| Abstract
| - The redox chemistry of 2-palmitoylhydroquinone (H2Q), a recently introduced synthetic transmembrane Ca2+transporter, was studied with cyclic and square-wave voltammetry in an artificial thin organic-film membranesandwiched between a pyrolytic graphite electrode and an aqueous solution. The membrane has a micrometerdimension and consists of the water immiscible organic solvent nitrobenzene, which contains suitable electrolyteand H2Q as a redox active compound. The potential drop at the electrode/membrane interface is controlledby the potentiostat, whereas the potential drop at the membrane/water interface is dependent on the ClO4-concentration, which is present in a large excess in both liquid phases. The redox transformation of H2Q atthe electrode/membrane interface is accompanied by a corresponding ion-transfer reaction at the other sideof the membrane. Proton transfer at the membrane/water interface is critical for the redox transformation ofH2Q in the interior of the membrane, as a strong dependence of the voltammetric response on the pH of theaqueous medium was observed. H2Q undergoes two oxidation processes due to existence of two distinctiveredox forms of H2Q. The electrochemical mechanism can be explained with two tautomer forms of H2Qformed by migration of a proton between the 1-hydroxyl group and the adjacent carbonyl group of the palmitoylresidue. Both tautomers undergo 2e/2H+ distinctive redox transformations to form the quinone form of thestudied compound. In the presence of Ca2+ in the aqueous phase, voltammetric experiments confirmed thecapability of both tautomers to form 1:1 complexes with Ca2+ and to extract it into the organic membrane.Upon the oxidation of the complexes, Ca2+ is expelled back to the aqueous phase. The studied compoundexhibits very similar complexing affinity toward Mg2+, implying that it is not highly selective for transmembraneCa2+ transport.
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