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.).
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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.