title: Functional mimic of dioxygen-activating centers in non-heme diiron enzymes: mechanistic implications of paramagnetic intermediates in the reactions between diiron(II) complexes and dioxygen.
abstract: Two tetracarboxylate diiron(II) complexes, [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(C(5)H(5)N)(2)] (1a) and [Fe(2)(mu-O(2)CAr(Tol))(4)(4-(t)BuC(5)H(4)N)(2)] (2a), where Ar(Tol)CO(2)(-) = 2,6-di(p-tolyl)benzoate, react with O(2) in CH(2)Cl(2) at -78 degrees C to afford dark green intermediates 1b (lambda(max) congruent with 660 nm; epsilon = 1600 M(-1) cm(-1)) and 2b (lambda(max) congruent with 670 nm; epsilon = 1700 M(-1) cm(-1)), respectively. Upon warming to room temperature, the solutions turn yellow, ultimately converting to isolable diiron(III) compounds [Fe(2)(mu-OH)(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (L = C(5)H(5)N (1c), 4-(t)BuC(5)H(4)N (2c)). EPR and Mössbauer spectroscopic studies revealed the presence of equimolar amounts of valence-delocalized Fe(II)Fe(III) and valence-trapped Fe(III)Fe(IV) species as major components of solution 2b. The spectroscopic and reactivity properties of the Fe(III)Fe(IV) species are similar to those of the intermediate X in the RNR-R2 catalytic cycle. EPR kinetic studies revealed that the processes leading to the formation of these two distinctive paramagnetic components are coupled to one another. A mechanism for this reaction is proposed and compared with those of other synthetic and biological systems, in which electron transfer occurs from a low-valent starting material to putative high-valent dioxygen adduct(s).
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Dongwhan
authors.initials: D
authors.lastname: Lee
authors.forename: Brad
authors.initials: B
authors.lastname: Pierce
authors.forename: Carsten
authors.initials: C
authors.lastname: Krebs
authors.forename: Michael P
authors.initials: MP
authors.lastname: Hendrich
authors.forename: Boi Hanh
authors.initials: BH
authors.lastname: Huynh
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Lippard
mesh_terms: D001665:Binding Sites; D004578:Electron Spin Resonance Spectroscopy; D004798:Enzymes / Q000737:chemistry* / Q000378:metabolism; D007501:Iron / Q000737:chemistry*; D008667:Metalloproteins / Q000737:chemistry / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D018716:Molecular Mimicry; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D010105:Oxygenases / Q000737:chemistry / Q000378:metabolism; D010636:Phenols / Q000737:chemistry; D012264:Ribonucleotide Reductases / Q000737:chemistry / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet; D015204:Spectroscopy, Mossbauer
chemical_list: D004798:Enzymes; D008667:Metalloproteins; D009942:Organometallic Compounds; D010636:Phenols; D007501:Iron; D006899:Mixed Function Oxygenases; D010105:Oxygenases; C021555:methane monooxygenase; C018747:acyl-(acyl-carrier-protein)desaturase; D012264:Ribonucleotide Reductases; C108427:ribonucleotide reductase R2 subunit; D010100:Oxygen