Electrochemical Redox Processes of Uranium In Aqueous Solutions of Acetylacetone

Electrochemical redox processes of uranium (VI) and uranium (V) in aqueous solutions of acetylacetone have been studied by means of various electrochemical techniques. The presence of acetylacetone accelerates the rate of disproportionation of uranium (V), even under conditions such that uranium (VI) is not in the form of the acetylacetonato complex. The corresponding rate constants of disproportionation were determined. The influence of the acetylacetonato ion concentration on the potential and on the rate of the uranium (VI) - uranium (V) electron transfer was investigated by means of cyclic voltammetry and squa,re-wave polarography. Both reduction and oxidation of uranium (V) were investigated by using the Kalousek commutator technique. A mechanism for those processes is proposed. It was proved by electrocapillary measurements that besides the adsorption of acetylacetone, adsorption of several uranium acetylacetonato species plays an important role in the overall mechanism. Taking into account the experimental results, the redox processes of uranium (VI) and uranium (V) in the presence of acetylacetone can be explained in terms of an ECE mechanism

First record of the North American paddlefish (Polyodon spathula walbaum, 1792) in the Serbian part of the Danube river

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Employing machine learning to assess the accuracy of near-infrared spectroscopy of spent dialysate fluid in monitoring the blood concentrations of uremic toxins

Hemodialysis (HD) removes nitrogenous waste products from patients’ blood through a semipermeable mem- brane along a concentration gradient. Near-infrared spectroscopy (NIRS) is an underexplored method of monitoring the concentrations of several molecules that reflect the efficacy of the HD process in dialysate samples. In this study, we aimed to evaluate NIRS as a technique for the non-invasive detection of uremic solutes by assessing the correlations between the spectrum of the spent dialysate and the serum levels of urea, creatinine, and uric acid. Blood and dialysate samples were taken from 35 patients on maintenance HD. The absorption spectrum of each dialysate sample was measured three times in the wavelength range of 700-1700 nm, resulting in a dataset with 315 spectra. The artificial neural network (ANN) learn- ing technique was used to assess the correlations between the recorded NIR-absorbance spectra of the spent dialysate and serum levels of selected uremic toxins. Very good correlations between the NIR-absorbance spectra of the spent dialysate fluid with serum urea (R=0.91) and uric acid (R=0.91) and an excellent correlation with serum creatinine (R=0.97) were obtained. These results support the application of NIRS as a non-invasive, safe, accurate, and repetitive technique for online monitoring of uremic toxins to assist clinicians in assessing HD efficiency and individualization of HD treatments

First record of the North American paddlefish (Polyodon spathula walbaum, 1792) in the Serbian part of the Danube river

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Theoretical investigation of the electronic structure of Fe(II) complexes at spin-state transitions

The electronic structure relevant to low spin (LS)high spin (HS) transitions in Fe(II) coordination compounds with a FeN6 core are studied. The selected [Fe(tz)6]2+(1) (tz=1H-tetrazole), [Fe(bipy)3]2+(2) (bipy=2,2’-bipyridine) and [Fe(terpy)2]2+ (3) (terpy=2,2’:6’,2’’-terpyridine) complexes have been actively studied experimentally, and with their respective mono-, bi-, and tridentate ligands, they constitute a comprehensive set for theoretical case studies. The methods in this work include density functional theory (DFT), time-dependent DFT (TD-DFT) and multiconfigurational second order perturbation theory (CASPT2). We determine the structural parameters as well as the energy splitting of the LS-HS states (ΔEHL) applying the above methods, and comparing their performance. We also determine the potential energy curves representing the ground and low-energy excited singlet, triplet, and quintet d6 states along the mode(s) that connect the LS and HS states. The results indicate that while DFT is well suited for the prediction of structural parameters, an accurate multiconfigurational approach is essential for the quantitative determination of ΔEHL. In addition, a good qualitative agreement is found between the TD-DFT and CASPT2 potential energy curves. Although the TD-DFT results might differ in some respect (in our case, we found a discrepancy at the triplet states), our results suggest that this approach, with due care, is very promising as an alternative for the very expensive CASPT2 method. Finally, the two dimensional (2D) potential energy surfaces above the plane spanned by the two relevant configuration coordinates in [Fe(terpy)2]2+ were computed both at the DFT and CASPT2 levels. These 2D surfaces indicate that the singlet-triplet and triplet-quintet states are separated along different coordinates, i.e. different vibration modes. Our results confirm that in contrast to the case of complexes with mono- and bidentate ligands, the singlet-quintet transitions in [Fe(terpy)2]2+ cannot be described using a single configuration coordinate

Performance of falling film plate evaporators in reconstructed multiple-effect evaporation station in sugar factory

General trend of free trade in regional level as well as in the direction of European Union has motivated sugar factories located in Serbia to invest into technologies that are more efficient in order to make their products more competitive at the markets in Europe. The aim of this work was to evaluate effects of falling film plate evaporators on the energy consumption of evaporation plant, as well as to validate performance of this type of evaporators. It was found that this type of evaporator decreased energy requirements and in the same time evaporation process was more effective due to high values of heat transfer coefficients.

Heavy metal and trace element accumulation in muscle, liver and gills of the Pontic shad (Alosa immaculata Bennet 1835) from the Danube River (Serbia)

Pontic shad (Alosa immaculata Bennet 1835) is an anadromous species that lives in the heavily polluted north-western part of the Black Sea and migrates into the Danube River to spawn To assess their heavy metal contamination levels, samples of Politic shad were collected at 863 river kilometre of the Danube River Muscle, liver and gill samples were prepared using microwave digestion. and the analysis of Al, As, Cd, Cu, B. Ba. Fe, Mg. Sr. Zn. Li, Co, Cr. Mn. Mo, Ni and Pb was performed with inductively-coupled plasma-optic emission spectroscopy (ICP-OES). Significant differences in concentrations of analyzed elements were observed among different tissues, as well as between the genders Al, Sr, Ba. Mg, and Li had the highest concentrations in gills, while Cd. Cu, Zn. Fe and B were highest in the liver While the muscle had the lowest concentrations of most of the analyzed elements, it had the highest concentration of As. This study has revealed that the concentrations of Cd and As in Politic shad muscle tissue were above the maximum acceptable concentrations for human consumption, thus precautions need to be taken in order to prevent future heavy metal contaminatio

Determination of differential heavy metal and trace element accumulation in liver, gills, intestine and muscle of sterlet (Acipenser ruthenus) from the Danube River in Serbia by ICP-OES

The accumulation of heavy metals in fish has been extensively studied and well documented. However, the research has been mainly focused on the muscle tissue, while the distribution patterns among other tissues, such as liver and gills, have been mostly neglected. Within the present study, the concentrations of Ag, Al, As, B, Ba, Cd, Co, Cr, Cu, Fe. Mn, Mo, Ni, Pb, Se, Sr, Zn and Li in the muscle, gills, liver and intestine of the sterlet (Acipenser ruthenus) from the Danube River have been assessed by using the inductively-coupled plasma optical spectrometry. The analysis has revealed a high degree of differential accumulation of the studied heavy metals and trace elements in the tissues of the Danube sterlet. Liver appeared to be the main heavy metal storage tissue, while the lowest levels of analyzed metals were found in muscles. Heavy metal concentrations in the muscle were at acceptable levels for human consumption, except partly for cadmium. We conclude that, in order to enable a more efficient control of contaminants in fish products, there is an apparent need to resolve the problem of lack of legal limits for many metals in European legislation