THE ROLE OF INCIPIENT HYDROUS OXIDES IN THE OXIDATION OF GLUCOSE AND SOME OF ITS DERIVATIVES IN AQUEOUS-MEDIA

Gold in aqueous media, with its extensive working range apparently devoid of complications due to chemisorbed hydrogen and oxygen species, is frequently considered as the ideal electrode system for fundamental investigations in electrochemistry. However, this system displays significant electrocatalytic activity in base, an effect that has been attributed to a phenomenon known as pre-monolayer oxidation. Glucose oxidation at gold in base commences at ca 0.15 V (rhe), the reaction (evidently confined at low potentials to the aldehyde group) being mediated by an Au(I) incipient hydrous oxide species: in agreement with this approach to electrocatalysis the reaction of other species, eg formaldehyde and dimethylamine borane oxidation and nitrate ion reduction, commences in the same region. The alcohol groups in glucose (and its derivatives) are more resistant to oxidation; they only commence reaction above 0.65 V (rhe) where a different mediator, an Au(III) hydrous oxide species, is present at the interface. The glucose oxidation rate, which is of significant interest in the biosensor area, decreases as the pH of the solution is reduced.