One-electron oxidation and reduction of vitamin C derivatives : 6-bromo-and 6-chloro-6-deoxy-ascorbic acid
| Autor: | M. Bonifačić, M. Eckert-Maksić, Ivica Ljubenkov |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 1994 |
| Předmět: |
Radiological and Ultrasound Technology
Vitamin C Free Radicals Chemistry Radical Electrons Ascorbic Acid Photochemistry Ascorbic acid Redox Oxygen Reaction rate constant vitamin C derivatives one electron oxidation/reduction antioxidant bioreductive antitumor agents Yield (chemistry) Oxidizing agent Moiety Radiology Nuclear Medicine and imaging Oxidation-Reduction |
| DOI: | 10.1080/09553009414551021 |
| Popis: | 6-Bromo- and 6-chloro-6-deoxy derivatives of ascorbate anion are able to transfer an electron to the oxidizing radicals .OH, Br2.- and RS. with the same rate constants as the ascorbate anion itself. The resulting radicals also show the same kinetic stabilities and optical absorption spectra as the well-characterized ascorbate radical anion (lambda max = 360 nm; epsilon 360 = 330 m2 mol-1). This proves that there is no influence of the structural changes in the side chain on the antioxidant capacity of the ascorbate moiety. In contrast, measured reduction of the 6-halo-6-deoxy derivatives occurs significantly faster (up to one order of magnitude) than the reduction of unsubstituted ascorbate. For example, absolute rate constants of 4.6 x 10(9) and 2.2 x 10(7) dm3 mol-1 s-1 have been measured for the reactions of bromo-derivative with eaq- and (CH3)2COH respectively. These radical-induced reductions proceed via dissociative electron capture and, under cleavage of the C-halogen bond, yield C-6 carbon-centered radicals. In the presence of oxygen the corresponding peroxyl radical is readily formed. This radical is again able to oxidize the ascorbate moiety (rate constant 2 x 10(7) dm3 mol-1 s-1). Results are discussed in terms of biological relevance of the investigated compounds regarding their ability to act as efficient antioxidants and bioreductive antitumour agents simultaneously. |
| Databáze: | OpenAIRE |
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