H O M E


Electroanalytical techniques as relaxation methods in chemical kinetics:
investigation of complex compounds by polargraphy and voltammetry

Florinel Gabriel Banica1, Ana Ion2

1) Dept. of Chemistry, Norwegian University of Science and Technology, Trondheim, Norway

2) Department of Analytical Chemistry and Instrumental Analysis, "Politehnica" University of Bucharest, Bucharest,1 Polizu Street, 78126, Romania

Key words: electrochemistry, complex compounds, chemical kinetics, nickel, bioinorganic chemistry

The well known methods for investigating the complex equilibria by electrochemical methods enables the determination of the formation constants and composition for successive complexes of a metal ion with one or more ligands. In this instance, the perturbation of the equilibria is assumed as negligible owing to the very high rate constants for the ligand transfer processes. The cases involving a slow ligand transfer step is not so widely investigated, despite the possibility of determining relevant reaction rates and, under favorable circumstances, the formation constants for some complex species. Such methods are actually belonging to the larger class of relaxation methods for the investigation of the reaction kinetic. The electrochemical reaction plays in this case a double role: (i) it achieve the perturbation of the equilibrium state by the reduction (or oxidation) of one of the relevant species and, (ii) it enables the monitoring of the system response to this perturbation.
This projects dealt with some applications of polarography and linear scan voltammetry on the stationary Hg electrode for the investigation of the formation of complexes of nickel ion with some compounds of biological relevance, as, for example, nicotinamide (vitamin PP) and mercaptopurine riboside, one of the most outstanding anticancer drugs.
 
 

The METHOD relies on the electroreduction of a metal complex under the kinetic control by the regeneration of the complex in the presence of an excess of metal ion. This process occurs at a less negative potential compared with the main metal ion reduction signal (the pre-wave on curve 2 in the Fig.).
 
 
 


 
 
 

A simplified mechanism for such a process is presented in Scheme 1.

 Future works aims at investigating the kinetics of reactions involving nucleotides and related compounds
 

Some publications on this topics  (with links to reprints available in  NTNU Library, Trondheim)
 
 

    F. G. Banica,
     "Voltammetric study of a catalytic electrode process with parallel complexation reaction. Reduction
      of nickel ion in the presence of nicotinamide"
     Rev. Roum. Chim., 35, 693, (l990).
 

 F. G. Banica, L. I. Doicin, A. Fodor, A. Ion,
     "Ligand-catalysed metal ion reduction. Kinetics and analytical  applications of nickel reduction
      catalysed by nicotinamide".
      Electroanalysis, 6, 1051 (1994).
 

 A. Ion, F. G. Banica, C. Luca,
"Catalytic cathodic stripping voltammetry of 6-mercaptopurine-9-riboside in the presence of nickel ion"
Electroanalysis, 9, 945 (1997).
 

 A. Ion, F. G. Banica, C. Luca,
"Ligand-catalysed metal ion reduction. Voltammetric determination of the rate and formation constants for the nickel complex with 6-mercaptopurine-9-D-riboside".
J. Electroanal. Chem., Vol. 444 (1998) 11-18.