Electrochemical kinetic analysis of a 1,4-hydroxynaphthoquinone self-assembled monolayer

Electroactive 5-hydroxy-3-hexanedithiol-1,4-naphthoquinone (JUGthio) has been self-assembled on gold. Electrochemical results show the surface coverage is 2.2 × 10−10 mol cm−2, which is consistent with a dense monolayer. The JUGthio shows one quasi-reversible and stable voltametric wave in aqueous buffered solution. A kinetic analysis of the redox reactions involving both electron and proton transfer has revealed an unusual behaviour of this molecule due to the presence of the hydroxyl function in the vicinity of the quinone group. The apparent kinetic rate constant and the anodic coefficient transfer of this reaction depend on the pH. In acid medium, a classical concerted 2e−/2H+ mechanism is obtained. In basic medium (pH > 7), strong intramolecular hydrogen interactions between the quinone and the hydroxyl function have a strong influence on the redox kinetics. These results show that JUGthio electroactivity is very sensitive to hydrogen interactions in neutral and basic pH solution and is able to act as sensitive layer for electrochemical biosensing.