title: Disproportionation of hydroxylamine by water-soluble iron(III) porphyrinate compounds.
abstract: The reactions of hydroxylamine (HA) with several water-soluble iron(III) porphyrinate compounds, namely iron(III) meso-tetrakis-(N-ethylpyridinium-2yl)-porphyrinate ([Fe(III)(TEPyP)](5+)), iron(III) meso-tetrakis-(4-sulphonatophenyl)-porphyrinate ([Fe(III)(TPPS)](3-)), and microperoxidase 11 ([Fe(III)(MP11)]) were studied for different [Fe(III)(Porph)]/[HA] ratios, under anaerobic conditions at neutral pH. Efficient catalytic processes leading to the disproportionation of HA by these iron(III) porphyrinates were evidenced for the first time. As a common feature, only N(2) and N(2)O were found as gaseous, nitrogen-containing oxidation products, while NH(3) was the unique reduced species detected. Different N(2)/N(2)O ratios obtained with these three porphyrinates strongly suggest distinctive mechanistic scenarios: while [Fe(III)(TEPyP)](5+) and [Fe(III)(MP11)] formed unknown steady-state porphyrinic intermediates in the presence of HA, [Fe(III)(TPPS)](3-) led to the well characterized soluble intermediate, [Fe(II)(TPPS)NO](4-). Free-radical formation was only evidenced for [Fe(III)(TEPyP)](5+), as a consequence of a metal centered reduction. We discuss the catalytic pathways of HA disproportionation on the basis of the distribution of gaseous products, free radicals formation, the nature of porphyrinic intermediates, the Fe(II)/Fe(III) redox potential, the coordinating capabilities of each complex, and the kinetic analysis. The absence of NO(2)(-) revealed either that no HAO-like activity was operative under our reaction conditions, or that NO(2)(-), if formed, was consumed in the reaction milieu.
authors.affiliation: Departamento de Química Inorgánica, Analítica y Química Física and INQUIMAE-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón 2, Buenos Aires, C1428EHA, Argentina.
authors.forename: Sara E
authors.initials: SE
authors.lastname: Bari
authors.forename: Valentín T
authors.initials: VT
authors.lastname: Amorebieta
authors.forename: María M
authors.initials: MM
authors.lastname: Gutiérrez
authors.forename: José A
authors.initials: JA
authors.lastname: Olabe
authors.forename: Fabio
authors.initials: F
authors.lastname: Doctorovich
mesh_terms: D002384:Catalysis; D019811:Hydroxylamine / Q000737:chemistry*; D008665:Metalloporphyrins / Q000737:chemistry*; D009569:Nitric Oxide / Q000737:chemistry*; D010544:Peroxidases / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*; D012995:Solubility; D014867:Water / Q000737:chemistry
chemical_list: D008665:Metalloporphyrins; D011725:Pyridines; C510472:iron(III)-tetrakis(p-sulfonatophenyl)porphyrin; D014867:Water; D019811:Hydroxylamine; D009569:Nitric Oxide; D010544:Peroxidases; C021799:microperoxidase