Interactive Adsorption Behavior of NAD⁺ at a Gold Electrode Surface

Abstract

The adsorption of an oxidized form of nicotinamide adenine dinucleotide, NAD+, on a polycrystalline gold electrode surface and the subsequent surface conformation of the molecule were investigated over a wide temperature and potential range, using electrochemical differential capacitance and PM-IRRAS techniques. The adsorption process was described by the Langmuir adsorption isotherm. The corresponding thermodynamic parameters were determined: the Gibbs energy, enthalpy, and entropy of adsorption. The large negative Gibbs energy of adsorption (-43 +/- 4 kJ mol-1 and -39 +/- 2 kJ mol-1 on a positively and negatively charged surface, respectively) confirms that the NAD+ adsorption process is highly spontaneous, while the large entropy gain (285 J K-1 mol-1 and 127 J K-1 mol-1 on a positively and negatively charged surface, respectively) was found to represent the adsorption driving force. It was demonstrated that the energetics of the adsorption process is surface-charge controlled, while its kinetics is both mass-transport and surface-charge controlled. A surface-charge dependent conformation model for the adsorbed NAD+ molecule is proposed. These findings suggest that the origin of the NAD+ reduction overpotential is related to the surface conformation of the adsorbed NAD+ molecule, rather than to the electrode Fermi level position.

Electrochemical reduction of NAD+ on a polycrystalline gold electrode

“…According to the electrochemical double-layer theory [31], this decrease in the double-layer capacitance indicates that adsorption of reaction species occurs during the NAD + reduction reaction. Our electrochemical and PM-IRRAS adsorption measurements done at more positive potentials, where NAD + cannot be reduced (from −0.5 to 0.4 V versus SCE) [43], confirmed that NAD + is the species that adsorbs on the electrode surface in this positive potential region, and that this interaction is spontaneous, strong and irreversible (Gibbs energy of adsorption is −41 ± 4 kJ mol −1 , depending on the adsorption potential and temperature). However, since the measurements presented in Fig.…”

“…However, at reported "optimum conditions", only 10% of active NADH was formed on Au-Hg [13], while a higher yield, 50%, was obtained on Pt [13] and Hg [6]. Our experiments on a Cu electrode [30] have yielded a trend very similar to the one in Fig. 1b, but the highest yield of enzymatically active NADH formed was 73% at −1.0 V, while at −1.2 V a significantly higher amount, 53%, was obtained when compared to the gold electrode (Fig.…”

“…The data show that the value ranges from ca. 1.75 at −1.0 V, down to 1.28 at −1.4 V. A sudden change in the curve slope between −1.05 and −1.00 V could be prescribed to the onset of the HER, but the trend observed in the figure will be discussed in more detail in our subsequent paper [30] and is not relevant for the further analysis of results presented in this manuscript. Fig.…”

Regeneration of the NADH Cofactor by a Rhodium Complex Immobilized on Multi-Walled Carbon Nanotubes

“…In the direct regeneration of NADH, the cofactor NAD + is reduced at the electrode surface. Omanovic and coworkers have investigated and improved the performance of direct electrochemical regeneration of NADH by depositing Ru, 16 Pt, 17 Ni, 17 Au 18,19 and Pt-Au 19 on electrode surfaces. While this method has been shown to be effective, the high overpotential required for the reduction of NAD + along with the formation of enzymatically inactive NAD 2 dimers remain the two significant disadvantages.…”

Nickel-Based 3D Electrocatalyst Layers for Production of Hydrogen by Water Electrolysis in an Acidic Medium

“…5.13 (white and grey bars) yield a common "volcano-type" behaviour (i.e. a maximum), which is quite common in the area of electrocatalysts development [21,71]. ln conclusion, PANI30/Ni50-1.85V electrocatalyst shows the highest electrocatalytic activity in the HER, and will further be compared to the control (Ni plate), Ni-RVC, and…”