Lukáš Krivosudský

Effect of competing anions on pertechnetate adsorption by activated carbon

Activated carbon (AC) has a relatively high efficiency for retaining TcO4− compared to other materials. AC is used on a vast scale in gas and water purification, metal extraction, medicine and many other applications. The TcO4− adsorption mechanism on AC is not fully known, however there are assumptions of ion-exchange reaction between AC surface and TcO4− anions. Adsorption and anion competitive investigation have shown that perchlorate anions have most influence on TcO4− adsorption. Adsorption properties depend on standard absolute molar enthalpies of hydration. Anion competitiveness was investigated with five samples that were prepared in different ways (this was already published in previous article), we used several anions Cl−, Br−, ClO4−, CH3COO−, NO3−, HCOO− and SO42− at different concentrations. In general, the adsorption of TcO4− is influenced mostly by ClO4−, what is explained by its similar structure with TcO4−; however the co-existence of Fe3+ cations in the AC structure decreases TcO4− adsorption.

Vanadium‐Controlled Crystallization of Stereoisomers of NBu4[VO2(N‐Salicylidene‐isoleucinato)] through Epimerization

Reported herein is a simple synthetic and crystallization procedure for sequential isolation of two stereoisomers of isoleucine-derived vanadium(V) complexes from a racemic mixture with three stereogenic centers and therefore eight hypothetical species. The products of this crystallization were characterized by electronic and vibrational circular dichroism, NMR spectroscopy, and polarimetry to compare the chiroptic properties of the enantiomerically pure analogues prepared from L-isoleucine and D-allo-isoleucine. NMR studies pointed to the yet unobserved phenomenon of vanadium-catalyzed epimerization of isoleucine.

Unveiling of a Trinuclear Cyclic Peroxidovanadate: A Potential Oxidant in Vanadium-Catalyzed Reactions.

The first peroxidovanadium trimer was prepared in the form of its tetrabutylammonium salt, (NBu4)3[V3O3(O2)6]·2H2O. Its X-ray structure analysis revealed a unique cyclic structure of the [V3O3(O2)6](3-) ion incorporating the yet unobserved μ3-η(2):η(1):η(1) coordination mode of one of its peroxido ligands. While relatively stable in nonaqueous solvents, the [V3O3(O2)6](3-) ion quickly decomposes in diluted aqueous solutions. A higher vanadium concentration or a higher CH3CN content in the mixed CH3CN/H2O solvent facilitates the formation of oligomers [V2O2(O2)4(H2O)](2-) and [V3O3(O2)6](3-). (51)V NMR investigations indicated that the trinuclear species is incorporated in vanadium-catalyzed oxidations in the presence of H2O2.

Stereospecificity in vanadium Schiff base complexes: Formation, crystallization and epimerization processes.

The structures of two stereoisomers of the chiral anion [VO2(N-salicylidene-isoleucinato)](-) possessing three centers of chirality, the vanadium atom (configuration A/C) and the isoleucine moiety (configuration R/S on alpha and beta carbons), are presented. The absolute configuration of all available stereosiomers, CSS, ARR, CSR and ARS, was determined by electronic circular dichroism (ECD), which allows distinguishing between diastereomers, and by vibrational circular dichroism (VCD) capable of differentiating between all four stereoisomers. The comparison of experimental VCD and infrared (IR) spectra with simulated spectra for band assignment revealed the IR spectra of the diastereomers differing significantly in the CH stretching region of the aromatic part in the molecule. Crystallization from binary systems composed of equal ratio of two stereoisomers of isoleucine, unveiled the lower solubility of CSS and ARR stereoisomers, while a longer crystallization time of the CSR and ARS stereoisomers allowed proceeding the vanadium-catalyzed epimerization, leading to the subsequent presence of the CSS and ARR stereoisomers in the product obtained.

Tetrakis(2,6-di­methyl­pyridinium) di­hydrogen deca­vanadate dihydrate

The structure of the title compound, (C7H10N)4[H2V10O28]·2H2O, was solved from a non-merohedrally twinned crystal (ratio of twin components ∼0.6:0.4). The asymmetric unit consists of one-half decavanadate anion (the other half completed by inversion symmetry), two 2,6-dimethylpyridinium cations and one water molecule of crystallization. In the crystal, the components are connected by strong N—H⋯O and O—H⋯O hydrogen bonds, forming a supramolecular chain along the b-axis direction. There are weak C—H⋯O interactions between the chains.

Production, characterization and adsorption studies of bamboo-based biochar/montmorillonite composite for nitrate removal

Biochar is a promising immobilization tool for various contaminants in liquid wastes, aqueous solutions and soils. To further improve the sorption characteristics, a biochar/montmorillonite composite was produced and synthesized in an experimental pyrolysis reactor, using bamboo as biomass feedstock. The composite was characterized by physico-chemical and structural methods (FTIR, SEM, SEM/EDX, SSA, Low temperature nitrogen adsorption method). Based on these methods, the successful preparation of a bamboo based biochar/montmorillonite composite preparation has been demonstrated. The particles of montmorillonite were distributed across the biochar surface. The adsorption studies for removal nitrates from aqueous solutions were investigated by a batch method at laboratory temperatures. The experimental data were fitted by three adsorption models (Langmuir, Freundlich and DR; R2 > 0.93). The maximum adsorption capacity achieved by biochar at pH 4, was about 5 mg g-1 and by biochar/montmorillonite composite 9 mg g-1. The results suggest that the bamboo-based biochar/montmorillonite composite can be used effectively in the treatment of industrial effluents or waste water containing anionic pollutants such as nitrates.

Antibacterial Activity of Polyoxometalates Against Moraxella catarrhalis

The antibacterial activity of 29 different polyoxometalates (POMs) against Moraxella catarrhalis was investigated by determination of the minimum inhibitory concentration (MIC). The Preyssler type polyoxotungstate (POT) [NaP5W30O110]14− demonstrates the highest activity against M. catarrhalis (MIC = 1 μg/ml) among all tested POMs. Moreover, we show that the Dawson type based anions, [P2W18O62]6−, [(P2O7)Mo18O54]4−, [As2Mo18O62]6−, [H3P2W15V3O62]6−, and [AsW18O60]7− are selective on M. catarrhalis (MIC range of 2-8 μg/ml). Among the six tested Keggin type based POTs ([PW12O40]3−, [H2PCoW11O40]5−, [H2CoTiW11O40]6−, [SiW10O36]8−, [SbW9O33]9−, [AsW9O33]9−), only the mono-substituted [H2CoTiW11O40]6− showed MIC value comparable to those of the Dawson type group. Polyoxovanadates (POVs) and Anderson type POMs were inactive against M. catarrhalis within the tested concentration range (1-256 μg/ml). Four Dawson type POMs [P2W18O62]6−, [(P2O7)Mo18O54]4−, [As2Mo18O62]6−, [H3P2W15V3O62]6− and the Preyssler POT [NaP5W30O110]14− showed promising antibacterial activity against M. catarrhalis (MICs < 8 μg/ml) and were therefore tested against three additional bacteria, namely S. aureus, E. faecalis, and E. coli. The most potent antibacterial agent was [NaP5W30O110]14−, exhibiting the lowest MIC values of 16 μg/ml against S. aureus and 8 μg/ml against E. faecalis. The three most active compounds ([NaP5W30O110]14−, [P2W18O62]6−, and [H3P2W15V3O62]6−) show bacteriostatic effects in killing kinetics study against M. catarrhalis. We demonstrate, that POM activity is mainly depending on composition, shape, and size, but in the case of medium-size POTs (charge is more than −12 and number of addenda atoms is not being higher than 22) its activity correlates with the total net charge.

Specificities and origins of the Slovak nomenclature of inorganic chemistry

Nowadays the discussion on the symbiosis of the international and national nomenclature systems in different areas of science provides clear evidences that full implementation of conventional international (mainly English) nomenclature principles in the local ones is sometimes not only unnecessary, but even redundant or impossible. Rapid development of natural sciences necessitates creation of accurate, comprehensive and comprehensible nomenclature systems for objects and phenomena under research. This study outlines the origins and development of the Slovak chemical nomenclature which is based on the Czech model. We analyze the unique Slovak nomenclature items as well as the re-evaluation of linguistic means in the field of inorganic chemistry in the international context. A part of this work is devoted to the syntactical structure of the names of inorganic compounds. At the same time we draw a parallel between chemical nomenclature and the phenomenon of controlled language.

Structural and spectral properties of tartrato complexes of vanadium(V) from quantum chemical calculations

AbstractStructural and spectral properties of three complex anions of vanadium(V) with tartrato ligands were theoretically studied by all-electron DFT calculations employing various functionals, such as BP86, BLYP, B3LYP, BHHLYP, and the M06-family. Results were statistically evaluated, with the aim to find a reliable, fairly accurate, and yet computationally efficient combination of methods and basis sets to be used in computational chemistry of vanadium(V) complex anions at even larger scale. Subsequent vibrational analysis based upon BP86 and B3LYP data provided a fair agreement with the experimental vibrational spectra. Additionally, the absorption UV–Vis and the electronic circular dichroism spectra of studied compounds were simulated via time-dependent density functional theory calculations with the long-range corrected functionals (CAM-B3LYP, LC-ωPBE, and ωB97XD). Finally, the 51V NMR chemical shifts were calculated using the GIAO approach at the B3PW91 level. The solvent effect was simulated within the PCM model. Where available, the calculated spectral properties were compared with experimental data.

catena-Poly[[(pyrazine-2-carboxamide-κN4)copper(I)]-μ3-iodido]

In the title metal–organic polymeric complex, [CuI(C5H5N3O)]n, the asymmetric unit is composed of one monomer unit of the polymer and one CuI atom linked to one iodide anion and one pyrazine-2-carboxamide molecule. The CuI atom is in a distorted tetrahedral coordination completed by one pyrazine N atom of the pyrazine-2-carboxamide ligand and three iodide anions. The polymeric structure adopts a well-known ladder-like motif of {CuNI3} tetrahedra running in the b-axis direction. The molecules of the organic ligand are connected via medium-to-strong N—H⋯O and N—H⋯N hydrogen bonds and weak π–π interactions [the distance between two parallel planes of the rings is 3.5476 (14) Å and the centroid–centroid contact is 4.080 (2) Å]. The title compound has a relatively high decomposition temperature (564 K) as a result of relatively strong covalent and non-covalent interactions inside and between the chains.