Bulk Electrocatalytic NADH Cofactor Regeneration with Bipolar Electrochemistry

Abstract

Electrochemical regeneration of reduced nicotinamide adenine dinucleotide (NADH) is an extremely important challenge for the electroenzymatic synthesis of many valuable chemicals. Although some important progress has been made with modified electrodes concerning the reduction of NAD + , the scale-up is difficult due to mass transport limitations inherent to large-size electrodes. Here, we propose instead to employ a dispersion of electrocatalytically active modified microparticles in the bulk of a bipolar electrochemical cell. In this way, redox reactions occur simultaneously on all of these individual microelectrodes without the need of a direct electrical connection. The concept is validated by using [Rh(Cp*)(bpy)Cl] + functionalized surfaces, either of carbon felt as a reference material, or carbon microbeads acting as bipolar objects. In the latter case, enzymatically active 1,4-NADH is electroregenerated at the negatively polarized face of the particles. The efficiency of the system can be fine-tuned by controlling the electric field in the reaction compartment and the number of dispersed microelectrodes. This wireless bioelectrocatalytic approach opens up very interesting perspectives for electroenzymatic synthesis in the bulk phase.

Fine-Tuning the Electrocatalytic Regeneration of NADH Cofactor Using [Rh(Cp*)(bpy)Cl]+-Functionalized Metal–Organic Framework Films

“…After 5.8 h of electrolysis, UV–vis spectra were used to characterize the produced 1,4-NADH, based on its intrinsic absorption peak at 340 nm. To make sure that the product is enzymatically active 1,4-NADH, and not some parasitic byproduct, NAD-dependent alcohol dehydrogenase and acetaldehyde substrate were added to the solution, following a reported protocol . The amount of produced 1,4-NADH was calculated from the decrease of the absorption at 340 nm (Figure B), based on a previously recorded calibration curve (inset in Figure B).…”

“…To make sure that the product is enzymatically active 1,4-NADH, and not some parasitic byproduct, NAD-dependent alcohol dehydrogenase and acetaldehyde substrate were added to the solution, following a reported protocol. 10 The amount of produced 1,4-NADH was calculated from the decrease of the absorption at 340 nm (Figure 4B), based on a previously recorded calibration curve (inset in Figure 4B). These measurements we also used to study potential leaching of the catalyst.…”

“…Among them, the organometallic catalyst [Rh­(Cp*)­(bpy)­Cl] + belongs to the most efficient ones and has been immobilized on electrodes, not only to increase the reusability of the catalyst but also to prevent undesirable interactions between the functional groups of enzymes and [Rh­(Cp*)­(bpy)­Cl] + . Rhodium-functionalized electrodes have been prepared, among others, by depositing polymers bearing Rh moieties, or using π–π stacking interactions with carbon materials, as well as through the covalent immobilization of Rh catalysts on the electrode surfaces. − Efficient NADH regeneration rates were obtained, but due to the irregular porosity of the final electrode layer (carbon nanotubes (CNTs), polymers) and an uncontrolled position of the molecular catalyst units after immobilization via adsorption, encapsulation, or diazonium grafting, it is difficult to predict and fine-tune the efficiency of the electrode. Thus, a rational design of the porous structure and a precise control of catalyst loading is highly desirable for the development of efficient functional bioelectrodes.…”

Bioelectrocatalysis with a palladium membrane reactor

“…However, this high voltage introduces new complications in the form of heat and a strong electric field at the electrode surface, both of which can inactivate and/or denature enzymes 24 – 27 . A mediator can be added to prevent NAD + dimerization and bypass the need for a high cathode voltage 28 , 29 , but this mediator reintroduces separation challenges similar to those found in enzymatic regeneration 10 , unless the mediator is immobilized on the electrode surface 30 . The development of electrocatalytic cofactor regeneration methods that completely circumvent NAD• formation would enable NADH regeneration to be performed without high cathode voltages or the use of a mediator, while producing O 2 as the sole byproduct.…”

Monitoring Bipolar Electrochemistry and Hydrogen Evolution Reaction of a Single Gold Microparticle under Sub-Micropipette Confinement

“…The wireless bipolar electrode (BPE) is a kind of wireless electrode or array , that is polarized by driving electrodes to produce a cathode and anode with Faraday reactions at both ends. After development for more than two decades, it has a wide range of applications in metal corrosion, − bioanalysis, − electroanalysis, − synthesis of functional materials, − and nanomotors. − …”