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In situ Fourier-transform infrared (FTIR) spectroscopy and scanning tunnelling microscopy (STM) have been used to investigate the nature of the 'activated' gold surface. The results suggest that the activation procedure leads to a situation where various relatively well defined surfaces can be formed on polycrystalline gold.

A series of three meso-tetra-alkyl porphyrins (H 2 TAPs) were synthesised and their electrochemical properties were studied in dichloromethane containing either tetra-butyl ammonium perclorate (TBAP) or tetra-butyl ammonium hexafluorophosphate TBA(PF 6 ) as supporting electrolyte (SE) by cyclic voltammetry and in situ UV/vis spectroelectrochemistry. Values of E 1/2 for the recorded four redox processes of these porphyrins and of the meso-tetra-phenyl porphyrin (H 2 TPP) on glassy carbon and platinum were measured and compared. The redox data collected on the first oxidation and the first reduction processes predict that the value of (LUMO − HOMO) for the H 2 TAPs is lower than for meso-tetra-phenyl porphyrin and, therefore, that the first Q band of the electronic spectra of the H 2 TAPs is red shifted relatively to the same band in the spectrum of H 2 TPP; this shift was indeed found. The second oxidation process of the H 2 TAPs is influenced by the supporting electrolyte used and the dication then formed is consumed by an irreversible chemical reaction. The species produced in this reaction is irreversibly reduced at a considerably lower potential. The electrochemical and spectroelectrochemical data collected are consistent with the occurrence of structural distortion in the macrocycle rings of the H 2 TAPs.

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In a previous work from this laboratory, it was shown that it is possible to electrochemically modify a polycrystalline surface of gold so that it behaves towards O 2 reduction like the (100) gold plane. To check whether this similarity in behavior is due to the presence on the (100)-like surface of suciently large (100) spots, the process of the upd of Pb(II) was used in this work as a probe of the surface crystallographic orientations both in deaerated and in O 2 À saturated solutions. The observed cyclic voltammograms (CV) and polarization curves were entirely dierent from those reported in the literature for a typical polycrystalline gold surface. The CV data were analyzed in an attempt to gain insight on the crystallography of the (100)-like surface. The in¯uence of adsorbed lead on the electroreduction of oxygen in 1 M NaOH on the (100)-like surface was also scrutinised. It was found that the reduction is dierently aected by adsorbed Pb(II) ions and by underpotential deposited Pb adatoms. Adsorbed Pb(II) do not change the reduction mechanism, it only alters the rate constant for HO 2 À disproportionation, whereas the surface becomes able to reduce O 2 to OH À without desorption of HO 2 À to the solution bulk when modi®ed by Pb adatoms. The details of the electroreduction of O 2 and of HO 2 À are thoroughly discussed in relation to the surface processes underneath. Together with the CV data, they show that there are no signi®cant (100) spots on the (100)-like surface and that this surface is structurally dierent from the gold (100) plane. #

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