Electrocatalytic Biosynthesis using a Bucky Paper Functionalized by [Cp*Rh(bpy)Cl](+) and a Renewable Enzymatic Layer

A bioelectrode for electroenzymatic synthesis was prepared, combining a layer for NADH regeneration and a renewable layer for enzymatic substrate reduction. The covalent immobilization of a rhodium complex mediator ([Cp*Rh(bpy)Cl](+)) on the surface of a bucky paper electrode was achieved by following an original protocol in two steps. A bipyridine ligand was first grafted on the electrode by electro-reduction of bipyridyl diazonium cations generated from 4-amino-2,2-bipyridine, and the complex was then formed by reaction with [RhCp*Cl-2](2). A turnover frequency of 1.3s(-1) was estimated for the electrocatalytic regeneration of NADH by this immobilized complex, with a Faraday efficiency of 83%. The bucky paper electrode was then overcoated by a bio-doped porous layer made of glassy fibers with immobilized D-sorbitol dehydrogenase. This assembly allowed for the efficient separation of the enzyme and the rhodium catalyst, which is a prerequisite for effective bioelectrocatalysis with such bioelectrochemical system, while allowing effective mass transport of NAD(+)/NADH cofactor from one layer to the other. Thereby, it was possible to reuse the same mediator-functionalized bucky paper with three different enzyme layers. The bioelectrode was applied to the electroenzymatic reduction of D-fructose to D-sorbitol. A turnover frequency of 0.19s(-1) for the rhodium complex was observed in the presence of 3mM D-fructose and a total turnover number higher than 12000 was estimated.