Electrochemical study in both classical cell and microreactors of flavin adenine dinucleotide as a redox mediator for NADH regeneration

Abstract

a b s t r a c tThe electrochemical reduction of flavin adenine dinucleotide (FAD) is studied in a classical electrochemical cell as well as in two types of microreactors: the first one is a one-channel reactor and the other one, a multichannel filter-press reactor. The ultimate goal is to use the reduced form of flavin (FADH 2 ), in the presence of formate dehydrogenase (FDH), in order to continuously regenerate the reduced form of nicotinamide adenine dinucleotide (NADH) for chiral syntheses. Various voltammetric and adsorption measurements were carried out for a better understanding of the redox behavior of the FAD as well as its adsorption on gold. Diffusivity and kinetic electrochemical parameters of FAD were determined.

Electrochemical Behavior of Flavin Adenine Dinucleotide Adsorbed onto Carbon Nanotube and Nitrogen-Doped Carbon Nanotube Electrodes

“…Table presents the equilibrium constant and the Gibbs free energy of adsorption for FAD on all three types of CNT electrodes. The calculated values do not show a significant difference between CNT types, and are quite similar to the value reported for FAD adsortion on Au …”

“…Carbon nanotubes (CNTs) are only one of the many conductive carbon materials available for electrochemical applications, but provide attractive features over traditional carbon electrodes such as increased surface area, high mechanical strength, improved electronic conductivity, and enhanced electrocatalysis. , Their use as an electrode material for chemical sensing is ubiquitous, ,, and is often coupled with enzymes for biosensor and biofuel cell applications. − Flavoenzymes are one of the most common enzymes employed (e.g., glucose oxidase), identified by their use of the enzymatic cofactor flavine adenine dinucleotide (FAD). FAD is electroactive and generally displays a two-electron two-proton redox reaction shown in eq : FAD + 2 normalH + + 2 normale − ↔ FADH 2 Although FAD has been studied on electrode materials such as Hg, − Au, , Ti, TiO 2 , TiO 2 nanoparticles, Ni oxide, Zr oxide, SiO 2 /ZrO 2 /C ceramic electrode, Co oxide, conducting polymers, − poly(FAD) films, , glassy carbon, − and graphite, , its electrochemical behavior on CNTs has only been minimally investigated. The vast majority of studies involving FAD and CNTs have been focused on glucose oxidase (GOx) and an apparent direct electron transfer (DET) between GOx and CNTs. ,,− Thus, subsequent electrochemical characterizations of FAD on CNTs are limited to conditions appropriate for enzymatic activity and ignore inherent electrochemical benefits of FAD as a surface sensitive redox probe.…”

Applications of Flow Microreactors in Electrosynthetic Processes

“…Although various regeneration methods have been developed, electrochemistry is a promising tool for NADH regeneration . The feasibility of continuous electrogeneration of NADH in an electrochemical filter-press microreactor, with flavin adenine dinucleotide (FAD)/FADH 2 as a redox mediator, was experimentally demonstrated by Tzedakis and co-workers. ,, This work also involved mass balance experiments in which electrogenerated NADH was applied to the synthesis of chiral l -lactate from achiral pyruvate (Figure ). The optimized device allowed quantitative yields to be reached during both nicotinamide dinucleotide (NAD + ) conversion and l -lactate production.…”

Detection of magnetic field effects by confocal microscopy

“…Firstly, as the bright edges appear symmetrically and only in the later (partially photobleached) images, they are unlikely to be optical artefacts but rather illustrate the discrepancy between the diffusion constants of FMN inside and outside the crystal. 41 The diffusion coefficient of FMN in aqueous solution has been determined as 5.57 Â 10 À10 m 2 s À1 in work by Tzedakis et al 46 This is three orders of magnitude larger than the diffusion coefficient inside the crystal, as determined by our uorescence recovery aer photobleaching (FRAP) studies (3.4 Â 10 À13 m 2 s À1 , see Fig. 7 for details).…”