Naslov
One-electron oxidation and reduction of vitamin C derivatives : 6-bromo-and 6-chloro-6-deoxy-ascorbic acid
(One-electron oxidation and reduction of vitamin C derivatives : 6-bromo-and 6-chloro-6-deoxy- ascorbic acid)

Autori
Bonifačić, Marija ; Ljubenkov, Ivica ; Eckert- Maksić, Mirjana

Izvornik
International journal of radiation biology (0955-3002) 66 (1994), 2; 123-131

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
vitamin C derivatives ; one electron oxidation/reduction ; antioxidant ; bioreductive antitumor agents

Sažetak
6-Bromo- and 6-chloro-6-deoxy derivatives of ascorbate anion are able to transfer an electron to the oxidizing radicals ·OH, Br· −2 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 (λmax = 360 nm ; ε360 = 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 × 109 and 2·2 × 107 dm3 mol−1 s−1 have been measured for the reactions of bromo- derivative with e−aq and (CH3)2ĊOH 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 × 107 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.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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