Dehydroascorbic acid chemistry

Welch RW, Wang Y, Crossman A Jr, Park JB, Kirk KL, and Levine M (1995) Accumulation of vitamin C (ascorbate) and its oxidized metabolite dehydroascorbic acid occurs by separate mechanisms./owma/ of Biological Chemistry 270,12584-92. 

A cofartor can be any chemical required by an enzyme, that is, a metal ion, coenzyme, lipid, or accessory pmtein. A coenzyme is a small organic molecule required by an enzyme that participates in the chemistry of catalysis. Most of the coenzymes work according to the following principle. They shuttle back and forth between two or more different forms. I lere, one of the forms may be considered to be the coenzymatically active form, and the other may be seen as requiring regeneration to the active form. This is the case for folate, vitamin B, riboflavin-and niacin-based cofactors, ascorbic acid, and vitamin K. The coenzymatically active (inactive) forms of three of these coenzymes are tetrahydrofolate (dihydro-folate), ascorbic acid (dehydroascorbic acid), and vitamin KH2 (vitamin K). 

Oxidation of the reductone functionality of ascorbic acid is certainly its single most important reaction and results in the formation of its most biologically important derivative, dehydroascorbic acid, 28. As chemistry and biochemistry of dehydroascorbic acid will be covered in a separate section of this volume, only a few of its reactions will be covered here. 

During the last 20 years a better understanding of the structure and chemical nature of DHA and the free radical intermediate that may be formed during the oxidation of AA has developed. These developments were based on modem instrumental techniques including NMR and NMR spectroscopies and pulsed radiation electron spin resonance (ESR) spectroscopy. The chemistry and properties of mono-dehydroascorbic acid (AA ), a free radical intermediate that may be formed in the oxidation of AA, is covered elsewhere in this volume. This chapter concerns DHA, its reactions, structure, and physiological chemistry. 

On the basis of their redox thermodynamics and reaction chemistry with 02"- in aprotic media, ascorbic acid S and some catechols may be subject to an (O2 -)-catalyzed auto-oxidation to dehydroascorbic acid and o-quinones, respectively. 

A review article on dehydroascorbic acid (72 refs.) covered, in addition to its chemistry, many methods for its separation and analysis. ... 

Bessey, O.A., 1938. A method for the determination of small quantities of ascorbic acid and dehydroascorbic acid in turbid and colored solutions in the presence of other reducing substances. Journal of Biological Chemistry. 126 771-784. 

Tolbert, P. and Ward, J. (1982). Dehydroascorbic Acid, in P Seib and P. Tolbert (eds). Ascorbic Acid Chemistry, Metabolism, and Uses, American Chemical Society, Washington, DC, pp. 101-123. 

Here we begin to encroach upon carbohydrate chemistry, especially with ascorbic acid, the most important member of the class. However, the reader should refer to Berger s study, which includes details of 13C-NMR spectra, a discussion of how the pH dependence is determined by the various protonation sites, and details of the transition of the quinone, dehydroascorbic... 

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