Serb. Chem. Soc. 62(8) 619-622 (1997)
Original scientific paper
The alkanes from some plants of Micromeria genus
RADOSAV PALIC, NOVICA RISTIC*, NEBOJSA SIMIC, DUSANKA KITIC** and RADOMIR KAPETANOVIC*
Department of Chemistry, Faculty of Science University of Niš,
Cirila i Metodia 2, YU-18000 Niš,
*Department of Chemistry, Faculty of Science, University of Priština, YU-38000 Priština and
**Faculty of Occupational Safety and Health, University of Niš, Carnojevica 14, YU-18000 Niš, Yugoslavia
27 January 1997)
Hydrocarbon fractions of hexane extracts of Micromeria thymifolia (Scop.) Fritsch and Micromeria albanica (Griseb. ex. K. Maly) Šilic were investigated. Non-branched, saturated, aliphatic hydrocarbons (C17 to C34) were identified by GLC with triacontane and dotriacontane being the prevailing compounds. It was also observed that the relation between hydrocarbons with even and odd number of C-atoms was about 7:1.
Key words: Micromeria thymifolia, Micromeria albanica, hydrocarbons.
Preparation of thermoplastic starch
SLOBODAN JOVANOVIC, KATARINA JEREMIC, RENATA JOVANOVIC*, JASNA DJONLAGIC and BRANKO DUNJIC
Faculty of Technology and Metallurgy, University of Belgrade,
Karnegijeva 4, P.O. Box 494 YU-11000 Belgrade,
*Vinca Institute of Nuclear Sciences, Laboratory GAMA, P.O.Box 522, YU-11001 Belgrade, Yugoslavia
5 February, revised 29 April 1997)
Native starch and WX-starch, i.e., native starch enriched with amylopectin, were mixed with plasticizers and thermomechanically treated in a twin screw mixer in order to obtain thermoplastic starch. Ethylene glycol, propane triol (glycerine) or poly(ethy- lene glycol) with a molar mass less than 1000 g/mol were used as plasticizers. Transformation to thermoplastic starch was only successful when glycerine or ethylene glycol were used as the plasticizers, the temperature of the thermomechanical treatment being dependent on the plasticizer and starch used. Rheological properties of the obtained thermoplastic starch were determined using a mechanical spectrometer. As a result of these measurements, the complex viscosity (h*), shear modulus of stored (G') and of lost energy (G'') were obtained as a function of frequency at constant temperature. The measurements were performed at three temperatures: 140, 170 and 210°C. The results obtained showed that the thermoplastic starch behaved like a typical thermoplastic polymer.
Key words: thermoplastic starch, preparation, rheological properties.
Hydriding and dehydriding of palladium-doped charcoal
MILENKO V. SUSIC
Serbian Academy of Sciences and Arts, Belgrade, and Faculty of Physical Chemistry, University of Belgrade, P.O.Box 137, YU-11001 Belgrade, Yugoslavia
20 March 1997)
The hydrogen absorption capability of wood charcoal doped with 0.0049% of palladium was examined by differential scanning calorimetry. Hydriding and subsequent dehydriding (oxidation) indicate that the absorbent, due to the spill-over effect, absorbs substantial quantities of hydrogen at atmospheric pressure.
Key words: charcoal, palladized charcoal, hydriding.
The melting temperature and atomization energy of f2-7 lanthanides from the viewpoint of the configurational model of solids
A. M. MARICIC, V. M. MINIC, M. V. NIKOLIC, S. M. RADIC and M. M. RISTIC
Joint Laboratory for Advanced Materials of the Serbian Academy of Sciences and Art, Knez Mihailova 35, Belgrade, Yugoslavia
26 March 1997)
In this paper the dependence of the melting temperature and the atomization energy on the electronic structure of lanthanides in the series Ce --> Eu was studied. It is shown that the configurational model of solids enables the establishment of relations which define these dependencies.
Key words: melting, atomization, lantanides, configurational model of solids.
Thermodynamics and kinetics of the crystallization process of Fe75Ni2Si8B13C2 amorphous alloys
A. M. MARICIC, M. V. ŠUŠIC and M. M. RISTIC
Joint Laboratory for Advanced Materials of the Serbian Academy of Sciences and Arts, Knez Mihailova 35, YU-11000 Belgrade, Yugoslavia
26 March 1997)
In this paper the crystallization process of the Fe75Ni2Si8B13C2 amorphous alloy has been investigated. The thermodynamic and kinetic parameters of the process were determined, using the method of differential scanning colorimetry. Measurements of the changes in the specific electric resistivity with time under isothermal conditions indicated changes in the electronic structure of the material.
Key words: amorphous alloys, crystallization, differential scaning calorimetry, electrical resistivity.
Studies of formation of strontium and barium phosphate compounds by atomic absorption inhibition release titration
DIMITRIJE DJ. STOJANOVIC and VILIM J. VAJGAND*
Institute for the Application of Nuclear Energy (INEP) P.O.Box
46, YU-11081 Zemun and
*Faculty of Science, University of Belgrade YU-11000 Belgrade, Yugoslavia
24 April 1996, revised 23 April 1997)
The method of atomic absorption inhibition release titration (AAIRT) was used for the study of formation of strontium and barium phosphate compounds. The principle of this method is the continual titration of a solution of releasing element with a solution of the metal and a refractory forming anion, with the simultaneous aspiration of the titrand into an air-hydrogen flame. The clanges in the metal absorption are registered on the recorder. In this work, magnesium was selected as the monitor metal because of the sensitivity of its measurement. Thus, by titration of some solutions of SrCl2 and BaCl2 with a solution of magnesium chloride and phosphoric acid, curves having a characteristic shape are obtained. The mole ratios of phosphate-to-alkaline earth elements (PO43-/Ae) at the successive characteristic points on the titration curves are constant, while the concentration of phosphate in the titrant is variable. On the basis of these ratios, a possible mechanism for the formation of alkaline earth phosphate compounds is presented.
Key words: phosphate compounds, formation, strontium, barium, atomic absorption, titration.
N O T E
D. POLETI and LJ. KARANOVIC*
Department of General and Inorganic Chemistry, Faculty of
Technology and Metallurgy, P.O.Box 494, YU-11001 Belgrade and
*Laboratory of Crystallography, Faculty of Mining and Geology, Djušina 7, YU-11000 Belgrade, Yugoslavia
24 February 1997)
The title compound is monoclinic, space group P21/a, a = 1.0050(3), b = 2.3435(9), c = 0.67830(10) nm, ß = 99.50(3)°, V = 1.5756(8) nm3, Z = 2. The complex is heteronuclear with a structure consisting of polymeric chains joined together by van der Waals forces. The bridging ligand is the 1,2-benzenedicarboxylate ion with each COO group chelately coordinated to the metal ions. The central ions are in a strongly distored octahedral environment. The spectroscopic and magnetic properties of the com- plex are described and discussed in view of its structure.
Key words: cobalt(II), nickel(II), heteronuclear complex, polymeric structure, 1,2-benzenedicarboxylate ion, 2,2'-dipyridylamine.
Electrochemical properties of polypyrrole in nonaqueous solutions
OLIVERA PAVLOVIC, MILAN VOJNOVIC* and NEDELJKO KRSTAJIC*
Faculty of Technology, University of Novi Sad, B. Cara Lazara 1,
YU-21000 Novi Sad,
*Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, YU-11000 Belgrade, Yugoslavia
22 October 1996)
The electrochemical properties of polypyrrole (pPy) films of various thickness, galvanostatically deposited on a Pt anode, have been studied in solutions of LiClO4 (1.0 M) in propylene carbonate (PC) by employing the cyclic voltammetric technique. The experimental results have been interpreted on the basis of the model developed for intercalation electrodes. The pPy films were found to have reproducible behaviour. The charge transport through the polymer internal volume of the film is a composite process of electron hopping in conjunction with counterion, polymer chain and solvent motion, driven by the effective electrochemical potential. The kinetics of oxidation (doping) and reduction (undoping) reactions in the pPy films were found to be limited by ionic flow into the polymer phase. Active mass utilization decreases with increasing the film thickness and with increasing potential sweep rate, meaning that the electrochemical conversion of the whole film becomes incomplete and only a fraction of the polymer layer takes part in the doping-undoping process. The experimental results proved to be useful to optimise a pPy electrode when utilizing it as the cathode active material of a rechargeable lithium battery.
Key words: polypyrrole electrodes, non-aqueous solutions, cyclic voltammetry.
A kinetic method for the determination of selenium(IV) in ethanol solution
GORDANA A. MILOVANOVIC, MIRA M. CAKAR* and RADIVOJ B. PETRONIJEVIC**
Faculty of Chemistry, University of Belgrade, P.O. Box 158,
*Faculty of Pharmacy, University of Belgrade, YU-11001 Belgrade and
**Institute for Technology of Nuclear and Other Mineral Raw Materials, Belgrade, Yugoslavia
27 March 1997)
A kinetic method for the determination of selenium(IV) in ethanol solution is proposed. The method is based on the action of selenium(IV) upon the oxidation of Nile Blue A by hydrogen peroxide in the presence of phosphate buffer (pH 10.8). The reaction rate was followed spectrophotometrically at 637.5 nm. It was established that the action of selenium(IV) on the indicator reaction is maximal with a 0.25% ethanol solution. The kinetic expression for the reaction in the presence and absence of selenium(IV) are postulated. Optimal experimental conditions for the determination of selenium(IV) were established and selenium(IV) was determined in concentrations from 0.95×10-2 to 12.6×10-2 ng cm-3, with a relative standard deviation of 5.2%. A lower detection limit (1.6×10-3 ng cm-3) and higher selectivity compared to the determination in aqueous solution are obtained. The method was applied for the determination of selenium(IV) in mineral water.
Key words: Selenium(IV) kinetic determination; Nile Blue A oxidation in ethanol solution; hydrogen peroxide.
Application of the C18 column chromatography mobile phase polarity parameter PmN to thin layer chromatography
TOMISLAV J. JANJIC, GORDANA VUCKOVIC and MILENKO B. CELAP
Faculty of Chemistry, Univresity of Belgrade, P.O.Box 158, YU-11001 Belgrade, Yugoslavia
19 February 1997)
On the basis of literature data it was established that the earlier described Bosch and co-workers model, developed on C18 columns, which makes possible an estimation of the retention of substances by means of only one substance parameter (p) and one mobile phase polarity parameter (PmN), can be applied to planar chromatography on thin layers paraffin-oil impregnated silica gel, but not to thin layers of paraffin-oil impregnated aluminium oxide to cellulose layers.
Key words: Mobile phase polarity parameter PmN, thin layer chromatography, paraffin-oil impregnated silica gel, 3,5-dinitrobenzoic acid esters.
Determination of midazolam in pharmaceutical dosage forms by second-order derivative ultraviolet spectrophotometry
LIDIJA B. PFENDT, GORDANA V. POPOVIC*, VIOLETA M. STEFANOVIC and MIRJANA B. RAJIC
Faculty of Chemistry, University of Belgrade, P.O.Box 158,
Studentski trg 16, YU-11001 Belgrade and
*Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, YU-11000 Belgrade, Yugoslavia
13 February 1997)
A second-order derivative ultraviolet spectroscopic method for the determination of midazolam in the presence of maleic acid is described. The assays were carried out in borate buffer (pH 9.2) at a wavelength of 222 nm, which corresponds to the position of the peak of 2D spectrum of midazolam and to the intersection point of the 2D spectrum of maleic acid with the abscissa (zero-crossing point). These conditions were chosen as optimum on the basis of the knowledge of acid-base equilibria of midazolam and maleic acid and of investigations of the absorption and 2D spectra of midazolam and maleic acid and their mixtures. A calibration graph was obtained in the range of midazolam concentrations of 0.25-2.5×10-5 mol dm-3 with a correlation coefficient of 0.99996. The method is simple and rapid, and was successfully applied to the determination of midazolam in the presence of maleic acid in laboratory mixtures and in commercial tablets containing midazolam in the maleate form.
Key words: midazolam, derivative spectrophotometry, midazolam formulation.
The kinetics of lead leaching from lead(II) sulphate in aqueous magnesium chloride solutions
DRAGAN SINADINOVIC and ZELJKO KAMBEROVIC
Department of Nonferrous Metallurgy, Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, P.O.Box 494, YU-11001 Belgrade, Yugoslavia
27 February 1997)
The kinetics of lead leaching from lead(II) sulphate in aqueous magnesium chloride solutions was studied. The lead leaching rates were measured using an agitated vessel at atmospheric pressure. The effects of the MgCl2 concentration, temperature, stirrer velocity and leaching time on the leaching rate were examined. It was established that lead leaching by magnesium chloride solutions is a diffusion and chemically controled reaction (mixed kinetics).
Key words: lead(II) sulphate, magnesium chloride, leaching kinetics.
The dependence of the boride layer thickness and the microstructure of the boride layer with sub-boride zone on steel composition
Z. Z. ACIMOVIC-STOJADINOV, N. M. NOVOVIC-SIMOVIC and N. P. VIDOJEVIC
Faculty of Technology and Metallurgy, Karnegijeva 4, P.O.Box 494, YU-11001 Belgrade, Yugoslavia
3 April 1997)
The influence of the carbon content of steel (0.15, 0.45 and 1.0%) and the present alloying elements silicon and chromium, on the thickness and morphology of the formed Fe2B boride layer as well as on the microstructure of the transitional zone next to the boride layer (sub-boride layer) were investigated. Boriding was performed using for boriding granulate in the temperature interval 850 to 1050°C for 2 to 9 h. Besides optical microscopy and quantitative metallography, microchemical analysis was used in the investigations. The obtained results were analyzed with special emphasis placed on the disagreement with existing ones. Regarding certain issues, new observations were made and are discussed.
Key words: carbon and low-alloyed steels, boride layer thickness and morphology, microstructure of sub-boride layer, quantitative metallography and microchemical analysis.