bluuebunny/crossref_metadata_2025 huggingface dataset:
Preconcentration method for trace metals in natural waters using 4-morpholine dithiocarbamate
Authors: Todorovic Zoran , Polic Predrag , Sabo Tibor , Cakic Milorad
Published: August 2005

The optimum conditions were found for the preconcentration of trace metals in natural waters and model samples with standard metals concentrations by using 4-morpholine dithiocarbamate. The formed complexes were extracted with chloroform. Different methods for recovering the metals from the organic solvent were studied and compared before AAS metal analysis. The developed preconcentration method was successfully applied to the determination of trace metals concentrations in water samples from the "Barje" lake (Leskovac, Yugoslavia).
Residues of atrazine in agricultural areas of Serbia
Authors: Gasic S. , Budimir M. , Brkic Dragica , Neskovic N.
Published: August 2005

In this paper the results of a five-year investigation of the pollution of soil, as well as of surface and groundwater by atrazine are reported. The soil samples were collected from different localities, from the tillage level, at two depths (0?15 and 15?30 cm) during the period September-November from 1995 to 1999. The surface and groundwater samples were taken from the same localities during the same period. The residues were detected by the ELISA test. The results showed that almost all the analysed soil samples contained residues of atrazine. These quantities varied from 0.02 to 0.10 mg/kg (0?15 cm), and up to 0.05 mg/kg (15?30 cm) depending on the locality, soil type and the year of investigation. Concerning the residues in the surface and groundwater, it was found that most of the analysed samples contained atrazine residues. In the case of the surface water, the quantity of the residues ranged from 1.0 to 4.13 ?g/L whille the ground water contained up to 0.3 ?g/L depending on the locality and the year of investigation.
Hydrogen bonding in push-pull 5-substituted-2-alkylidene-4-oxothiazolidines: 1H-MNR spectroscopic study
Authors: Markovic R. , Shirazi A. , Dzambaski Zdravko , Baranac Marija , Minic-Popovic Dragica
Published: August 2005

Application of dynamic 1H-NMR spectroscopy added to the understanding of the hydrogen bonds existing in the structurally related 5-substituted-2-alkylidene-4-oxothiazolidines in polar and apolar solvents. The equilibrated mixtures of these typical push-pull alkenes in CDCl3 consist of the intramolecularly H-bonded (E)-isomer and intermolecularly H-bonded (Z)-isomer in varying proportions which depend on the solvent polarity. For the representative of the series (Z)-2-(5-ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-1-phenylethanone a concentration effect on the degree of intermolecular hydrogen bonding in apolar CDCl3 has been studied.
Rheokinetic study of crosslinking of α,ω-dihydroxy oligo(alkylene maleate)s with a trisisocyanate
Authors: Dunjic Branko , Djonlagic Jasna , Vukasinovic Slavko , Sepulchre Maurice , Sepulchre Marie-Odile , Spassky Nicolas
Published: August 2005

The crosslinking reaction of three series of ?,?-dihydroxy oligo(alkylene maleate)s with a trifunctional isocyanate was followed by dynamic mechanical analysis and FTIR spectroscopy. The evaluation of rheological parameters such as storage G? and loss modulus G", was recorded. A typical G?versus time curve has a characteristic "S" shape, indicating autoacceleration of the crosslinking reaction. The whole curing process starting from G?equal G", or the beginning of gelation is described by a second - order phenomenological rheokinetic equation which takes into account the autoacceleration effect, the latter being a consequence of the superposition of both the chemical reaction and phase segregation. It appears that the crosslinking reaction rate depends on the concentration of the functional groups, i.e., on the molecular weight of the polyester prepolymer and on the length of the aliphatic sequence in the repeating unit or the segmental mobility. The crosslinking rate decreases in the order: poly(octamethylene maleate) > poly(hexamethylene maleate) > poly(butylene maleate).
Electrochemical oxidation of carbon monoxide: From platinum single crystals to low temperature fuel cells catalysts - Part II: Electrooxidation of H2, CO and H2/CO mixtures on well characterized PtMo
Authors: Grgur Branimir , Markovic Nenad , Ross Philip
Published: August 2005

The oxidation of hydrogen and hydrogen?carbon monoxide mixture has been investigated on well-characterized metallurgically prepared platinum?molybdenum (PtMo) alloys. It was concluded that the optimum surface concentration of molybdenum is near 23 mol.%. Based on experimentally determined parameters and simulations, the mechanism of the oxidation of CO/H2 mixtures is discussed.
Acid-catalyzed and photolytic reactivity of some unsaturated B-nor-5, 10-secosteroidal ketones
Authors: Bjelakovic Mira , Pavlovic Vladimir , Dabovic Milan , Lorenc Ljubinka
Published: August 2005

The acid-catalyzed reaction of (Z)- and (E)-B-nor-5,10-seco-ketones 2 and 3 resulted in an intramolecular cyclization to give the 5-hydroxy-A-nor-1?,5?-10(19)-methylidene derivative 8, the 5?-hydroxy-A-nor-1(10)-unsaturated compound 9 and the 5?,10?-dihydroxy A-nor-product 10, from the (Z)-isomer and the 5-hydroxy-A-nor-1?,5?-10(19)-methylidene product 11, from the (E)-isomer. Upon UV-irradiation, the (Z)- and (E)-seco-ketones 2 and 3 underwent a reversible (Z)/(E) and (E)/(Z)-isomerization and in addition to a transannular photocyclization to afford the 10(19)-methylidene derivatives 8 and 11, respectively, while photolysis of the 10(19)-methylidene-B-nor-5,10-seco-ketone 4 gave the oxetane derivative 12.
Roughness development in electrodeposited soft magnetic CoNiFe films in the presence of organic additives
Authors: Tabakovic Ibro , Riemer Steve
Published: August 2005

The effects of three additives, sodium lauryl sulfate (NaLS), saccharin (Sacc), and NaLS + Sacc, on roughness development during the electrodeposition of CoNiFe films were investigated. The characterization of these films by atomic force microscopy shows that the electrodeposits produced from NaLS containing solution result in a rough surface. The role of NaLS surfactant is to change the interfacial tension and clean non-polar species like hydrogen bubbles from the surface. In Sacc containing solution the evolution of a smooth surface is controlled by adsorbed Sacc molecule at the interface. The kinetic roughening of these deposits was investigated by dynamic scaling analysis. It was demonstrated that the roughness of CoNiFe films, obtained in the presence of NaLS + Sacc additives, was also dependent on current density, roughness of substrate, and the temperature of plating bath.
Thermokinetic study of the inactivation reaction of 1-methyl phthalazinium ylids
Authors: Carposu Maria , Odochian Lucia , Dima St. , Dumitras M. , Petrovanu Magda
Published: August 2005

The present paper consists in a thermokinetic study on the dimerization reactions of 1-methylphthalazinium ylids with ?NO2 (ylid 1) and respectively, ?O?CH3 (ylid 2) substituents in the p position of the benzoyl radical bound to the ylidic carbanion. From experimental data, the reaction order and rate constants have been calculated. The reaction order n = 2 confirmed the ylids? dimerization reactions, while the values of the rate constants, k2 = 3.093x10-2L/mol s and, respectively, 2.16 x?10-1 L/mol s for the dimerization of ylids 1 and 2 made evident the higher reactivity of ylid 2 versus ylid 1. The same conclusion is also supported by the results of the thermodynamic study based on the chemical affinity of the two reactions, when Ao dim,1 < Aodim,2.
Gas chromatographic retention indices for N-substituted amino s-triazines on capillary columns - Part IV: Influence of column polarity on retention index
Authors: Mijin Dusan , Antonovic Dusan , Boncic-Caricic Gordana , Jovanovic Bratislav , Rajkovic Olga
Published: August 2005

The retention index increment for the addition of a methylene group to the alkyl group of an analyte molecule is shown to be lower than 100 i.u. for N-substituted amino s-triazines. In temperature programmed gas chromatography, a linearly interpolated retention index I, determined from the linear regression equation, I = AZ + (GRF)z, with the number of atoms (Z) in the molecule as variable, was used to describe the retention of 25 N-substituted amino s-triazines, on DB-1, DB-5 and DB-WAX capillary columns divided into five series according to the similarity of the alkyl groups in the particular series. In the above equation, A is the linear regression coefficient or the retention index increment per atom addition, Z the number of C,N and Cl atoms in the molecule, and (GRF)z the group retention factor or functionality constant for functional groups in the molecule, based on the number Z. It is possible to estimate the retention indices of an unknown member of the series from the Z, A and (GRF) values.
Extraction and separation studies of Ga(III), In(III) and Tl(III) using the neutral organophosphorous extractant, Cyanex-923
Authors: Pawar S.D. , Dhadke P.M.
Published: August 2005

The neutral extractant, Cyanes-923 has been used for the extraction and separation of gallium(III), indium(III) and thallium(III) from acidic solution. These metal ions were found to be quantitatively extracted with Cyanex-923 in toluene in the pH range 4.5?5.5, 5.0?6.5 and 1.5?3.0 respectively, and from the organic phase they can be stripped with 2.0 mol dm-3 HNO3, 3.0 mol dm-3 HNO3 and 3.0 mol dm-3 HCl, respectively. The effect of pH equilibration period, diluents, diverse ions and stripping agents on the extraction of Ga(III), In(III) and Tl(III) has been studied. The stroichiometry of the extracted species of these metal ions was determined on the basis of the slope analysis method. The reaction proceed by solvation and the probable extracted species found were [MCl3. 3Cyanex-923]?[where M = Ga(III) or In(III)]?and [HTlCl4. 3Cyanex-923]. Based on these results a sequential procedure for the separation of Ga(III), In(III) and Tl(III) from each other was developed.
Radiolytic splitting of water molecules in the presence of some supramolecular compounds
Authors: Cecal Aleksandru , Paraschivescu Andrei , Popa Karin , Colisnic Dan , Timco Grigore , Singenerean Lidia
Published: August 2005

This paper deals with the study of the hydrogen output during the catalyzed radiolysis of water in the presence of the supramolecular compounds Fe2NiO(TMAc)6.3HTMAc, FeCoO (TMAc)6. 3HTMAc, [Cr3O(C6H5COO)6]?? ClO4 Fe3Ni2O(OH)(TMAc)7(Aacet)3, Ni2(H2O) (TMAc)4(HTMAc)4 [Cr3O(TMAc).3H2O](TMAc), and Cr8F8(TMAc)16. A60Co ?-source of 5.1x1014 Bq activity at a rate dose of 8.038 kGy h-1 was used. The radiolysis products were determined by mass spectrometry. For a given irradiation time, it was found that quantity of hydrogen obtained by water radiolysis is 6 ? 18 times greater in the presence of the supramolecular compounds as catalysts than in their absence from the irradiated system.
Kinetic and structural aspects of tantalum hydride formation
Authors: Simonovic B.R. , Mentus Slavko , Dimitrijevic Radovan
Published: August 2005

Tantalum hydrides of various composition were synthesized by equilibrating tantalum with hydrogen at six different temperatures from 573 to 823 K under a constant hydrogen pressure of 1 bar. Both the exact Ta/H mole ratios and the kinetic parameters of hydriding were determined on the basis of the dependence of the H/Ta mole ratio on time. The influence of stoichiometry on the appearance of X-ray powder diffractograms at room temperature was studied. As a consequence of hydriding, for ratios H/Ta > 0.2, the original bcc Ta-lattice undergoes distortion, manifesting itself as both a shift and a splitting of the X-ray patterns in the X-ray diffractograms. For samples with H/Ta < 0.2, the appearance of some superstructure reflections at low Bragg angles was noted, which suggests a long range ordering of hydrogen with orthorhombic symmetry.
Calculation of activities in some gallium-based systems with a miscibility gap
Authors: Manasijevic Dragan , Zivkovic Dragana , Katayama Iwao , Zivkovic Zivan
Published: August 2005

The calculations of thermodynamic properties in some gallium-based systems with a miscibility gap ? Ga?Tl, Ga?Hg and Ga?Pb are presented in this paper. The determination of the gallium activities in the mentioned liquid alloys was based on their known phase diagrams using the Zhang-Chou method for calculating activities from phase diagrams involving two liquid or solid coexisting phases. The activities of gallium in Ga?Tl, Ga?Hg and Ga?Pb system were calculated in the 973?1273 K, 573?873 K and 1000?1100 K temperature ranges, respectively. The activities of the other component in all the investigated systems were obtained by the Gibbs-Duhem equation. The results of the calculations are compared with literature data.
FTIR study on N-H·hydrogen bonding: N-alkylpropanamides - aromatic donor system
Authors: Nikolic Aleksandar , Mladenovic Marko , Gobor Ladislav , Antonovic Dusan , Petrovic Slobodan
Published: August 2005

This paper reports the results of an FTIR study in the region of the fundamental NH stretching vibration for N-methyl, N-isopropyl, N-tert-butyl and N-1,2,2-trimethylpropanamide ? aromatic hydrocarbon systems. In addition to the spectroscopic parameters, the equilibrium constant for the 1:1 N-H???? complexes (at 298 K) are given.
Spectral and thermal behaviors of rare earth element complexes with 3,5-dimethoxybenzoic acid
Authors: Ferenc Wieslawa , Walkóv-Dziewulska Agnieszka , Chrusciel Janusz
Published: August 2005

The conditions for the formation of rare earth element 3,5-dimethytoxybenzoates were studied and their quantitative composition and solubilities in water at 293 K were determined. The complexes are anhydrous or hydrated salts and their solubilities are of the orders of 10-5 ? 10-4 mol dm-3. Their FTIR, FIR and X-ray spectra were recorded. The compounds were also characterized by thermogravimetric studies in air and nitrogen atmospheres and by magnetic measurements. All complexes are crystalline compounds. The carboxylate group in these complexes is a bidentate chelating ligand. On heating in air to 1173 K, the 3,5-dimethoxybenzoates of rare earth elements decompose in various ways. The hydrated complexes first dehydrate to form anhydrous salts which then decompose in air to the oxides of the respective metals while in nitrogen to mixtures of carbon and oxides of the respective metals. The complexes are more stable in air than in nitrogen.
A glucan from active dry baker’s yeast (Saccharomyces cerevisiae): A chemical and enzymatic investigation of the structure
Authors: Zlatkovic Dragan , Jakovljevic Dragica , Zekovic Djordje , Vrvic Miroslav
Published: August 2005

The structure of a polysaccharide consisting of D-glucose isolated from the cell-wall of active dry baker?s yeast (Saccharomyces cerevisiae) was investigated by using methylation analysis, periodate oxidation, mass spectrometry, NMR spectroscopy, and enzymic hydrolysis, as a new approach in determination of structures. The main structural feature of the polysaccharide deduced on the basis of the obtained results is a linear chain of (1?3)-linked ?-D-glucopyranoses, a part of which is substituted through the positions O-6. The side units or groups are either a single D-glucopyranose or (1?3)-?-oligoglucosides, linked to the main chaing through (1?6)-glucosidic linkages. The low optical rotation as well as the 13C-NMR and FTIR spectra suggest that the glycosidic linkages are in the ?-D-configuration.
Immobilization of periodate oxidized invertase by adsorption on sepiolite
Authors: Prodanovic Radivoje , Simic Milos , Vujcic Zoran
Published: August 2005

Periodate oxidized invertase was immobilized by adsorption on sepiolite. The obtained immobilized enzyme was more resistant to washing out by concentrated salt solution, and had an eight times higher half-life at 60 ?C than adsorbed native invertase. In packed bed reactor 50 % conversion of 500 g/dm3 sucrose at 40 ?C and a flow rate of 1 bv/h was achieved. The specific productivity of the immobilized invertase was O.187 kg/dm3/h.
The effect of microalloying with silicon and germanium on microstructure and hardness of a commercial aluminum alloy
Authors: Maksimovic Vesna , Zec Slavica , Radmilovic Velimir , Jovanovic Milan
Published: August 2005

The effect of small additions of Si and Ge on the microstructure and hardness was investigated during aging of a commercial 2219 aluminum alloy. It was found that for the same level of microalloying in alloy 2219SG (containing Si and Ge), a maximum hardness was achieved 3 times faster than in alloy 2219S (without Ge). The accelerated precipitation kinetics is a consequence of the presence of fine Si?Ge particles, serving as heterogeneous precipitation sites for ?" strengthening particles.
HPLC methods for the determinatiuon of acetyl- and benzoyl-tiazofurin in rat plasma
Authors: Petrovic Ljiljana , Piperski Vesna , Ristic Slavica , Tasic Jelena , Matovic Vesna , Jokanovic Milan
Published: August 2005

Reverse-phase HPLC methods for determination of 5?-O-acetyl-tiazofurin (AT) and 5?-O-benzoyl-tiazofurin (BT) in rat plasma were developed and validated in terms of specificity, linearity, precision, accuracy and sensitivity. Linear calibration curves were constructed in the concentration range of 2.50 ? 100.00 ?mol/L for both compounds. The separations were achieved on a Supelcosyl LC-18-DB analytical column (250x4.6 mm; 5_?m particle size) by isocratic elution, with a mixture of 0.1Mdisodium hydrogen phosphate ? methanol. UV detection was performed at a wavelength of 254 nm. The proposed methods enable the detection and quantification of nanomolar concentrations of AT and BT in rat plasma.
Photochemistry of aromatic ketones in sodium dodecyl sulphate micelles in the presence of unsaturated fatty acids
Authors: Markovic Dejan
Published: August 2005

Laser-flash photolysis has been employed to characterize the behaviour of the free radicals created in the photochemical reaction of benzophenone (BZP), as well as of its lipoidal derivative, benzophenone-4-heptyl-4?-pentanoic acid (BHPA), with chosen unsaturated fatty acids in sodium dodecyl sulphate micelles. The calculated rate constants were used to study the "cage effect" i.e., the recombination of the created radical-pairs (BZP, BHPA ketyl radical - lipid radical) inside the highly limited space of the SDS micelles. The "cage effect" appears to be the dominant event inside SDS micelles, dependent on the structure of both the reactants-precursors. The fractions of the initially created radical-pairs which escape the "cage effect" and exit into the surrounding aqueous phase do not exceed 16 %. This fact is of enormous importance for the self-control of the pathogenic process of lipid peroxidation.
Unexpected cycloreversion of a tosylated sugar oxetane under E2 conditions: The facile formation of 2-(2-furanyl)-1, 3-dioxolane from a novel 2, 5:4, 6-dianhydro-L-idose derivative (Preliminary commun
Authors: Popsavin Velimir , Radic Ljubica , Popsavin Mirjana , Cirin-Novta Vera
Published: August 2005

2,5:4,6-Dianhydro-3-O-p-toluenesulfonyl-L-idose ethylene acetal (4) was synthesized with the aim of studying its chemical behaviour in the presence of several basic agents (Bu4NF/MeCN, NaOMe/MeOH, KOBut/ButOH/THF, and NaH/DMSO). Treatment of 4 with sodium hydride in dimethyl sulphoxide at room temperature unexpectedly gave the 2-(2-furanyl)-1,3-dioxolane. The mechanism of the process presumably involved the initial conversion of 4 to the corresponding 2,3-unsaturated derivative 5, followed by a facile oxetane ring cycloreversion by the elimination of formaldehyde.
Investigation of Pd-catalysed Co(III)-EDTA/hypophosphite inhibition: Reaction kinetics, mechanism and the evaluation of its analytical application possibilities
Authors: Bicer N. , Gürkan R. , Akcay M. , Altunata T.
Published: August 2005

The reaction between Co(III)-EDTA and hypophosphite ion, catalyzed by Pd(II) was chosen as the indicator reaction. The inhibition kinetics of this catalytic reaction have been investigated by a mechanistic approach in the presence of some inhibitors. Catalysts other than PdCl2, that is Pt, Au, Ni salts, did not exhibit any effect on the reaction. An original reaction mechanism is proposed based on the experimental data. The important variables were optimized for maximum sensitivity. The calibration graph, which was prepared following the inhibition kinetic method, showed a linear relationship (r = ? 0.9878) between the initial rate and iodide in the concentration range of 2?35 ng/cm3 I- with a detection limit of 1.2 ng/cm3 I (3Sb/m criterion). The RSDs of the method, (N = 5) for 7 and 14 ng/cm3 were 1.19 and 0.81 %, respectively, depended on iodide concentration. The method was only applied to the determination of iodide in water, urine, iodized table salt and some drug samples and was compared with the modified Sandell?Kolthoff method.
The adsorption characteristics and porous structure of bentonite adsorbents, determined from the adsorption isotherms of benzene vapor
Authors: Brezovska Snezana , Marina Biljana , Panova Biljana , Burevski Donco , Bosevska Vasa , Stojanovska Lepa
Published: August 2005

The adsorption of benzene vapor on natural and acid activated bentonites was treated by the theory of volume filling of micropores. The micropore volume and characteristic values of the free energy of adsorptionwere determined from the adsorption isotherms. The Dubinin?Radushkevish?Stoeckli and Dubinin?Astakhov equations were used for this purpose. The results showed that natural bentonite has a more homogeneous micropore structure than the acid activated ones. The characteristic values of the free energy of adsorption for the natural bentonite were higher than those of the acid activated bentonite. This is due to differences in its structure and the pore size.
Electrochemical formation and characterization of Ag2O
Authors: Jovic Borka , Jovic Vladimir
Published: August 2005

The process of Ag2O formation has been investigated in 0.1M, 0.3 M, 1.0Mand 2.0 M NaOH solutions on polycrystalline Ag electrodes by cyclic voltammetry potentiostatic pulse and SEM techniques. The SEM micrographs of the chemically polished Ag surface and the surface after oxide formation revealed considerable roughening of the Ag surface after Ag2O formation and reduction. The roughening was more pronounced at higher NaOH concentrations, indicating that only the first cycle or pulse applied on a freshly polished Ag electrode should be considered in mechanistic studies of Ag2O formation. In the given range of NaOH concentrations, it was shown that the process is not controlled simply by the diffusion of the reacting species.Anucleation phenomenon was clearly detected in all the examined solutions. The SEM micrographs confirm that the two anodic peaks, present on the voltammograms of Ag2O formation correspond to two types of oxide film, i.e., non-homogeneously and homogeneously distributed ones. Potentiostatic formation of the oxide at potentials corresponding to the first and second anodic peak yielded simple cubic Ag2O but of very different grain size.
The effect of β-cyclodextrin and pH on bifonazole hydrosolubility
Authors: Popovic Gordana , Cakar Mira
Published: August 2005

The equlibria of bifonazole in saturated water solution within the pH range 4 to 10 [I = 0.1 mol/dm3 (NaCl); 25 ?C] were studied spectrophotometrically. Based on the equlibrium constants determined in a heterogeneous system, the acidity constant (pKa = 5.72) and solubility in water (S=10-5.79+10-(pH + 0.07))were calculated. The influence of ?-cyclodextrin on bifonazole solubility was examined in the presence of 10-3 and 10-4 mol/dm3 ?-cyclodextrin. At pH values over 8, bifonazole solubility was two- and 13-fold increased in the presence of 10-4 and 10-3 mol/dm3 ?-cyclodextrin respectively, compared to its solubility in water. The ratio of bifonazole solubility in the presence of ?-cyclodextrin and that in water decreased in parallel to the increase of acidity.
Physico-chemical studies of some aminobenzoic acid hydrazide complexes
Authors: El Abd , El Abd , El Gamel , El Abd
Published: August 2005

The stability constants and related thermodynamic functions characterizing the formation of divalent Ni, Cu, Zn, Cd and Hg complexes with o- and p-aminobenzoic acid hydrazide were determined potentiometrically at different temperatures. The formations of the complexes are endothermic processes. The formed bonds are mainly electrostatic. Conductometric titration was carried out to determine the stoichiometry and stability of the formed complexes. The structures of complexes were characterized by their IR, 1H-NMR and 13C-NMR spectra, as well as X-ray diffractograms. The coordination process takes place through the carbonyl group and the terminal hydrazinic amino group. The thermal stability of the complexes was followed in the temperature range 20?600 ?C.
Physicochemical and structural characteristics of HEU-type zeolitic tuff treated by hydrochloric acid
Authors: Radosavljevic-Mihajlovic Ana , Dondur Vera , Dakovic Aleksandra , Lemic Jovan , Tomasevic-Canovic Magdalena
Published: August 2005

Samples of natural HEU-type zeolites ? clinoptilolite-Ca, from the Novakovici deposit (near Prijedor, Bosnia and Herzegovina) were treated with the hydrochloric acid of various concentrations (from 10-3Mto 2M). Zeolitic tuffs before and after the acid treatment were examined using IR, XRPD, and chemical analyses. The changes in the crystal structure of acid treated samples showed a significant reduction in the crystallinity of zeolitic tuffs (60?70 %), which were effected by hydrochloric acid with concentrations of 1 M and above.
Pectinases partitioning in aqueous two-phase systems: An integration of the systems poly(ethylene glycol)crude dextran and poly(ethylene glycol)ammonium sulphate
Authors: Antov Mirjana , Pericin Draginja , Pejin Stana
Published: August 2005

The partitioning of pectinases in the poly(ethylene glucol)4000/ammonium sulpohate system was studied and also its application for enzymes extraction from the top phase of the poly(ethylene glucol)4000/crude dextran system. Almost complete one-sided partition of endo-pectinase and exo-pectinase to the bottom phase of the polymer/salt system was achieved at a tie-line length of 37.16 %. The concentration factors were 1.73 and 3.25, respectively. The highest total endo- and exo-pectinase yields (72.41 % and 69.46 % respectively) were obtained by integration of the polymer/polymer system at a tie-line of 8.61 % and a high phase volume ratio and the polymer/salt system at a tie-line of 30.23%and a low phase volume ratio. Integration of the partitioning at a high tie-line length in the polymer/polimer and a low tie-line length in the polymer/salt system resulted in a total concentration factor of 1.5 and a purification of 1.66 fold for exo-pectinase. The addition of phosphate to this integrated system improved the total concentration factor and purification fold of the activity to 1.73 and 2.14, respectively.
Regioselectivity of the bromination of 1-oxo-1, 2, 3, 4-tetrahydronaphthalene and 6, 7-dimethyl-1-oxo-1, 2, 3, 4-tetrahydronaphthalene, and thiabiscyclanones synthesis on their basis
Authors: Pankratov Alexei , Fedotova Olga , Barabanova Antonina , Alyonkina Tatiana , Eliseev Yuri
Published: August 2005

On the basis of quantum chemical (PM3 andRHF/6-31G*) study, the regioselectivity of the bromination of 1-oxo-1,2,3,4-tetrahydronaphthalene (1) and 6,7-dimethyl-1-oxo-1,2,3,4-tetrahydronaphthalene (2) at their alicyclic and aromatic fragments was quantum chemically substantiated and confirmed experimentally. It was found that the above compounds undergo aromatic at the ?-methylene position. The conditions for bromination at the positions 5, 8 of benzannelated ring were established. For the first time non- and 2,2?-dibromosubstituted with respect to the oxo group bis(6,7-dimethyl-1-oxo-1,2,3,4-tetrahydronaphth-2-yl) sulphides (7, 8a, b) were obtained. The latter were found to show promise as stabilizing agents for the storage of cholera sera.
Dynamical mechanical analysis of photocrosslinked hyperbranched urethane acrylates
Authors: Dzunuzovic Enis , Tasic Srba , Bozic Branislav , Babic Dragan , Dunjic Branko
Published: August 2005

A series of acrylate functionalized samples based on hyperbranched hydroxy-terminated polyesters with different molecular weights and different degrees of acrylation were synthesized. The obtained urethane acrylates were slightly yellow viscose liquids. Their composition was characterized by FTIR and 1H-NMR spectroscopy and their molecular weights were measured by GPC. All the synthesized samples were diluted with 25 wt.% 1,4-butanediol dimethacrylate (BDDM). The rheological properties of the uncured samples and the dynamic mechanical properties of the UV cured samples were examined. All the samples exhibit Newtonian behavior, which indicates the absence of physical entanglements in these polymers. The viscosity increases with increasing number of acrylic groups permolecule. The glass transition temperature of the UV cured samples increases with increasing the number of acrylic groups permolecule. The value of the storage modulus in the rubber-elastic plateau and the cross-link density increase with increasing number of acrylic groups permolecule. The formed networks are inhomogeneous and the residual unsaturation is the highest in the samples with the largest number of acrylic groups per molecule.
Influence of transition and heavy metal ions on ATP-ases activity in rat synaptic plasma membranes
Authors: Vujisic Ljubica , Krstic Danijela , Krinulovic Katarina , Vasic Vesna
Published: August 2005

The influence of transition metal (Cu2+, Zn2+, Fe2+ and Co2+) and heavy metal ions (Hg2+, Pb2+ and Cd2+) on the activities of Na+/K+-ATPase and Mg2+-ATPase isolated from rat synaptic plasma membranes (SPM) was investigated. The aim of the study was to elucidate the inhibition of both ATPase activities by exposure to the considered metal ions as a function of their affinity to bind to the ?SH containing ligand L-cysteine, as a model system. The half-maximum inhibitory activities (IC 50) of the enzymes were determined as parameters of rectangular hyperbolas and correlated with the stability constant (K s) of the respectivemetal- ion-L-cysteine complex. The linear Dixon plots indicate equilibrium binding of the investigated ions to both enzymes.
Study of sulfur dioxide adsorption on Y zeolite
Authors: Marcu Ioan-Cezar , Sdjndulescu I.
Published: August 2005

Sulfur dioxide adsorptive properties of Y zeolite, the structure of which was confirmed by XRD, were investigated at temperatures within the 25?200 ?C range and sulfur dioxide concentrations between 0.9 to 6%(vol./vol). It was found that this sorbent possesses a relatively high adsorption capacity. The Y zeolite did not lose its activity during 20 adsorption desorption-regeneration cycles. The manner in which sulfur dioxide is adsorbed on Y type zeolite was also investigated by analyzing the sample with and without adsorbed SO2, using IR spectroscopy, as well as total and Lewis acidity measurements. The sulfur dioxide molecule is probably adsorbed by hydrogen bonding to one or two conveniently positioned surface hydroxyl groups.
High-performance liquid chromatographic separation of surface flavonoid aglycones in Artemistia annua L. and Artemisia vulgaris L
Authors: Nikolova Milena , Gevrenova Renata , Ivancheva Stephanka
Published: August 2005

External flavonoid aglycones from Artemisia annua L. and Artemisia vulgaris L. were analyzed by the HPLC method. The mobile phase was composed of t-butanol-methanol- 20 mmol l-1 phosphate buffer, pH 3.22. The linear gradient elution method within 22 min was applied. The main aglycones in A. annua and A. vulgaris are methyl ethers of quercetagetin and quercetin. Quercetagetin 3,6,7-trimethyl ether in A. annua and quercetin 3,7,3?-trimethyl ether in A. vulgaris are the most abundant compounds.
Potentiometric stripping analysis of lead and cadmium leaching from dental prosthetic materials and teeth
Authors: Nikolic Ruzica , Kalicanin Biljana , Nikolic Goran
Published: August 2005

Potentiometric stipping analysis (PSA) was applied for the determination of lead and cadmium leaching from dental prosthetic materials and teeth. The soluble lead content in finished dental implants was found to be much lower than that of the individual components used for their preparation. Cadmiumwas not detected in dental implants and materials under the defined conditions. The soluble lead and cadmium content of teeth was slightly lower than the lead and cadmium content in whole teeth (w/w) reported by other researchers except in the case of a tooth with removed amalgam filling. The results of this work suggest that PSA may be a good method for lead and cadmium leaching studies for investigation of the biocompatibility of dental prosthetic materials.
The examination of parameters for lactic acid fermentation and nutritive value of fermented juice of beetroot, carrot and brewer’s yeast autolysate
Authors: Rakin Marica , Baras Josip , Vukasinovic Maja , Maksimovic Milan
Published: August 2005

The conditions for lactic acid fermentation based on a mixture of beetoot juice (Beta vulgaris L) and carrot juice (Daucus carota L) and different content of brewer?s yeast autolysate with Lactobacillus plantarum A112 and with Lactobacillus acidophilus NCDO 1748 has been studied. Both cultures showed good biochemical activity in these mixtures. The production of lactic acid has been stimulated using a higher content of brewer?s yeast autolysate. In these mixtures, L. plantarum A112 showed better growth and lactic acid production than L. acidophilus NCDO 1748. From the data obtained through chemical analyses of the fermented products, it can be seen that the mixture of beetroot and carrot juice and brewer?s yeast autolysate is richer in minerals (Ca, P, Fe) and ?-carotene than fermented beetroot juice with the same content of brewer?s yeast autolysate.
Synthesis and characterization of Ni(II), Cu(II) and Co(III) complexes with polyamine-containing macrocycles bearing an aminoethyl pendant arm
Authors: Rafat Fouzia , Siddiqi M.Y. , Siddiqi K.S.
Published: August 2005

Reaction of [M(ppn)2]X2 (where M = Cu(II), Ni(II), Co(II) and ppn = 1,3-diaminopropane) with formaldehyde and ethylenediamine in methanol results in the ready formation of a 16-membered macrocyclic complex. The complexes were characterized by elemental analysis, IR, EPR, electronic spectral data magnetic moments and conductance measurements. The Cu(II), Ni(II) and Co(III) complexes are coordinated axially with both pendant groups of the hexadentate macrocycle. These pendant donors are attached to the macrocycle by a carbon chain. The electrical conductivities of the Cu(II) and Ni(II) chelates indicated them to be 1:2 electrolytes whilst those of Co(III) is a 1:3 electrolyte in DMSO. The EPR spectrum of the copper complex exhibited G at 3.66, which indicates a considerable exchange interaction in the complex. Spectroscopic evidence suggests that in all of the complexes the metal ion is in an octahedral environment.
Dependence of the total -electron energy on large number of non-bonding molecular orbitals
Authors: Gutman Ivan , Stevanovic Dragan , Radenkovic Slavko , Milosavljevic Svetlana , Cmiljanovic Natasa
Published: August 2005

Using a recently developed method for computing the effect of non-bonding molecular orbitals (NBMOs) on the total ?-electron energy (E), it was found that the dependence of E on the number n0 of NBMOs is almost perfectly linear. We now show that this regularity remains valid for very large values of n0, in particular, to hold up to n0 = 20.
Oxidative performance and surface properties of Co-containaing mixed oxides having the K2NiF4 structure
Authors: Luo Laitao , Zhong Hua , Yang Xiaomao
Published: August 2005

The complexed oxides Nd2?xSrxCoO4 (0.4?x?1.2) and LnSrCoO4 (Ln = Pr, Nd Eu) having the K2NiF4 structure were synthesized by the citric-acid-complexion method. The results of XRD confirmed that the complexed oxides have the K2NiF4 structure. Other phases were found when x = 0.4 and x = 1.2. The influences of Nd, Pr, Eu on the activities of LnSrCoO4 for CO oxidation and C3H8 oxidation were different. The oxidative activities average crystalline size and lattice distortion of Nd2?xSrxCoO4 increased with increasing x value in the oxides. When x > 0.8, the lattice distortion decreased with increasing x. The results of O2?TPD showed that amount of desorption of lattice oxygen over Nd2?xSrxCoO4 increased with x, however, the amount of chemidesorption of oxygen decreased. With increasing x, the high-temperature reduction peak in H2?TPR of Nd2?xSrxCoO4 shifted to higher temperatures, however, the low-temperature reduction peak shifted to lower temperatures, which showed that the activity of the lattice oxygen and the thermal stability of Nd2?xSrxCoO4 increased with increasing x.
Electrochemical deposition and characterization of Zn-Fe alloys
Authors: Bajat Jelena , Miskovic-Stankovic Vesna , Maksimovic Miodrag , Drazic Dragutin , Zec Slavica
Published: August 2005

Zn?Fe alloy electrochemically deposited on steel under various deposition conditions were investigated using anodic linear sweep voltammetry (ALSV) and X-ray diffraction (XRD) analysis for phase structure determination, energy dispersive X-ray (EDX) analysis for determination of chemical composition and polarization measurements and open circuit potential measurements for determination of corrosion properties. The influence of deposition current density on the chemical composition, phase structure and corrosion stability of Zn?Fe alloys was studied. It was shown that deposition current density strongly affects the corrosion stability of Zn?Fe alloys, while Zn?Fe alloy electrodeposited at 4Adm-2 exhibited the lowest corrosion rate.
Energy and economy savings in the process of methanol synthesis unsig Pinch technology
Authors: Kijevcanin Mirjana , Djordjevic Bojan , Ocic Ozren , Crnomarkovic Mladen , Maric Maja , Serbanovic Slobodan
Published: August 2005

A heat exchanger network (HEN) for the process of methanol synthesis has been studied by pinch design analysis. Great economic and energy savings were realized by the pinch analysis in comparison to the existing plant. Also, it was found that it is possible to reduce the requirements for the consumption of utilities. The HEN was reconstruded by adding new heat exchangers. In order to produce new HEN, the capital costs had to be increased, but the total cost trade-off between the capital and energy costs will be decrease by 30 %.
Geometry and conformation of benzenecarboxylic acids
Authors: Markovic Zoran , Bajduk Dalibor , Gutman Ivan
Published: August 2005

The geometry, conformations and energy of mono-, di-, and tri-carboxylic derivatives of benzene were studied by means of the AM1 molecular-orbital method. Whereas the species having no carboxylic groups in the ortho-position (benzoic, isophthalic, terephthalic, and trimesic acids) are planar in all their (stable) conformations, those possessing carboxylic groups in the ortho-position (phthalic, 1,2,3-benzenetricarboxylic, and 1,2,4-benzenetricarboxylic acids) assume a non-planar geometry, with one carboxyl group almost orthogonal to the plane of the benzene ring. Various rotamers of each of the studied benzenecarboxylic acids have nearly the same energy.
Antifungal activity of davanone-type sesquiterpenes from Artemisia lobelli var. conescens
Authors: Vajs Vlatka , Trifunovic Snezana , Janackovic Pedja , Sokovic Marina , Milosavljevic Slobodan , Tesevic Vele
Published: August 2005

Five tetrahydrofuran sesquiterpenes, so-called davanones, and coumarin umbelliferone isolated from Artemisia lobelii All. var. canescens (DC) Briqu, were tested for antifungal activity. All the compounds inhibited the growth of the applied fungi. The overall activity of one of them 2-hydroxy-2,6,10-trimethyl-7,10-epoxydodeca- 3,11-dien-5-on, was comparable to that of the antibiotic bifonazole.
Stereoselective synthesis of α-hydroxy-β-amino acids: The chiral pool approach
Authors: Tasic Gordana , Matovic Radomir , Saicic Radomir
Published: August 2005

A method for the stereoselective homologation of ?-amino acids into syn-?-hydroxy-?-amino acids is described, based on the conversion of stereoisomeric cyanohydrins into trans-oxazolines. The synthetic potential of the method is illustrated in the enantioselective formal synthesis of Bestatin.
Superoxide dismutase activity as a function of culture aging of B-16 mouse melanoma cells
Authors: Radojicic Ratko , Spasic Snezana , Saicic Zorica , Jovanovic Tamara , Simic-Krstic Jovana
Published: August 2005

The C3 clone of B-16 mouse melanoma was cultured for 1, 6 and 9 days and analyzed. The changes which are not directly linked to melanogenesis in the B-16 / C3 cultures during their maturation were characterized. Early (1 day) confluent (6 days) and old (9 days) cell cultures are distinguished by their leucine aminopeptidase (LAP) and ?-naphthyl acetate esterase (ANAE) isoenzyme patterns. Both quantitative and qualitative changes in LAP and ANAE isoenzyme can be observed during culture maturation. There is an increase in the activity of the enzyme copper, zinc-containing superoxide-dismutase (CuZn SOD). The increaase in the CuZn SOD enzyme activity might be related to B-16/C3 cell melanogenesis and / or to differentiation.
The effect of heterocyclic S,S’-ligands on the electrochemical properties of some cobalt(III) complexes in acid
Authors: Jovanovic Vladislava , Babic-Samardzija K. , Sovilj Sofija
Published: August 2005

Eight mixed-ligand cobalt(III) complexes with the macrocyclic amine 1,4,8,11-tetraazacyclotetradecane (cyclam) and a heterocyclic dithiocarbamate (Rdtc-)i.e., morpholine-(Morphdtc), thiomorpholine- (Timdtc), piperazine-(Pzdtc), N-methylpiperazine-(Mepzdtc), piperidine- (Pipdtc), 2-, 3- or 4-methylpiperidine-(2-, 3- and 4-Mepipdtc) carbodithionato-S,S ions, of the general formula [Co(cyclam)Rdtc](ClO4)2, were investigated in deoxygenated 0.1 MHClO4 solutions. Cyclic voltammetry data at a glassy carbon (GC) electrode demonstrate a redox reaction of cobalt(III) from the complexes at potentials strongly influenced by the presence of different heterocyclic Rdtc- ligands. In this respect, the complexes were separated into two groups: the first, with a heteroatom O, S or N in the heterocyclic ring, and the second, with a methyl group on the piperidine ring of the Rdtc- ligand. Anodic polarization of an Fe electrode in the presence of the complexes shows their influence not only on the dissolution of iron but also on the hydrogen evolution reactions and on this basis complexes the complexes could be divided into the same two groups. It was found that the weaker the inhibiting effect of the free heterocyclic amines is, the significantly higher is the efficiency of the corresponding complexes.
The concentrating of alizarin using a reverse osmosis process
Authors: Madaeni S.S. , Daneshvar H.
Published: August 2005

Membrane technologies in general and reverse osmosis in particular have been employed for the concentrating of solutions. In this study, the concentrating of a heat sensitive alizarin extracted from madder root was realized using an FT30 reverse osmosis membrane. The effects of cross flow velocity, transmembrane pressure and pH on the flux and rejection were studied. Increasing the transmembrane pressure increased the flux while the rejection was constant. At pH 7-8, the highest flux was achieved. This study showed that reverse osmosis is the process of choice for the concentrating of alizarin solutions. The optimum operating conditions were 1.0 m/s cross flow velocity, 16 bars transmembrane pressure and pH 7. The system was tested for 12 h without severe fouling problems.
Kinetics and mechanism of the oxidation of methionine by quinolinium chlorochromate
Authors: Pandeeswaran M. , Bincy John , Bhuvaneshwari D.S. , Elango K.P.
Published: August 2005

The oxidation of methionine by quinolinium chlorochromate (QCC) has been studied, in the presence of chloroacetic acid, and in water-acetic acid mixtures of varying mole fractions. The reaction is first order with respect to methionine, QCC and acid. The reaction rates were determined at three different temperatures (25, 35 and 45 ?C) and the activation parameters were computed. The reaction rate increased with increasing mole fraction of acetic acid in the mixture and specific solvent-solvent-solute interactions were found to predominate (81 %). A solvation model and a suitable mechanism for the reaction are postulated.
Heterocyclic systems containing S/N regioselective nucleophilic competition: Facile synthesis, antitubercular and antimicrobial activity of thiohydantoins and iminothiazolidinones containing the benzo
Authors: Kachhadia V.V. , Patel M.R. , Joshi H.S.
Published: August 2005

The required compounds N-aryl-N'-(3-chloro-2-benzo[b]thenoyl)-thioureas 1a-k were prepared by condensing 3-chloro-2-benzo[b]thenoyl chloride with different arylamines using ammonium thiocyanate, which in turn when treated with chloroacetic acid, yielded 1-aryl-3-(3-chloro-2-benzo[b]thenoyl)thiohydantoins 2a-k, while in the presence of sodium acetate treated with chloroacetic acid, yielded 2-arylimino-3-(3-chloro-2-benzo[b]thenoyl)-4-thiazolidinones 3a-k. All the synthesized compounds were screened for their antitubercular and antimicrobial activities. Some selected compounds were selected for their further antitubercular screening.
Transition metal complexes with thiosemicarbazide-based ligands, Part 49: New complexes of iron(III) with deprotonated tridentate Schiff base - pyridoxal derivatives
Authors: Jovanovic Ljiljana , Jevtovic Violeta , Leovac Vukadin , Bjelica Luka
Published: August 2005

Three new bis(ligand) iron(III) complexes were prepared with the deprotonated ONX ligands (X = O,S,N), pyridoxal semi-, thiosemi- and S-methylisothiosemicarbazones (H2L1, H2L2 and H2L3, respectively) of the formulas [Fe(HL1,2)L1,2].4H2O and [Fe(HL3)2]OAc.2H2O. The compounds were characterized by elemental analysis, conductometric and magnetochemical measurements, as well as by IR and UV-vis spectra. Detailed voltammetric investigations were carried out in DMF solutions in the presence of several supporting electrolytes to study the nature of the electrochemical processes and solution equilibria.
Coulometric generation of H+ ions by the anodic oxidation of esters of gallic acid
Authors: Jaksic Ljiljana , Dzudovic Radmila , Mihajlovic Randjel
Published: August 2005

The application of esters of gallic acid (propyl, butyl and dodecyl gallate) for the coulometric generation of H+ ions in aqueous media is described. The current-potential curves recorded for these depolarizers, as well as for tris(hydrosymethyl) aminomethane (?THAM?) and the employed solvent showed that the investigated depolarizes are oxidized at potentials lower than the oxidation potentials of the other components in the solution. The H+ ions formed by the oxidation of these depolarizers (in 1 mol/L sodium perchlorate in water) were used for the titration of THAM with potentiometric end-point detection using a hydrogen/palladium indicator electrode. The current efficiency was 100 %.
Liquid membrane ion-selective electrodes for potentiometric dosage of coper and nickel
Authors: Pleniceany Maria , Isvoranu Marian , Spinu Cezar
Published: August 2005

This paper presents experimental and theoretical data regarding the preparation and characterization of three liquid-membrane electrodes, which have not been mentioned in the specialized literature so far. The active substances, the solutions of which in nitrobenzene formed the membranes on a graphite rod, are simple complex combinations of Cu(II) and Ni(II) ions with an organic ligand belonging to the Schiff base class: N-[2-thienylmethilidene]-2-aminoethanol (TNAHE). The Cu2+ -selective and Ni2+ -selective electrodes were used to determine the copper and nickel ions in aqueous solutions, both by direct potentiometry and by potentiometric titration with EDTA. They were also used for the determination of Cu2+ and Ni2+ ions in industrial waters by direct potentiometry.