Electrocatalytic activity of [(bpy)2(H2O)RuIIIORuIII(H2O)(bpy)2]4+ towards sugar oxidation

The oxo-bridged dinuclear cation [(bpy)2(H2O)RuIII ORuIII(H2O)(bpy)2]4+ (1) (bpy = bipyridine), when oxidized to the RuIVRuV oxidation state, is an effective catalyst for the oxidation of a series of sugars with acetalic structure, like methyl-α-d-glucopyranoside (MGP), methyl-α-d-mannopyranoside (MMP), phenyl-β-d-glucopyranoside (PGP) and octyl-α-d-glucopyranoside (OGP). Cyclic voltammetry was applied to study the reactivity of 1 in basic solution towards oxidation of MGP, MMP and PGP. The electrogenerated RuIVRuV form of 1 oxidizes MGP, MMP, PGP, ethanol and 2-propanol in reactions that are first-order both in catalyst and in substrate. The second-order rate constant, Kcat, for the oxidation of MGP, MMP, PGP, ethanol and 2-propanol in 1 M NaOH, are 16.1±0.4, 35.0 ±1.0, 26.8±0.4, 16.0±1.0, and 6.6±0.7 M−1·−1, respectively. Bulk electrolysis of 1 in 0.1 M NaOH in presence of MGP, or OGP, was carried out with the purpose of identifying the carbohydrate oxidized products. HPLC analyses of the MGP and OGP oxidation mixtures after electrolysis revealed that in both cases the only oxidized products are the corresponding alkyl glucuronides.