Cobalt(II) and Nickel(II) Compounds with 2-Thiobarbituric Acid
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ICAL CHEMISTRY OF SOLUTIONS
Cobalt(II) and Nickel(II) Compounds with 2-Thiobarbituric Acid A. P. Lakeeva, * and N. M. Korotchenkoa aNational
Research Tomsk State University, Tomsk, 634050 Russia *e-mail: [email protected]
Received February 3, 2020; revised April 5, 2020; accepted April 6, 2020
Abstract—Interaction between the systems containing cobalt(II) or nickel(II) chlorides and 2-thiobarbituric acid (C4H4N2O2S, H2L) was examined by spectrophotometry and pH-metry at pH < 4, I = 0.1 (NaCl) and T = 20°C. The compositions and the overall stability constants (logβ11) of protonated complex species were determined: [CoHL]+ (3.69 ± 0.04), [NiHL]+ (3.68 ± 0.08), and [M(HL)2]. The compositions of the Co(C4H3N2O2S)2 · 4H2O and Ni(C4H3N2O2S)2 · 5H2O salts isolated from the studied systems were confirmed by different physicochemical methods; their solubility constants (logKS) were calculated to be –12.82 ± 0.22 and –12.30 ± 0.10, respectively. A spectrophotometric technique was developed for determining thiobarbiturate ion in aqueous solutions. This technique is based on the absorbance of iron(III) thiobarbiturate complex [FeL]+ and can be recommended for analytical chemists and pharmacists. Keywords: thiobarbituric acid, cobalt, nickel, complex compounds DOI: 10.1134/S0036023620080082
INTRODUCTION Thiobarbituric acid (C4H4N2O2S, H2thioBar, H2L, 2-thiobarbituric acid, or malonylthiourea, a derivative of barbituric acid) is a parent compound giving rise to the thiobarbiturate class of drugs, which exhibit pronounced sedating, anesthetic, anticonvulsant, antisclerotic, and bacteriostatic properties. The best-known of them are sodium thiopental, thiobarbital, thiobutabarbital, thialbarbital, and methitural [1, 2]. Thiobarbituric acid is widely used for determining malonic dialdehyde [3], a product of lipid peroxidation, in experimental and clinical pharmacology. The researchers from the Laboratory of Biochemistry and Immunology of the Pitié-Salpêtrière Hospital (Paris, France) proposed a procedure for the colorimetric determination of phosphohexoisomerase with thiobarbituric acid to quantify the amount of fructose formed in enzyme-catalyzed processes [4]. Due to specific colorimetric reactions of H2thioBar, it can be used as an analytical reagent to detect p- and d-metal ions (Bi3+, Cu2+, Pd2+, Fe3+, Ru3+, etc.) [5]. Thiobarbiturate complexes of rare-earth elements are also used as precursors to synthesize the respective oxides, sulfides, oxysulfides, and oxysulfates [6–8], which are broadly employed in electrical engineering and materials science. In addition, the complexes containing thiobarbiturate anions as ligands possess biological and pharmacological properties. The tin(IV) complex was found to exhibit antibacterial and anticancer activities [9], while mixed-ligand salts of cobalt(II), nickel(II), and copper(II) with malonylthiourea and
derivatives of arylidene-anthranilic acid possess antimicrobial activity [10]. Malonylthiourea can occur in a large number of keto-enol or lactam-lactim tautomeric forms. The isomeric
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