title: Factors affecting the electrochemical regeneration of NADH by (2,2'-bipyridyl) (pentamethylcyclopentadienyl)-rhodium complexes: impact on their immobilization onto electrode surfaces.
abstract: Complexes of the (2,2'-bipyridyl) (pentamethylcyclopentadienyl)-rhodium family ([Cp*Rh(bpy)Cl](+), which is actually hydrolyzed in the form of [Cp*Rh(bpy)H(2)O](2+) in aqueous medium) are suitable solution-phase mediators likely to regenerate nicotinamide cofactors associated to dehydrogenases involved in many biocatalytic applications. Their practical application as bioelectrocatalysts, e.g., in fine chemicals synthesis or biosensors, remains however restricted to their durable immobilization in an active form onto solid electrode surfaces. This paper reports some new observations on the electrocatalytic properties of this mediator towards NAD(+) reduction, notably the critical effect of pH and cofactor-to-mediator concentration ratio, and investigates the behavior of a series of ([Cp*Rh(bpy)Cl](+)) derivatives bearing various substituents on the bipyridine ligand in view of their subsequent integration in electrochemical bioreactors. It will be shown that such compounds containing S- or N- moieties (i.e., often used as precursors to functionalize electrode surfaces) lead to inactivation of the electrocatalyst because their interaction with the Rh center prevents the formation of the active rhodium hydride complex. It was thus necessary to find another strategy of immobilization, and we found that adsorption of [Cp*Rh(bpy)Cl](+) by π-stacking on single-walled carbon nanotubes is an effective mean to reach this goal, leading to efficient and stable catalytic responses for NAD(+) reduction. Preliminary electroenzymatic experiments in the presence of d-sorbitol dehydrogenase further point out the interest of this approach for bioelectrocatalysis purposes and provide the proof-of-concept for this immobilization strategy.
authors.affiliation: Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, CNRS - Nancy-University, France. alain.walcarius@lcpme.cnrs-nancy.fr
authors.forename: Alain
authors.initials: A
authors.lastname: Walcarius
authors.forename: Rihab
authors.initials: R
authors.lastname: Nasraoui
authors.forename: Zhijie
authors.initials: Z
authors.lastname: Wang
authors.forename: Fengli
authors.initials: F
authors.lastname: Qu
authors.forename: Veronika
authors.initials: V
authors.lastname: Urbanova
authors.forename: Mathieu
authors.initials: M
authors.lastname: Etienne
authors.forename: Mehmet
authors.initials: M
authors.lastname: Göllü
authors.forename: Ayhan S
authors.initials: AS
authors.lastname: Demir
authors.forename: Janine
authors.initials: J
authors.lastname: Gajdzik
authors.forename: Rolf
authors.initials: R
authors.lastname: Hempelmann
mesh_terms: D015082:2,2'-Dipyridyl / Q000737:chemistry*; D015374:Biosensing Techniques; D055664:Electrochemical Techniques; D004566:Electrodes; D004926:Escherichia coli / Q000201:enzymology; D009243:NAD / Q000737:chemistry* / Q000378:metabolism; D037742:Nanotubes, Carbon / Q000737:chemistry; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism; D012238:Rhodium / Q000737:chemistry*
chemical_list: D037742:Nanotubes, Carbon; D009942:Organometallic Compounds; D009243:NAD; D015082:2,2'-Dipyridyl; D012238:Rhodium; D010088:Oxidoreductases