These calculations were supplemented with ab initio calculations, using STO-3G, 4-31G and 6-31G basis sets, on the energetics of oxygen binding to 1,4-dihydroxy and 1,4-diaminobenzene. It was found that for anthraquinones possessing hydroxyl groups, the formation of hydroperoxides is significantly favored energetically compared with the formation of peroxides. In the case of anthraquinones containing only amino groups, the formation of hydroperoxides is less favorable, owing to a greater enthalpy of amino group deprotonation compared with that of hydroxyl group. The effect of electrostatic solvation on the energetics of oxygen addition was also investigated using the Conductor-like Screening Model (COSMO) approach. The effect of solvation on peroxide formation was found to be small, while in the case of hydroperoxides solvation was found to lower the enthalpy of this reaction by approximately 10 kcal/mol for epsilon = 78 (simulating an aqueous environment). Significant stabilization of hydroperoxides was estimated in weakly polar media (epsilon = 4) which can simulate the quinone-reducing center of the mitochondrial NADH dehydrogenase. The enthalpies obtained for oxygen addition to anthraquinones involving the formation of the most stable of the peroxide and hydroperoxide species are in good correlation with the rates of NADPH oxidation stimulated by these compounds and, in turn, with their peroxidating properties. This correlation can be directly implemented in the design of non-peroxidating anthraquinone-derived anti-cancer drugs.

An alternative concept for the molecular nature of the peroxidating ability of anthracycline anti-tumor antibiotics and anthracenodiones.

Quantum chemical calculations of model anthraquinone molecules using the CNDO/2 method have revealed that superoxide anion radical formation following the single electron transfer mediated by anthraquinone anti-tumor antibiotics may occur in aerobic conditions as a result of the direct addition of an electron to the anthraquinone-oxygen low energy charge transfer complex that is formed with singlet oxygen. Cyclovoltammetric measurements have been performed in order to provide experimental evidence supporting the hypothesis. The structural requirements for an anthraquinone molecule not exhibiting peroxidating ability by the above mechanism have been postulated. They include maximum symmetry of electron density distribution (symmetry of the molecule), a decrease of the electron density of the pi electron system and an increase in the rigidity of the molecule.