Electrochemical investigations of the reaction mechanism and kinetics between NADH and riboflavin immobilised on amorphous zirconium phosphate |
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Authors: | L T Kubota L Gorton |
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Affiliation: | (1) Instituto de Química Unicamp, P.O. Box 6154, 13083-970 Campinas, SP, Brazil, BR;(2) Department of Analytical Chemistry, University of Lund, P.O. Box 124, SE-221 00 Lund, Sweden, SE |
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Abstract: | Electrochemical investigations of the reaction mechanism and kinetics between riboflavin immobilised on zirconium phosphate
(ZPRib) in carbon paste and NADH showed results yielding reliable information about aspects on the mechanism of the electron
transfer reaction between the flavin and NADH. The formal potential (E°′) of the adsorbed riboflavin was −220 mV versus SCE at pH 7.0. A shift about 250 mV towards a more positive potential compared
with its value in solution was assigned to the interaction between the basic nitrogen of riboflavin and the acid groups of
ZP. The invariance of the E°′ with the pH of the contacting solution and the effect of different buffer constituents were attributed to the protection
effect of ZP over the riboflavin. The electrocatalytic oxidation of NADH at the electrode was investigated using cyclic voltammetry
and rotating disk electrode methodology using a potential of −50 mV versus SCE. The heterogeneous electron transfer rate constant,
k
obs, was 816 M−1 s−1 and the Michaelis-Menten constant, K
M, was 1.8 mM (confirming a charge transfer complex intermediate in the reaction) for an electrode with a riboflavin coverage
of 6.8 × 10−10 mol cm−2. This drastic increase in the reaction rate between NADH and the immobilised riboflavin was assigned to the shift of the
E°′. A surprising effect with addition of calcium or magnesium ion to the solution was also observed. The E°′ was shifted to −150 mV versus SCE and the reaction rate for NADH oxidation increased drastically.
Received: 22 February 1999 / Accepted: 10 March 1999 |
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Keywords: | Riboflavin NADH Zirconium phosphate Chemically modified carbon paste electrode |
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