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Some electrochemical properties of laccase immobilised on the Au, IrOx, or C60-Pd polymer electrode supports
|Katarzyna Klimek 1,2, Wlodzimierz Kutner 3, Andrzej Czerwiński 1,2, Hanna Elzanowska 1, Lo Gorton 4|
1. Warsaw University, Faculty of Chemistry, Pasteura 1, Warszawa 02-093, Poland
In the experiments which aimed at unravelling electrochemical activity of laccase (Trametes hirsuta) redox centres, the enzyme has been adsorbed and its properties studied on the Au, IrOx, or C60-Pd electrode support in McIlvaine's buffer at pH»4.0, using cyclic (CV) and square wave (SW) voltammetry. In case of the Au electrode, only one redox couple was detected for laccase at ca. 0.30 V vs. SCE. However, a redox signal of this couple was split into three peaks at ca. 0.25 V, 0.40 V, and 0.55 V in the presence of catechol, i.e. one of the enzyme substrates that is not oxidized below 0.60 V. Presumably, these peaks, which increased after co-immobilization of Cu(II) ions within the enzyme film, corresponded to the oxidation of various copper centres of laccase. The heights of these peaks depended on both catechol and oxygen concentration in solution. It appeared that the laccase redox centres were inter-exchangeable when the enzyme was allowed to react with both reagents. For instance, after the addition of catechol, which is typically oxidized by laccase causing its reduction, the enzyme anodic peak at 0.40 V increased, while the anodic peak at 0.25 V decreased in the presence of oxygen. Moreover, catechol has been used as a mediator to study oxygen reduction catalysed by laccase. For these investigations, laccase was immobilized on a nanoparticulate iridium oxide (IrOx) film and also on a Pd-containing C60-Pd polymer film. The oxygen reduction potential on laccase-coated IrOx was close to +0.1 V, compared to -0.1 V on Au. However, the reaction mechanism involving oxygen reduction to water rather than to hydrogen peroxide still remains to be proven. The most promising results have been obtained with the use of the C60 polymer film. This film was prepared by CV electropolymerisation of C60 in the presence of Pd(II) acetate trimer using a mixed solvent of 4:1 (v:v) toluene and acetonitrile. The C60-Pd polymer features a pair of anodic and cathodic reversible CV peaks at ca. 0.25 V. In the absence of the catechol mediator, reduction of oxygen is enhanced only slightly by the adsorbed laccase. However, the addition of catechol, which reveals a quasi-reversible CV anodic and cathodic peak pair at ca. 0.35 V, results in the mediated reduction of oxygen by laccase at the reduction potential of this mediator.
Presentation: Poster at SMCBS'2005 Workshop, by Hanna Elzanowska
See On-line Journal of SMCBS'2005 Workshop
Submitted: 2005-10-31 18:41 Revised: 2009-06-07 00:44