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Shashidhargouda H. R. and Shridhar N. Mathad

Abstract

This paper describes synthesis and structural properties of Ni0.45Cu0.55Mn2O4 nanopowder, obtained by co-precipitation route. XRD pattern reveals cubic structure with lattice parameter 8.305 Å. We report crystallite size (D), micro strain (ε), dislocation density (ρD), and hopping lengths (LA and LB). We also report preferential orientation by texture coefficients [Tc (h k l)]. The Williamson-Hall plot and stress-strain plot also employed to understand the mechanical properties of materials.

Open access

Zlatina Peteva, Bernd Krock, Stanislava Georgieva, Anelia Gerasimova, Mona Stancheva and Lubomir Makedonski

Abstract

The presence of phytoplankton responsible for the production of marine biotoxins (phycotoxins) is well recognized globally. Phycotoxins accumulate in filter feeding bivalves and through the food chain find their way to humans. In certain quantities they can cause severe illness. According to the symptoms they cause marine biotoxins are classified as paralytic (e.g. saxitoxin), amnesic (e.g. domoic acid), which are hydrophilic and diarrheic (e.g. okadaic acid) toxins etc. which have lipophilic nature. The aim of this study was to assess the presence of lipophilic toxins in both cultivated and wild mussel (Mytilus galloprovincialis) samples, harvested in summer 2017 from the south coast of the Black Sea, Bulgaria. Determination was performed by liquid chromatography coupled to tandem mass spectrometry. Despite of the recent evidence for the presence of a variety of potentially toxigenic producers in the investigated area, only yessotoxins were found in the studied samples. Mean levels of YTX in cultivated mussels were determined as 5832.86 pg YTX/g hepatopancreas (hp) and as 920.42 pg YTX/g hp in wild mussels. In both cases, YTX levels did not exceed the legislative limit of 3.75 mg/kg shellfish meat. These results indicated that the risk through consumption of studied shellfish is low.

Open access

Habibat Faith Chahul, Gloria Ihuoma Ndukwe and David Ogwu Ogwu

Abstract

The dissolution of aluminum alloy AA 1060 in 0.5 M and 1.0 M HCl was investigated using thermometric measurements. The reaction number of the aluminum coupons varied linearly with the concentration of the acid. Addition of Napoleonaea imperialis seed extract to the dissolving aluminium coupons lowered the reaction number in both concentrations of HCl by inhibiting the dissolution process. The inhibition efficiency of Napoleonaea imperialis seed extract was enhanced to a considerable extent in the presence of iodide ions with the synergistic parameter S > 1. The adsorption of Napoleonaea imperialis extract on the aluminium surface best aligned with the Langmuir adsorption isotherm model. The values of the free energy, ΔGadsfor the adsorption process revealed the process to be spontaneous and physisorptive.

Open access

Ana Leahu, Cristina Ghinea, Mircea-Adrian Oroian and Cristina Damian

Abstract

The main goal of this paper was to evaluate total macro- and microelement contents of different cabbage leaves of two varieties of cabbage (Brassica oleracea var. capitata f. alba and Brassica oleracea var. capitata f. rubra) and to determine the ascorbic acid content and color parameters (L*, a*, b* and -ΔE). Also, the anthocyanins content of Brassica oleracea var. capitata f. rubra was investigated. The highest mean contribution of elemental interactions regarding total macroelements in white cabbage leaves from inside (14-16 leaf), was observed for calcium and selenium, whereas the lowest was found for heavy metals, nickel, cadmium, and cobalt. The total contents of calcium and selenium in red cabbage leaves from inside (14-16 leaf) were highest. Results showed that the red-purple hue is more pronounced outside of the red cabbage than inside and it was also found that there are losses of yellowish hues for white cabbage from the outer leaves to the inner ones. Regarding the content of anthocyanins, it was obtained a value of 65.124 mg/100 g fresh weigh for outer leaves of red cabbage. Our results indicated that ascorbic acid content of red cabbage is approximately 3 times higher than in the white cabbage.

Open access

Viera Illeová and Milan Polakovič

Abstract

Thermal inactivation of a commercial β-galactosidase from Aspergillus oryzae in a 300 g/L lactose solution was studied in the temperature range of 65–75 °C. Lactose exhibited a stabilisation effect when similar inactivation rates as those in lactose solution were observed in a lactose-free solution at temperatures lower by 5°C. Inactivation process in the lactose solution was biphasic. A kinetic model based on the Lumry-Eyring mechanism was proposed and successfully verified. Estimated activation energy values were very different. Rather high activation energy values of the forward reactions were responsible for both the significant change of rate constants and the rate-controlling reaction with temperature. For these two reasons, an increase of the operational lifetime of the enzyme from 7 days at 60 °C to 580 days at 55 °C was predicted.

Open access

Amina S. Yusuf, Ibrahim Sada, Yusuf Hassan, Temitope O. Olomola, Christiana M. Adeyemi and Sunday O. Ajibade

Abstract

The synthesis of five monocarbonyl analogues of curcumin is described. In vitro anti-malarial assay of the compounds was carried out and the effect of the substituents on the aryl ring has been described. The results show that all the five compounds exhibited some reasonable activity against the chloroquine-resistant plasmodium parasite. Molecular docking studies further confirmed the observed biological activity of the compounds.

Open access

Denisa Cagardová, Martin Michalík, Peter Poliak and Vladimír Lukeš

Abstract

A systematic theoretical study using density functional theory is presented to estimate the structural, electronic, and charge-transfer characteristics of a symmetric fluorination of acenequinones outer rings. The change in aromaticity of model derivatives was described by different types of aromaticity indices. By considering a hopping mechanism and using the Marcus theory in combination with the Einstein-Smoluchowski relation, electronic drift mobilities were predicted for selected dimer configurations obtained from X-ray structures of anthraquinone, 6,13-pentacenequinone and its octafluorinated derivatives. The analysis of obtained data showed that the fluorination of the outer rings of acenequinones can lower the energy of the lowest unoccupied molecular orbital to the range from −3.0 to −4.0 eV, i.e. typical for organic n-type semiconducting materials. Finally, potential electric semiconductivity of available X-ray structures relating to drift mobilities was discussed.

Open access

Vladimír Štefuca, Lukáš Rada, Alžbeta Chochulová and Michal Rosenberg

Abstract

Leaves of the plant Plantago lanceolata contain many economically interesting bioactive compounds, among them aucubin and catalpol are the most attractive. However, soluble saccharides passing to water extracts during isolation complicate chromatographic purification of these compounds. Their degradation by microbial cells transforming, for example, glucose, fructose, or sucrose to ethanol could bring important production costs savings and improved final product quality. It has been shown that the best saccharide degradation in extracts is achieved with the Saccharomyces cerevisiae cells. The cells were very active also in their immobilized form and they were able to completely remove glucose from the extract within four hours in a packed bed reactor combined with a stirring system with infinite medium recirculation.

A simple mathematical model involving reaction kinetics and mass transfer limitations in the cell particles was proposed for the evaluation of cell effectiveness in their immobilized form in term of effectiveness factor. Values of the effectiveness factor calculated from the model were far below 1, indicating strong mass transfer limitations of the reaction. The model is suitable for optimization of preparation of immobilized cell particles, mainly from the point of view of cell charge in particles.

Open access

Ronald Zakhar, Ján Derco and František Čacho

Abstract

Arsenic (As) is metalloid, naturally present in the environment but also introduced by human activities. It is toxic and carcinogenic and its exposure to low or high concentrations can be fatal to human health. Arsenic contamination in drinking water threatens more than 150 million peoples all over the world. Therefore, treatment of As contaminated water is of unquestionable importance. The present review begins with an overview of As chemistry, distribution and toxicity, which are relevant aspects to understand and develop remediation techniques. The most common As removal processes (chemical precipitation, adsorption, ion exchange, membrane filtration, phytoremediation and electrocoagulation) are presented with discussion of their advantages, drawbacks and the main recent achievements.

Open access

Martin Klaučo, Ľuboš Čirka and Juraj Kukla

Abstract

This paper deals with the analysis and design of a model predictive control (MPC) strategy used in connection with level control in conically shaped industrial liquid storage tanks. The MPC is based on a non-linear dynamic model describing changes of the liquid level concerning changes in the inlet flow of the liquid. Euler discretization of the dynamic system was applied to transform con-tinuous time dynamics to its discrete-time counterpart used in non-linear MPC (NMPC) design. By means of a simulation case study, NMPC has been shown to track the changes of the liquid level, hence provides increased control performance. This paper also compares the traditional approach of optimal control, linear MPC, with the NMPC strategy.