bluuebunny/crossref_metadata_2025 huggingface dataset:
The effects of fine grinding on the physicochemical properties and thermal behavior of bentonite clay
Authors: Filipovic-Petrovic Leposava , Kostic-Gvozdenovic Ljiljana , Eric-Antonic Stanka
Published: August 2005

In this study, the results obtained by the mechanical treatment of bentonite clay Zavidinci, Serbia in a laboratory vibration mill with rings for different periods of time are presented. The successive structural changes of the minerals were studied by X-ray diffraction analysis, DTA analysis, IR spectroscopy and particle size distribution. The reactivity changes were controlled by CEC. The starting material and the material mechanically treated for 30 min were sintered at several temperature and for different time periods examined by X-ray diffraction. Mechanical treatment by fine grinding of bentonite clay produces structural changes of the powdered material and influences its behavior in further processing steps in particular after thermal treatment.
TPD-MS study of glassy carbon surfaces oxidized by CO2 and O2
Authors: Peric-Grujic Aleksandra , Neskovic Olivera , Veljkovic Miomir , Lausevic Mila , Lausevic Zoran
Published: August 2005

The temperature-programmed desorption (TPD) method combined with mass spectrometric (MS) analysis has been applied to investigate the surface properties of carbon materials. The apparatus consisting of a temperature-programmed furnace and a quadrupole mass spectrometer was constructed in order to characterize the surface of differently treated glassy carbon samples. In this work, samples of glassy carbon exposed to air, CO2 and O2 were examined. The desorption of H2O,CO and CO2, as major products, indicated the presence of different oxide groups. The amount of these groups for all samples was calculated. It is concluded that oxidation affects the nature and the amount of the surface oxide groups and contributes to their increased stability.
The estimation of solid copper surface tension in copper sulfate solutions
Authors: Popov Konstantin , Nikolic Nebojsa , Rakocevic Zlatko
Published: August 2005

In metal electrodeposition in the limiting diffusion current density range the deposition current density remains constant regardless of the deposition overpotential used. At the same time, the larger the deposition overpotential is the more disperse is the formed deposit, which is characterised by an increased specific surface. The difference in the specific surface of disperse deposits obtained at two different overpotentials in the limiting diffusion current density range is correlated with the difference between the deposition overpotentials. A method for the estimation of the surface tension of solid copper in copper sulfate solutions is also proposed.
Dissolution of chromium in sulfuric acid
Authors: Drazic Dragutin , Popic Jovan
Published: August 2005

By combining electrochemical corrosion rate measurements and spectrophotometric analysis of the electrolyte it was shown that at room temperature chromium dissolves in deaerated 0.1M Na2SO4 + H2SO4 (pH1) solution as Cr(II) and Cr(III) ions in he ratio Cr(II):Cr(III)?7:1. This process was stable over 4h without any detectable change. The total corrosion rate of chromium calculated from the analytical data is about 12 times higher, than that determined electrochemically by cathodic Tafel line extrapolation to the corrosion potential. This finding was confirmed by applying the weight-loss method for the determination of the corrosion rate. This enormous difference between these experimentally determined corrosion rates can be explained by the rather fast, "anomalous" dissolution process proposed by Kolotyrkin and coworkers (chemical reaction of Cr with H2O molecules) occurring simultaneously with the electrochemical corrosion process.
Kinetic determination of lysine in pharmaceutical sample
Authors: Mitic Snezana , Miletic Gordana , Petrovic A.N. , Tosic Snezana
Published: August 2005

Akinetic method for the determination of micro quantities of the amino acid lysine (Lys) is described in this paper. The catalytic activity of cobalt in the reaction of the oxidation of purpurin (1,2,4-trihydroxyanthraquinone PP) by hydrogen peroxide in alkaline buffer solution decreases in the presence of micro quantities of lysine, because of the formation of a complex.1,2 The experimental conditions for the successful determination of lysine were optimized. The relative error ranges from 7.7 to 1.9% in the concentration range from 0.118 to 23.520?g cm-3. The detection limit is 0.023?g cm-3. Kinetic equations are proposed for the investigated process. The effects of certain foreign ions and amino acids on the reaction rate were determined in order to assess the selectivity of the method. The method was applied to the determination of lysine in a pharmaceutical sample Riborn-P (Medecon?Belgrade).
An optimized synthesis of a key pharmaceutical intermediate methyl 4-[(1-oxopropyl)phenylamino]piperidine-4-carboxylate
Authors: Kiricojevic Vesna , Ivanovic Milovan , Micovic I.V. , Djordjevic J.B. , Roglic Goran , Dosen-Micovic Ljiljana
Published: August 2005

An efficient synthesis of methyl 4-[(1-oxopropyl)phenylamino]piperidine-4-carboxylate (7) has been developed starting from 1-benzylpiperidin-4-one (1). The compound is a key intermediate in the synthesis of new generation, highly active narcotic analgesics, such as remifintanil, as well as the novel classes of fentanyl analogues. An optimized Strecker-type condensation of piperidone 1 with aniline and HCN yielded the anilino-nitrile 2(?90%) which, upon selective hydrolysis with conc. H2SO4, gave the anilino-amide 3.After vigorous basic hydrolysis of 3, followed by acidification and successive treatment with SOCl2 and MeOH, the anilino-ester 5 was obtained (40?45%, in 3 steps). N-Acylation of 5 with propionyl chloride yielded the anilido-ester 6(70?80%) In the final step, the catalytic N-debenzylation of 6 was examined under various conditions and optimized to yield 7 in near quantitative yields.
Synthesis characterization of Cr(III), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) complexes of 2,12-dimethyl-3-13-di-n-propyl-l,4,ll,14-tetraazacycloeicosa-1,13,l1,13-tetraene
Authors: Prasad Raghu , Mathur Mala
Published: August 2005

Metal complexes of a 20-membered tetraazamacrocycle 2,12-dimethyl-3,13-di-n-propyl 1,4,11,14-tetraazacycloeicosa-1,3,11,13-tetraene(L) of the type [MLX2]X(M=Cr(III), Fe(III); X=NO3)[CoLNO3]NO3, [NiL(NO3)2], [CuL]Cl2 and [ZnLCl2]have been prepared by 2+2 cyclocondensation of 2,3-hexanedione with 1,6-diaminohexane in the presence of metal ions as templates. These complexes were characterized by elemental analyses, conductances, IR and electronic spectra and magnetic measurements.
Insulin-induced lipid binding to hemoglobin
Authors: Tomasevic Nenad , Nikolic Milan , Klappe Karen , Hoekstra Dick , Niketic Vesna
Published: August 2005

Under hypoglycemic conditions, concomitant hyperinsulinism causes an apparent modification of hemoglobin (Hb) which is manifested by its aggregation (Niketic et al., Clin. Chim. Acta 197 (1991) 47). In the present work the causes and mechanisms underlying this Hb modification were studied. Hemoglobin isolated from normal erythrocytes incubated with insulin was analyzed by applying 31P-spectrometry and lipid extraction and analysis. To study the dynamics of the plasma membrane during hyperinsulinism, a fluorescent lipid-analog was applied. In the presence of insulin phosphatidylserine (PS), phosphatidylethanolamine (PE) and cholesterol were found to bind to Hb. Lipid binding resulted in Hb aggregation, a condition that can be reproduced when phospholipids are incubated with Hb in vitro. Using a fluorescent lipid-analog, it was also shown that exposing erythrocytes to supraphysiological concentrations of insulin in vitro resulted in the internalization of lipids. The results presented in this work may have relevance to cases of diabetes mellitus and hypoglycemia.
Simultaneous correlation of the excess enthalpy and W-shaped excess heat capacity of 1, 4-dioxane- n-alkane systems by PRSV-HVOS CEOS
Authors: Kijevcanin Mirjana , Djordjevic A.B. , Grguric Ivona , Djordjevic Bojan , Serbanovic Slobodan
Published: August 2005

In this work the Peng-Robinson-Stryjek-Vera (PRSV) equation of state coupled with the Huron-Vidal-Orbey-Sandler (HVOS) rule was tested for the correlation of the excess enthalpy (HE) and the excess heat capacity (cp E) alone and simultaneously. The HVOS mixing rule incorporates the NRTL equation as the GE model. All calculations were performed using the linear and reciprocal forms of the temperature dependent parameters of the models. For all the evaluations the 1,4-dioxane+n-alkane systems were chosen having in mind the unusually W-shaped concentration dependence of cp E for these systems. The correlation of the HE and cp E data alone for all the investigated systems using four coefficients and for the simultaneous correlation of HE+cp E data using six coefficients of the temperature dependent parameters of the PRSV-HVOS models could be considered as being very satisfactory.
Synthesis, structural study and electrochemical properties of copper(II) complexes derived from benzene- and p-toluenesulphonylhydrazone
Authors: Larabi L. , Harek Y. , Reguig A. , Mostafa M.M.
Published: August 2005

The synthesis and characterization of benzene- and p-toluenesulphonylhydrazones derived from salicylaldehyde and 2-hydroxy-1-naphthaldehyde and their Cu(II) complexes are reported. The compounds were characterized on the basis of elemental analyses, electronic and IR spectra, magnetic moments, and conductance measurements. The electrochemical behavior of the Cu(II) complexes was investigated in DMSO by cyclic voltammetry (CV), rotating disc electrode (RDE) and coulometry. The oxidative polymerization of the copper complexes on a glassy carbon electrode was carried out in DMSO.
Thermochemical equilibrium calculations of high-temperature O2 generation on the early Earth: Giant asteroid impact on land
Authors: Premovic Pavle
Published: August 2005

Earth?s atmosphere is composed primarily of N2 and O2. The origin of free O2 in the early Earth?s atmosphere is still subject of considerable debate.1 Theoretical models suggest that the initial form of free O2 in the atmosphere has been oceanic H2O. Recent computation modeling has suggested that a superheated (ca. 2000 K) H2O vapor atmosphere of 1.4x1021 kg (the present mass of the oceans) lasting for about 3000 y could probably have been formed on Earth by an enormous (ca. 1028 J) asteroid impact. In this report, the occurrence of the thermochemical dissociation of the vapor, creating a primitive oxygenic (ca. 0.1 of the present level (PAL) of free O2) atmosphere.
Sulfur retention by ash during coal combustion - Part II: A model of the process
Authors: Manovic Vasilije , Grubor Borislav , Ilic Mladen , Jovancicevic Branimir
Published: August 2005

An overall model for sulfur self-retention in ash during coal particle combustion is developed in this paper. It is assumed that sulfur retention during char combustion occurs due to the reaction between SO2 and CaO in the form of uniformly distributed non-porous grains. Parametric analysis shows that the process of sulfur self-retention is limited by solid diffusion through the non-porous product layer formed on the CaO grains and that the most important coal characteristics which influence sulfur self-retention are coal rank, content of sulfur forms, molar Ca/S ratio and particle radius. A comparison with the experimentally obtained values in a FB reactor showed that the model can adequately predict the kinetics of the process the levels of the obtained values of the SSR efficiencies, as well as the influence of temperature and coal particle size.
Chemical modification of β-lactoglobulin by quinines
Authors: Novakovic Irena , Vujcic Zoran , Bozic Tatjana , Bozic Natasa , Milosavic Nenad , Sladic Dusan
Published: August 2005

The avarone/avarol quinone/hydroquinone couple, as well as their derivatives show considerable antitumor activity. In this work, covalent modifications of ?-lactoglobulin, isolated from cow milk, by avarone, its model compound 2-tert-butyl-1,4-benzoquinone, and several of their alkylthio derivatives were studied. The techniques applied for assaying the modifications were UV/VIS spectrophotometry, SDS PAGE and isoelectrofocusing. The results of the SDS PAGE suggest that polymerisation of the protein occurs. The shift of the pI of the protein upon modification toward lower values indicates that lysine amino groups are the principal site of the reaction of ?-lactoglobulin with the quinines.
The hypothetical ancestral animal the Urmetazoa: Telomerase activity in sponges [Porifera]
Authors: Werner E.G. , Müller W.E.G. , Müller I.M.
Published: August 2005

Sponges (Porifera) represent the lowest metazoan phylum, characterized by a pronounced plasticity in the determination of cell lineages, and they are the closest related taxon to the hypothetical ancestral animal, the Urmetazoa, from which the metazoan lineages diverged. In a first approach to elucidate the molecular mechanisms controlling the switch from the cell lineage with a putative indefinite growth capacity to senescent, somatic cells, the activity of the telomerase as an indicator for immortality has been determined. The studies were performed with the marine demosponges Suberites domuncula and Geodia cydonium, in vivo with tissue but also in vitro using the primmorph system. Primmorphs are formed from dissociated cells which have retained their proliferation potency. It was found that the activity of telomerase in tissue of both sponges is high. Based on this and additional findings it is assumed that the separation of the senescent sponge cell lineage from the immortal germ-/somatic cell lineage is triggered by the loss of contact to cell adhesion factors. First evidence is included which suggests that the final progress of the senescent telomerase- negative cells to cell death is caused by apoptosis.
Conformation analysis of three germacranolides by the PM3 semi-empirical method
Authors: Milosavljevic Slobodan , Juranic Ivan , Aljancic Ivana , Vajs Vlatka , Todorovic Nina
Published: August 2005

The conformations of the C-6 lactonized germacranolides 1?3 were calculated by applying the PM3 semi-empirical method. The low-temperature 1H-NMR spectra of parthenolide (1) were also measured. The relations between the calculated and the experimentally determined geometries were established using a modified Karplus equation. The applied quantum-chemical calculations proved to be an efficient and easy-to-use tool for the elucidation and prediction of the properties of germacranolide-type sesquiterpene lactones.
Effects of pH on kinetics of the structural rearrangement that gates the electron-transfer reaction between zinc cytochrome c and plastocyanin: Analysis of protonation states in a diprotein complex
Authors: Crnogorac Milan , Kostic Nenad
Published: August 2005

Electron transfer from zinc cytochrome c to copper(II)plastocyanin in the electrostatically- stabilized complex [Crnogorac MM, Shen C, Young S Hansson O, Kostic NM (1996) Biochemistry 35, 16465?74]. We study this rearrangement in four complexes Zncyt/pc(II), which zinc cytochrome c makes with the wild-type form and the single mutants Asp42Asn, Glu59Gln, and Glu60Gln of plastocyanin. The rate constant for the rearrangement, kF differs for the four forms of plastocyanin but is independent of pH from 5.4 to 9.0 in all four cases. That kF is affected by the single mutations but not by pH changes suggests that the residues Asp 42, Glu59, and Glu60 in the wild-type plastocyanin remain deprotonated (i.e., as anions) within the Zncyt/pc(II) complex throughout the pH range examined. This fact agrees with the notion that loss of salt bridges in the initial (redox-inactive) configuration of the complex is compensated by formation of new salt bridges in the rearranged (redox-active) configuration.
Use of the group theory for classification of electronic states of acetylene
Authors: Jerosimic Stanka , Peric Miljenko
Published: August 2005

The electronic states of the acetylene molecule are classified employing the group theory combined with the use of the Walsh diagrams and some elementary quantum chemical considerations. The results of this analysis are compared with those obtained by explicit ab initio calculations. It is shown that the global structure of the electronic spectrum can be reproduced/predicted without carrying out detailed ab initio calculations. .
Akinetic study of the depyritization of oil shale HCl-kerogen concentrate by Thiobacillus ferrooxidans at different temperatures
Authors: Vrvic Miroslav , Dragutinovic Vesna , Matic Valerija , Spasic Snezana , Cvetkovic Olga , Vitorovic Dragomir
Published: August 2005

The results of kinetic studies of bacterial depyritization of HCl-kerogen concentrate of Aleksinac (Serbia) oil shale by the chemolithoautotrophic thionic bacteria Thiobacillus ferrooxidans under discontinuous laboratory conditions at various temperatures (0, 20, 28 and 37 ?C) at a pH of ca. 1.5 are presented in this paper. Low pH prevents the occurrence of the precipitation of iron(III)-ion hydrolysis products on the substrate particles and thereby reduces the process efficiency. Bacterial depyritization is developed as per kinetics of the first order. The activation energy which points to a successive mechanism of pyrite biooxidation, was computed from the Arrhenius plot. The biochemical kinetics indicators point to a high affinity of the bacteria toward pyrite but small values of Vmax, which are probably the result of decelerated metabolic processes due to the low pH value of the environment resp. the large difference of thepHbetween the external medium and the cell interior.
Effect of Na2O/SiO2 mole ratio on the crystal type of zeolite synthesized from coal fly ash
Authors: Vucinic Dusica , Miljanovic Igor , Rosic Aleksandra , Lazic Predrag
Published: August 2005

Coal fly ash was modified to zeolitic materials by hydrothermal treatment at 90 ?C. The zeolite synthesis was studied as a function of the mole ratio of Na2O/SiO2 in the reaction mixtures. The results showed that NaP1 zeolite is obtained when the Na2O/SiO2 mole ratio was 0.7. Hydroxysodalite is the dominant zeolite phase in modified fly ash treated with a higher Na2O concentration solution (Na2O/SiO2 = 1.3). The IR and XRD methods were used to determine the phases present in the starting sample and in the zeolitic materials.
The kinetics of the reactions of 2-substituted nicotinic acids with diazodiphenylmethane in various alcohols
Authors: Drmanic Sasa , Jovanovic Bratislav , Marinkovic Aleksandar , Misic-Vukovic Milica
Published: August 2005

The rate constants of 2-substituted nicotinic acids in reaction with diazodiphenylmethane (DDM) in eight alcohols at 30 ?C have been determined. In order to explain the obtained results through solvent effects, the second order reaction rate constants (k) of the examined acids were correlated using the appropriate solvent parameters by the equation: logk=logk0 af(?) + b?* + cn?H where f(?) is the measure of solvent ability as a dielectric to stabilize the separation of opposite charges in the activated complex, ?* is the measure of solvent ability to stabilize proton in the initial state and n?H represents the ability of protic solvents to form hydrogen bond with the negative end of the ion-pair intermediate. These constants were correlated also by using solvatochromic equation of the form logk=logk0 + s?* + a? + b? where ?* is the measure of the solvent polarity, ? represents the scale of the solvent hydrogen bond donor acidities (HBD) and ? represents the scale of the solvent hydrogen bond acceptor basicities (HBA). The correlations of the kinetic data were carried out by means of multiple linear regression analysis. The results obtained for 2-substituted nicotinic acids were compared with the results for ortho-substituted benzoic acid under the same experimental conditions.
Sol-gel preparation and electrical behaviour of Ln: YAG (Ln = Ce, Nd, Ho, Er)
Authors: Garskaite Edita , Jasaitis Darizus , Kareiva Aivaras
Published: August 2005

A sol-gel method has been developed to prepare pure yttrium aluminum garnet Y3Al5O12 (YAG), and rare-earth substituted (Ce-Y3Al5O12, Nd-Y3Al5O12 Ho-Y3Al5O12, and Er-Y3Al5O12) samples. The XRD patterns of the polycrystalline powders sintered at 1000 ?C showed the formation of monophasic garnet materials. The micro-structural features in the polycristalline samples were studied by scanning electron microscopy. A homogeneous distribution of rare-earth do pants in the YAG lattice was achieved in all of the cases. Electrical conductivity measurements were also performed on the compacts of sol-gel derived Ln-YAG samples. In contrast to the expected dielectric behavior, the conducting properties of the examined specimens indicate metallic behavior with the resistivity increasing gradually with increasing temperature.
Potentiometric and spectrophotometric studies of the complexation of Schiff-base hydrazones containing the pyrimidine moiety
Authors: Seleem H.S. , El-Shetary B.A. , Khalil S.M.E. , Shebl M.
Published: August 2005

Three Schiff-base hydrazones (ONN ? donors) were prepared by condensation of 2-amino-4-hydrazino-6-methylpyrimidine with 2-hydroxyacetophenone 2-methoxybenzaldehyde and diacetyl to yield 2-OHAHP, 2-OMeBHPand DHP respectively. The structures of these ligands were elucidated by elemental analysis, UV, IR, 1H-NMR and mass spectra. The metal?ligand stability constants of Mn2+, Fe3+,Co2+,Ni2+,Cu2+, Zn2+,Cd2+,UO22+ and Th4+ chelates were determined potentiometrically in two different media (75%(v/v) dioxane?water and ethanol?water) at 283, 293, 303 and 313 K at an ionic strength of 0.05 M (KNO3). The thermodynamic parameters of the 1:1 and 1:2 complexes were evaluated and are discussed. The dissociation constants of 2-OHAHP, 2-OMeBHP and DHPligands and the stability constants of Co2+, Ni2 and Cu2+ with 2-OHAHP were determined spectrophotometrically in 75 % (v/v) dioxane?water.
Investigation of the adsorption of anionic surfactants at different pH values by means of active carbon and the kinetics of adsorption
Authors: Zor Sibel
Published: August 2005

In this study, the effect of pH on the removal of anionic surfactants, such as linear alkyl benzene sulfonate (LABS) and dodecyl benzene sulfonate (DBS) bymeans of adsorption by activated carbon was investigated. For this purpose activated carbon was used as adsorbent. Anionic surfactant solutions with initial pH values of 3, 6, 8 and 12 were used. The adsorption isotherms for the adsorption of anionic surfactants by active carbon at different pH were determined. These adsorption isotherms were seen to be consistent with Freundlich?s adsorption isotherm. k and n constants were determined from Freundlich?s linear equation. Adsorption rate constants were determined from the obtained kinetic curves which were suitable for the first order of rate kinetics.
Chaotic, mixed-mode and periodic oscillations during the electro-oxidation of copper in trichloroacetic acid
Authors: Li Liang , Chena Shenhao , Wu Hongtai , Cui Haitao
Published: August 2005

The current oscillations of a copper electrode in trichloroacetic acid solutions were studied in this paper. The Cu/CCl3COOH system is a new electrochemical oscillator, showing rich dynamic behaviour on two controllable parameters: the trichloroacetic acid concentration (CCCl3COOH) and the imposed potential (E). Phase trajectories were reconstructed from time series using time delaymethods in order that the complex oscillations could be analyzed. Five kinds of oscillations, periodic and quasiperiodic mixed-mode, aperiodic, small amplitude and chaotic current oscillations, were observed. The EDS (energy dispersive spectroscopy) technique was used to analyze the elemental composition of the film formed on the surface of the copper electrode after the current oscillations.
Thermostability and surface morphology of nano- and micro-filled NBR/CSM rubber blends
Authors: Markovic G. , Radovanovic Blaga , Simendic-Budinski J. , Marinovic-Cincovic Milena
Published: August 2005

Acrylonitrile-butadiene rubber (NBR), polychloroprene rubber (CR) chlorosulphonated polyethylene rubber (CSM) and their blends were cross-linked with sulphur, ethylene- thiourea, magnesium oxide or their combination. The effect of nano- and micro- particle sized of 35 pphr SiO2 on the thermostability and surface morphology of all the crosslinked systems was investigated. Identification of the structure of nano- and micro- particle sized SiO2 filled NBR/CSM and CR/CSM crosslinked systems was carried out by Fourier transform infrared spectroscopy (FTIR) with an attenuated total reflectance (ATR) extension. The thermal stability of the nano- and micro particle sized SiO2 filled NBR/CSM and CR/CSM crosslinked systems were carried out by thermogravimetric analysis (TGA). The glass transition temperature (Tg) of the samples was determined by differential scanning calorimetry (DSC). The morphology of the fracture surface of the crosslinked systems was carried out by scanning electron microscope (SEM). The results show when filledwith nano-particle sized of SiO2 NBR/CSM and CR/CSM polymer matrix have a strong peak from SiO?C at 1079 cm-1. This suggests the an interaction between the SiO2, which should lead to an increased thermal stability, higher values of Tg, better dispersion the nano-SiO2 andmore polish, without cracks than micro-filled NBR/CSM and CR/CSM crosslinked systems.
Facile rearrangement of push-pull 5-substituted 4-oxothiazolidines induced by pyridinium hydrobromide perbromide under homogeneous reaction conditions
Authors: Markovic Rade , Baranac Marija , Dzambaski Zdravko
Published: August 2005

Pyridinium hydrobromide perbromide (PHBP) is a highly efficient reagent for the conversion of 5-substituted-2-alkylidene-4-oxothiazolidine derivatives to the corresponding thiazolidines with two fully delocalized exocyclic double bonds at the C(2) and C(5) positions. This conversion as a two-step bromination-rearrangement process occurs in acetonitrile under homogeneous reaction conditions.
Noble metal binding on macroporous poly(GMA-co-EGDMA) modified with ethylenediamine
Authors: Nastasovic Aleksandra , Jovanovic Slobodan , Jakovljevic Dragica , Stankovic Slavka , Onjia Antonije
Published: August 2005

Macroporous crosslinked poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate), p(GME), was synthesized by suspension copolymerization and modified by reaction of the pendant epoxy groups with ethylenediamine. The sorption rate and capacity of themodified copolymer, p(GME)-en for Rh(III) Au(III) and Pt(IV) ions were determined in batch experiments under non-competitive conditions. The uptake of Rh(III) was faster than those ofAu(III) and Pt(IV). The sorption capacity for Pt(IV)was determined in the pHrange 0.9?6.0. The maximum Pt(IV) uptake capacity onto p(GME)-en at pH 5.5 was 1.30 mmol/g.
IgG binding of mugwort pollen allergens and allergoids exposed to simulated gastrointestinal conditions measured by a self-developed ELISAtest
Authors: Polovic Natalija , Cirkovic-Velickovic Tanja , Gavrovic-Jankulovic Marija , Burazer Lidija , Djergovic-Petrovic Danica , Vuckovic Olga , Jankov Ratko
Published: August 2005

This study considers the influence of exposure to simulated gastrointestinal conditions (saliva, gut, intestine and acidic conditions of the gut) on IgG binding of unmodified allergens and three types of LMW allergoids of Artemisia vulgaris pollen extract obtained by means of potassium cyanate succinic and maleic anhydride. It also concerns the optimization of a self-developed ELISA assay for comparison of the specific IgG binding of mugwort pollen extract and modified mugwort pollen derivatives. The ELISA was conducted with a mugwort pollen extract coupled to the plate, using the sera from 12 mugwort- pollen allergic patients. The exposure to saliva fluid for 2 min did not influence the IgG binding properties of allergens and allergoids. Exposure of mugwort pollen allergens and LMW allergoids to the acidic conditions of the gut did not dramatically change their IgG binding properties. By exposing mugwort pollen extract and LMW derivatives to the SGF conditions for 1 h, the percent of IgG binding epitopes was reduced to a half of its starting value in the extract and to about 30%in all the allergoid samples. After prolonged exposure only the carbamyl derivative showed reduced IgG binding. Changes of the IgG binding potential of all four samples after exposure in SIF followed a similar pattern.
Axial dispersion of the liquid phase on a three-phase Karr reciprocating plate column
Authors: Nikolic Ljubisa , Nikolic Vesna , Veljkovic Vlada , Lazic Miodrag , Skala Dejan
Published: August 2005

The influence of the gas flow rate and vibration intensity in the presence of the solid phase (polypropylene spheres) on axial mixing of the liquid phase in a three phase (gas-liquid-solid) Karr reciprocating plate column (RPC) was investigated. Assuming that the dispersionmodel of liquid flow could be used for the real situation inside the column, the dispersion coefficient of the liquid phase was determined as a function of different operating parameters. For a two-phase liquid-solid RPC the following correlation was derived: DL = 1.26(Af)1.42 UL 0.51 ?S 0.23 and a similar equation could be applied with ? 30 % confidence for the calculation of axial dispersion in the case of a three-phase RPC: DL = 1.39(Af)0.47 UL0.42UG0.03 ?S -0.26.
Isobaric vapour-liquid equilibrium calculations of binary systems using neural network
Authors: Bilgin Mehmet
Published: August 2005

A model on a feed forward back propagation neural network was employed to calculate the isobaric vapour?liquid equilibrium (VLE) data at 40, 66.67, and 101.32 ??0.02 kPa for the methylcyclohexane ? toluene and isopropanol ? methyl isobutyl ketone binary systems, which are composed of different chemical structures (cyclic, aromatic, alcohol and ketone) and do not show azeotrope behaviour. Half of the experimental VLE data only were assigned into the designed framework as training patterns in order to estimate the VLE data over the whole composition range at the mentioned pressures. The results were compared with the data calculated by the two classical models used in this field, the UNIFAC and Margules models. In all cases the deviations the experimental activity coefficients and those calculated by the neural network model (NNET) were lower than those obtained using the Margules and UNIFAC models.
An impedance investigation of corrosion protection of copper by self-assembled monolayers of alkanethiols in aqueous solution
Authors: Li Guiyan , Ma Houyi , Jiao Yongli , Chen Shrnhao
Published: August 2005

Self-assembled monolayers (SAMs) of three n-alkanethiols, 1-octadecanethiol (C18SH), 1-dodecanethiol (C12SH), and 1-hexanethiol (C6SH), were formed on fresh, oxide- free copper surfaces obtained by HNO3 etching. The corrosion protection abilities of the three alkanethiol SAM s were evaluated in 0.2 mol cm-3 NaCl, 0.2 mol cm-3 HCl and 0.2 mol dm?3 H2SO4 solutions using the electrochemical impedance spectroscopy (EIS) method. The SAMs act as a hydrophobic barrier layer, which effectively prevents the copper substrate from contacting corrosive ions, thereby inhibiting corrosion of the copper to a considerable degree. A general equivalent circuit for the SAM-covered electrodes was proposed, bymeans of which the impedance behavior of the electrodes was interpreted and the corresponding electrochemical parameters were acquired. In addition, the quality of the SAMs and development of defects in the SAMs were also been evaluated based on the equivalent circuit. The dependence of the capacitance of the SAMs on the applied potentials was used to determine the stability of the SAMs at the applied potentials.
Synthesis of 5-azaandrostane-3β, 17β-diol protected at the 17-hydroxyl group
Authors: Pavlovic Vladimir , Dabovic Milan , Martinovic Sasa , Lorenc Ljubinka , Kalvoda Jaroslav
Published: August 2005

In the present paper, the preparation of 3?-hydroxy-17?-dimethyl-tert-butylsilyloxy- 5-azaandrostane (15) in fourteen steps is described. B-nor-17-oxoandrost- 5-en-3?-yl acetate (1)1,2 was used as the starting material, which was transformed to the key intermediate of the synthesis, B-nor-17?-dimethyl-tert-butylsilyloxyandrost- 4-en-3?-yl acetate (7).
Flavonoids from flowers of Cephalaria pastricenis and their antiradical activity
Authors: Godjevac Dejan , Vajs Vlatka , Menkovic Nebojsa , Tesevic Vele , Janackovic Pedja , Milosavljevic Slobodan
Published: August 2005

Two flavonoid glycosides 1 and 2 having the luteolin structure were isolated from flowers of the endemic plant species Cephalaria pastricensis. They were identified by 1H and 13C NMR, as well as UV/Vis spectroscopy. The structures of 1 and 2 were also confirmed by the spectral data of aglycones and TLC of the sugars obtained after acid hydrolysis. Flavones 1 and 2 showed significant antiradical activity in the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay.
Thionation of N-methyl- and N-unsubstituted thiazolidine enaminones
Authors: Markovic Rade , Rasovic Aleksandar , Baranac Marija , Stojanovic Milovan , Steel Peter , Jovetic Stanka
Published: August 2005

The potential of directional non-bonded 1,5-type S???O interactions to initiate the incipient stage of an in situ rearrangement of N-unsubstituted thiazolidine enaminones to functionalized 1,2-dithioles has been demonstrated. The spectral characteristics, as well as X-ray structural analysis of a selected rearranged product, indicate that a dynamic interconversion occurs in solution between the 1,2-dithiole and the 3,3a?4,4-trithia-1-azapentalene bicylic form. The lack of the rearrangement in the case of a N-methyl substituted enaminone precursor is attributed to an unfavorable methyl migration in the last reaction step.
7, 8, 15, 16-Tetraoxa-dispiro [5. 2. 5. 2]hexadecane-3-carboxylic acid derivatives and their antimalarial activity
Authors: Opsenica Igor , Terzic Natasa , Opsenica Dejan , Milhous Wilbur , Solaja Bogdan
Published: August 2005

Several C2 symmetrical mixed tetraoxanes were prepared starting from a gemdihydroperoxide and a ketone. The obtained tetraoxanes showed pronounced antimalarial activity against P. falciparum chloroquine resistant W2 and chloroquine susceptible D6 strains, with N-(2-dimethylamino)ethyl-7,8,15,16-tetraoxa-dispiro S5.2.5.2Chexadecane-3-carboxamide being as active as artemisinin.
Synthesis and characterization of biodegradable aliphatic copolyesters with hydrophilic soft segments
Authors: Jovanovic Danijela , Nikolic Marija , Djonlagic Jasna
Published: August 2005

segmented poly(ester-ether)s based on poly(butylene succinate) and two different types of polyethers were investigated. The poly(ester-ether)s were synthesized by transesterification reaction of dimethyl succinate 1,4-butanediol and poly(ethylene oxide) (PEO, Mn = 1000 g/mol) in the first series, and poly(tetramethylene oxide) (PTMO,Mn = 1000 g/mol) in the second. The mass fraction of soft segments was varied between 10 and 50 mass. %. The effect of the introduction of two different polyether soft segments on the structure, thermal and rheological properties were investigated. The composition of the poly(ester-ether)s, determined from their 1H-NMR spectra showed that incorporation of soft polyether segments was successfully performed by the transesterification reaction in bulk. The molecular weight was estimated from solution viscosity measurements and complex dynamic viscosities. The thermal properties investigated by DSC indicated that the presence of soft segments lowers the melting and crystallization temperature of the hard phase, as well as the degree of crystallinity. Dynamical mechanical analysis was used to investigate the influence of composition on the rheological behavior of the segmented poly(ester-ether)s. The results obtained from an enzymatic degradation test performed on some of the synthesized polymers showed that the biodegradability is enhanced with increasing hydrophilicity.
Investigation of the mechanism of mercury removal from silver- amalgam alloy
Authors: Odanovic Zoran , Djurdjevic M.
Published: August 2005

An investigation of silver dental amalgam decomposition and the mercury removal mechanism was performed. The decomposition process was analyzed during thermal treatment in the temperature interval from 400 ?C to 850 ?C and for times from 0.5 to 7.5 h. The chemical compositions of the silver dental amalgam alloy and the treated alloy were tested and microstructure analysis using optical and scanning electron microscopy was carried out. The phases were identified using energy disperse electron probe microanalysis. A mechanism for the mercury removal process from silver dental amalgam alloy is suggested.
Modeling of adsorber/desorber/catalytic reactor system for ethylene oxide removal
Authors: Arsenijevic Zorana , Grbavcic Zeljko , Grbic Bosko
Published: August 2005

The removal of ethylene oxide (EtO) in a combined system adsorber desorber/catalytic reactor has been investigated. The combined system was a modified draft tube spouted bed reactor loaded with Pt/Al2O3 catalyst. The annular region was divided into two sectons, the "hot" section contained about 7 % of catalyst and it behaved as a desorber and catalytic incinerator while the "cold" section, with the rest of the catalyst, behaved as a sorber. The catalyst particles were circulated between the two sections by use of a draft tube riser. The Computational Fluid Dynamics (CFD) program package FLUENT was used for simulations of the operation of the combined system. In addition, a one-dimensional numerical model for the operation of the packed bed reactor was compared with the corresponding FLUENT calculations. The results of the FLUENT simulations are in very good agreement with the experimental observations, as well as with the results of the one-dimensional numerical simulations.
Depleted uranium in the air during the cleanup operation at Cape Arza
Authors: Radenkovic Mirjana , Andjelic Tomislav , Kovacevic Milojko , Vukotic Perko
Published: August 2005

Cape Arza was contaminated with depleted uranium (DU) in the air strikes of NATO aeroplanes on May 30, 1999. The cleanup and decontamination of the site started in 2001. Here the results of air monitoring performed during the cleanup operations in Spring 2002. are presented. The collected air samples were analyzed by high-resolution alpha spectrometry. The obtained concentrations of airborne uranium are about ten times higher than the average value usually reported for air. The ratio of the 234U/238U activities indicates the presence of depleted uranium in the air during the cleanup action, due to resuspension and soil disturbance in the contaminated teritory.
Gamma-radiation induced agglomeration of chicken muscle myosin and actine
Authors: Niciforovic Ana , Radojcic Marija , Milosavljevic Bratoljub
Published: August 2005

Radiolytic behaviour of themajor vertebrate muscle proteins: fibrillarmyosin (molar mass, Mm = 520,000 g/mol) and filament forming actin (Mm = 42,050 g/mol) was studied using a SDS-polyacrylamide gel electrophoresis and quantified by high precision laser-densitometry. In order to study the OH radical contribution to the radiation damage, purified chicken myosin and actin (4 ?M) were prepared in N2O saturated solution and irradiated with 1?3 kGy at 60Co gamma source. With respect to changes in the molecular mass, the only observed myosin and actin damage was dose dependent agglomeration of proteins. The corresponding radiation chemical yields of 5 x?10-8 mol J-1 and 6.3 x?10-8 mol J-1 were obtained for myosin and actin, respectively. This result confirmed that only the radiation-induced agglomeration is initiated with the reaction of the OH radical even in the situation where the OH radical concentration produced exceeds the protein concentration 500 times thus enabling the multi-radical attack to occur.
Protolytic equilibria in homogeneous and heterogeneous systems of ketoconazole and its direct spectrophotometric determination in tablets
Authors: Vojic Mirjana , Popovic Gordana , Sladic Dusan , Pfendt Lidija
Published: August 2005

The acid-base equilibria of a diprotic, slightly hydrosoluble base ketoconazole were studied in homogeneous and heterogeneous water systems. The determinations were performed at 25?C at a constant ionic strength of M(NaCl). The acidity constant Ka1 was determined by potentiometric (pKa1 3.20) and spectrophotometric (pKa1 3.26) methods. A pKa2 constant of 6.10 was obtained based on the equilibrium constants pKs0 4.84 and pKs1 -1.26, determined in a heterogeneous ketoconazole system. The obtained values of the constants served to calculate the solubility and the distribution of the equilibrium forms of ketoconazole as a function of pH. On the basis of the distribution of the equilibrium forms of ketoconazole, a spectrophotometric method for the determination of its content in commercial tablets was developed. The determinations were performed at 225 nm in 0.1 M HCl. The method is simple and rapid and enables the direct spectrophotometric determination of the content of ketoconazole without previous isolation.
The influence of different parameters on the hydration process of binders based on alkali activated slag
Authors: Krzan Darko , Komljenovic Miroslav , Zivanovic Branislav
Published: August 2005

The influence of certain types of activators (water glass Na2O.nSiO2 and sodium-metasilicate Na2SiO3.5H2O) on the hydration process of alkali activated slag was investigated in this study. The influence of activator concentration, specific surface area of the slag and the modulus n of the water glass (mass ratio between SiO2 and Na2O) on the kinetics of the hydration process i.e., the change of compressive strength were also investigated. Poorly crystallized low base calcium silicate hydrate C-S-H (I) is the main hydration product of alkali activated slag regardless of the activator used. This is the reason for the rapid increase in the strength of alkali activated slag and also of the very high strength values. The strength growth rate and strength values were significantly higher when sodium-metasilicate was used as the activator than when water glass was used. The specific surface area of the slag and the activator concentration are parameters which have a closely connected influence on strength and their action is cumulative. The modulus n of water glass does not have an explicit influence on the strength of alkali activated slag.
An EPR spin-probe and spin-trap study of the free radicals produced by plant plasma membranes
Authors: Mojovic Milos , Spasojevic Ivan , Vuletic Mirjana , Vucinic Zeljko , Bacic Goran
Published: August 2005

Plant plasma membranes are known to produce superoxide radicals, while the production of hydroxyl radical is thought to occur only in the cell wall. In this work it was demonstrated using combined spin-trap and spin-probe EPR spectroscopic techniques, that plant plasma membranes do produce superoxide and hydroxyl radicals but by kinetically different mechanisms. The results show that superoxide and hydroxyl radicals can be detected by DMPO spin-trap and that the mechanisms and location of their production can be differentiated using the reduction of spin-probes Tempone and 7-DS. It was shown that the mechanism of production of oxygen reactive species is NADH dependent and diphenylene iodonium inhibited. The kinetics of the reduction of Tempone, combined with scavengers or the absence of NADH indicates that hydroxyl radicals are produced by a mechanism independent of that of superoxide production. It was shown that a combination of the spin-probe and spin-trap technique can be used in free radical studies of biological systems, with a number of advantages inherent to them.
A new dimensionless group for the estimation of the current density distribution in an electrochemical cell
Authors: Popov Konstantin , Pesic S.M. , Zivkovic Predrag
Published: August 2005

Anew dimensionless group for the estimation of the current density distribution in an electrochemical cell is defined as the ratio of the sum of the absolute values of the anodic and cathodic over potentials to the overall cell voltage.
Structure-activity relationship study of steroidal 1,2,4,5-tetraoxane animalarials using computational procedures
Authors: Bhattacharjee Apurba , Carvalho Keith , Opsenica Dejan , Solaja Bogdan
Published: August 2005

A three-dimensional QSAR pharmacophore model for antimalarial activity of steroidal 1,2,4,5-tetraoxanes was developed from a set of 17 substituted antimalarial derivatives out of 27 analogues that exhibited remarkable in vitro activity (below 100 ng/mL) against sensitive and multidrug-resistant Plasmodium falciparum malaria. The pharmacophore, which contains two hydrogen bond acceptors (lipid) and one hydrophobic (aliphatic) feature, was found to map well onto the potent analogues and many other well-known antimalarial trioxane drugs including artemisinin, arteether, artesunic acid, and tetraoxanes. The presence of at least one hydrogen bond acceptor in the trioxane or the tetraoxane moiety appears to be necessary for potent activity of this class of compounds. Docking calculations of some of these compounds with heme are consistent with the above observation as the proximity of the heme iron to the oxygen atom of the trioxane or the tetraoxane moiety favors potent activity of the compounds. Electron transfer from the oxygen of trioxane or the tetraoxane appears to be crucial for mechanism of action of the compounds. This information together with the pharmacophore should enable search for new peroxide containing antimalarial candidates from databases and custom designed synthesis of more efficacious and safer analogues.
Overview of the most commonly used methods in allergen characterization
Authors: Cirkovic-Velickovic Tanja , Gavrovic-Jankulovic Marija , Jankov Ratko
Published: August 2005

The characterization of an allergen is a troublesome and difficult process, as it requires both the precise biochemical characterization of a (glyco)protein molecule and the establishment of its susceptibility to IgE antibodies, as they are the main link to histamine release in some hypersensitivity states (type I allergies). As the characterization of an allergen includes molecular weight determination of the allergenic molecule, its structure determination, physicochemical properties, IgE binding properties of the allergen molecule, and its allergenicity, an overall review of which biochemical and immunochemical methods are used in achieving this goal are presented in this paper. The information on the molecular level on the structures of allergens indicates that allergens are considerably heterogeneous protein structures, and that there is no particular aminoacid sequence which is responsible for the allergenicity. Therefore, information gained from detailed structural, functional and immunochemical studies of these intriguing molecules, which nowadays modulate a variety of pathophysiological conditions, would greatly improve our understanding of the underlying disease mechanisms, and the way to handle them.
A primer on electrocatalysis
Authors: O`Bockris M.J.
Published: August 2005

A short review of the development and achievement of electrocatalysis in the last 50 years is given. The need for the knowledge of the reaction mechanism and position of the rate determining step for rational choice of catalyst is particularly stressed. Fundamental aspects of electrocatalysis are elaborated in more detail on the examples of electrochemically important reactions of hydrogen evolution and oxygen reduction, as well on the reaction of electrochemical oxidation of organic fuels (e.g., methanol).