Ascorbic acid (ASC) is biochemically essential inside cells and within organisms. However, the electrophilicity of its oxidation products, e.g., ascorbyl radical, dehydroascorbate (DHA), 2,3-diketogluonate (DKG), and erythrulose (ERU) can be problematic. ASC finds widespread use as a nutrient with mammalian cell culture and aquaculture as illustrative examples, and as an additive to food, skincare, and cosmetic products. Derivatizing ASC at hydroxyl positions on the furanone ring markedly improves resistance to oxidation. Of these derivatives, ascorbic acid 2-phosphate (PASC) is the most heavily used. Hydrous manganese oxides (HMO)s were used as oxidants because (i) they are present in some aquaculture settings and during drinking water treatment, (ii) reactions can be conveniently quenched by removing HMOs by filtration, and (iii) dissolved Mn(II) measurements using AAS also us to explore redox stoichiometry. We have documented phosphate generation using capillary electrophoresis (CE) in indirect detection mode. (CE in both direct and indirect mode also allows us to quantify some organic oxidation intermediates and products.) Our next task is to establish whether phosphate is generated by dephosphorylation prior to the first oxidation step or in a subsequent step. Prior dephosphorylation would not be surprising, since manganese oxyhydroxides are known to catalyze the hydrolysis of polyphosphate and other phosphate anhydrides. Dephosphorylation after the first oxidation step would raise the possibility that oxidation products not seen with ASC might be generated. Other ASC derivatives, including ascorbic acid 2-sulfate (SASC), offer opportunities to make reactivity comparisons.

Oxidation kinetics and pathways for ascorbic acid derivatives: A quantitative case study using manganese oxide and capillary electrophoresis

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