CHEMISTRY

SPECTROPHOTOMETRIC INVESTIGATION OF IRON (III) COMPLEXES WITH ERIOCHROME CYANINE R IN THE PRESENCE OF SOME CATIONIC SURFACTANTS
Chr. Ivanova

A FLOW-INJECTION SYSTEM FOR ANALYSIS OF LACTATE IN BIOLOGICAL FLUIDS BY MEANS OF IMMOBILIZED LACTATE OXIDASE
T. Kolusheva, A. Marinova

OXIDATION OF METAL COMPLEXES OF 1,10-PHENANTHROLINE AND 5-NITRO-1,10-PHENANTHROLINE BY HYDROGEN PEROXIDE
M. Atanassova G. Dimitrov

NEW N-PYRROLYLACETIC AND 3-(N-PYRROLYL)PROPANOIC ACIDS VIA PAAL-KNORR CONDENSATION
A. Bijev, N. Nedelchev, A. Nankov

ELECTROLYTIC COLORING OF POROUS ALUMINA FILMS IN CuSO₄ SOLUTIONS.
I. EFFECT OF THE COLORING CONDITIONS ON THE COLOR CHARACTERISTICS OF THE FILMS
A. Girginov, A. Zahariev, Y. Sokolova, R. Aleksieva

ELECTROLYTIC COLORING OF POROUS ALUMINA FILMS IN CUSO₄  SOLUTIONS
II. DETERMINATION OF SOME FUNCTIONAL PROPERTIES OF THE COLORED FILMS
A. Girginov, A. Zahariev, Y. Sokolova, R. Aleksieva

ADSORPTION EQUILIBRIUM IN THE SYSTEM NATURAL ADSORBENT – DYE SOLUTIONS
S. Veleva, A. Georgieva, D. Pishev, B. Staneva

ELECTROCHEMICAL PROPERTIES OF SKELETON COPPER CATHODES PREPARED BY THERMAL ARC SPRAYING
N. Vaszilcsin, W. Brandl, A. Kellenberger

ADSORPTION AND SPECTROSCOPIC STUDIES ON THE INTERCALATIONS OF COPPER (II) CHELATE INTO BENTONITE
M. Atanassova, V. Jordanov

INVESTIGATION OF THE POLAROGRAPHIC BEHAVIOR OF
NIO, CoO ,SnO₂ AND WO₃  IN SLAG MELT OF  Na₂ O . SiO₂. B₂O₃ USING A ROTATING DISK ELECTRODE
T. Tzvetkoff

SPECTROPHOTOMETRIC INVESTIGATION OF IRON (III) COMPLEXES WITH ERIOCHROME CYANINE R IN THE PRESENCE OF SOME CATIONIC SURFACTANTS
Chr. Ivanova

University of Chemical Technology and Metallurgy8, Kl. Ohridski Blvd., 1756 Sofia, Bulgaria E-mail: christina@top.bg

Received 10 October 2000 Accepted 10 November 2000

 

The effect of cationic surfactants (CS) - benzyldimethylcethyl-ammonium chloride and benzyldimethyltetradecylammonium chloride on spectrophotometric characteristics of Fe(III) complexes with Eriochrome Cyanine R(ECR) has been investigated. Significant batochromic and hyper-chromic effects (Dl_max=100-110nm;e ~ 9.3¸9.4õ10⁴ at l=656(660) nm) have been established at the optimum conditions (Fe:ECR:CS – 1:4:40; 0.05M acetate buffer with pH 5-5.5). A spectrophotometric method is proposed for determination of 1-20 ìg Fe(III) in the presence of great excess of other cations (masking of Al(III) with NaF and of Cu(II) with thiourea). It is applied for determination of 10^-4-10^-3% iron in cooking salt.

 A method for titration of >0.5 mg Fe(III) with EDTA using ECR and ECR+CS as indicators at pH~2 is suggested. For that purpose a violet complex in excess of iron has been investigated (Fe₂R, e~ 2.4õ10⁴; â^’=0.525).

Keywords: spectrophotometric analysis, Eriochrome Cyanine R, iron, cationic surfactants.

 

A FLOW-INJECTION SYSTEM FOR ANALYSIS OF LACTATE IN BIOLOGICAL FLUIDS BY MEANS OF IMMOBILIZED LACTATE OXIDASE
T. Kolusheva, A. Marinova

University of Chemical Technology and Metallurgy Kl. Ohridski 8, Blvd., 1756 Sofia, Bulgaria E-mail: kolusheva@yahoo.com

Received 11 November 2000 Accepted 21 November 2000

An original FIA– system for analysis of lactate in biological objects is created, comprising of a combination of an enzyme bioreactor and an enzyme membrane, in which the enzyme lactate oxidase is immobilized. An original method is developed for obtaining of the enzyme lactate oxidase membrane, incorporated directly in a trielectrode amperometric detector cell. The elimination of the negative influence of the low molecular electroactive components of the biological fluids is achieved through the placement of the medium physiological amounts of ascorbic acid, urate and cystein in the callibratory solutions of lactate. The product inhibition of the immobilized lactate oxidase from the H₂O₂, formed under the oxidation of the lactate, is avoided through the combination enzyme bioreactor – enzyme membrane. The FIA-system is applied for the analysis of lactate in control serums, human serum and fermentation fluids. The linear range of the calibration curve is 5.10^-4  - 5.10^-2Ì when 50 µl standard lactate solutions are injected. The obtained data shows good reproducibility, as the coefficient of variation when analysing blood serums does not exceed 3 % and when analysing fermentation fluids – 3.5%.

Keywords and phrases: Flow-injection system, Enzyme bioreactor, Enzyme membrane, Lactate, Lactate oxidase, Zeolyte

Oxidation of metal complexes of 1,10-phenanthroline and 5-nitro-1,10-phenanthroline by hydrogen peroxide
M. Atanassova G. Dimitrov

University of Chemical Technology and Metallurgy, 8 Kl. Ohridski, 1756 Sofia, Bulgaria gdd@uctm.edu

Received 16 November r 2000 Accepted 24 November 2000

The Cu(II) and Fe(II) complexes of 1,10-phenanthroline and 5-nitro-1,10-phenanthroline were subjected to oxidation by hydrogen peroxide in aqueous medium. The kinetics of the reaction for the Cu(II) complexes in a homogeneous solution as well as on silica gel was studied. The products of oxidation were analyzed by IR-spectroscopy. The spectra indicate that as a result of complicated oxidation processes which probably involve free radicals (OH ^., O₂^.  )a profound destruction of the phenanthroline aromatic system occurs. The following polymer structure of the product obtained

 

after oxidation of the Cu²⁺ and Fe²⁺- complexes of 1,10-phenanthroline is proposed:

Keywords: phenanthroline, peroxide, oxidation, kinetics

NEW N-PYRROLYLACETIC AND

3-(N-PYRROLYL)PROPANOIC ACIDS VIA PAAL-KNORR CONDENSATION

A. Bijev, N. Nedelchev, A. Nankov

 

10 new N-pyrrolylacetic- and 3-(N-pyrrolyl)propanoic acids have been synthesized via Paal-Knorr condensation of 1,4-dicarbonyl compounds with glycine or beta-alanine. A literature study supports the pharmaceutical interest in this class of compounds as potential anti-inflammatory agents and perspective building blocks for drug design.  The new products enrich the available database for forthcoming pharmacological evaluations. They supplement the related structures reported in previous papers of ours by introduction of new substituents in 5-position of the pyrrole ring.
IR and NMR-spectra as well as analytical thin-layer chromatography prove the chemical structure and the purity of the new compounds.

Keywords: Carbonyl compounds, Carboxylic acids, Condensation, Heterocycles, Pyrroles, Synthetic methods.

ELECTROLYTIC COLORING OF POROUS ALUMINA FILMS IN CuSO₄ SOLUTIONS

I. EFFECT OF THE COLORING CONDITIONS ON THE COLOR CHARACTERISTICS OF THE FILMS

A. Girginov, A. Zahariev, Y. Sokolova, R. Aleksieva

       The dependence of some parameters of the electrolytic coloring of porous anodic alumina films on their color characteristics was investigated. The porous alumina films were colored by alternating current, in solutions, containing CuSO₄ and a combination of CuSO₄ + NiSO₄. By recording the spectral reflection curves of the colored specimens the intensity and the mode of the color were estimated. The influence of the coloring duration, coloring current density, frequency and current displacement were studied.

Keywords:  porous alumina films, anodized aluminium, electrolytic coloring, colored porous oxide films on aluminium.

ELECTROLYTIC COLORING OF POROUS ALUMINA FILMS IN CuSO₄  SOLUTIONS

II. DETERMINATION OF SOME FUNCTIONAL PROPERTIES OF THE COLORED FILMS

A. Girginov, A. Zahariev, Y. Sokolova, R. Aleksieva

       Anodic alumina films (20mm) were formed by galvanostatic anodizing in sulfuric acid solution. These films were electrochemically colored in two different solutions containing CuSO₄ and CuSO₄ + NiSO₄ respectively. The quantity of copper and nickel in the colored films’ pores is determined by emission spectrum analysis. Complex films are obtained through re-anodizing in a non-dissolving electrolytic solution. Films featuring different thickness of the barrier sub-layer were achieved by varying the re-anodizing voltage value. The corrosion resistance was estimated via the well known drop method. The color characteristics of the films colored in CuSO₄ – containing solution were valued by studying the spectral reflection curves. A possibility exists to get high quality colored oxide films, featuring improved corrosion resistance, on aluminium.

Keywords: porous alumina films, anodized aluminium, electrolytic coloring, complex films, corrosion resistance.

ADSORPTION EQUILIBRIUM IN THE SYSTEM NATURAL ADSORBENT – DYE SOLUTIONS

S. Veleva, A. Georgieva, D. Pishev, B. Staneva

       The study of new materials with wellpronounced adsorption properties along with their application is an important priority for the recovery and recycling of waste and polluted industrial water.
       A natural polymineral material [Grus] was found to have an adsorption ability with respect to a lot of dyes largely used in the textile, leather, and etc. industries.
       The aim of this work is to present the specific characteristics observed in the application of the Freundlich isotherm for investigation of the adsorption equilibrium in the system natural adsorbent [Grus] – water solution of direct and acid dyes.
       As a result of theoretical analysis a dependence between the constant K in the Freundlich isotherm and the parameter n, which is related to the surface inhomogenity, was established. It can be expressed according to the equation:
K = Ã_m K₁ⁿ ,
which includes the maximum adsorption quantity Ã_m and the equilibrium adsorption constant K₁ for monolayer formation. The latter were evaluated from, the dependence between K and n for a set of similar adsorption experiments at a constant temperature. The equilibrium concentration of the adsorbate upon the monolayer was calculated knowing K₁. Obviously, any further increase of adsorption would imply a transition to a polymolecular adsorption mechanism.
Based on the results obtained, the adsorption could be considered as a polymolecular one for the major part of the dyes investigated. For those dyes the adsorption ability of the adsorbent is strongly pronounced.

Keywords: Adsorption, Freuendlich isotherm, acid and direct dyes, natural polymineral material [Grus].

ELECTROCHEMICAL PROPERTIES OF SKELETON COPPER CATHODES PREPARED BY THERMAL ARC SPRAYING

N. Vaszilcsin*, W. Brandl**, A. Kellenberger*

The aim of this paper is the achievement of efficient cathodes for the hydrogen evolution reaction (HER) and for the reduction of organic compounds, for example the reduction of nitrobenzene to aniline. The cathodes consist of a Cu-Al coating deposited by thermal arc spraying technique on a carbon steel support using two identical wires of CuA18 alloy. In order to clean the surface and to assure an adequate adherence, the support was sanded with corundum. The thickness of the coating was 1.8 mm. A porous structure of metallic copper was obtained by leaching out the aluminium in a 4% KOH solution at 80°C at different times of treatment (60 or 120 min). The surface morphology was studied using scanning electronic microscopy (SEM) and the elemental composition was determined by energy dispersive X-ray microanalysis (EDX). The electrochemical behaviour of the cathodes was studied by linear voltammetry. A depolarisation of approximately 200 mV for the HER, at 100 mA/cm² current density in 1 M KOH solution has been found on the skeleton copper cathode compared to the smooth copper cathode.

Keywords: thermal arc spraying, skeleton copper, nitrobenzene electroreduction, hydrogen evolution reaction.

ADSORPTION AND SPECTROSCOPIC STUDIES ON THE INTERCALATIONS OF COPPER (II) CHELATE INTO BENTONITE

M. Atanassova, V. Jordanov

       The intercalation of Cu(acac)₂, (acac = acetylacetonate) into the bentonite interlayers is studied. The intercalation is carried out in water suspensions containing bentonite as well as activated bentonite and 1.78x10^-2 mol.dm^-3 Cu(II) chelate. The sampels have been characterized by Atomic absorption analysis, Infrared spectroscopy, X-ray diffraction measurements. TG-DTA curves were recorded too. It was found that the activated bentonite adsorbed 4.9x10^-4 mol until not activated bentonite adsorbed 1.6x10^-5 mol Cu(acac)₂. These results could be explained with the presence of exchangeable cations in the interlayer space obtained by the treatment of  the clay with 1M NaCl solution.

Keywords: A. intercalation; B. exchangeable cation; C. clay-chelate hybrid material.

INVESTIGATION OF THE POLAROGRAPHIC BEHAVIOR OF NIO, CoO ,SnO₂ AND WO₃  IN SLAG MELT OF  Na₂ O . SiO₂. B₂O₃ USING A ROTATING DISK ELECTRODE

T. Tzvetkoff

A polarographic investigation on silicate melts background present great practical interest. That is why we present in this work a systematic polarographic investigation of several heavy metal oxides (NiO, CoO, SnO₂ and WO₃) in slag melt (Na₂O.SiO₂.B₂O₃) at 1100° C. Pt Rotating Disk Electrode is used. Polarographic and derivative polarographic methods are applied. A linear dependence is observed between the limiting diffusion current and the concentration of the oxides of NiO, CoO and SnO₂. For WO₃ this linear dependence is not clearly outlined. The extent of reduction for Sn(IV) is found, while Ni(II), Co(II) and W(VI) reduce directly to the corresponding metals. The polarographic waves for W (VI) and Sn(IV) are better described by Heirovsky-Ilkovich equation when compared to that of the concentration polarization. The waves of Ni(II) and Co(II) can not be described by the  equations mentioned above. Most probably electrochemical as well as concentration polarization exist in this case. The former may be attributed to delayed deformation and orientation of Si-O complexes in the electric field.

Keywords:  polarography, ionic melts, slags, electrochemical kinetics, a rotating disk electrode