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

GUTIERREZ, MARIA MARTA; ALMARAZ, GRACIELA; BARI, SARA E.; OLABE, JOSÉ A.; AMOREBIETA, VALENTÍN T.

JOURNAL OF COORDINATION CHEMISTRY

TAYLOR & FRANCIS LTD

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

0095-8972

The hydroxamic acids (RC(O)NHOH, HA) exhibit diverse biological activity, includinghypotensive 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 alloweddetecting the hydroxamate radical, (C6H5)C(O)NO? −, as a 1-electron oxidation product, as wellas N2O as a final product. Successive UV-vis spectra of mixtures containing [Fe(CN)5NH3]2−(though not [Fe(CN)6]3−) at pH 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 ligandinterchangein the initially formed reduction product, [Fe(CN)5NH3]3−, and characterized byFTIR 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)OHand HNO, postulated as precursor of N2O. Minor quantities of NO are formed only with anexcess of oxidant. The intermediacy of HNO was confirmed through its identification as[Fe(CN)5(HNO)]3− (λmax, 445 nm) as a result of hydrolysis of [Fe(CN)5(NOC(O)(C6H5)]3− at pH11. The results demonstrate that hydroxamic acids behave predominantly as HNO-donors.