JSCS Vol 64, No. 10
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J. Serb. Chem. Soc. 64(10) 563-570 (1999)
UDC 547.6.547.568.5:66.094.3
JSCS-2695
Original scientific paper
On the oxidation of dibenzo[fg,ij]pentaphene and
dinaphtho[2,1,8,7-defg:2',1',8',7'-ijkl]pentaphene dianions
IVAN GUTMAN
Faculty of Science, University of
Kragujevac, P.O. Box 60, YU-34000 Kragujevac, Yugoslavia
Received 6 April 1999)
The dianion of dibenzoSfg,ijCpentaphene has
recently been synthesized and shown to react with oxygen, forming the
15,16-dioxo derivative in nearly quantitative yield. Oxidation of the dianion
of dinaphtho[2,1,8,7-defg:2',1',8',7'-ijkl]pentaphene under
similar conditions does not result in any dioxo product. It is shown that these
findings are a consequence of the different modes of cyclic conjugation in the
two dianions. Cyclic conjugation in the mentioned two dianions, as well as in a
number of other structurally related benzenoid dianions is assessed by means of
a quantum-chemical method, developed earlier by the author.
Key words: dianions, benzenoid hydrocarbons,
cyclic conjugaiton.
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J. Serb. Chem. Soc. 64(10) 571-576 (1999)
UDC 612.018:612.4
JSCS-2696
Original scientific paper
The synthesis of a small library of
prospective growth hormone secretagogues
VOJISLAV PEJOVIC*, VUKIC SOSKIC*,** and JELENA
JOKSIMOVIC***
*Institute for Chemistry,
Technology and Metallurgy, Centre for Chemistry, Njegoseva 12, YU-11000
Belgrade,
**Faculty of Chemistry, University of Belgrade, Studentski trg
12-16, P.O.Box 158, YU-11001 Belgrade and
***Institute for Biological Research, 29. Novembra 142, YU-11060
Belgrade, Yugoslavia
(Received 16 October
1998)
Employing tools of combinatorial chemistry, an
original methodological approach has been developed and applied for the design
and synthesis of a small library of peptide-like compounds, prospective growth
hormone (GH) secretagogues. For this purpose seven building blocks of tBoc- and
Fmoc-protected amino acids was used. In this way, a small, tripeptoid library
on polyethylene glycol monomethyl ether 5000 (PEG 5000) as a soluble support
was obtained. The library was screened by a new, simple system, based on
polyclonal rabbit antiserum raised against "GH secretagogue
pharmacophore" of a known growth hormone secretagogue GHRP-6 (Hexarelin®)
and the most promising GH secretagogue candidate was selected.
Key words: secretagogue, growth hormone,
combinatorial chemistry.
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J. Serb. Chem. Soc. 64 (10) 577-587 (1999)
UDC 678.742:62.001.57
JSCS-2697
Original scientific paper
Dependence of the structural
parameters and properties of low density polyethylene on the synthesis
conditions
DRAGOSLAV M. STOILJKOVIC, RADMILA Z. RADICEVIC and MILOVAN R.
JANKOVIC
Faculty of Technology, University
of Novi Sad, Bulevar Cara Lazara 1, YU-21000 Novi Sad, Yugoslavia
(Received 19 January,
revised 30 March 1999)
In a previous publicaitons from the authors'
laboratotry a method was developed to predict the structure and properties of
low density polyethylene (PE-LD) that could be obtained over a very wide range
of polymerization conditions. The method was proved using experimental data
from the literature. However, some shortcomings of the method were noticed. The
aim of this work was to overcome the shortcomings and to enable the better
manipulation of experimental data using a computer. A computer program has been
developed to establish the mathematical relationships between ethylene entropy
and the structural parameters and density of Pe-LD. All available experimental
data (more than 300 experimental points) have elaborated and confirmed our
mathematical models and our theoretical predictions.
Key words: low density polyethylene,
structure, properties, mathematical model.
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J.
Serb. Chem. Soc. 64 (10) 589-598 (1999)
UDC 661.888.1:622.337
JSCS-2698
Original scientific
paper
The kerogen vanadyl porphyrins:
incorporation during catagenesis
PAVLE I. PREMOVIC, IVANA R. TONSA, DRAGAN M. DJORDJEVIC and
MIROSLAV P. PREMOVIC
Laboratory for Geochemistry and
Cosmochemistry, Department of Chemistry, Faculty of Science, University of Nis,
P.O.Box 91, YU-18000 Nis, Yugoslavia
(Received 18 February
1999)
Natural vanadyl (VO2+)-deoxophylloerythroetioporphyrins (DPEP) have been shown to be
capable of reacting and quantitatively incorporating into immature kerogen
model materials (torbanite, lignites, subbituminous coal and immature
lacustrine kerogen) at 200°C for 72 h in the absence/presence of air. Electron
spin resonance was used to monitor the incorporation of VO2+-DPEP into the kerogen models. The products of the incorporation
resemble natural kerogen enriched with VO2+. The simulation
experiments described in this paper clearly show that the kerogen VO2+-P may originate from VO2+-DPEP incorporation into
the kerogen macromolecular structures during catagenesis.
Key words: vanadyl porphyrins, kerogen,
electron spin resonance.
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J.
Serb. Chem. Soc. 64(10) 599-608 (1999)
UDC 547.973.8:547.98:667.622.3:543.51
JSCS-2699
Original scientific paper
A spectrophotometric study of the
reaction of copigmentation of malvin and tannic acid
JELISAVETA M. BARANAC, NADEZDA A. PETRANOVIC and JASMINA M.
DIMITRIC-MARKOVIC
Faculty of Physical Chemistry,
University of Belgrade, Studentski trg 16, P.O.Box 137, YU-11000 Belgrade,
Yugoslavia
(Received 9 December
1998, revised 20 April 1999)
The reaction of copigmentation of malvidin
3,5-diglucoside and tannic acid of the ester type was studied. The interactions
of these molecules were observed via UV-VIS absorption spectroscopy. It was
established that the pH of the medium, the concentration of the copigmentating
molecules, and the temperature affect the copigmentation process. The
calculated equilibrium constant of the reaction of pH 3.00 is K = 226.9,
and at pH 3.65 it is K = 277.0. The change of the Gibbs free energy in
pH 3.00 buffer is DG = -13.4 kJ/mol, and in pH 3.65 buffer it is DG = -13.9 kJ/mol. The stoichiometric ratio of the components in
the copigment is 1:1, at both pH values. It is evident from the calculated
values of the thermodynamic functions that the process is thermodynamically
favorable in the lower temperature range. Temperature appears as the basic
parameter of the thermodynamic feasability of the process, since the
copigmentation process is exothermic ( DHpH=3.00 = - 41.6 kJ/mol and DHpH=3.65 = - 41.6 kJ/mol) and proceeds with a decrease in entropy ( DSpH=3.00 = - 94.4 J/mol K and DSpH=3.65 = -92.7 J/mol K).
Key words: malvin, tannic acid,
copigmentation, UV-VIS spectra.
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J.
Serb. Chem. Soc. 64(10) 609-620 (1999)
UCC 547.821/547.583.2:541.428.49:536.4
JSCS-2700
Original scientific paper
The thermal decomposition of the
pyridine saccharinates of Co, Ni and Cu: A correlation of the structural and
the infrared data
PANCE NAUMOV, GLIGOR JOVANOVSKI, VERA JORDANOVSKA and BOYAN
BOYANOV*
Institute of Chemistry, Faculty of
Science, "Sv. Kiril i Metodij" University, P.O.Box 162, 91001 Skopje,
Macedonia and
*Faculty of Chemistry, Plovdiv University, Paisii Hilendarski,
4025 Plovdiv, Bulgaria
(Received 16 February
1999)
In order to investigate the differences in the
stability of the isomorphous pyridine saccharinates [Co(H2O)4(C5H5N)2](C7H4NO3S)2·H2O and [Ni(H2O)4(C5H5N)2[ (C7H4NO3S)2·4H2O, their thermal behavior (TG, DTG and DTA
curves) from ambient temperature up to 1000°C in a static air atmosphere was
studied. For comparative purposes, the thermoanalytical curves of [Cu(H2O)(C5H5N)2(C7H4NO3S)2] were recorded as well. The decomposition
pathways and the stability of the compounds are interpreted in the terms of the
structural data. A possible mechanism for the decomposition of the saccharinato
ion/ligand in an oxidizing atmosphere is proposed. The infrared spectral
characteristics of the complexes are also discussed.
Key words: thermal decomposition, pyridine
complexes, saccharinates, structure, infrared spectra.
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J.
Serb. Chem. Soc. 64(10) 621-635 (1999)
UDC 547.498:541.428.49(546.47' 56'' 73''' 74'''')
JSCS-2701
Original scientific paper
Metal complexes of triazine -
Schiff bases: Spectroscopic and
thermodynamic
studies of complexation of some divalent metal ions with
3-(a-acetylethylidenehydrazino)-5,6-diphenyl-1,2,4-triazine
M. MASHALY H. A. BAYOUMI* and A. TAHA
Faculty of Education, Ain Shams
University, Roxy, Cairo and
*University College for Girls, Ain Shams University, Heliopolis,
Cairo, Egypt
(Received 4 November
1998, revised 1 April 1999)
Metal complexes of some divalent metal ions (Co,
Ni, Cu and Zn) with 3-(a-acetylethylidenehydrazino)-5,6-diphenyl-1,2,4-triazine
(AHDT) as a Schiff-base have been investigated potentiometrically and
spectrophotometrically and found to have the stoichiometric formulae 1:1 and
1:2 (M:L). The formation constants of the proton-ligand and metal-ligand
complexes have been determined potentiometrically at different temperatures
(10, 20, 30, 40 and 50°C) at an ionic strength of 0.1 M KNO3 in 75% (v/v) dioxane-water solution. The standard thermodynamic
parameters, viz. DG°, DH°, and DS°, for the proton-ligand and the
stepwise metal-ligand complexes have been evaluated.
Key words: thermodynamic parameters;
Schiff-base; metal(II)-complexes; cobalt(II)-complexes; nickel(II)-complexes;
copper(II)-complexes; Zn(II)-complexes; formation constant; potentiometry and
spectroscopy.
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J.
Serb. Chem. Soc. 64(10) 637-646 (1999)
UDC 548.55/546.34' 882'' 21'''/:535.84
JSCS-2702
Original scientific paper
The optical properties of LiNbO3 single
crystals obtained in air atmosphere
ALEKSANDAR GOLUBOVIC, SLOBODANKA NIKOLIC, RADOS GAJIC*, STEVAN
DJURIC**, ALEKSANDAR JELISIJEVIC*, DRAGANA VUKOVIC***, and ANDREJA VALCIC****
Institute of Chemistry, Technology
and Metallurgy, Njegoseva 12, YU-11000 Belgrade,
*Institute of Physics, P.O.Box 57, YU-11001 Belgrade,
**Faculty of Mining and Geology, Djusina 7, P.O.Box 162, YU-11000
Belgrade,
***IRITEL, D. D. for Telecommunications and Electronics,
Batajnicki put 23, YU-11080 Belgrade and
****Faculty of Technology and Metallurgy, Karnegijeva 4, YU-11000
Belgrade, Yugoslavia
(Received 15 January,
revised 28 March 1999)
Single crystals of LiNbO3 were grown by the Czochralski technique in an air atmosphere. The
critical diameter and the critical rate of rotation were calculated. X-Ray
measurements of the powder were carried out to obtain the lattice parameters.
The optical constants were calculated by Kramers-Kronig analysis of reflectance
data. The optical properties of LiNbO3 single crystals were
studied for samples grown in an air atmosphere to investigate the influence of
air on the optical properties of the formed crystals. A peak due to OH- gtroups appears in the transmission spectrum at 3385 cm-1. It was still present after annealing in an air atmosphere at
temperature up to 873 K, but it was no longer detectable after annealing at
1473 K in an electric field. Thick films of the high-temperature superconductor
YBa2Cu3O7 (Ag) were obtained on plates of LiNbO3 single crystals. The obtained results are discussed and compared
with published data.
Key words: single crystals, Czochralski
technique, lithium niobate, critical rotation rate, critical crystal diameter,
optical properties.
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