836674-64-7Relevant academic research and scientific papers
Efficient photodissociation of O2 from synthetic heme and heme/M (M = Fe, Cu) complexes
Fry, H. Christopher,Hoertz, Paul G.,Wasser, Ian M.,Karlin, Kenneth D.,Meyer, Gerald J.
, p. 16712 - 16713 (2007/10/03)
Single wavelength excitation (λex = 355 or 532 nm) of low-temperature stabilized (198 K) synthetic heme-dioxygen and heme-dioxygen/M complexes, where M = copper or iron in a non-heme environment, results in the dissociation of dioxygen as indicated by the generation of the ferrous heme (Soret band, 427 nm) and the bleaching of the ferric-superoxide (FeIII(O2-)) 410-nm Soret band in the transient absorption difference spectrum. Dioxygen rebinds to the four heme complexes studied with comparable rate constants (～6-9 × 105 M-1 s-1). However, the quantum yield for complete dissociation of O2 from our simplest heme-O2 complex (F8)FeIII(O2-) (φ = 0.60) is higher than the other complexes measured (φ = 0.2-0.3) as well as that for oxy-myoglobin (φ = 0.3). Copyright
Low-temperature UV-visible and NMR spectroscopic investigations of O2 binding to (6L)FeII, a ferrous heme bearing covalently tethered axial pyridine ligands
Ghiladi, Reza A.,Karlin, Kenneth D.
, p. 2400 - 2407 (2008/10/08)
In this report, we describe the reversible dioxygen reactivity of (6L)FeII (1) {6L = partially fluorinated tetraphenylporphyrin with covalently appended TMPA moiety; TMPA = tris(2-pyridylmethyl)amine} using a combination of low-temperature UV-vis and multinuclear (1H and 2H) NMR spectroscopies. Complex 1, or its pyrrole-deuterated analogue (6L-d8)FeII (1-d8), exhibits downfield shifted pyrrole resonances (δ 28-60 ppm) in all solvents utilized {CH2Cl2, (CH3)2C(O), CH3CN, THF}, indicative of a five-coordinate high-spin ferrous heme, even when there is no exogenous axial solvent ligand present (i.e., in methylene chloride). Furthermore, (6L)FeII (1) exhibits non-pyrrolic upfield and downfield shifted peaks in CH2Cl2, (CH3)2C(O), and CH3CN solvents, which we ascribed to resonances arising from the intra- or intermolecular binding of a TMPA-pyridyl arm to the ferrous heme. Upon exposure to dioxygen at 193 K in methylene chloride, (6L)FeII (1) {UV-vis: λmax = 433 (Soret), 529 (sh), 559 nm} reversibly forms a dioxygen adduct {UV-vis: λmax = 422 (Soret), 542 nm}, formulated as the six-coordinate low-spin {δpyrrole 9.3 ppm, 193 K} heme-superoxo complex (6L)FeIII-(O2-) (2). The coordination of the tethered pyridyl arm to the heme-superoxo complex as axial base ligand is suggested. In coordinating solvents such as THF, reversible oxygenation (193 K) of (6L)FeII (1) {UV-vis: λmax = 424 (Soret), 542 nm} also occurs to give a similar adduct (6L)FeIII-(O2-) (2) {UV-vis: λmax = 418 (Soret), 537 nm. 2H NMR: δpyrrole 8.9 ppm, 193 K}. Here, we are unable to distinguish between a bound solvent ligand or tethered pyridyl arm as axial base ligand. In all solvents, the dioxygen adducts decompose (thermally) to the ferric-hydroxy complex (6L)FeIII-OH (3) {UV-vis: λmax = 412-414 (Soret), 566-575 nm; ～δpyrrole 120 ppm at 193 K}. This study on the O2-binding chemistry of the heme-only homonuclear (6L)FeII (1) system lays the foundation for a more complete understanding of the dioxygen reactivity of heterobinuclear heme-Cu complexes, such as [(6L)FeIICuI]+, which are models for cytochrome c oxidase.
