engleski

OXIDATION OF HYDROXAMIC ACIDS BY POTASSIUM HEXACYANOFERRATE(III)

Hydroxamic acids (Scheme 1), a group of naturally occurring and synthetic weak organic acids fulfill a variety of important roles in biology and medicine. A number of them exhibit antitumor, antimalarial or antibacterial activity, they are used in treatment of iron overload disorders and in treatment of lung silicosis. Much of their biological activity is related to their capability to form very stable chelates with various metal ions, most specific with ferric ions [1]. Hydroxamic acids are effective and selective inhibitors of enzymes such as peroxidases, ureases and matrix metalloproteins [2]. The pharmacological effects of hydroxamic acids and their derivatives have been attributed not only to metal chelation or enzyme inhibition but also to their ability to serve as nitroxyl (HNO/NO) and nitric oxide (NO) donors [3]. However, the mechanism underlying the formation of these reactive nitrogen species is not clear and requires further elucidation. In the present study, the oxidation of acetohydroxamic, N-methylacetohydroxamic and benzohydroxamic acids with hexacyanoferrate(III) complex anion were investigated using stopped-flow technique. The obtained pH dependences of the oxidation rates indicate that for all three hydroxamic acids the reactive species are the deprotonated ones. The second order rate constants, the activation enthalpies and the activation entropies for the reactions of hydroxamic acids anions with Fe(CN)63− at 25 ºC, I = 2 mol dm−3 (NaClO4) were determined.

hydroxamic acids; oxidation; potassium hexacyanoferrate(III)

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