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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.

Iron epitaxial electrodeposition on Au(111) substrates is investigated using in situ scanning tunneling microscopy (STM) and ex situ X-ray diffraction (XRD). STM observations show that Fe grows quasi layer-by-layer at sufficiently negative potentials. XRD results indicate that Fe layers thicker than 3 ML are bcc and present the epitaxial relationship Fe(110) [1−10]||Au(111) [11−2]. They also show that the Fe lattice is uniaxially in-plane strained along Fe[1−10] and that the strain is progressively relieved with increasing layer thickness. The growth of Fe on a Ni layer deposited on Au(111) leads to strain free Fe layers with the same epitaxial relationship. The specific shape of Fe of monatomic islands suggests that the first Fe monolayer deposited on Au(111) presents a centered rectangular lattice similar to that of bcc Fe(110) but is stretched along Fe[1−10] by more than 8%.