Ján Híveš

Voltammetry of hypoxic cells radiosensitizer etanidazole radical anion in water

Cytotoxic properties of radiosensitizers are due to the fact that, in the metabolic pathway, these compounds undergo one-electron reduction to generate radical anions. In this study we focused our interest on the electrochemical transfer of the first electron on radiosensitizer Etanidazole (ETN) and, consequently, on the ETN radical-anion formation in the buffered aqueous media. ETN was electrochemically treated in the broad pH range at various scan rates. Three reduction peaks and one oxidation peak were found. At strong alkaline pH the four-electron reduction peak was separated into one-electron and three-electron reductions. Under these conditions the standard rate constant k(0) for the redox couple ETN-NO(2)+e(-) <--> ETN-NO(2)(*-) was calculated. Moreover, the value of a so called E(7)(1) potential that accounts for the energy necessary to transfer the first electron to an electroactive group at pH=7 in aqueous medium to form a radical anion was also determined. The obtained value of E(7)(1) indicates that lower energy compared to the other possible chemical radiosensitizers is necessary for the system to transfer the first electron to ETN. On the other hand, the necessity of the strong alkaline pH may decrease the ability of ETN to act as hypoxic radiosensitizer in the human body.

Comparison of Ferrate(VI) Synthesis in Eutectic NaOH–KOH Melts and in Aqueous Solutions

The electrochemical synthesis of ferrate(VI) was studied in a eutectic NaOH-KOH molten salt environment and in a highly alkaline mixed NaOH-KOH aqueous solution. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the processes taking place on the stationary iron electrode. Cyclic voltammetric curves show similar characteristics in both environments in the potential region of the active iron dissolution. The anodic current peak corresponding to the ferrate(VI) production was identified for both systems in a similar position close to the potential region denoting the start of the oxygen evolution. A well-defined cathodic current peak corresponding to the ferrate(VI) reduction appearing during the reverse potential scan is shifted to the significantly less cathodic potential in the molten salt when compared to the aqueous environment. This indicates significant differences in the properties of surface film developing in the transpassive potential region. This finding was confirmed by means of electrochemical impedance spectroscopy.

Zerovalent iron and iron(VI): Effective means for the removal of psychoactive pharmaceuticals and illicit drugs from wastewaters

Herein we report the analysis of 27 selected psychoactive compounds found in the wastewater of the largest suburb in the eastern part of Central Europe Bratislava—Petržalka, Slovakia. Thirteen of them (MDMA, methamphetamine, amphetamine, THC-COOH, benzoylecgonine, codeine, tramadol, venlafaxine, oxazepam, citalopram, methadone, EDDP, cocaine) were found in concentrations above 30 ng/L. These compoundswere selected for further monitoring. The possibility of complete degradation of these 13 substances by zerovalent iron and iron(VI) was studied in thewastewater from the Petržalka treatment plant. During the week the concentration of themajority of the studied compounds inwastewaterwas stable. Concentrations of MDMA, cocaine, tramadol, and oxazepam reached significantly higher levels during the weekend.Only about 10% removal efficiency for tramadol, venlafaxine, oxazepam, MDMA, citalopram, methadone, and EDDP was observed at the treatment plant. In contrast, methamphetamine, amphetamine, and codeine were removed with 68%, 83%, and 53% efficiency, respectively. The degradation of synthetic drugs (methamphetamine, cocaine, MDMA) in wastewater is limited, while cannabis (of natural biological origin) is degradedwith efficiency greater than 90%. After utilization of the Fenton reaction, its modification, and use of ferrate(VI), a high efficiency of eliminating all of these substances to values below the limit of detection was achieved.

Cathodic overvoltage and the contents of sodium and lithium in molten aluminium during electrolysis of cryolite-based melts

Abstract The cathodic concentration overvoltage in Na 3 AlF 6 –AlF 3 –Al 2 O 3 (sat.) melts was investigated at the temperature of 1000°C. The melts contained 10 and 20 wt.% of AlF 3 . Experimental data on the cathodic overvoltage agreed well with values calculated from the content of sodium in aluminium. The dependence of the cathodic overvoltage on temperature was studied as well. It was shown that the addition of 5 wt.% CaF 2 or 5 wt.% MgF 2 does not influence the overvoltage significantly, while the addition of 2 wt.% LiF decreases the overvoltage by 20 mV at a cathodic current density of 0.25 A cm −2 and by 50 mV at 0.75 A cm −2 . These results are consistent with the influence of these additions on the content of sodium in aluminium.

Electrolytic ferrate preparation in various hydroxide molten media

Ferrate(VI) has the potential to be used as an environmentally friendly treatment for wastewater and drinking water. The electrochemical preparation of ferrate can be considered a “green” and simple approach because it typically involves a one-step reaction without harmful or expensive chemicals for the oxidation of Fe(0) to Fe(VI). The electrolyses are performed in three molten systems (i.e. NaOH–H2O, KOH–H2O and NaOH–KOH–H2O). In the first molten system, soluble ferrate was prepared in relatively low yield and current efficiency for continuous addition to wastewater. In the second system, highly stable ferrate that is easily transported and insoluble is produced with high yield. In the third system, the properties and yield of ferrate depend on the Na/K ratio in the melt. The influence of the anode material, current density and temperature on the electrolysis yield and current efficiency during ferrate preparation is discussed.

Preparation of magnesium hydroxide from nitrate aqueous solution

Nucleation of Mg(OH)2 was investigated by measuring the electrical conductivity and pH of the Mg(NO3)2 reaction solution to which ammonia containing different amounts of NH4NO3 was added. NH4NO3 increases solubility and slows down precipitation of Mg(OH)2 in the system. Data are presented on the influence of NH4NO3 on the solubility of Mg(OH)2 at 25°C. The phenomena observed can be explained by the solvation effect of nitrate ions brought to the system with the addition of ammonium nitrate, which was proved by NMR spectroscopy. When the mass fraction of NH4NO3 exceeds 15 %, homogeneous nucleation does not proceed. It was found that seeding of the system with Mg(OH)2 crystals only influenced the rate of Mg(OH)2 crystallisation, not the size and shape of the crystals. Primary crystals are smaller than 0.1 μm. The large difference in the surface energy of individual crystal planes leads to oriented agglomeration. This process is accelerated in a pressure reactor at 130°C. The resulting polycrystals are hexagonal plates 0.2 μm thin with a diameter of 1–2 μm. Under variable reaction conditions, agglomerates as big as 30 μm can be prepared.

Dominant psychoactive drugs in the Central European region: A wastewater study

The aim of this study was to analyze 26 various illicit drugs, psychopharmaceuticals and metabolites thereof in sewer from 17 selected wastewater treatment plants (WWTPs) in the Slovak and Czech Republics. Urinary bio-markers used were analyzed using liquid chromatography coupled with the tandem mass spectrometry (LC-MS/MS). We then compared our results with data obtained in other parts of Europe and the world. The present study shows that the Slovak and Czech Republics have one of the highest methamphetamine consumption rates in Europe. Within Slovakia, the highest level of methamphetamine consumption was found in Dunajská Streda with the mean specific load of the drug in sewage being up to 479mg/day/1000 inhabitants; the next highest load was detected in Trnava (354mg/day/1000 inhabitants). The methamphetamine, ecstasy and cannabis consumptions in our study were comparable to those found in other European cities, whereas cocaine consumption was lower. Among all of the studied psychopharmaceuticals, tramadol and venlafaxine were represented in the highest concentrations. The highest mean specific load of tramadol was detected in the spa town of Piešťany (371mg/day/1000 inhabitants) and Košice (372mg/day/1000 inhabitants), while the highest mean loads of venlafaxine were recorded for the towns of Trenčín (230mg/day/1000 inhabitants) and Piešťany (108mg/day/1000 inhabitants).

Electrical conductivity of molten fluoride-oxide melts with high addition of aluminium fluoride

Abstract Electrical conductivity of NaF-AlF3 melts with an addition of 2 wt % Al2O3 and/or 5 wt % CaF2 was measured using a pyrolytic boron nitride tube-type cell with a constant distance of electrodes. The molar cryolite ratios MR = n(NaF)/n(AlF3) were 1.8 and 1.6, and the temperature was varied from 865 °C to 1005 °C. Ac-techniques with a sine wave signal with small amplitude in the high frequency range were applied. Electrolyte resistance was obtained from nonlinear regression analysis according to equivalent circuit. Experimental data were used to describe the dependence of the electrical conductivity in fluoride melts with lower temperature on the amount of various additions and temperature.

Electrochemical behaviour of the LiF-(CaF2)-La2O3 system

The electrochemical behaviour of the LiF-La2O3 and LiF-CaF2-La2O3 systems was investigated by means of cyclic voltammetry. Several types of working electrodes (spectrographic pure graphite, W, Mo, Ni, Cu) were used. It was found that chemical reactions take place in the system during the dissolution of lanthanum oxide. The reduction of lithium cations occurred at the most positive potential from the species formed in the melt on ‘inert’ cathodes (W, Mo). The reactive cathodes (Cu, Ni) allowed the lanthanum deposition with depolarisation.

Effect of ferrate on green algae removal

Green algae Cladophora aegagropila, present in cooling water of thermal power plants, causes many problems and complications, especially during summer. However, algae and its metabolites are rarely eliminated by common removal methods. In this work, the elimination efficiency of electrochemically prepared potassium ferrate(VI) on algae from cooling water was investigated. The influence of experimental parameters, such as Fe(VI) dosage, application time, pH of the system, temperature and hydrodynamics of the solution on removal efficiency, was optimized. This study demonstrates that algae C. aegagropila can be effectively removed from cooling water by ferrate. Application of ferrate(VI) at the optimized dosage and under the suitable conditions (temperature, pH) leads to 100% removal of green algae Cladophora from the system. Environmentally friendly reduction products (Fe(III)) and coagulation properties favour the application of ferrate for the treatment of water contaminated with studied microorganisms compared to other methods such as chlorination and use of permanganate, where harmful products are produced.