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32 results on '"Tavadyan, L. A."'

23. Inactivation kinetics of Escherichia Coli and Staphylococcus Aureus by a hydrogen peroxide based disinfectant

Author

Grigoryan, K., Badalyan, G., Nersisyan, L., Tavadyan, L., Sargsyan, M., and Publica

Abstract

Pathogenic bacteria in food industries may have several origins, including raw materials, workers, equipment and containers. If these bacteria are not destroyed during processing, they can grow during production, thus reducing the quality and safety of food. Hydrogen peroxide possesses many advantages comparing to other disinfectants. One of them is that it does not produce toxic residues. The aim of this study was to evaluate the efficiency of a hydrogen peroxide based disinfectant against Escherichia coli and Staphylococcus aureus, to reveal the nature of the inactivation kinetics and to determine the decimal reduction time (D-value) for mentioned bacteria. Quantitative suspension test method was designed for the evaluation of bactericidal activity of mentioned disinfecting agent. The requirement of this standard is a minimum 5 log10 reduction within 5 min. The contact times were 0, 1, 2, 3, 4, 5 minutes. The D-value experiments were done by inoculating 8 mL of disinfecting solution with 1 mL of a bacterial suspension. At regular intervals (every 1min.), 1 mL aliquots of this mixture were transferred to 8 mL of growth media containing a neutralizing agent, and incubated at 37 0C. Modeling of survival curves was carried out by using the first order log-linear regression model log〖Nt/No〗= -t/D. The D-value was determined from the negative reciprocal of the slopes of the regression lines, using the linear portions of the survivor curves (log10 CFU/mL versus time of exposure to the disinfectant solution). After 5 min. of contact time hydrogen peroxide possessed better inhibition activity (more than 6 log10 reduction) against S. aureus comparing with inhibition activity against E. coli (more than 5 log10 reduction) (P < 0.05). Linear death kinetics was observed during 5 min. contact frame. D-values for 2% solution of hydrogen peroxide based disinfectant at 20 0C were E. coli (D = 0.89 min.) and S. aureus (D = 0.81 min.). The results of this study have shown that log-linear inactivation models could be applied to suspension test for modeling of efficiency of disinfecting agents during particular contact time frame.

Published
2018

26. Reforming of cyclohexane and n-heptane on nanosized Mo2C and W2C obtained by the carbidization of WO3and MoO3activated by vibrationally excited molecules of hydrogen

Author

Arsentev, S., Minasyan, V., Grigoryan, S., and Tavadyan, L.

Abstract

The catalytic activity of nanosized powders of hexagonal α-Mo2C and α-W2C with average particle size of 17 nm obtained by thermal carbidization of MoO3and WO3oxides in the flow of methane–hydrogen mixture, preliminarily activated by the vibrationally excited molecules of hydrogen was studied. Amorphous powders obtained by this method exhibit high activity associated with structural features. This was a crucial factor for the low-temperature synthesis of nanosized carbides (500 °C for Mo2C and 600 °C for W2C). It was shown that nanosized carbides exhibit high catalytic activity in cyclohexane dehydrogenation yielding benzene, and cyclodehydrogenation of n-heptane yielding toluene. The analysis of the obtained data allow to conclude that the observed drastic difference in activity and selectivity of the carbides with nano- and microsized particles is conditioned by the effect of nanocarbides particle size and defects of structure that have been formed during low-temperature synthesis. The synthesized carbide catalysts are stable in air and keep their catalytic activity over a long period.

Published
2017
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28. Antioxidant and Electron Donating Function of Hypothalamic Polypeptides: Galarmin and Gx-NH2.

Author

Tavadyan, L. A., Galoian, K. A., Harutunyan, L. A., Tonikyan, H. G., and Galoyan, A. A.

Subjects
PARTICLES (Nuclear physics), TYROSINE, ANALYTICAL chemistry, AMINO acids, ASTRONOMICAL photometry
Abstract

Chemical mechanisms of antioxidant and electron donating function of the hypothalamic proline-rich polypeptides have been clarified on the molecular level. The antioxidant-chelating property of Galarmin and Gx-NH2 was established by their capability to inhibit copper(II) dichloride catalyzed H2O2 decomposition, thus preventing formation of HO• and HOO• radicals. The antiradical activity of Galarmin and Gx-NH2 was determined by their ability to react with 2,2-diphenyl-1-picrylhydrazyl radical applying differential pulse voltammetry and UV–Vis spectrophotometry methods. Galarmin manifest antiradical activity towards 2,2-diphenyl-1-picrylhydrazyl radical, depending on the existence of phenolic OH group in tyrosine residue at the end of the molecule. The presence of antiradical activity and reduction properties of Galarmin are confirmed by the existence of an oxidation specific peak in voltammograms made by differential pulse voltammetry at E∘ = 0.795 V vs. Ag/Ag+ aq. [ABSTRACT FROM AUTHOR]

Published
2010
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32. Differential pulse voltammetric studies of ethidium bromide binding to DNA.

Author

Minasyan SH, Tavadyan LA, Antonyan AP, Davtyan HG, Parsadanyan MA, and Vardevanyan PO

Subjects
Animals, Cattle, Electrochemistry, Osmolar Concentration, Thermodynamics, DNA chemistry, Ethidium chemistry
Abstract

The interaction of ethidium bromide (EtBr) with calf thymus DNA is investigated electrochemically with the use of differential pulse voltammetry (DPV) at two different ionic strengths of a solution (0.154 M and 0.02 M [Na+], pH 7.0). It is revealed that EtBr binds with DNA in more than one way. The appropriate values of constants (K) and number site sizes (n) of EtBr binding to DNA are determined. The values of binding constants are equal to 1.9 x 10(6) and 5.6 x 10(5) M(-1), and number site sizes to 9 and 3.6 for strong interactions at ionic strengths of solutions 0.02 and 0.154 M Na+ at 28 degrees C, respectively. For a weaker interaction, these parameters are equal to 7 x 10(4) and 8 x 10(4) M(-1) and 1.5 and 1 at the mentioned ionic strengths of solutions, respectively. Thus, EtBr interacts with DNA in more than one way--intercalative and electrostatic at low ionic strength, and semi-intercalative and electrostatic at a higher strength of the solution. These results are in good accordance with the ones obtained by spectroscopic (absorption and fluorimetric) methods.

Published
2006
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