The HNO donor ability of hydroxamic acids upon oxidation with cyanoferrates(III)

GUTIÉRREZ, M.M.; A. E. ALMARAZ; BARI, S.E.; JOSÉ A. OLABE; AMOREBIETA, V.

JOURNAL OF COORDINATION CHEMISTRY

TAYLOR & FRANCIS LTD

Lugar: Londres; Año: 2015 vol. 68 p. 3236 - 3246

0095-8972

AbstractThe hydroxamic acids (RC(O)NHOH, HA) exhibit diverse biological activity, including hipotensive properties associated with formation of nitroxyl (HNO) or nitric oxide (NO). Oxidation of two HA´s, benzohydroxamic and acetohydroxamic acids (BHA, AHA) by [Fe(CN)5NH3]2− or [Fe(CN)6]3− was analyzed by spectroscopic, mass spectrometric techniques, and flow EPR measurements. Mixing BHA with both Fe(III) reactants at pH 11 allowed detecting the hydroxamate radical, (C6H5)C(O)NO? −, as a 1-electron oxidation product, as well as N2O as a final product. Successive UV-vis spectra of mixtures containing [Fe(CN)5NH3]2− (though not [Fe(CN)6]3−) at pHs 11 and 7 revealed an intermediate acylnitroso-complex, [Fe(CN)5(NOC(O)(C6H5)]3− (λmax, 465 nm, very stable at pH 7), formed through ligand-interchange in the initially formed reduction product, [Fe(CN)5NH3]3−, and characterized by the FTIR spectra through the stretching vibrations ν(CN−), ν(CO) and ν(NO). Free acylnitroso derivatives, formed by alternative reaction paths of the hydroxamate radicals, hydrolyze forming RC(O)OH and HNO, postulated as precursor of N2O. Minor quantities of NO are formed only with an excess of oxidant. The intermediacy of HNO was confirmed through its identification as [Fe(CN)5(HNO)]3−, (λmax, 445 nm) as a result of hydrolisis of [Fe(CN)5(NOC(O)(C6H5)]3− at pH 11. The results demonstrate that hydroxamic acids behave predominantly as HNO-donors.