JSCS - Vol 65, No 3

JSCS Vol 65, No. 3

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J.Serb.Chem.Soc. 65(3)147-156(2000)
UDC 547.922/.923:661.852.712:66.094.3
JSCS-2733
Original scientific paper

Lead tetraacetate oxidation of the Diels-Alder adduct of 7-dehydrocholestryl acetate with maleic anhydride

LIDIJA G. BONDARENKO-GHEORGHIU, LJUBINKA B. LORENC and MIHAILO LJ. MIHAILOVIC

Faculty of Chemistry, University of Belgrade, Studentski trg 12 - 16, P. O. Box 158, YU-11001 Belgrade, and
Center for Chemistry ICTM, P. O. Box 815, Njegoseva 12, YU-11001 Belgrade, Yugoslavia

(Received 12 September 1999)
The Diels-Alder adduct (3), obtained by cycloaddition of 7-dehydrocholesteryl acetate (1) and maleic anhydride (2), was heated at ca. 90°C with a large excess of lead tetraacetate in pyridine solution for 5 h. Under these conditions, compound 3 underwent lactonization with the participation of the olefinic D⁶-double bond to give two isomeric monolactone derivatives, 9 and 10 (in a total yield of ca. 6%), and the bislactone product 11 (in 11.5% yield). The starting material was recovered in 36% yield.
Keywords: Diels-Alder adduct, cholesteryl acetate, maleic anhydride, oxidative mono- and bis-lactonization.

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J.Serb.Chem.Soc. 65(3)157-166(2000)
UDC 547.96/.962.3:547.022
JSCS-2734
Original scientific paper

Inter-protein bonding and other molecular interactions in hen egg white

MARIJA VUCKOVIC, MARIJA RADOJCIC and BRATOLJUB H. MILOSAVLJEVIC

Vinca Institute of Nuclear Sciences, P.O. Box 522, YU-11001 Belgrade, Yugoslavia

(Received 30 July, revised 10 December 1999)
The analysis of the SDS-polyacrylamide gel electrophoresis (SDS-PAGE) data, combined with the comparison of viscosity data corresponding to the thin fraction of hen egg white and 2 mM purefied ovalbumin solution, showed that the thin fraction is a protein solution. Dissolution of the thick fraction of hen egg white in SDS and urea solutions followed by SDS-PAGE, in the presence or absence of b-mercaptoethanol, revealed that it is a protein gel. It was also found that the gel structure consists of the three-dimensional ovomucine-ovomucoid network (matrix) held together by S-S bridges which captures the rest of the proteins (ovalbumin, conalbumin, etc). The captured proteins can also be interconnected by S-S bridges thus forming agglomerates or conglomerates, but they are predominantly held by weak electrostatic interactions, as demonstrated by the washing out and dissolving experiments. The matrix structure does not prevent denaturation of the captured proteins as indecated by the 50% decrease in turbidity following gel swelling by the addition of 1 part of an 8 M urea solution to 9 parts of the gel.
Keywords: protein, gel, disulfide bond, bound water, denaturation.

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J.Serb.Chem.Soc. 65(3)167-171(2000)
UDC 547.415.1/547.313.2/:546.733//54-386/
JSCS-2735
Original scientific paper

The preparation and characterization of uns-cis-(ethylene-diamine-N,N'-di-3-propionato)(N-alkylethylenediamines)cobalt(III) complexes

TIBOR J. SABO and SANJA R. GRGURIC

Faculty of Chemistry, University of Belgrade, P. O. Box 158, YU-11001 Belgrade, Yugoslavia

(Received 15 March, revised 29 October 1999)
Three octahedral cobalt(III) complexes of the general formula uns-cis-SCo(eddp)(R-en)CCl˙2H₂O, where eddp = the tetradentate ONNO-type ligand ethylenediamine-N,N'-di-3-propionate and R-en = a bidentate NN-type ligand, either N-methyl, N-ethyl or N-isopropylethylenediamine. The complexes were prepared by the reaction of sodium uns-cis-(ethylenediamine-N,N'-di-3-propionato)(carbonato)cobaltate(III)dihydrate with the corresponding diamine. They were isolated chromatographically and characterized by elemental analysis, infrared and electronic absorption spectroscopy.
Keywords: cobalt(III) complexes, ethylenediamine-N,N'-di-3-propionic acid, N-alk-ylethylenediamines.

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J.Serb.Chem.Soc. 65(3)173-179(2000)
UDC 549.67:1/192.53:536.42
JCS-2736
Original scientific paper

An investigation of the effects of a silicalite type zeolite on PDMS-composites

BORIVOJ ADNADJEVIC and JELENA JOVANOVIC*

Faculty of Physical Chemistry, Studentski trg 16, YU-11000 Belgrade, and
*Institute of General and Physical Chemistry, Studentski trg 12/V, YU-11000 Belgrade, Yugoslavia

(Received 10 March 1999)
The aim of this paper was to investigate the effect of a silicalite type zeolite on PDMS-zeolite composites. The obtained results show that the introduction of a silicalite type zeolite into polysiloxane matrices results in a change of the equilibrium degree of swelling of the composites in toluene, their hardness and their thermal stability. With increasing amount of zeolite, the time required to achieve the equilibrium degree of swelling (DSe) is reduced, the DSe decreases and the hardness increases. Two ranges of the effect of the zeolite concentration on the composite characteristics were noted. At zeolite concentrations up to about 12 % there are significant changes of the DSe and the hardness with zeolite concentration, while these effects are considerably less pronounced at higher concentrations. The results obtained show that the silicalite type zeolite acts as a reinforcing filler. We believe that with increasing zeolite concentration in the composite the total number of established polymer-zeolite interactions increases, as does the spatial irregularity of the polymer network, but that the density of the interactions decreases. This could be the most probably explanation for the changes in the characteristics of the composite with changing zeolite concentration.
Keywords: PDMS-composite, silicalite type zeolite, degree of swelling, hardness, thermal stability.

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J.Serb.Chem.Soc. 65(3)181-193(2000)
UDC 539.213/546.27'28''41''':546.2'283''
JSCS-2737
Original scientific paper

The formation of boron, silicon and calcium containing molecular species in a graphite furnace in Ar/O₂ mixtures

JELENA RADIC-PERIC and MILAN MARKICEVIC

Faculty of Physical Chemistry, University of Belgrade, Studentski trg 12-16, P. O. Box 137, YU-11001 Belgrade, Yugoslavia

(Received 18 June 1999)
The composition of the Ar/O₂/C gas system in the presence of traces of either B, Si or Ca was calculated under the assumption of thermal equilibrium in the temperature range 500-5500 K. The mole concentration of oxygen was taken to be 1-4 %. Two sets of calculations were carried out. In the first one the presence of solid phase (graphite) was ignored and the calculations were performed for a single-phase (gas) system, at variable ratios C/O (0.5, 0.96, 1 and 2). In the second set of calculations the presence of solid carbon (graphite) was taken into account and the composition of the gas system in equilibrium with solid carbon, at p = 1 atm, was determined. The results presented show that the equilibrium composition, particularly the concentration of different compounds involving the trace elements , is very sensitive to the amounts, and the ratio of the amounts of oxygen and carbon. Increasing the O/C ratio results in increasing partial pressures of molecular and atomic oxygen, which favours the formation of oxides of the trace elements and moves their atomization temperatures to higher values. On the other hand, increasing the C/O ratio (C/O >>1) favours atomization, but also carbide formation in the lower-temperature region. It was found that, over a relatively wide temperature interval (1000 << T << 3500 K), the composition of the Ar/O₂/C/X (X = B, Si, Ca) system, with comparable amounts of oxygen and carbon (C/O = 1), does not significantly depend on the presence of the solid phase. The results of calculations enable a reasonable interpretation of numerous experiments carried out on similar systems.
Keywords: atomization in a graphite furnace, thermal equilibrium.

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J.Serb.Chem.Soc. 65(3)195-200(2000)
UDC 546.57/541.182.65:537.12:535.85
JSCS-2738
Original scientific paper

Influence of negative charge on the optical properties of a silver sol

VESNA V. VODNIK and JOVAN M. NEDELJKOVIC

Vinca Institute of Nuclear Sciences, P. O. Box 522, YU-11001 Belgrade, Yugoslavia

(Received 6 July 1999)
The effects of negative charge on the optical properties of a silver sol prepared using sodium borohydride as a reductant were studied. The oscillations in the position of the maximum and the intensity of the surface plasmon absorption band were obesrved. The observed effects were explained as a consequence of the fluctuation of the density of free electrons due to the alternate charging and discharging of the silver particles. The charging process involves electron injection from borohydride ions and intermediate species formed during the course of the metal-catalyzed hydrolysis of borohydride ions (BH₃OH^-, BH₂(OH)₂ and BH(OH)₃^-) into the silver particles, while discharge of the silver sol, by reduction of water to hydrogen, limits the attainable negative charge on the particles.
Keywords: silver sol, sodium borohydride, surface plasmon, electron transfer.

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J. Serb. Chem. Soc. 65(3)201-206(2000)
UDC 546.3/54-44/:66.062:536.7
JSCS-2739
Original scientific paper

Investigation of the effect of organic solvents on kinetic parameters in metal catalyzed reactions

LJILJANA TRIFKOVIC and GORDANA A. MILOVANOVIC

Faculty of Chemistry, University of Belgrade, P. O. Box l58, YU-11001 Belgrade, Yugoslavia

(Received 21 July 1999)
The effects of acetone And acetonitrile on the kinetic parameters of azorubin S oxidation by hydrogen peroxide catalyzed by manganese(II), pyrocatechol violet oxidation by hydrogen peroxide catalyzed by copper(II), and carminic acid oxidation by hydrogen peroxide catalyzed by copper(II) and activated by bifenox, were examined. It was established that the examined solvents exhibit various effects on the kinetic parameters of the above said reactions. In a11 instances a change in the solvent concentration effects both the anthalpy and the entropy contributions to the free activation energy during the transition of the system into the active state, as well as the constant of the active complex formed at this point.
Keywords: Kinetics, metal catalyzed reactions, acetone, acetinitrile, azorubin S, pyrocatechol violet, carminic acid, hydrogen peroxide.

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