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ELECTRODE-IMMOBILIZED ENZYME SYSTEMS FOR ELECTROCHEMICALLY DRIVEN CHIRAL REDUCTION REACTIONS

Objective

THE ADVANTAGE OF USING ELECTRICITY IN COMBINATION WITH OXIDATION-REDUCTION ENZYMES IS THE LOW COSTS AND CLEAN FORM OF THIS POWER. A DIRECT ELECTRON TRANSFER BETWEEN AN ELECTRODE AND A REDOX ENZYME IS, HOWEVER, VERY INEFFICIENT. REDOX MEDIATORS OR CONDUCTING POLYMERS CAN HELP TO BRIDGE THIS TRANSFER. AFTER IMMOBILISATION THESE REACTIONS CAN TAKE PLACE WITHOUT CONTAMINATING THE PRODUCTS WITH THE USUAL REDOX MEDIATORS AND AT THE SAME TIME THE PRODUCTS CAN BE EASILY SEPARATED. THESE SYSTEMS CAN THEREFORE BE USED FOR ELECTRO-ENZYMATIC, STEREOSPECIFIC REDUCTION REACTIONS AT A PREPARATIVE SCALE AND IN, FOR EXAMPLE, AMPEROMETRIC BIOSENSORS FOR ANALYTICAL PURPOSES.
In order to apply redox biocatalysts in an economic way, electrodes of electrochemcial cells should be useful as a source or sink for electrons. However, enzymes are usually not able to exchange electrons directly with electrodes and need in general very expensive biological electron carriers, which are also not able to exchange electrons with electrodes.

Enzymes have been found which react with simple artificial and cheap electron carriers which can be oxidised or reduced on electrodes. The enzymes are enoate reductase (ER) and a viologen dependent nicotinamide adenine dinucleotide (phosphate) oxidoreductase (VAPOR). VAPOR enables the use of a large number of nicotinamide adenine dinucleotide (phosphate) dependent oxidoreductases for preparative scale synthesis via electrochemical mediator regeneration. Bifunctional mediators have been synthesized and their suitability as spacers and molecular wires has been tested. Enzyme kinetic parameters of ER, lipodehydrogenase and VAPOR with viologens and cobalt cage complexes and rate constants by electrochemical measurements have been determined. The new mediators were immobilized on carbon electrodes and enzymes were immobilized on the mediator carrying electrode. In order to optimize such systems, mathematical modelling was successfully developed.

Covalent coimmobilization of bifunctional mediators and enzyme (VAPOR) on carbon electrodes led to protein monolayers or multilayers doped with mediator molecules acting as electron relays and molecular wires between the electrode and the enzyme layer. These completely immobilized systems are the first in which electrons reach the active centre of the enzyme directly. This is different from the known case of mediated diffusion controlled homogenous catalysis. So far, these new systems produced up to 3.5 nmol h{-1} cm{-2} of reduced nicotinamide adenine dinucleotide. Immobilized on carbon felt (750 m{2} inner surface/m{2} macroscopic area) a current density of 1A m{-2} of m acroscopic area could be expected. Optimization of the systems is in progress. One of the main drawbacks is that the mediators either showed insufficient long term stability during the production process or that the long term stability was sufficient but the electron transfer rate from the mediator to the mediator to the enzyme was too low.
THE DIRECT AIM OF THIS PROJECT IS TO IMMOBILISE EONATE- AND 2- OXOCARBOXYLATE REDUCTASE AS WELL AS VIOLOGEN DEPENDENT NAD(P) OXIDOREDUCTASES COVALENTLY AT THE SURFACE OF CARBON ELECTRODES. THE IMMOBILISATION WILL BE PERFORMED IN SUCH A WAY THAT THE ELECTRODE IS CAPABLE OF REDUCING THE ENZYME, FOLLOWED BY STEREOSPECIFIC SUBSTRATE REDUCTION. TO MEET THIS CONDITION, REDOX MEDIATORS WILL BE CO-IMMOBILISED TO BRING ABOUT AN EFFICIENT ELECTRON TRANSFER BETWEEN ELECTRODE AND ENZYME. THE KINETICS OF THE ENZYMES WILL BE DETERMINED WITH SEVERAL CLASSES OF REDOX MEDIATORS. SUITABLE MEDIATORS ARE CO-IMMOBILISED WITH THE ENZYME AND THE KINETICS AND STABILITY OF THAT SYSTEM WILL BE STUDIED. THE IMMOBILISATION ITSELF WILL BE STUDIED IN DETAIL IN ORDER TO ARRIVE AT THE MOST EFFICIENT AND REPRODUCTIBLE SYSTEM. SUCCESSFUL SYSTEMS ARE TO BE TESTED IN THE PRESENCE OF ORGANIC SOLVENTS WITH THE IDEA TO PERFORM REDUCTION REACTIONS WITH HYDROPHOBIC SUBSTRATES.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Technische Universitaet Muenchen
Address
Lichtenbergstrasse 4
85748 Garching
Germany

Participants (1)

TNO
Netherlands
Address

Delft