ЖУРНАЛ НЕОРГАНИЧЕСКОЙ ХИМИИ, 2015, том 60, № 11, с. 1500-1505
_ ФИЗИЧЕСКИЕ МЕТОДЫ _
- ИССЛЕДОВАНИЯ -
STUDY ON THE COMPLEX FORMATION OF ANIONIC CHELATES OF Co(H)-4-(2-THIAZOLYLAZO)RESORCINOL
WITH DITETRAZOLIUM CATIONS © 2015 V. Divarova*, K. Stojnova**, P. Racheva*, V. Lekova**
*Department of Chemistry and Biochemistry, Faculty of Pharmacology, Medical University Plovdiv, 15A Vasil Aprilov Boulevard, Plovdiv 4002, Bulgaria **Department of General and Inorganic Chemistry, Faculty of Chemistry, University of Plovdiv "Paisii Hilendarsk", 24 Tzar Assen Street, Plovdiv 4000, Bulgaria
E-mail: firstname.lastname@example.org Поступила в редакцию 16.02.2015 г.
The ion-associated complexes formed between anionic chelates of Co(II)—4-(2-thiazolylazo)resorcinol (TAR) and cations of ditetrazolium salts (DTS) — Nitro Blue Tetrazolium Chloride (NBT), Blue Tetrazolium chloride (BTC) and Neotetrazolium chloride (NTC) — in the liquid-liquid extraction system Co(II)—TAR— DTS—H2O—CHCl3 were studied. The optimum conditions for the formation and the solvent extraction of the ternary ion-associated complexes Co—TAR—DTS were found. The molar ratio of the components in the associates was determined by independent methods. Based on this, a reaction scheme and a general formula of the complexes were suggested. The extraction equilibria were investigated quantitatively. The following key constants were calculated: association constant, distribution constant, extraction constant and recovery factor. The validity of Beer's law was checked and some analytical characteristics were calculated. Based on the obtained results and the lower price of the ditetrazolium salt BTC compared with NBT, the ion-associated complex of Co—TAR—BTC can be successfully used for determining of cobalt in alloys, biological, medical and pharmaceutical formulations.
Keywords: complex formation, cobalt(II) chelate, extraction equilibria, tetrazolium salt DOI: 10.7868/S0044457X15110033
Cobalt is a typical transition and complex formation metal. It refers to a group of essential biochemical elements. One of the cobalt containing complexes compounds is Vitamin B12. It participates in the synthesis of the hemoglobin and affects the protein and lipid metabolism. Cobalt deficiency, especially deficiency of Vitamin B12, can lead to hematologic, neuropsychiatry and cardiovascular disorders [1—3]. The excessive consumption of cobalt with the food can lead to seriously toxicological poisoning [4—6]. The complexes of cobalt with chelating ligands, containing N and O donor atoms have industrial, biological, pharmacological and medical applications [7—11].
Azo compounds are widely used for dyeing of textile fibers, in the modern organic synthesis, in analytical methods as chromogenic reagents for indicators for many metals. The complex formation with azo derivatives resorcinol through phenolic oxygen, azo nitrogen and thiazolyl or pyridylazo nitrogen, produces colored negatively charged chelates with metal cations [12—17]. They can react with bulky organic cations (e. g. zephiraminium, xylometazolinium, tetraphenylarso-nium, tetraphenylphosphonium, nitronium) to give ternary ion-associated complexes (TIAC), which are
less soluble in water and readily dissolved in organic solvents [18—23]. Tetrazolium salts are used as ion-association reagents for the extraction-spectrophoto-metric determination of metals, e.g. Mo(VI), W(VI), Nb(V), V(IV), V(V), Ga(III) [24-31].
Preparation and application of ion-associated complexes formed between anionic chelates of metals with various natural organic and inorganic ligands with N- and O-containing donor atoms and with the participation of ion-association reagents is a special scientific research field of the chemistry of coordination compounds. It is up-to-date topic, not only as a theoretical background for the preparation of novel ion-associated complexes, but mainly concerning the possibility of their application in analytical chemistry for determination of metals in natural, industrial, pharmaceutical and biological samples, addressing a number of ecological issues. In our previous research were described ion-associates formed between anionic chelates of cobalt and tetrazolium salts by spectrophotometry investigation of liquid-liquid extraction systems [32-34]. The extraction equilibria were characterized quantitatively (association constant, distribution constant, extraction constant and recovery factor)
and the analytical characteristics (molar absorptivity, Sandell's sensitivity, adherence to Beer's Law, limit of detection, limit of quantification) were calculated. The present work is a part of thorough and comprehensive study on the ion-associated complexes of cobalt containing tetrazolium salts.
The aim ofresearch is to study the complex formation of ternary ion-association complexes formed between anionic chelates of Co(II)-4-(2-thiazolylazo)resorcinol (TAR) and cations of ditetrazolium salts (DTS) — Nitro Blue Tetrazolium Chloride (NBT), Blue Tetrazolium chloride (BTC) and Neotetrazolium chloride (NTC). The purpose is application of the extraction systems for determining of cobalt in alloys, biological, medical and pharmaceutical formulations.
EXPERIMENTAL Reagents and apparatus
CoSO4 ■ 7H2O (Sigma-Aldrich Chemie GmbH, p. a.), 1.7 x 10-2 mol dm-3 aqueous solution. Working solution (CCo(II) = 1.7 x 10-4 mol dm-3) was prepared by dilution.
4-(2-Thiazolylazo)resorcinol (TAR) (96%, Sigma-Aldrich Chemie GmbH) dissolved in slightly alkalized distilled water, CTAR = 2.0 x 10-3 mol dm-3.
3,3' -(3,3' - dimethoxy-4,4' -biphenylene)bis[2-(4-nitrophenyl)-5-phenyl-2H-tetrazolium chloride (Nitro Blue Tetrazolium Chloride, NBT) (Merck KGaA, p. a.), CNBT = 2.0 x 10-3 mol dm-3.
3,3' -(3,3' - dimethoxy-4,4' -biphenylene)bis(2,5-diphenyl-2H-tetrazolium chloride) (Blue Tetrazolium Chloride, BTC) (Sigma-Aldrich Chemie GmbH, p.a.), CBTC = 2.0 x 10-3 mol dm-3.
3,3'-(4,4'-biphenylene)bis(2,5-diphenyl-2H-tet-razolium chloride) (Neotetrazolium Chloride, NTC) (Sigma-Aldrich Chemie GmbH, p .a.), CNTC = 2.0 x x 10-3 mol dm-3.
The acidity of the aqueous medium was set using the buffer solution prepared by mixing 2.0 mol dm-3 aqueous solutions of CH3COOH and NH4OH.
Organic solvent - CHCl3 (additionally distilled).
The pH was checked by HI 83140 pH meter (Romania).
A Camspes M 508 spectrophotometer (United Kingdom), equipped with 10 mm path length cells, was employed for reading the absorbance.
Procedure for establishing the optimum extraction-spectrophotometric conditions
Aliquots of the solutions of Co(II), TAR, DTS (NBT, BTC, NTC) and buffer solution to adjust the pH of the aqueous phase were introduced into 100 cm3 separatory funnels. The resulting solutions were diluted with distilled water up to 10 cm3. Then 10 cm3 of
chloroform was added and the funnels were shaken. A portion of the organic extract was filtered through a filter paper into a cell and the absorbance was read against a blank.
Procedure for determination of the distribution constant
The distribution constant KD was found by Eq. (1), where A1 is the light absorbance for the extracted specie obtained after a single extraction at the optimum conditions and A3 is the absorbance for the organic extract obtained after a triple extraction under the same conditions.
Kd = AJA - A1). (1)
The single extraction and the first stage of the triple extraction were performed with 10 mL chloroform. The organic layers were transferred into 25 cm3 calibrated flasks and the flask for the single extraction was brought to volume with chloroform. The second stage of the triple extraction was performed by adding a 7 cm3 of chloroform to the aqueous phase that remained after the first stage. The third stage was performed in the same way. The two successive organic layers were transferred to the flask containing the organic layer obtained after the first stage. The volume was brought to the mark with chloroform and shaken for homogenization. Ab-sorbencies A1 and A3 were measured against a blank.
RESULTS AND DISCUSSION
Absorption Spectra, Effect of pH and the Shaking Time
The absorption spectrum of the extract of the ternary ion-associated complexes Co-TAR-DTS in CHCl3 is characterized by an absorption maximum in the visible range (^max = 520 nm) (Fig. 1). The acidity of the aqueous phase has a substantial effect on the extraction of the ion-associated complexes into the organic phase. The maximum and constant extraction of the ternary ion-association complexes Co-TAR-DTS is achieved in the pH range 5.00-6.00 (DTS = NBT), 5.00-5.75 (DTS = BTC) and 4.75-6.00 (DTS = NTC), respectively (Fig. 2). The carried out experiments, showed that the extraction equilibrium was achieved in less than 60 s. The longer shaking time does not affect the absorbance in both cases. The further experiments were performed for 2 min.
Effect of Reagents Concentration
The effect of concentration of TAR and DTS on the extraction of the TIAC was studied. The chelate formation of Co(II)-TAR requires a 7.1-fold excess of TAR for TIAC with NBT (>1.2 x 10-4 mol dm-3), 4.7-fold excess for TIAC with BTC (>0.8 x x 10-4 mol dm-3) and 8.2-fold excess for TIAC with NTC (>1.4 x 10-4 mol dm-3). For a maximum extraction of the TIAC Co-TAR-DTS, requires a 5.9-fold excess of NBT (>1.0 x 10-4 mol dm-3), 2.9-fold excess of
Fig. 1. Absorption spectra of the TIAC Co(II)-TAR-DTS in CHCl3 against blanks CCo(II) = 1.7 x 10-5 mol dm-3. A CTAR = 2.0 x 10-4 mol dm-3, CNBT = 2.0 x x 10-4 mol dm-3; ♦ CTAR = 1.4 x x 10-4 mol dm-3, CBTC = 1.0 x 10-4 mol dm-3; • CTAR = 2.0 x 10-4 mol dm-3; CNTC = 2.0 x 10-4 mol dm-3.
BTC (>0.5 x 10-4 mol dm-3) and 7.1-fold excess of NTC (>1.4 x 10-4 mol dm-3).
3 4 5 6 7 8 pH
Fig. 2. Absorbance of Co—TAR—DTS extracts against TAR—DTS extracts vs. pH of the aqueous phase plots: cCo(H) = 1.7 x 10-5 mol dm-3; CTAR = 2.0 x 10-4 mol dm-3; CDTS = 2.0 x 10-4 mol dm-3.
= 0.7340X + 0.0071 with correlation coefficien
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