Browsing by Author "Revenco, Mihail"

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ADSORPTION WAVE OF VAN ADIUM COMPLEX WITH 2,3–DIHYDROXYBE NZALDEHYDE
(Academia de Știinițe a Moldovei, 2009) Kiriyak, Ludmila; Cecoi, Natalia; Cazac, Tatiana; Revenco, Mihail
The polarographic behavior of the complex formed by V(V) and 2,3–ihydroxybenzaldehyde (2,3–DHBA) in the solution containing acetate buffer (pH 5,2) has been investigated. By means of a.c. polaro-graphy, chronovoltammetry and other techniques, it has been shown that the electrode process is complicated by the adsorption of 2,3-DHBA and its vanadium complex. The kinetic and adsorption parameters of the electrode process have been determined: adsorption equilibrium constant B= 1,32⋅105 mol-1⋅dm3, the attraction constant γ = 1,2, the maximum surface concentration Гmax = 9,10⋅10-11 mol⋅ cm-2; the share of the electrode surface occupied by one particle of the adsorbed complex S = 1,81 nm2 and the free adsorption energy ∆G = - 39,1 kJ· mol-1.
ADSORPTION WAVE OF VANADIUM COMPLEX WITH 2,3–DIHYDROXYBENZALDEHYDE
(Institute of Chemistry of ASM, 2009) Kiriyak, Ludmila; Cecoi, Natalia; Cazac, Tatiana; Revenco, Mihail
The polarographic behavior of the complex form ed by V(V) and 2,3–dihydroxybenzaldehyde (2,3–DHBA) in the solution containing acetate buffer (pH 5,2) has been investigated. By means of a.c. polarography, chronovoltammetry and other techniques, it has been shown that the electrode process is complicated by the adsorption of 2,3-DHBA and its vanadium complex. Th e kinetic and adsorption para meters of the electrode process have been determined: adso rption equilibrium constant B= 1,32⋅105 mol-1⋅dm3, the attraction constant γ = 1,2, the maximum surface concentration Гmax = 9,10 ⋅10-11 mol⋅ cm-2; the share of the electrode surface occupied by one particle of the adsorbed complex S = 1,81 nm2 and the free adsorption energy ∆G = - 39,1 kJ· mol-1.
COORDINATION PECULIARITIES OF THE SALICYLALDEHYDE S-METHYLISOTHIOSEMICARBAZONE IN THE PALLADIUM COMPLEXES
(Academia de Ştiinţe a Moldovei, 2006) Revenco, Mihail; Bourosh, Pavlina; Duca, Gheorghe; Simonov, Yurii; Bulmaga, Petru; Jora, Elena; Gdaniec, Maria; Ketrush, Petru
Two coordination modes of salicylaldehyde S-methylthiosemicarbazone (Me-S-HSATSC-NH2) have been observed in the palladium complexes with this ligand. The interaction between Me-S-HSATSC-NH2 and tetrachloropalladate gives rise to the formation of a compound of the composition Pd(Me-S-SATSC-NH2)Cl which one has a planar structure. The organic ligand behaves as a monodeprotonated acid coordinated by O,N,S donor atoms set. This is the only case when the thioalkylated thiosemicarbazone uses the sulfur atom for coordination. The forth position in the coordination polyhedron of the complex is occupied by the chloride ion.figureMolecular structure of [Pd(Me-S-SATSC-NH2)Cl] and [Pd(Me-S-SATSC-N-NO)NO2]When the solution of K2[Pd(NO2)4] was treated with Me-S-HSATSC-NH2, the organic reagent undergoes a more dramatic chemical transformation carrying out to the formation of a new derivative of thiosemicarbazide – nitrozothioamide Me-S-SATSC-N-NO. The newly synthesized organic reagent is a monodeprotonated acid bound via O,N,N donor set, while the alkylated sulfur atom is uncoordinated. The forth site is occupied by NO2-ion coordinated by nitrogen atom (see fig.). The possible causes, driving the system to the formation of nitrosothioamide, and the impact of the anion on the coordination mode of the organic ligand will be discussed.
CRISTOFOR SIMIONESCU
(2007) Duca, Gheorghe; Vlad, Pavel; Gulea, Aurelian; Turtă, Constantin; Batîr, Dumitru; Lupașcu, Tudor; Revenco, Mihail
ELECTROCHEMICAL BEHAVIOUR OF THE LEAD IN THE PRESENCE OF THE PIRUVIC ACID THIOSEMICARBAZONE
(Academia de Ştiinţe a Moldovei, 2006) Cazac, Tatiana; Revenco, Mihail
Continuing our efforts to ind new organic agents for adsorptive accumulation of the toxic metal ions on the mercury dropping electrode, allowing to reduce signiicantly the detection limits, we present here the results of investigation of the electrochemical behavior of the lead ions in the presence of the piruvic acid thiosemicarbazone, APTSC ( see ig.). In water solutions Pb(II) forms in presence of the piruvic acid thiosemicarbazone a complex of the molar ratio Pb:L = 1:2, conirmed by amperometric titration, which one is easily adsorpted on the mercury electrode. On the voltamogramme of the water solutions in the pH range 5-6 the reduction peak of the adsorpted species is observed at the potential -0,5 V. Adsorptive nature of this peak is conirmed by the value of the rate coeficient and by variation of the dropping time with applied potential in separate solutions and their mixtures (see ig.). Interferences of the Zn(II), Cd(II), Ni(II), Co(II), Cl-, Br-, I- CNS-, CH COO-, etc. ions have been investigated and optimized for the maximal manifestation of the Pb(II) signal. The optimal potential for accumulation of the lead ions from solution containing the given thiosemicarbazone is -0,15 V. The maximal admitted time for accumulation is 3 min. For the linear cathodic scanning of the potential (1 V/s), the function Ip=f(CM) is linear in conditions of stationary diffusion and dropping mercury electrode up to the concentration of the lead 2⋅10-6 M. Using the accumulation of the lead species during 180 s on the stationary mercury drop the detection limit diminished to the 3⋅10-8 M. Smaller detection limits should be reached increasing the surface of mercury drops. The main parameters of the adsorption, such as adsorption constant, particles transfer coefficients, free adsorption energy, maximal concentration on the interface, as well as the surface corresponding to one adsorbed particle on the electrode, were determined. Analytical potentialities of the investigated phenomenon for determination of small lead concentration were evaluated.figureFig. Variation of the dropping time with applied potential in solutions of 1) 0.01 M KCl; 2) 0.01 M KCl + 5·10-5 M APTSC 3) 0.01 M KCl+5·10-5M APTSC + 5·10-5 M Pb2.
ELECTROD CU MATRICE POLIMERICĂ, SELECTIV LA SURFACTANTUL ANIONIC LAURILSULFAT
(CEP USM, 2011) Revenco, Mihail; Dîru, Mariana; Dayyih, Waell A.A.
A new anionic surfactant sensor has been prepared, based on trinuclear chromium(III) pivalate as sensing material incorporated into the plasticized PVC-membrane. The sensor exhibited Nernstian response (59-61mV/decade) in the region between 10-3-10-5mol/l for dodecylsulfate. The potentiometric selectivity coefficients were determined by fixed interferential method. Application of these electrodes to the analysis of some products containing anionic surfactants has been realized and results have been compared with the two-phase titration method
THE INTERACTION OF COBALT(II), NICKEL(II) AND COPPER(II) WITH 5- (METHYLENETRIMETYLAMONIUM)SALICYLALDEHYDE THIOSEMICARBAZONE
(Academia de Ştiinţe a Moldovei, 2015) Sîrbu, Angela; Secu, Mihail; Revenco, Mihail
MANGANESE - PROMOTED OXIDATIVE DIMERIZATION OF THE SALICYLALDEHYDE THIOSEMICARBAZONE: STRUCTURE AND MAGNETIC STUDIES
(Academia de Ştiinţe a Moldovei, 2012) Palamarciuc, Oleg; Clerac, Rodolphe; Revenco, Mihail; Bourosh, Pavlina; Kravtsov, Victor
MONITORING THE REACTIVITY OF THE COORDINATED THIOSEMICARBAZONES USING PHYSICAL METHODS
(Academia de Ştiinţe a Moldovei, 2012) Revenco, Mihail
NITRATE-SELECTIVE ELECTRODES BASED ON THE TRINUCLEAR CHROMIUM(III) PIVALATES
(Academia de Știinițe a Moldovei, 2008) Revenco, Mihail; Martin, Mariana; Dayyih, Waell A.A.
The paper describes the analytical potentialities of the trinuclear chromium(III) complexes as potentiometric ionophores for the construction of electrodes sensitive to the presence of nitrate anion. The electroactive material containing 4,4’-bipyridil was synthesized in situ. The membrane was prepared using dioctylphthalate as a solvent mediator and poly (vinyl chloride) as a polymeric matrix. The electrodes presented a slope of 56 mV/decade, a low limit of detection (3,2.10-6 mol/l), an adequate lifetime (4 months), and suitable selectivity characteristics when compared with other nitrate electrodes. The good parameters of this electrode made possible its application to the determination of nitrate in different types of fertilizers.
NITRATE-SELECTIVE ELECTRODES BASED ON THE TRINUCLEAR CHROMIUM(III) PIVALATES
(Institute of Chemistry of ASM, 2008) Revenco, Mihail; Martin, Mariana; Dayyih, Waell A.A.
The paper describes the analytical potentialities of the trinuclear chromium(III) complexes as potentiometric ionophores for the construction of electrodes sensitive to the presence of nitrate anion. The electroactive material containing 4,4’-bipyridil was synthesized in situ. The membrane was prepared using dioctylphthalate as a solvent mediator and poly (vinyl chloride) as a polymeric matrix. The electrodes presented a slope of 56 mV/decade, a low limit of detection (3,2.10-6 mol/l), an adequate lifetime (4 months), and suitable selectivity characteristics when compared with other nitrate electrodes. The good parameters of this electrode made possible its application to the determination of nitrate in different types of fertilizers.
THE ROLE OF PHYSICAL METHODS IN INVESTIGATION OF METAL-PROMOTED REACTIONS
(Academia de Ştiinţe a Moldovei, 2006) Revenco, Mihail
In the so-called metal-promoted reactions the role of the metal is to contribute to the progress and development of the given process. The reactions concerning the transformations of the organic reagents involved in the formation of the complexes, will be discussed in this presentation. More attention will be paid to the metal controlled reaction accompanied by: § assemblage of the organic ligsons into new chemical edifice; § change of the reactivity of the different functional groups and their transformations; § redox transformations of the organic reagent; § stabilization of unusual configurations. Unlike the catalytic reactions, in the metal-promoted transformations, consumption of the metal is possible, when it is able to form a stable compound with the reaction product. Sometimes the metal ion can be found at the end of the reaction as a component of a newly formed metal complex with an unusual composition and structure. Determination of the composition and structure of the final product using only chemical methods is sometimes impossible, because of unexpected development of the process and deviation from the general chemical standards. In these cases the usual logical conclusions can lead into labyrinth, whence it is difficult to go out. The credible results can be obtained only using a large set of physical methods based on different phenomena, and able to supply undoubted experimental data. The priority in this sense belongs to the X-ray methods for the cases when the suitable crystals are available. Nevertheless the localization de facto of the atoms in molecular structure is sometimes insufficient to judge about oxidation state of the central atom or organic ligand. The spectral methods are more suitable for this purpose. The ESR spectroscopy is used for the paramagnetic systems to establish the localization of the odd electrons and the oxidation states of the protagonists. Some cases when this method gives inadequate data will be presented. The possibilities of the NMR methods for identification of the composition of the complexes, and their priority in the case of diamagnetic compounds, is discussed The role of mass-spectroscopic methods is underlined for the non-crystalline systems. Depending on the ionization sources, this method is used for a large number type of compounds. The possibility to investigate the compounds in gas phase as well as in solutions is an advantage of MS methods.
SENZOR POTENŢIOMETRIC SALICILAT-SENZITIV PE BAZĂ DE PIVALAŢI TRINUCLEARI AI CROMULUI(III)
(CEP USM, 2008) Revenco, Mihail; Martin, Mariana; Gavriliţa, Anatolie; Dayyih, Wael Ahmad Abu
New salicylate-selective electrodes based on trinuclear chromium(III) pivalates are described. The electrodes were prepared by incorporating the ionophores into plasticized poly(vinylchloride) membranes. The electrode displays a linear –log [C 7H6O3-] vs emf response over the concentration range 3,2.10-6 – 1.10-1 M in buffer solutions of pH 7, with a Nernstian slope of 56 mV/decade of salicylate concentration. The electrodes exhibit fast response times and micromolar detection limits and could be used over a wide pH range of 7 – 11. The proposed electrode was applied to determine the salicylates in real samples.
SINTEZA, STRUCTURA ȘI PROPRIETĂȚILE COMPUȘILOR COORDINATIVI AI CUPRULUI(II) CU UNELE TIOSEMICARBAZONE SOLUBILE ÎN APĂ
(2020) Sîrbu, Angela; Revenco, Mihail
Scopul lucrării: studiul proceselor de formare şi separare ale compuşilor coordinativi ai cuprului(II) cu tiosemicarbazonele aldehidelor 5-sulfosalicilice și 5-metilentrimetilamoniusalicilice, stabilirea structurii, proprietăţilor compuşilor obţinuţi şi determinarea posibilităților de valorificare a proprietăţilor lor utile.
STRUCTURE AND ANTIMICROBIAL ACTIVITY OF THE COPPER(II) COMPLEX WITH 8-FORMYLQUINOLINE 4-ETHYL-THIOSEMICARBAZONE
(Academia de Ştiinţe a Moldovei, 2012) Bourosh, Pavlina; Stratulat, Elena; Corja, Ion; Dizdari, Anna; Gdaniec, Maria; Revenco, Mihail; Prisakari, Viorel I.
STRUCTURE OF PALLADIUM COMPLEXES WITH 8-QUINOLINEALDEHYDE THIOSEMICARBAZONE
(Academia de Ştiinţe a Moldovei, 2006) Bourosh, Pavlina; Bulmaga, Petru; Revenco, Mihail; Jora, Elena; Gdaniec, Maria; Simonov, Yurii A.
The coordination compounds of palladium(II) with 8-quinolinaldehyde thiosemicarbazone (HQATSC) have not been described yet. When a solution of K2[PdCl4] is treated with an equimolar amount of HQATSC in warm ethanol or dimethylformamide a yellow crystalline precipitate of Pd(QATSC)Cl is formed. The solubility of the resulted compound in DMF is increased when thiourea (Thio) is added. During 3 days yellow well defined crystals were formed and selected for X-ray investigation. The composition of the separated crystals can be described with a conventional formula Pd(QATSC)Cl⋅1,5Thio⋅H2O. A detailed X-ray investigation showed that the product is a new type of palladium complexes with HQATSC, formed by the cation [Pd(QATSC)(Thio)]+, Cl- anion, water and thiourea uncoordinated molecules. This result suggests that increasing of the ion solubility in the presence of Thio is due to the substitution of the chloride-ion from the inner sphere by thiourea molecule, resulting in formation of a cation-anion type of the complex. The structure of the complex cation is presented in the figure. The square-planar coordination of Pd(II) is provided by two nitrogen atoms and sulfur atom of the monodeprotonated residue of 8-quinolinealdehyde thiosemicarbazone. The bond distances in the palladium coordination polyhedron are: Pd(1)N(1) 2.116(4), Pd(1)-N(2) 2.013(4), Pd(1)-S(1) 2.44(1), PdS(1A) 2.336(1) Å. The real composition of the complex is [Pd(Q ATSC)(Thio)]Cl.0,5Thio.0.5H2O. The non-coordinated Thio and H2O molecules are randomly disordered over two positions with occupancy factors equal to 0.5. The components are involved into system of hydrogen bonds, and the composition should be formally described by the dimeric formula [Pd(QATSC)(Thio)]2Cl2 .Thio.H2O.
THIOCYANATE ION-SELECTIVE PVC MEMBRANE ELECTRODE
(Academia de Știinițe a Moldovei, 2010) Revenco, Mihail; Martin, Mariana; Dayyih, Waell Abu
A potentiometric selective sensor based on trinuclear chromium(III) complex as a novel ionophore for the thiocyanate-selective electrode is reported. The sensor displays a near Nernstian slope of 57 ± 2 mV per decade, over a wide pH range 3 - 11. The working concentration range of the electrode is 1.10-5 – 1.10-1 mol/L with a detection limit of 5. 10-6 mol/L. The sensor has a response time of 20 s and can be used for at least 6 months without any considerable fluctuation of the potential. The selectivity coeffi cients determined at using the fi xed interference method indicate a good discriminating ability towards other anions. The prepared sensor was applied as an indicator electrode in the titration of thiocyanate with Ag+.
THIOCYANATE ION-SELECTIVE PVC MEMBRANE ELECTRODE
(Institute of Chemistry of ASM, 2010) Revenco, Mihail; Martin, Mariana; Dayyih, Waell Abu
A potentiometric selective sensor based on trinuclear chromium(III) complex as a novel ionophore for the thiocyanate-selective electrode is reported. The sensor displays a near Nernstian slope of 57 ± 2 mV per decade, over a wide pH range 3 - 11. The working concentration range of the electrode is 1.10-5 – 1.10-1 mol/L with a detection limit of 5.10-6 mol/L. The sensor has a response time of 20 s and can be used for at least 6 months without any considerable fluctuation of the potential. The selectivity coefficients determined at using the fixed interference method indicate a good discriminating ability towards other anions. The prepared sensor was applied as an indicator electrode in the titration of thiocyanate with Ag+.