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Impresum (89 KB - WinZip file);  Content of Vol 64, No. 5-6 (72 KB - WinZip file);  Instruction for authors (37 KB - pdf file)

(Received 2 February 1999)
1. Introduction
2. Mass transfer in the steady state periodic condition
 2.1. Reversing current
 2.2. Pulsating current
 2.3. Alternating current superimposed on direct current
3. The influence of the charge and discharge of the electrical double layer
4. The validity of the mathematical model
 4.1. Reversing current in the millisecond range
 4.2. Reversing current in the second range
 4.3. Pulsating current
 4.4. Pulsating overpotential
5. Conclusion

Key words: mass-transfer, electrodeposition, reversing current, pulsating current, alternating current superimposed on direct current, pulsating overpotential.

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(Received 26 January, revised 25 February 1999)
It was shown that the current density-cell voltage curves recorded in a cell with parallel plate electrodes for different distances between the edges of the electrodes and side walls of the cell can be used to determine the current distribution in cells of the Haring-Blum type.

Key words: metal electrodeposition, electrochemical cell, current distribution.
 

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(Received 2 September 1998, revised 11 February 1999)
High concentrations (up to 4000 ppm) of copper(II) porphyrins have been detected in the kerogen of the Cretaceous/Tertiary (KT) boundary informal type sediment, the Fish Clay, at Stevns Klint, Denmark. These pigments have also been found in the Danish KT sediment at Nye Klov, which is about 300 km away from Stevns Klint. However, copper(II) porphyrins cannot be detected in the Danich boundary rock of the Dania site, which is separated from Stevns Klint by about 200 km. It is proposed that the kerogen copper(II) porphyrins are derived from humic materials of terrestrial (peat/soil) sources already enriched with these compounds, which were redeposited in the Danish KT boundary Basin. In addition, our results show that the kerogen copper(II) porphyrins are present, for comparison, in the Permian Kupferschiefer shale from Poland. The amounts are comparable to those in the Fish Clay kerogen. To our opinion, the same processes responsible for the kerogen copper(II) porphyrin enrichment have occurred in the Stevns Klint KT boundary sediment and in the Kupferschiefer.

Key words: copper, porphyrins, kerogen, electron spin resonance.

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(Received 25 November 1998, revised 5 February 1999)
The influence of the anionic surfactant sodium dodecyl sulfate on the rate of the reaction between the cationic form of Nile Blue A and hydrogen peroxide was investigated in the pH range from 5 to 8.5. A retardation of the oxidation of Nile Blue A with hydrogen peroxide of three orders of magnitude was observed at pH 8.5 in the presence of anionic micelles compared to the kinetic data in water. The retardation effect was less pronounced at lower pH values. These effects were explained by the electrostatic interaction of the species involved in the reaction with the negatively charged micellar surface and their effective separation in the vicinity of the micellar surface.

Key words: Nile Blue A, hydrogen peroxide, sodium dodecyl sulfate, micelles.
 

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(Received 21 December 1998, revised 8 February 1999)
This paper presents a thermodynamic analysis of possible, but insufficiently studied, chemical reactions occurring during the chlorination of copper(I) sulfide by calcium chloride in the presence of oxygen. It formed the basis for assessing the probability and priority of their occurrence. Phase stability diagrams have been plotted for the Cu-S-O-Cl system in the coordinates log p(S₂)-log p(O₂)-log p(Cl₂) in the temperature range from 473 to 773 K.

Key words: thermodynamic analysis, Cu-S-O-Cl system, chlorination, calcium chloride.
 

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(Received 18 December 1998)
The in vitro stability of ^99mTc(Sn)-pyrophosphate solution was examined in dependence on the preparation conditions of the samples, the radioactive concentration of ^99mTc in the kit and the time elapsed after labeling. The samples without any protection are highly unstable. The formation of ^99mTc-pertechnetate does not depend on the radioactive concentration. Nitrogen purging provides protection in the case of low radioactive concentrations (37 MBq ^99mTc/ml) but exhibits no effect at higher concentrations. The best stabilization was achieved by using ascorbic acid. A concentration of 60 µg/ml keeps the content of ^99mTc-pertechnetate below 1% during six hours after labeling, even in solutions of high readioactive concentrations (740-814 MBq/ml). Gentisic acid is less effective. Concentrations about ten times higher than required using ascorbic acid are needed to keep the content of ^99mTc-pertechnetate below 5% during six hours.

Key words: pyrophosphate, technetium-99m, ascorbic acid, gentisic acid, chemical stabilization.
 

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(Received 21 October 1998, revised 15 January 1999)
The preparation and properties of some complexes of cobalt(II), zinc(II) and copper(II) with several newly synthesized benzimidazole derivatives (L) are reported. The complexes, of the general formula [MCl₂L₂] (M=Co(II), Zn(II)) and [CuCl₂L(H₂O]), have a tetrahedral structure. The complexes were characterized by elemental analysis, molar conductivity, magnetic susceptibility measurements, IR and absorption electronic spectra. The antibacterial activitiy of the benzimidazoles and their complexes was evaluated against Erwinia carotovora subsp. carotovora and Erwinia amylovora. The complexes were found to be more toxic than the ligands.

Key words: complexes, cobalt(II), zinc(II), copper(II), benzimidiazole derivatives, physico-chemical characterization, biological activity.

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(Received 30 October 1998, revised 4 February 1999)
The content and composition of fatty acids and alkanes of Satureja adamovicii Silic and Satureja fukarekii Silic were analized by GC. It was found that unsaturated acids prevailed and that the major components were palmitic, oleic, linoleic and linolenic acids. The hydrocarbon fractions of pentane extracts were shown to consist of the alkane homologues (C₁₇ to C₃₄) with nonacosane and hentriacontane being prevailing compounds.

Key words: Satureja adamovicii Silic, Satureja fukarekii Silic, fatty acids, hydrocarbons.
 

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(Received 14 May 1998, revised 16 February 1999)
Starting from 3-benzyloxy-17-hydroxy-16,17-secoestra-1,3,5(10)-triene-16-nitrile (1b), 17-tosylate 2b and also 17-chloro-, 17-bromo- and 17-iodo-derivatives 4b, 5b, and 6b, were obtained. The fluoro-derivative 3b was obtained from 2b in the reaction with tetrabutyl ammonium fluoride. The deprotection of the 3-hydroxyl group was achieved by action of hydrogen in presence of Pd/C as a catalyst, yielding six new 3-hydroxy-16,17-seco-estrone derivatives.

Key words: 3-hydroxy-16,17-seco-estrone derivatives, halogeno steroids, hydrogenolysis.
 

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