title: Mechanistic analysis of reductive nitrosylation on water-soluble cobalt(III)-porphyrins.
abstract: The reactions of NO and/or NO2- with three water-soluble cobalt porphyrins [Co(III)(P)(H2O)2]n, where P = TPPS, TCPP, and TMPyP, were studied in detail. At pH < 3, the reaction with NO proceeds through a single reaction step. From the kinetic data and activation parameters, the [Co(III)(P)(NO)(H2O)]n complex is proposed to be the primary product of the reaction with NO. This complex reacts further with a second NO molecule through an inner-sphere electron-transfer reaction to generate the final product, [Co(III)(P)(NO-)](n-1). At pH > 3, although a single reaction step is also observed, a systematic study as a function of the NO and NO2- concentrations revealed that two reaction steps are operative. In the first, NO2- and NO compete to substitute coordinated water in [Co(III)(P)(H2O)2]n to yield [Co(III)(P)(NO)(H2O)]n and [Co(III)(P)(NO2-)(H2O)](n-1) as the primary reaction products. Only the nitrite complex could be detected and no final product formation was observed during the reaction. It is proposed that [Co(III)(P)(NO)(H2O)]n rapidly reacts with NO2- to form the nitrite complex, which in the second reaction step reacts with another NO molecule to generate the final product through an inner-sphere electron-transfer reaction. The reported results are relevant for the interaction of vitamin B(12a) with NO and NO2-.
authors.affiliation: Institute for Inorganic Chemistry, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058 Erlangen, Germany.
authors.forename: Federico
authors.initials: F
authors.lastname: Roncaroli
authors.forename: Rudi
authors.initials: R
authors.lastname: van Eldik
mesh_terms: D003035:Cobalt / Q000737:chemistry*; D004579:Electron Transport; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008665:Metalloporphyrins / Q000737:chemistry*; D009569:Nitric Oxide / Q000737:chemistry*; D009573:Nitrites / Q000737:chemistry*; D012995:Solubility; D013056:Spectrophotometry, Ultraviolet; D014805:Vitamin B 12 / Q000737:chemistry / Q000378:metabolism; D014867:Water / Q000737:chemistry*
chemical_list: D008665:Metalloporphyrins; D009573:Nitrites; D014867:Water; D009569:Nitric Oxide; D003035:Cobalt; D014805:Vitamin B 12