Aqueous Fe^IV=O: Spectroscopic Identification and Oxo‐Group Exchange.

Abstract

Iron I 7100 Aqueous Fe IV =O: Spectroscopic Identification and Oxo-Group Exchange. -[(H2O)5Fe=O] 2+ species are generated from [Fe(H2O)6] 2+ and O3 in aqueous solution at pH 1 and characterized by Moessbauer spectroscopy, XANES, DFT calculations, and chemical reactions with Me2SO. Criteria are developed that make it possible to distinguish between hydroxyl radicals and aqueous ferryl-oxo species. [(H2O)5Fe IV =O] 2+ can be unambiguously ruled out as a crucial Fenton intermediate in acidic and neutral aqueous solutions. -(PESTOVSKY, O.; STOIAN, S.; BOMINAAR, E. L.; SHAN, X.; MUENCK*, E.; QUE, L. J.; BAKAC, A.; Angew. Chem., Int. Ed. 44 (2005) 42, 6871-6874; Dep. Chem., Carnegie Mellon Univ., Pittsburgh, PA 15213, USA; Eng.) -W. Pewestorf 02-025

Spectroscopic evidence for the presence of a high‐valent Fe(IV) species in the ferroxidase reaction of an archaeal ferritin

“…Because for the addition of 48 Fe(II) per ferritin 24-mer 7-8 subunits were in the A II B II C II form [10], the Fe(IV) species was detected in~2 subunits. We conclude that an Fe(III)-Fe(IV) species was formed as a result of decay of the peroxodiferric species because: (a) no Fe(IV) was observed at 0.7 s when all of the Fe(II) in the ferroxidase center was converted to the peroxodiferric species (Table 1), (b) formation of Fe(IV) species in solution due to Fenton chemistry has been ruled out previously [24], (c) the M€ ossbauer parameters of the high-spin Fe(III) and the Fe(IV) species are close to those reported for the Fe(III)-Fe(IV) couple in RNR (Table 2), and (d) the sum of the amount of the high-spin Fe(III) (9%) and the Fe(IV) (5%) species 1.0 s after the addition of dioxygen (doublets 4 and 5 in Table 1) is equal to the sum of the amount of Fe(II) oxidized in site C (8%) and the amount of Fe(III) species in the form of the peroxodiferric species disappeared (6%) from 0.7 s to 1 s after the addition of dioxygen (Table 1). Therefore,~5% of the high-spin Fe(III) species is coupled to Fe(IV) to form a Fe(III)-Fe(IV) mixed-valence species.…”

New Insight into the Oxidation of Arsenite by the Reaction of Zerovalent Iron and Oxygen. Comment on “pH Dependence of Fenton Reagent Generation and As(III) Oxidation and Removal by Corrosion of Zero Valent Iron in Aerated Water”

“…Recently, Pestovsky and coworks have characterized aqueous ferryl species spectroscopically, theoretically, and chemically that was generated by the reaction of ozone and ferrous ion, and developed criteria that made it possible to distinguish between OH radicals and this species for the first time (9)(10)(11). Their criteria allow them to unambiguously rule out aqueous ferryl species as active intermediates in the Fenton reaction in acidic and neutral aqueous solution (10). Their excellent work further strengthens our belief that it is the pH-dependent mechanism of arsenite removal rather than the pH-dependent mechanism of the Fenton reaction that is responsible for the different effects of 2-propanol observed at acidic and circumneutral pH.…”

Toward the Synthesis of More Reactive S = 2 Non-Heme Oxoiron(IV) Complexes

“… 5 The initial investigations of these new S = 1 oxoiron(IV) complexes were discussed in a 2007 Account by one of us. 7 At the time, the only reported S = 2 oxoiron(IV) complex was [Fe IV (O)(OH 2 ) 5 ] 2+ ( 1 ) ( Figure 1 ), characterized by Bakac, 8 in which the oxoiron(IV) center is supported by weak-field aqua ligands. Complex 1 was found to be a powerful oxidant that can undergo fast hydrogen-atom transfer (HAT) reactions with a range of organic substrates.…”

“… Structures of S = 2 oxoiron(IV) complexes 1 and 14 , based on DFT-derived coordinates from refs ( 8 ) and ( 10 ), and of 2 and 4 , based on crystallographic data from refs ( 11 ) and ( 12 ). …”