ABSTRACT
The overall formation constants of 1:1:1 ternary complexes of Cu(II), Zn(II), Cd(11) with glycine, dl-alanine or dl-leucine as primary ligands and o-hydroxyphenylyazo derivatives of 2-cyanomethyl benzimidazole (ABI) and barbituric acid (ABA) as secondary ligands have been investigated potentiometrically in 40% (v/v) EtOH. Formation constants of binary systems were also determined under the same experimental conditions (37 degrees C and mu=0.15 mol dm(-3)). The stability of ternary complexes have been quantitatively compared with those of the corresponding binary complexes in terms of the parameters DeltalogK, logX and logX'. The data were interpreted on the basis of statistical considerations and the nature of complexes. The concentration distribution of various species formed in solution was evaluated. The Cu(II) complexes have been synthesized and the coordination sites of the ligands were characterized by means of IR spectroscopy.
ABSTRACT
The stability constants of binary and ternary complexes of copper(II) and nickel(II) with some amino acids (d-histidine, dl-serine, lysine) as primary ligands and benzimidazole as a secondary ligand were determined pH-metrically. The study was conducted in 10% (v/v) ethanol-H(2)O medium and at an ionic strength of 0.1 mol dm(-3) NaNO(3) at 20 +/- 1 degrees C, Values of Delta log K were discussed on the basis of statistical considerations and the nature of the species formed. The stability of the binary and mixed ligand complexes are discussed in terms of the molecular structure of benzimidazole and the amino acids as well as the nature of the metal ion.
ABSTRACT
The complex formation between uric acid and zinc, cadmium and lead ions has been investigated using differential pulse polarography in 0.01M NaNO(3). It is found that the complexes formed by Cd(II) and Pb(II) ions with uric acid have the stoichiometry of 1:2 and the logarithmic values of the apparent stability constant are 9.47 and 11.7, respectively. On the other hand, zinc(II) ions do not give any indication of complexation with uric acid. A sensitive voltammetric method is developed for the quantitative determination of uric acid. This method is based on controlled adsorptive preconcentration of uric acid on the hanging mercury drop electrode (HMDE), followed by tracing the voltammogram in the cathodic going potential scan. The modes used are direct current stripping voltammetry (DCSV) and differential pulse stripping voltammetry (DPSV). The detection limits found were 8 x 10(-9)M (quiescent period 15 sec) by DPSV and 1.6 x 10(-8)M by DCSV.
