Electrochemical reduction of NAD+ on a polycrystalline gold electrode

Zaid

et al. 2014

J. Electrochem. Soc.

The electrochemical response of two biologically important phenazine derivatives was examined by using cyclic, differential pulse and square wave voltammetry in a wide pH range of 2.0 -12.0. Cyclic voltammetry was employed for the determination of heterogeneous electron transfer rate constant and diffusion coefficient of the analytes. The value of electron transfer rate constant was used for evaluation of Gibbs free energy, enthalpy and entropy changes of redox reactions of the compounds. Differential pulse voltammetry was used for the determination of number of protons and electrons involved in the redox processes. Limits of detection and quantification were assessed by square wave voltammetry. The detailed pH dependent redox mechanisms of the compounds were proposed on the basis of experimental results which were further supported by theoretical calculations. These redox mechanistic pathways are expected to play a key role in understanding the necessary aspects of structure-activity relationships and exploring the hidden routes by which this class of compounds exert its biochemical actions. Phenazines have broad range applications in biology and chemistry.1 This class constitutes a large group of nitrogen containing heterocyclic compounds, the members of which differ in their chemical and physical properties on the basis of type and position of functional groups present. Naturally, phenazines are produced by limited genera of bacteria including Pseudomonas, Burkholderia and Brevibacterium.2 Starting from different parent materials, phenazines can be synthesized by various reactions including oxidative condensation, electrochemical reduction, reductive cyclization and photochemical reactions.From the last 50 years, phenazines are the subject of extensive research investigations because of their broad range applications in pharmaceutical and clinical research.3 Such compounds have been reported for their wide variety of biological activities such as antitumor, anti-parasitic and antibiotic activities. Benzo [a] phenazine acts as efficient DNA intercalating ligand with antitumor activity in leukaemia and solid tumors. 4 1-Hydroxyphenazine has been reported to have promising antifungal activity against various microbes such as aspergillus fumigatus and candida albicans.5 Macrolactone synthesized from benzo [a] phenazine shows good activity against mycobacterium tuberculosis. 6 In general, natural and synthetic phenazines find useful applications against malaria 7 and hepatitis C viral replication. 8The biological activity of phenazines is due to their redox reactions leading to the formation of toxic radicals. 9 Different functional groups attached to phenazine determine their redox potential and solubility. The redox behavior and concomitant modulation of biological activities of phenazines by changing the nature and position of substituents attached to their aromatic rings have been reported by several research groups.10-12 Phenazines can alter cellular redox states and act as transporters of electrons to altern...

Section: Resultsmentioning

confidence: 99%

pH Dependent Electrochemical Characterization, Computational Studies and Evaluation of Thermodynamic, Kinetic and Analytical Parameters of Two Phenazines

Zaid

et al. 2014

J. Electrochem. Soc.

Proc. Natl. Acad. Sci. U.S.A.

“…• radical intermediate (18,19). Two flavoenzymes in the mitochondrial electron-transfer chain, respiratory complexes I and II (the NADH: and succinate:ubiquinone oxidoreductases), catalyze reversible C-H bond formation.…”

Section: Interconversion Of H 2 and Hmentioning

confidence: 99%

Reversibility and efficiency in electrocatalytic energy conversion and lessons from enzymes

Armstrong

Hirst²

2011

330

294

Enzymes are long established as extremely efficient catalysts. Here, we show that enzymes can also be extremely efficient electrocatalysts (catalysts of redox reactions at electrodes). Despite being large and electronically insulating through most of their volume, some enzymes, when attached to an electrode, catalyze electrochemical reactions that are otherwise extremely sluggish (even with the best synthetic catalysts) and require a large overpotential to achieve a useful rate. These enzymes produce high electrocatalytic currents, displayed in single bidirectional voltammetric waves that switch direction (between oxidation and reduction) sharply at the equilibrium potential for the substrate redox couple. Notoriously irreversible processes such as CO 2 reduction are thereby rendered electrochemically reversible-a consequence of molecular evolution responding to stringent biological drivers for thermodynamic efficiency. Enzymes thus set high standards for the catalysts of future energy technologies.electrocatalysis | catalysis | electrochemistry | electron transport | solar fuels A n electrocatalyst catalyzes a redox "half reaction" in which a chemical transformation is coupled to electron transfer at an electrode (1). The active sites of surface electrocatalysts such as platinum are integral to the electrode and contribute to the Fermi level, whereas molecular electrocatalysts are distinct entities with their own electronic and chemical properties. Molecular electrocatalysts can be attached to the electrode surface or diffuse freely in solution, but depend upon interfacial electron transfer (IET). Enzymes, a special category of molecular electrocatalysts, are distinguished by their extraordinary activities, yet limited by their size and fragility. Driven by industrial and technological needs for significant improvements in rates and efficiency, enzymes can provide crucial insights into the principles underpinning the design and performance of synthetic molecular electrocatalysts.The efficiency of enzyme catalysis is widely accepted (2-4): Enzymes have highly selective substrate binding sites, avoid releasing reactive intermediates, and decrease activation energies (here, substrate refers to the species being transformed, not the supporting material). Traditional definitions of enzyme efficiency focus on how closely the rate approaches diffusion control (4). Recently, electrochemistry has revealed a hitherto unquantified dimension in enzyme catalysis; many redox enzymes minimize the energy needed to drive a reaction-a quantity that is easily visualized electrochemically and that we refer to as the overpotential requirement. The energy efficiency of enzyme catalysis is expected because biology must fully exploit available energy resources and minimize energy losses.The performance of an electrocatalyst is readily visualized by cyclic voltammetry, a technique for driving reactions, measuring kinetics and thermodynamics, detecting activation/inactivation processes, and observing catalytic efficiency-all in a single...

“…It has been established that the direct electrochemical reduction of NAD + proceeds through the following two simplified steps:

S t e p 1 : {N A D}^{+} + {normale}^{-} \to N A D •

S t e p 2 a : N A D • + {normale}^{-} + {normalH}^{+} \to N A D H

where Step 2a – Equation represents a rate‐determining step, favouring the dimerization of the radical to produce enzymatically inactive dimer (NAD 2 ):

S t e p 2b : N A D • + N A D • \to {N A D}_{2}

…”

Section: Introductionmentioning

confidence: 99%

Direct electrochemical regeneration of enzymatic cofactor 1,4‐NADH on a cathode composed of multi‐walled carbon nanotubes decorated with nickel nanoparticles

et al. 2017

Self Cite

Multi‐walled carbon nanotubes (MWCNTs) were grown on a stainless steel mesh and decorated with nickel nanoparticles (Ni NPs). The developed Ni NP‐MWCNT material was then used as a cathode in an electrochemical batch reactor to electrocatalytically convert NAD+ to enzymatically‐active 1,4‐NADH. The regeneration of 1,4‐NADH was studied at various electrode potentials. At electrode potential of −1.6 V, a very high recovery (relative amount of 1,4‐NADH in the product mixture) was obtained, 98 ± 1 %. In comparison, to achieve the same recovery on a non‐decorated MWCNT cathode, a much higher cathodic potential was needed (−2.3 V), establishing the importance of Ni NPs on the electrocatalytic activity in reducing NAD+ to 1,4‐NADH. It was postulated that hydrogen adsorbs on Ni NPs immobilized on MWCNTs to form Ni‐Hads, and this activated hydrogen rapidly reacts with neighbouring NAD‐radicals, preventing the dimerization of the latter species, ultimately yielding 1,4‐NADH.