Levon Agasy Tavadyan

Levon Agasy Tavadyan
National Academy of Sciences of Armenia | NAS RA · Laboratory of Kinetics and Catalysis

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54
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229
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Publications

Publications (54)
Article
Full-text available
Copper(II)-, Fe(III)-, Zn(II)-, and Mn(II)-3,5-di-iso-propylsalicylate (3,5-DIPS) chelates and Cu(II)2(acetyl-3,5-DIPS)4, and 3,5-DIPS, salicylidene Schif base chelates Mn(III), Co(II), Ni(II), were kinetically examined as antioxidants in the scavenging of tert-butyl peroxyl radical (tert − butylOO∙ ) in non-polar and polar aprotic solvents. Using...
Article
Full-text available
The catalytic activity of tungsten carbide WC and a mixture of tungsten carbides (WC + W2C) obtained by mechanochemical and plasma-mechanochemical methods in the reaction of dry reforming of methane at a pressure of 650 Torr, the ratio CH4 : CO2 = 1 : 1 in the temperature range of 400–960°C was studied. It was shown that the nanopowder of tungsten...
Article
Full-text available
The catalytic activity of tungsten carbide WC and a mixture of tungsten carbides (WC + W 2 C) obtained by mechanochemical and plasma-mechanochemical methods in the reaction of dry reforming of methane at a pressure of 650 Torr, the ratio CH 4 : CO 2 = 1 : 1 in the temperature range of 400-960°C was studied. It was shown that the nanopowder of tungs...
Article
Full-text available
The influence of the initial concentration of oxygen and temperature on the oxidative conversion of propane in a two-sectional flow reactor at constant pressure and contact time was studied. It was shown that an increase in the initial concentration of oxygen not only increases the conversion of propane, but also affects the ratio of the reaction p...
Article
Full-text available
It has been shown that in the case of noncatalytic oxidative pyrolysis of propane, the admixture of ethylene in the reactants significantly increases the concentration of propylene in the products. This process can be arranged in such a manner that the ethylene will not be noticeably consumed, i.e., will actually act as a propylene formation cataly...
Article
By using the ORAC method, the values of the antiperoxyradical capacity of binary mixtures of bioflavonoids (quercetin, rutin, morin and naringin) with trolox or ascorbic acid, and individual antioxidants in the aqueous medium were determined. Through these values and the data of square wave voltammetry (SWV) method, the non-additive effects in the...
Article
The binding of both ethidium bromide (EtBr) and Hoechst 33258 (H33258) to calf thymus DNA differing by the mechanism at different ionic strengths of NaCl water solutions (2, 20 and 150(Formula presented.)mM) has been quantitatively studied by square wave voltammetry (SWV). It was revealed that EtBr binds to DNA by more than one mode: at the solutio...
Article
Full-text available
The oxygen radical absorbance capacity (ORAC) method was used to detect the antiperoxyradical ability of organoselenium compounds: selenophene and its derivative, 2-amino-4,5,6,7-tetrahydro-1-selenophene-3-carbonitrile (ATSe); while as a comparison, the sulfur-containing analogue of selenophene—thiophene and its derivative—2-amino-4,5,6,7-tetrahydr...
Article
A number of possibilities to increase the yield of propylene in the processing of light gaseous hydrocarbons are considered, including the oxidative pyrolysis of propane, conjugated oxidation of propane and ethylene, conjugated oxidation of ethylene and methane, and introduction of methane into the products of a rich methane flame. The principal po...
Article
Full-text available
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 MoO3 and WO3 oxides 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...
Article
Full-text available
It has been shown that in the case of noncatalytic oxidative pyrolysis of propane, the admixture of ethylene in the reactants significantly increases the concentration of propylene in the products. This process can be arranged in such a manner that the ethylene will not be noticeably consumed, i.e., will actually act as a propylene formation cataly...
Article
Full-text available
The 2nd International Symposium «Fundamental Aspects of Rare-earth Elements Mining and Separation and Modern Materials Engineering» (REES2015) was jointly organized by Tomsk State University (Russia), National Academy of Science (Armenia), Shenyang Polytechnic University (China), Moscow Institute of Physics and Engineering (Russia), Siberian Physic...
Chapter
DDT (dichlorodiphenyltrichloroethane), used as a pesticide, is a persistent pollutant and rests one of the main dangers to human health and to the environment. Being chemically stable in ordinary conditions, its oxidation or oxidative degradation, especially, in large amounts or in industrial scale, is problematic in certain aspects. In this work i...
Article
Oxidation of DDT (1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane) by the dioxo-Mo(VI) complex (dioxo-molybdenum(VI)-dichloro[4,4′-dicarboxylato-2,2′-bipyridine]), anchored on a TiO2, in the presence of dioxygen under UV-irradiation (λ = 253.7 nm) in acetonitrile suspension has been examined. The reaction has catalytic character. Conversion of DDT (3...
Article
Full-text available
The influence of the ratio of the reactants on the characteristics of the cooxidation of ethylene and methane in a two-section flow reactor is examined. It is shown that the radical oxidation of ethylene implicates methane into the oxidation process. The interaction of the thereby formed methyl radicals with ethylene leads to a significant increase...
Article
Full-text available
The influence of the initial concentration of oxygen and temperature on the oxidative conversion of propane in a two-sectional flow reactor at constant pressure and contact time was studied. It was shown that an increase in the initial concentration of oxygen not only increases the conversion of propane, but also affects the ratio of the reaction p...
Article
In the reaction of ZnII(3,5-DIPS)2 with tert-butylOO radical, a mediated kinetic medium (solvent) effect is observed. The essence is that electron pair donors such as DMSO at molar equivalent quantities do not directly impede the reaction center of radical scavenging, but act indirectly by bonding axially to the central metalloelement zinc, which c...
Article
The nanopowders of Ni and Co metals and their alloy were prepared by plasma-assisted milling, and the activity of catalysts on their basis was studied in the carbon dioxide reforming of methane (CDRM) at atmospheric pressure. It was found that the catalytic activity of Ni nanopowder rapidly decreased because of the blocking of its surface by coking...
Book
This book presents the results of the study in the field of kinetic and numerical simulation of complex (multistep) chemical reactions. Numerical analysis methods of kinetic models of multistep chemical reactions are elucidated. Also the new value method of computerized study of the kinetic models of reaction systems is proposed which is distinguis...
Article
Solvent effect of dimethyl sulfoxide (DMSO) on the oxidation-reduction properties of ascorbic acid (AA) was studied by the electroanalytical method of differential pulse voltammetry (DPV) in a three-electrode cell at 37 °C. Dimethylsulfoxide was found to considerably decrease the oxidation ability of AA due to the formation of molecular complexes b...
Article
Determination of the oxygen radical absorption capacity (ORAC) served to discover antiperoxyradical activity of dimethyl selenoxide (DMSeO). The antiperoxyradical capacity of DMSeO is higher than that of the water-soluble analog of α-tocopherol and trolox and close to the value determined for the butylated hydroxy toluene (BHT). The redox parameter...
Article
The decomposition of 1-chloro-4-ethylbenzene under UV irradiation (λ = 253.7 nm) in the presence of dioxygen and the dioxomolybdenum(VI)dichloro[4,4′-dicarboxylato-2,2′-bipyridine] complex anchored on the TiO2 surface has been investigated. The catalytic cycle includes the photostimulated transfer of the oxo-oxygen atom from the surface dioxomolybd...
Article
Full-text available
The catalytic activity of dioxo-molybdenum(VI)-dichloro[4,4′-dicarboxylato-2,2′-bipyridine] covalently anchored through the carboxylate function to the surface of TiO2 has been tested for the oxidative degradation of 1-chloro-4-ethylbenzene in MeCN solution under argon and UV irradiation (λ = 254 nm). After 4–5 h of photochemical reaction, the Mo c...
Article
Full-text available
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...
Article
Absolute rate constants (keff) for the chemical reactions of Cu(II)2(3,5-di-iso-propylsalicylate)4(H2O)3, Cu(II)2(3,5-di-tert-butylsalicylate)4, Cu(II)2(3,5-di-tert-butylsalicylate)4(H2O)4, Cu(II)2(3,5-dimethylsalicylate)4(H2O)3, Cu(II)2(3-ethylsalicylate)4(H2O), Cu(II)2(3-phenylsalicylate)4, and Cu(II)(3,5-di-iso-propylsalicylate)2(pyridine)2 with...
Article
Carboxylate and salicylic OH coordinate bonding as well as intramolecular and intermolecular hydrogen bonding of bis-3,5-diisopropylsalicylatozinc(II), [ZnII(3,5-DIPS)2], with Lewis bases were studied to determine mechanisms accounting for antioxidant reactivity of ZnII(3,5-DIPS)2. Apparent thermodynamic parameters: K eq, ΔS 0, ΔH 0, and ΔG 0 were...
Article
Salicylidene Schiff base chelates (R,R)-(–)-N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminomanganese(III) chloride, (R,R)-(–)-N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminocobalt(II), N,N′-bis(salicylidene)-ethylenediaminocobalt(II), N,N′-bis(salicylidene)ethylenediaminonickel(II), and N,N′-bis(salicylidene)ethylenedi...
Article
A kinetic model was constructed to describe the reactions involved in the oxidation of methyl linoleate (ML) inhibited by alpha-tocopherol (TH). The initial model of the reaction mechanism included 53 individual steps, which were numerically analyzed by the value method based on Hamiltonian systematization of kinetic equations. Good accord was obta...
Article
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 sit...
Conference Paper
A numerical method of researching kinetic models’ predictive abilities is suggested. As a criterion of predictive abilities of the kinetic model were chose the degree of coincidence of the kinetic models reduced by the value numerical analysis for experimentally studied and predicted conditions. The present approach is illustrated by means of the k...
Article
Differential pulse voltammetry was used to assess the interaction of ethidium bromide with calf thymus DNA. It was confirmed that the binding may involve intercalation, hemi-intercalation, and electrostatic mechanisms. The corresponding binding constants and numbers of basepairs per ligand were determined. The results thus obtained agreed well with...
Conference Paper
A new numerical method to calculate explosion limits of gas mixtures based on Hamiltonian systematization of kinetic models is offered. As a criterion for the critical state of reaction system the extreme behaviour of functions describing total concentration of chemical species is selected. The present approach enables numerical calculation of kin...
Article
Bioactive copper(II), iron(III) and manganese(II) 3,5-di-i-propylsalicylate (3,5-DIPS) chelates were investigated to determine their ability to inhibit the free radical initiated chain reactions leading to the peroxidation of isopropylbenzene (i-PrPh) and ethylbenzene (EtPh). The manganese(II)-(3,5-DIPS) 2 and copper(II)2(3,5-DIPS)4 chelates exhibi...
Article
The kinetic significance of elementary steps in the liquid-phase reaction of ethylbenzene oxidation inhibited by ionol (2,6-di-tert-butyl-4-methylphenol) was determined with the use of the “value” method. The nature of the effectiveness of ionol from the class of ortho-substituted phenols was considered. It consists in a ponderable role of the reac...
Conference Paper
The method of numerical calculation of kinetic significance (value magnitude) of the individual steps is suggested by means of Hamiltonian systematization multystep chemical reaction model. The given computation method is desplayed on the Chapman analyse model for ozone kinetics, as well as a tools of reduction model of formaldehyde oxidation react...
Article
A conceivable method (“value” method) for analyzing the reaction kinetics models of inhibited liquid-phase oxidation of organic compounds was considered. A procedure for the numerical calculations of the molecular structure parameters of an inhibitor and an inhibitor concentration that results in a maximum inhibition of the reaction was presented....
Article
Full-text available
Copper(II)-, Fe(III)-, and Mn(II)-3,5-di-iso-propylsalicylate (3,5-DIPS) chelates and Cu(II)2(acetyl-3,5-DIPS)4, and 3,5-DIPS acid were examined as antioxidants in scavenging tert-butylperoxyl radical (tert-butylOO). Using kinetic EPR methods it was established that the order of anti-tert-butylOO reactivity is: Mn(II)(3,5-DIPS)2≫Cu(II)2(3,5-DIPS)4∼...
Article
The low-temperature periodical activation of the catalysts based on the metal complexes of nitrogen-containing carbon is observed in the course of isopropylbenzene oxidation. The concentration of the surface hydroperoxide groups responsible for the chain process affects both catalyst deactivation and reactivation. Possible reactions responsible for...
Article
The problem on the impact of media on chemical reactions through changes in dynamic characteristics of reacting molecules is reduced to a transport problem. This problem is solved using Ambartsumyan's invariance principle (IP). The behavior of a bimolecular reaction being continuously "transferred" from a rarefied gas into a dense gas medium and th...
Article
The kinetics of benzaldehyde liquid-phase oxidation is studied in the presence of heterogeneous catalysts, metal-complex compounds of nitrogen-containing carbon. The dependence of the selectivity to perbenzoic acid on kinetic parameters of the reaction is analyzed. It is shown that cobalt complexes of nitrogen-containing carbon are efficient as cat...
Article
The data about the rate constants of the hydrogen atom abstraction for the reactions of tert-butylperoxy radicals (t-BuO˙2) with aldehydes, ethers, and aliphatic amines are summarized in the present work. The rate constants were measured by using a kinetic EPR-technique with a pulse introduction of the reagents. The problem of the reactivity has be...
Article
The data in the literature on the rate constants for reactions of peroxyl radicals with one another in the liquid and gas phases are analyzed. It is found that the reactivity of peroxyl radicals in reactions with one another is determined by the inductive property of the radical's molecular fragment connected with the peroxygroup. If α-hydrogen is...
Article
A new method has been proposed and kinetically justified for measuring the rate of chain initiation in the catalytic liquid-phase oxidation of organic compounds using a heterogeneous inhibitor, namely, tungsten selenide. Radical formation rates were measured in the oxidation of cyclohexene in the presence of a heterogeneous catalyst, namely, mangan...
Article
The products of the interaction of peroxy radicals of ethylbenzene and cyclohexane with a metallocomplex compound of nitrogen-containing carbon based on manganese (MCCNC-Mn) were investigated. Pathways of conversion of the peroxy radicals of ethylbenzene and cyclohexane in interaction with MCCNC-Mn are suggested.
Article
The authors have developed a new method for determining the rate constants for heterogeneous destruction of peroxide radicals in the liquid phase. In the interval 223-253 K in heptane, they have investigated the kinetics of the reaction of tertiary butylperoxide radicals with different heterogeneous catalysts. They have measured the rate constants...
Article
The heterogeneous action of molybdenum compounds: MoB, MoSe/sub 2/, MoSi/sub 2/, Mo/sub 2/C, MoO/sub 3/, Mo on the oxidation of n-decane, ethylbenzene, and nonene-1 has been investigated. A parameter representing the inhibiting effect of the heterogeneous catalyst was calculated theoretically. It was found that NoB, MoSe/sub 2/, and MoSi/sub 2/ inh...
Article
It has been established that copper selenide has a multifunctional effect in the process of cyclohexene oxidation; i.e., it participates in the degenerate branching stage and also in chain breaking. Partial dissolution of the heterogeneous catalyst in the reaction mixture has been observed; this leads to simultaneous occurrence of homogeneous and h...
Article
Analysis of results shows metal selenides (Mo, Ta, Cu) have an inhibiting effect in liquid-phase oxidation of cyclohexene, initiated by azoisobutyric acid dinitrile. MoSeâ participates both in the stage of termination and in degenerate chain branching. 4 references, 2 figures, 2 tables.

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Project
Main objectives of the research are: ● to determine kinetic characteristics and reactive centers at interactions of cobalamines with organic peroxyl radicals, hydroperoxides and peroxides; ● to estimate antioxidant and prooxidant properties of cobalamines at direct interactions with organic oxidizers and in model reaction systems of lipid oxidation on the basis of kinetic studies; ● to identify interactions forms of cobalamines with DNA, their quantitative characteristics; to estimate abilities of cobalamines to prevent or protect DNA against oxidative destruction by means of alkylperoxyl radicals, alkylhydroperoxides and alkylperoxides; ● to reveal interrelatios between the structure of cobalamines under study and their antiradical, antioxidant of possible prooxidant activities.