Volume 10 (2017): Edition 2 (December 2017)

Temperature dependency of densities of the liquid system magnesium nitrate hexahydrate - zinc nitrate hexahydrate was measured. Densities of liquid mixtures were experimentally measured at different temperatures by a method using submersible corpuscle. Based on the obtained data, temperature dependence on the density was obtained. A model describing the density in the whole concentration range very well was created.

Photochemistry has been subjected to the enormous development within the last two centuries. This development has been driven mainly by two key factors: inherent scientific thirst for knowledge and worldwide foodstuff and energy needs. Within the development of photochemistry, mutual conditionality of global needs, progress in theory, improving of existing and birth of qualitatively new experimental techniques can be identified. Photochemistry has found its application in various fields of our life, development and protection of the nature.

The quantum chemical calculations using DFT were performed for 2-alkyl-4X and 2,6-dialkyl-4-X substituted phenols. Based on the optimal geometries the bond dissociation enthalpies (BDEs), proton enthalpies (PAs) and the lipophilicities were computed. Additionally, simple geometry parameter was found correlating well with experimental leukemia cell toxicity of substituted phenols. Next, we have found no linear dependence between PA or BDE values and log1/C values in gas phase or in water despite the radical toxicity mechanism proposed in the literature.

Let G be a molecular graph, the eccentric connectivity index of G is defined as ξ^c(G) = Σ_u∈V(G)deg(u)·ecc(u), where deg(u) denotes the degree of vertex u and ecc(u) is the largest distance between u and any other vertex v of G, namely, eccentricity of u. In this study, we present exact expressions for the eccentric connectivity index of two infinite classes of nanostar dendrimers.

A comparison of the influence of two alloy pre-treatments and temperature treatments on the formation and composition of zirconium based conversion coating on the AA2024 alloy has been performed. The investigation employed mass changes, atomic force microscopy (AFM), XRD dispersive spectroscopy (EDX), infrared spectroscopy (IR) and electrochemical tests by open circuit potential (OCP) measurements. Pre-treatment using only alkaline etching is called alkaline pre-treatment. When alkaline etching is followed by de-oxidization in a phosphoric acid solution the process is called acidic pre-treatment. Conversion coatings were formed in Pragokor BL. IR analysis revealed the formation of a phosphate on the alloy surface. EDX analysis showed Mg dissolution. The Zr content increased with the temperature of the conversion coating formation. Both pre-treatment methods provided a phosphate layer on the alloy surface.

Approximately 1 300 Gt of municipal solid waste (MSW) are produced worldwide every year. Most of it is disposed of in landfills, which is very hazardous for the environment. Up to 10 % of produced MSW are incinerated. However, incineration is not very effective and requires specific conditions for preventing emissions. Gasification and pyrolysis are more effective processes which can be used not only for heat and electricity generation but also for fuel and valuable chemicals production. MSW can be transformed into refuse-derived fuel (RDF) which has higher heat of combustion. Synthesis gas produced by RDF gasification can be utilised in methanol production. Methanol is a very lucrative chemical which can be used as renewable liquid fuel or as a reagent in organic syntheses. Gasifier design and process optimisation can be done using a reliable mathematical model. A good model can significantly decrease the number of experiments necessary for the gasification process design. In this work, equilibrium model for RDF gasification was designed in Aspen Plus environment and the flow of oxygen and steam as gasification agents were optimised to achieve the highest theoretical methanol yield. Impact of the recycle of unreacted steam and produced tar on the methanol yield was evaluated. The highest theoretical methanol yield (0.629 kg_MEOH/kg_RDF) was achieved when the steam and tar recycle were switched on, the ratio between oxygen and RDF feed was 0.423 kg/kg and that between the steam and RDF feed was 0.606 kg/kg. In this case, fresh steam represented only 12 % of the total steam fed to the reactor, the rest consisted of recycled steam. Optimal gasifier temperature was 900 °C.

Formation and fragmentation of beryllium clusters up to 100 atoms were studied using molecular dynamics trajectory simulations. Association rate constants of a single Be atom attachment to Ben clusters, n = 2-20, 30, 40, 50, 60, 70, 80, 90 and 100, and dissociation rate constants of these clusters were calculated directly. Dependence of the dissociation rate constants on temperature is strong and follows the Arrhenius equation. An analysis of the dissociation reactions has shown that beryllium clusters dissociate mainly into single Be atoms. The monomer association reaction depends weakly on temperature but strongly on the size of the cluster.

Filamentous fungi belonging to Aspergilli genera produce many compounds through various biosynthetic pathways. These compounds include a spectrum of products with beneficial medical properties (lovastatin) as well as those that are toxic and/or carcinogenic which are called mycotoxins. Aspergillus flavus, one of the most abundant soil-borne fungi, is a saprobe that is able growing on many organic nutrient sources, such as peanuts, corn and cotton seed. In many countries, food contamination by A. flavus is a huge problem, mainly due to the production of the most toxic and carcinogenic compounds known as aflatoxins. In this paper, we briefly cover current progress in aflatoxin biosynthesis and regulation, pre- and postharvest preventive measures, and decontamination procedures.

Two homodimetallic dipicolinate compounds of the formulae [Co(H₂O)₅Co(dipic)2]·2H₂O (1) and [Ni(H₂O)₅Ni(dipic)2]·2H₂O (2) have been synthesized and their crystal structures have been determined by single-crystal X-ray diffraction analysis. The prepared isostructural compounds consist of cationic {MO₅O’}²⁺ and anionic {MN₂O₄}^2- moieties, where Co^II/Co^II or Ni^II/Ni^II metal centers are connected together by bridging μ-carboxylate oxygen atoms from dipicolinate anions. H-bond interactions involving aqua ligands, dipicolinate oxygens and lattice solvent molecules stabilize the dimeric units by linking them into 3-D polymeric networks.

An optimization-based control strategy is proposed to improve control performance of a primary PI controller. The strategy, referred to as a MPC-based reference governor, optimizes the performance of a primary PI controller by supplying optimal setpoints to the primary controller. This primary PI controller is responsible for reflux ratio manipulation in a distillation column, to control the temperature of the column head. This paper shows theoretical and experimental results obtained on the laboratory-scale.

Derivatives of anilide were studied systematically by the density functional theory (DFT) using the B3LYP hybrid functional and the 6-311+G(3df,2p) basis set. Characteristic frequencies of N-H and C=O stretching modes for cis and trans conformers distinguishing were compared with available experimental and theoretical data. Effect of substitution in ortho position and acidic residue group is discussed with respect to the bond length changes in the aromatic ring and aromaticity indexes. Energy differences between cis and trans conformations allow estimating the effect of intramolecular hydrogen bonds stabilizing the studied conformations. The trans conformation of parent formanilide is stabilized via the C_(aromatic) -H∙∙∙O=C interaction with the energy of around 4 kJ・mol^-1. The selected anilide series represent model compounds for drug design.

Effects of additions of buckwheat flour and sourdough on the total phenols content, antioxidant activity, and sensory properties of crackers were examined. Different mixtures of wheat flour with addition of buckwheat flour and sourdough were used for the prepartion of crackers. Two types of lactic acid bacteria (Lactobacillus plantarum and Lactobacillus brevis) were used for the preparation of buckwheat sourdough. Properties of crackers made with addition of buckwheat flour and sourdough were analysed in comparison to control crackers made only with wheat flour. Significant increase of total phenols in comparison to wheat flour dough (0.73 mg gallic acid equivalent (GA)/g of dry basis (d.b.)) was accomplished by adding buckwheat flour (1.12 mg GA/g d.b.) and sourdough (1.77 and 1.79 mg GA/g d.b.) regardless of the type of lactic acid bacteries used. All samples showed the decrease in total phenol content during baking process. Crackers with sourdough had higher antioxidant activity (16.84 and 15.84 mmol Fe³⁺/g d.b.) compared to crackers made with addition of buckwheat flour (10.42 mmol Fe³⁺/g d.b.) and control sample (7.76 mmol Fe³⁺/g d.b.). The result of sensory analysis showed positive influence of sourdough on taste and texture of crackers and insignificant differences in odour and appearance of tested samples. Also, the chewiness of crackers made with the addition of buckwheat flour and sourdough was improved compared to control crackers made from wheat flour.

Relativistic Atomic Natural Orbitals (ANO-RCC) are extrapolated to the complete basis set limit. ANO-RCC-VXZP (X = D, T, Q) basis sets were extrapolated using standard extrapolation techniques. Five noncovalent complexes, characterized by hydrogen, dispersion and halogen interactions, were chosen. Accurate description of the studied complexes is allowed only after the inclusion of electron correlation and large basis sets which have to include polarization and diffuse functions. Results are in quantitative agreement with the benchmark data obtained by standard aug-cc-pVXZ-DK (X = D, T, Q) basis sets considering chemical accuracy of ±1 kcal/mol.

Regeneration is the most efficient way of managing used oil. It saves money by preventing costly clean-ups and liabilities associated with mismanagement of used oil and it also helps to protect the environment. A numerical study of the flow, heat and mass transfer characteristics of the vertical evaporating tube with the films flowing down on both the inside and the outside tube surfaces has been carried out. Condensation occurs along the outside wall surface and evaporation at the free surface of the inside film. The calculation domain of two film flow regions and tube wall is solved simultaneously. The longitudinal variation of temperature, mass flow rate, and hence the thickness of the films downward the tube can be obtained by applying conservation of the energy requirement to the differential element.

We report here the crystal and electronic structure of a new spiro-derivative, namely methyl (2R,4S)- 4-(benzothiazol-2-ylamino)-8,8´-dimethoxyspiro[chroman-2,2´-chromene]-3´-carboxylate (I), C₂₈H₂₄N₂O₆S, which crystallizes as racemate in the space group C2/c. In this compound, the chromanone 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 N-H∙∙∙N hydrogen bonds and weak C-H∙∙∙O, C-H∙∙∙S, C-H∙∙∙ π, inter- and intra-molecular interactions resulting in a two-dimensional network in the crystal structure.

The aim of this work was to develop an on-line coupling of electrochemical preconcentration to atomic absorption spectrometry method and to apply the developed system in the determination of ultra-trace amounts of As in water samples. A flow-through electrochemical analyzer EcaFlow (Istran Ltd, Bratislava, Slovakia) was used as the preconcentration unit with a two-electrode cell. The working electrode was a reticular vitreous carbon electrode coated with gold. An atomic absorption spectrometer SP9 with a graphite furnace atomizer (Pye Unicam) was used to determine the preconcentrated As species. Preconcentration parameters were optimized for the electrochemical process.