Volumen 11 (2018): Heft 1 (April 2018)

We report here the crystal and molecular structure of a new chromane-derivative, namely isopropyl( 2R*,3S*,4S*)-4-(benzo[d]thiazol-2-ylamino)-2-hydroxy-2-ethylchromane-3-carboxylate (I), C₂₁H₂₂N₂O₄S, which crystallizes as racemate in the space group C2/c. Its structure has been solved using X-ray diffraction data obtained at low temperature (100(2) K). In this compound, the chromane moiety consists of a benzene ring fused with a six-membered heterocyclic ring which adopts a distorted half-chair conformation. The molecules are linked by a combination of O-H∙∙∙N and N-H∙∙∙O hydrogen bonds, resulting in a twodimensional network which helps stabilizing the crystal structure of the compound (I). Dihedral angle between the chromane and benzothiazol rings is 80.6(1)⁰.

The structures of camptothecin (CPT) lactone form and its complexes with Cu(II) were optimized at B3LYP/6-311G* level of theory. Their electronic structures were evaluated via QTAIM topological analysis of electron density and Mulliken population analysis. Stability, electron density distribution and geometrical factors of the optimized systems were compared. Both CPT nitrogen atoms show lower affinity to Cu(II) compared to the oxygen ones. Both the oxygen atom in the CPT lactone ring and the one in the neighbouring carbonyl group show the highest affinity to Cu(II) and the highest stability of Cu-CPT complexes which indicates the most probable CPT reaction sites.

Bioethanol is an example of a renewable energy source which can be produced not only by fermentation of simple sugars but also by depolymerisation of cellulose, as the second-generation feedstock, in the first step. This will help to further develop the bioethanol economy. Ethanol can be used as a promising platform molecule for the production of a variety of industrially important chemicals such as alkenes or oxygenates. Alkenes are produced industrially by petrochemical way mainly from crude oil, a non-renewable energy source. Conversion of ethanol to light olefins using an appropriate catalyst could replace the production of these key building blocks for the chemical industry. In this work, the focus is on the preparation and testing of heterogeneous catalysts in the transformation of ethanol to alkenes and acetaldehyde. In most cases, magnesia-based catalysts were used on a silica support during the experiment. Individual types of catalysts were compared in terms of yields of particular products, the effect of the feedstock load and that of calcination temperature of the catalyst on the catalytic activity are discussed. The highest ethylene yields (95 %) were achieved over an Mg-β-zeolite catalyst; the highest yield of 1,3-butadiene (29.1 %) was achieved in case of an Na/alumina catalyst; and the highest acetaldehyde yield (22.3 %) was achieved using a K-doped MgO/SiO₂ catalyst.

Three new nitrosalicylatocopper(II) complexes have been prepared and characterized. Compounds of the composition Cu(5-NSal)₂(2-ampy)₂ (1), Cu(5-NSal)₂(2-hmpy)₂ (2) and Cu(3,5-DNSal)₂(2-hmpy)₂ (3), where 2-ampy = (2-aminomethyl)pyridine, 2-hmpy = (2-hydroxymethyl)pyridine, 5-NSal = 5-nitrosalicylate anion and 3,5-DNSal = 3,5-dinitrosalicylate anion, were characterized by elemental analyses, EPR and IR spectroscopy. EPR spectra are consistent with the dx_2-y2ground electronic state. Spectral properties have shown “classic” monodentate coordination of 5-nitrosalicylate anion. Similarly, bonding mode of the 3,5‑dinitrosalicylate anion in (3) is assumed to be unidentate via the carboxyl group, which is surprising compared with the previously studied complex, where the preferred coordination via the phenolate group anion was observed.

Pincer type ligand 2,6-pyridinedimethanol was used as a useful tool in the preparation of the Co(II) pseudoctahedral complex together with 3,5-dinitrobenzoate counteranion. New complex of the composition [Co(pydm)₂](3,5-dnbz)₂(pydm = 2,6-pyridinedimethanol, and 3,5-dnbz = 3,5-dinitrobenzoate anion) has been prepared and characterized. Its XRD structure revealed pseudooctahedral {CoN₂O₄} chromophore around the cobalt atom with Co-N distances significantly shorter (Co-N_av = 2.038 Ǻ) in comparison to the Co-O ones (Co-Oav = 2.142 Ǻ), which was probably the reason of its relatively high zero-field splitting parameter (D/hc = 43.6 cm-1). Positive value of the D parameter causes slow relaxation process typical for Co(II) SMM behavior. The 3,5-dinitrobenzoate counteranions are strongly bonded to the [Co(pydm)₂] cation via rather strong hydrogen bonds (O∙∙∙Oav = 2.568 Ǻ) forming “quasi molecular” units. Solid state structure allowed different π-π stacking interactions of neighboring “molecular” unit aromatic rings probally leading to observation of the additional relaxation mode.

A computational study using density functional theory is reported for the coronene monomer and selected linear cata-benzocoronene oligomers. Local aromaticity was discussed and analysed using the theoretical Harmonic Oscillator Model of the Electron Delocalisation (HOMED) index and its geometric (GEO) and energetic (EN) contributions. The [n]acenes (n = 3, 7, 11 and 15) served as reference molecules. Local aromaticity of individual superbenzene rings has oscillating character. On the other hand, the highest HOMED parameters which are practically independent on the molecular lengths were found for the smallest molecules including condensed benzene rings in their structure. For the largest structure of [n]acenes (n = 15), the inner rings are less aromatic than the outer ones. Depending on the molecular length, the energy gaps between the B3LYP energy levels of the highest occupied and lowest unoccupied molecular orbitals vary from 2.71 eV to 4.04 eV for coronene series and from 0.61 eV to 3.59 eV for [n]acenes.

In recent years, the occurrence of micropollutants (MPs) in sewage-, surface-, ground- and drinking water, and their removal processes are widely discussed. The content of various chemical organic/inorganic pollutants (pharmaceuticals, drugs, pesticides, hormones, heavy metals etc.) has increased over the years. Most of these compounds are not eliminated or biotransformed in traditional wastewater treatment plants. Several advanced oxidation processes (AOPs) for the removal of resistant micropollutants from water sources have been studied. Ferrate (VI) has aroused interest as an alternative oxidizing agent in drinking water preoxidation treatment. Electrochemically prepared potassium ferrate was used to remove the studied organic micropollutants. The effect of ferrate on two widely occurring organic micropollutants in water sources, carbamazepine and caffeine, was investigated. High performance liquid chromatography (HPLC) was used for sample analysis.

Materials used for heat accumulation are substances with the phase change at temperatures below 80 °C. In such substances, a high amount of energy can be stored due the phase change. Because of possible corrosion of the heat container components, it is necessary to know their resistance in the given medium. In this work, the corrosion of aluminum, copper and carbon steel was studied in two liquid media: zinc nitrate hexahydrate and calcium chloride hexahydrate. Corrosion tests have shown that steel is the least resistant to corrosion in both media. Aluminum has been proved as the most durable material in zinc nitrate hexahydrate media. On the other hand, pitting corrosion on aluminum occurred in the calcium chloride hexahydrate making it unsuitable for the use in this media. From the comparison of two studied PCMs follows that zinc nitrate hexahydrate is a more aggressive medium in comparison with calcium chloride hexahydrate. From the point of view of corrosion, zinc nitrate hexahydrate is not suitable for heat accumulation when using the studied metals. When using the calcium chloride hexahydrate as PCM, copper is suitable as a construction material; aluminum and carbon steel show pitting corrosion.

The prevalence of antibiotic resistant coliform bacteria and enterococci in fresh raw cow milk obtained from four vending machines in Slovakia was assessed. Also, differences in the number of antibiotic-resistant bacteria in milk according to season (winter and summer) were compared. Number of total coliform bacteria ranged from 2.45 to 4.18 log CFU/mL. Majority of them were resistant to ampicillin. This was expected due to their intrinsic resistance apart from Escherichia coli which is sensitive to ampicillin. In addition, we observed also tetracycline and gentamicin resistance. Each of our samples contained E.coli. Number of total enterococci ranged from 1.95 to 3.78 log CFU/mL. We have observed predominantly vancomycin resistance in all tested samples. In samples taken during winter we have found higher number of total and resistant coliforms as well as total enterococci compared to those taken during summer.

Single drop microextraction technique uses microamounts of organic solvents. Simplicity, low cost, low environmental impact, compatibility with chromatographic systems as well as its applicability to different matrices are main advantages of single drop microextraction. This technique has become frequently used for the extraction of a broad scope of compounds for numerous analytical applications. This review provides an overview of the existing single drop microextraction modes of realisation and the main scope is devoted to the optimization of parameters influencing the efficiency. The state of the art is discussed on the basis of examples selected from representative application areas. Extraction parameters for toxic organic compounds extraction and microdrop stability were evaluated.

Apatite is a natural mineral from the group of phosphate minerals. It originates primarily in rocks and converted limestones. It is also one of the few minerals produced and used by microeconomic systems. Due to its low solubility in water and high sorption capacity, apatite is a suitable sorbent for heavy metals and radionuclides removal from aqueous radioactive waste. Increasing amount of radioactive waste (RAW) has a negative impact on human health as well as on the environment. Production of RAW is constantly increasing because of the use of nuclear energy as well as by the development of nuclear medicine. The aim of this work was to study the effect of pH and various anions on the sorption of pertechnetate anions from aqueous solution to Sn-Apatite. Sn-Apatite samples used in the experiment were prepared by the wet precipitation method and adsorption of ^99mTc was monitored by the radioisotope indication method. Sorption experiments were performed using the batch method. It was found that the sorption percentage was higher than 90 % in all Sn-Apatite samples and the dissociation constant, K_D, indicated high affinity of pertechnetate anions to the solid Sn-Apatite particles. The presence of competing anions did not significantly influence the ability of Sn-Apatite materials to adsorb ^99mTcO₄ - from aqueous solutions.

The method of samples processing and subsequent their analysis using Radionuclide X-ray Fluorescence Spectrometry for medical plant samples and drugs has been developed. Technical aspects of the measurement such as mutual geometrical arrangement of tablets (of various size and mass), semiconductor Si/Li detector and the primary source of radiation, 238Pu, are discussed. Technique of Radionuclide X-ray Fluorescence Spectrometry (RXFS) has been applied on samples of medical products and medicines used to treat liver diseases. Medicinal herbs, teas in infusion bags and the drug from this group, were analysed in the solid state (in the form of tablets) or as the leachate, applied to the ion exchanger resin. Chelating Extraction Disks EmporeTM have proven the ability to extract elements from liquid samples under certain conditions and thus to prepare samples for RXFS analysis and evaluation. To ensure correct results, an optimal pH environment has been found. The detection limits of selected elements (Cr, Mn, Fe, Ni, Cu, Zn and Pb) have been calculated for both solid and liquid state samples. Standard addition method and calibration curve parameters have been used to evaluate the concentration of each element in studied samples. Determined concentrations of the examined elements were compared with permissible contaminant limits for the relevant food law in Slovak Republic.