Electrochemical and EQCM investigation of a selenium derivatized carotenoid in the self-assembled state at a gold electrode

1-(β-Apo-8′-carotenoyl)-2-(7-selenaoctanoyl)-glycerol was attached to the gold electrode surface by chemisorption from an acetonitrile solution and the surface layer was investigated by electrochemical methods and piezoelectric nanogravimetry in aqueous solutions. The adsorbate binds to the gold surface by the selenium end group and adopts a roughly perpendicular orientation to the electrode surface. The carotenoid moiety in the adsorbate undergoes an anodic reaction (peak potential, 0.78 V vs. Ag∣AgCl (1 M KCl) electrode) which occurs via an electron transfer followed by the uptake of two hydroxyls. Hydrogen radicals also form and initiate a polymerization process which leads to a more compact and rigid structure of the surface layer. At more positive potentials, the product of these reactions undergoes a slow oxidative desorption which is accompanied by gold oxidation and partial oxidation of organic selenium to SeO32-. Redox probe investigations revealed that the anodic reaction at 0.78 V results in major changes in the film structure and morphology. At a moderate coverage degree, electrochemically generated O2H radicals cause the fragmentation of the conjugated system by addition to the double bonds but do not induce a cross-linking reaction. No cathodic desorption of the CSeOG generated layer occurred in a 0.5 M KOH solution.