JSCS - Vol 66, No 7

JSCS Vol 66, No. 7

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J.Serb.Chem.Soc. 66(7)429–434(2001)
UDC 678.84
JSCS–2871
Original scientific paper

Relative activities of siloxane monomers toward the cation exchange resin-catalyst in the equilibration reactions

M. N. GOVEDARICA

ICTM, Centre of Chemistry, Department of Polymeric Materials, Njegoseva 12, YU-11000 Belgrade, Yugoslavia

(Received 17 August 2000, revised 11 April 2001)
The relative activities of a number of siloxane monomers, both cyclic and linear, toward the cation exchange resin-equilibration catalyst were determined. The determination was based on the fact that when a particular siloxane compound is added to an arbitrarily chosen equilibrate, it takes part in the equilibration process, provoking certain viscosity changes of the reaction mixture. Taking these viscosity changes as a measure of activities, the following order was obtained: hexamethylcyclotrisiloxane > hexamethyldisiloxane > octamethylcyclotetrasiloxane > one linear all-methyl oligosiloxane of number average molecular weight of approximately 800 > decamethylcyclopentasiloxane. The results obtained by using the described viscosimetrical determination method were controlled by measuring the number average molecular weights of the reaction mixtures at the beginning and at the end of the equilibration process. The deviations of the experimentally measured from the calculated values were less than 20 %, as was found in one equilibration system. In most other systems the deviations were about 10 % which is a very good result which strengthens the validity of the applied determination method.
Keywords: cation exchange resin, catalyzed siloxane equilibration, activities of siloxane monomers, acidic equilibration catalyst.

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J.Serb.Chem.Soc. 66(7)435–441(2001)
UDC 547.426.1
JSCS–2872
Note

N O T E
The influence of a cryoprotective medium containing glycerol on the lyophilization of lactic acid bacteria

NADA TRSIC-MILANOVIC, ALEKSANDAR KODZIC, JOSIP BARAS* and SUZANA DIMITRIJEVIC-BRANKOVIC*

Institute of Immunology and Virology “Torlak”, Vojvode Stepe 458, YU-11221 Belgrade and
*Faculty of Technology and Metallurgy, Karnegijeva 4, YU-11000 Belgrade, Yugoslavia

(Received 11 December 2000, revised 11 April 2001)
The aims of liophilization (freeze-drying) of lactic acid bacteria are to preserve pure cultures or to prepare starters for the dairy industry. In both cases, the choice of the cryoprotectant is very important. In this work, samples of Bifidobacterium breve A71 and Bifidobacterium bifidum BbTD were freeze-dried in a new cryoprotective medium containing lactose, gelatine and glycerol (medium B). The reference medium contained saccharose, gelatine and skim milk (medium A). Before liophilization, the eutectic points of both media were determined, because the products must be cooled to a temperature below its freezing point. The success of the cryoprotectants was estimated in terms of the number of surviving organisms after lyophilization. Bifidobacterium breve A71 and Bifidobacterium bifidum BbTD freeze-dried in media A and B showed high survival rates. Bifidobacterium breve A71 showed a greater percentage survival in combination with medium B than with medium A. These results could be utilized in the manufacture of Bifidobacterium breve A71 as a starter in the diary industry because it is a human isolate which, except for acidification, has probiotic activity.
Keywords: lyophilization, lactic acid bacteria, Bifidobacterium bifidum, cryoprotectants.

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J.Serb.Chem.Soc. 66(7)443–449(2001)
UDC 549.766.8
JSCS–2873
Original scientific paper

Extraction of uranyl nitrate, sulphate and chloride with tri-n-octyl amine (TOA) from aqueous solutions

JOZEF. J. COMOR and DJORDJE M. PETKOVIC

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

(Received 4 April 2001)
Extraction of uranyl nitrate, chloride and sulphate with tri-n-octyl amine (TOA) in benzene as a function of the TOA concentration has been studied. The concentration based extraction equilibrium constants were calculated from the distribution data of the uranyl salts, fitting the parameters of a chemical model to the experimentally obtained extraction isotherms. The calculated equilibrium constants are 46.5, 89.4 and 4.2·10⁴ for uranyl nitrate, chloride and sulphate, respectively. These values are in good agreement with the previously reported extraction equilibrium constants calculated by the inflection point method.
Keywords: uranyl nitrate, uranyl chloride, uranyl sulphate, tri-n-octyl amine, extraction equilibria.

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J.Serb.Chem.Soc. 66(7)451–462(2001)
UDC 543.422/.423
JSCS–2874
Original scientific paper

A study of the IR spectra of the copigments of malvin chloride with organic acids

JASMINA M. DIMITRIC-MARKOVIC, UBAVKA B. MIOC, JELISAVETA M. BARANAC and ZORAN P. NEDIC

Faculty of Physical Chemistry, University of Belgrade, Studentski trg 16, P.O. Box 137, YU-11000 Belgrade, Yugoslavia

(Received 11 January, revised 5 April 2001)
The infrared spectra of the copigments of malvin with several organic acids: caffeic, ferulic, sinapic, chlorogenic, and tannic, were analyzed in order to elucidate the bonding of the molecules in the copigments. It was established that copigmentation is realized through hydrogen bonding between malvin molecules and the acids under study. The infrared spectra reveal that two groups of hydrogen bonds are formed, which include interactions of different molecular structures: hydroxy groups (bands around 3500 cm^–1) and oxonium ions of the molecules (bands below 3000 cm^–1). The formed hydrogen bonds were found to be of different strengths. The strengths of the hydrogen bonds were tentatively correlated with thermodynamic properties of the corresponding copigmentation reactions.
Keywords: malvin, organic acids, copigmentation, IR spectra.

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J.Serb.Chem.Soc. 66(7)463–475(2001)
UDC 543.54
JSCS–2875
Original scientific paper

Solid diffusion control of the adsorption of basic dyes onto granular activated carbon and natural zeolite in fixed bed columns

L. MARKOVSKA, V. MESHKO, V. NOVESKI and M. MARINKOVSKI

Faculty of Technology and Metallurgy, University "St. Cyril&Methodius", Ruger Boskovic 16, 91000 Skopje, Republic of Macedonia

(Received 31 July 2000)
The adsorption of basic dyes from aqueous solutions onto granular activated carbon and natural zeolite was studied using a fixed bed column. The design procedures for fixed bed adsorption columns were investigated for two basic dyes Maxilon Goldgelb GL EC 400 % (MG-400) and Maxilon Schwarz FBL-01 300 % (MS-300). A computer program based on the solid diffusion control model has been developed. The model parameters: solid diffusion coefficient, D_S, axial dispersion coefficient, D_L and external mass transfer coefficient, k_f for all the investigated systems were estimated by means of a best fit approach.
Keywords: solid diffusion control, dye adsorption, granular activated carbon, natural zeolite, adsorption modelling.

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J.Serb.Chem.Soc. 66(7)477–481(2001)
UDC 541.139:548.526
JSCS–2876
Original scientific paper

A study of the effect of magnetic fields on the diffusion layer at the Fe/H₂SO₄ interface by holographic microphotography

CHAO WANG*,*** and SHENHAO CHEN**^,***

*Department of Chemistry, Xuzhou Teachers' University, Xuzhou 221009, China,
**Department of Chemistry, Shandong University, Jinan 250100, China and
***State Key Laboratory for Corrosion and Protection of Metals, The Chinese Academy of Sciences, Shenyang 110015, China

(Received 9 March 2001)
The effect of externally imposed magnetic fields on the relaxation of the concentration diffusion layer at the Fe/0.5 mol dm^-3 H₂SO₄ interface after passivation of the iron electrode during potentiodynamic polarization was studied by holographic microphotography. The presence of a magnetic field was found to retard the relaxation process while the microturbulence was impeded.
Keywords: diffusion layer, relaxation process, magnetic field, holographic microphotography, microturbulence.

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J.Serb.Chem.Soc. 66(7)483–490(2001)
UDC 543.251
JSCS–2877
Original scientific paper

Surface roughness minimum: Ag thin layer deposited on a glass

R. PETROVIC, S. STRBAC*, N. BUNDALESKI** and Z. RAKOCEVIC**

Institute of Physics, P.O. Box 57, YU-11001 Belgrade,
*ICTM-Institute of Electrochemistry, P.O. Box 815, YU-11001 Belgrade and
**Vinca Institute of Nuclear Sciences, P.O. Box 522, YU-11001 Belgrade, Yugoslavia

(Received 9 March 2001)
In this paper the results of an examination of the surface roughness and morphology dependence of silver thin films up to 100 nm thick deposited on a microscope glass on the deposition rate and on the deposition time are presented. It was found that, for a constant deposition rate, the surface roughness exhibits minimum at a certain layer thickness. This coincides with the turning point when the influence of the substrate surface on the deposition process becomes negligible, i.e., to the change in the nature of the system substrate/deposit from Ag/glass to Ag/Ag. For a constant layer thickness, the surface roughness minimum, achieved at a certain deposition rate, coincides to the turning point when the average free path for vertical adatom mobility becomes zero.
Keywords: surface roughness, silver, glass.

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J.Serb.Chem.Soc .66(7)491–498(2001)
UDC 543.251
JSCS–2878
Note

N O T E
The current distribution in an electrochemical cell. Part VI. The quantitative treatment for cells with three plane parallel electrode arrangements

K. I. POPOV, S. M. PESIC* and P. M. ZIVKOVIC

Faculty of Technology and Mietallurgy, University of Belgrade, P.O. Box 35-03, Karnegijeva 4, YU-11001 Belgrade and
*EI-Stampana kola d.d., Printed Circuit Board Factory, Bul. Cara Konstantina 80–84, YU-18000 Nis, Yugoslavia

(Received 9 March, revised 9 April 2001)
A method for the quantitative determination of the current density distribuion in cells with a three plane parallel electrode arrangement is proposed. It is shown that the current density distribution can be determined using the data obtained by simple polarization measurements. The relation to the Haring-Blum cell with P = 2 is discussed.
Keywords: metal electrodeposition, electrochemical cell, current distribution.

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