Formation Of Dioxygen Adducts Research Articles

Synthetic Models of the Active Site of Cytochrome c Oxidase: Influence of Tridentate or Tetradentate Copper Chelates Bearing a HisTyr Linkage Mimic on Dioxygen Adduct Formation by Heme/Cu Complexes

Two synthetic models of the active site of cytochrome c oxidase--[(LN4-OH)CuI-FeII(TMP)]+ (1 a) and [(LN3-OH)CuI-FeII(TMP)]+ (2 a)-have been designed and synthesized. These models each contain a heme and a covalently attached copper moiety supported either by a tetradentate N4-copper chelate or by a tridentate N3-copper chelate including a moiety that acts as a mimic of the crosslinked His-Tyr component of cytochrome c oxidase. Low-temperature oxygenation reactions of these models have been investigated by spectroscopic methods including UV/Vis, resonance Raman, ESI-MS, and EPR spectroscopy. Oxygenation of the tetradentate model 1 a in MeCN and in other solvents produces a low-temperature-stable dioxygen-bridged peroxide [(LN4-OH)CuII-O2-FeIII(TMP)]+ {nuO--O=799 (16O2)/752 cm(-1) (18O2)}, while a heme superoxide species [(TMP)FeIII(O2-)CuIILN3-OH] {nuFe--O2: 576 (16O2)/551 cm(-1) (18O2)} is generated when the tridentate model 2 a is oxygenated in EtCN solution under similar experimental conditions. The coexistence of a heme superoxide species [(TMP)FeIII(O2-)CuIILN3-OH] and a bridged peroxide [(LN3-OH)CuII-O2-FeIII(TMP)]+ species in equal amounts is observed when the oxygenation reaction of 2 a is performed in CH2Cl(2)/7 % EtCN, while the percentage of the peroxide (approximately 70 %) in relation to superoxide (approximately 30 %) increases further when the crosslinked phenol moiety in 2 a is deprotonated to produce the bridged peroxide [(LN3-OH)CuII-O2-FeIII(TMP)]+ {nuO--O: 812 (16O2)/765 cm(-1) (18O2)} as the main dioxygen intermediate. The weak reducibility and decreased O2 reactivity of the tricoordinated CuI site in 2 a are responsible for the solvent-dependent formation of dioxygen adducts. The initial binding of dioxygen to the copper site en route to the formation of a bridged heme-O2-Cu intermediate by model 2 a is suggested and the deprotonated crosslinked His-Tyr moiety might contribute to enhancement of the O2 affinity of the CuI site at an early stage of the dioxygen-binding process.

An oxygen-releasing device: reversible oxygen release from a cobalt chelate–carbon composite in response to an applied voltage

A disk (e.g. diameter 2 cm×2 mm) was made of [N,N′-bis(salicylidene)ethylenediamine]cobalt [Co(salen)] and carbon powder. The composite disk selectively absorbed oxygen from air, e.g. 22 cm3 oxygen per gram of composite at room temperature, which is almost stoichiometrically ascribed to 2:1 cobalt–dioxygen adduct formation. The adduct formation was an exothermic reaction, and the absorbed oxygen was released above 80 °C. The application of 6 V to the disk sandwiched between platinum meshes induced a temperature elevation in the disk, which quickly released the absorbed oxygen. Under ambient conditions, the oxygen-releasing and -absorbing processes could be established within a few min and a 30 min interval, respectively, for the composite disk containing the 3-ethoxy derivative of Co(salen), while the oxygen absorption took several hours for the Co(salen) disk.

EPR of the Co(II) complexes of phenanthraquinonedioxime and benzoquinonedioxime. Formation of dioxygen adducts in the solid state

Cobalt(II) complexes of 9, 10-phenanthrenedionedioxime (pqdH2) and benzoquinonedioxime (bqdH2) and the doped sample, Co(pqdH)2/Ni(pqdH)2 were prepared and investigated by EPR. The EPR parameters, especially the small hyperfine splitting values, reveal the presence of oxygen adduct in the concentrated (undoped) samples, while the dilute (doped) sample has parameters corresponding to a2A1(¦z2>) ground state. It is proposed that the oxygen adducts are formed as intermediates, leading ultimately to thetris-chelate Co(III) complexes of these oximes, which however could not be isolated in pure form.

Manganese(II) catalysis of the autoxidation of dopamine resulting from dioxygen adduct formation

Manganese(II) catalysis of the autoxidation of dopamine resulting from dioxygen adduct formation

Spectrophotometric study of the reaction between cobalt(II)-dipeptide complexes and molecular oxygen

The influence of pH and ligand structure on the reaction of cobalt(II) complexes with various dipeptides and molecular oxygen was examined. The minimum pH value required for the formation of dioxygen adducts was found to be about 6.5. This value should be related to amidic deprotonation of dipeptides, which seems to occur in the examined systems at particularly low values. The location and steric hindrance of the side chains of the dipeptides have a strong influence on the reaction rate. The presence of a substituent group on the N-terminal amino acid promotes oxygen coordination, while, when the substituent group is on the C-terminal residual, a decrease of reaction rate is observed.

Synthesis and properties of binuclear nitride-bridged iron octaphenyltetraazaporphyrin. E.p.r. studies of dioxygen adduct formation

The synthesis and characterization are reported for (μ-nitrido)bis[(octaphenyltetraazaporphyrinato)iron] ([OPTAP)Fe]2N). The [(OPTAP)Fe]2N dimer is paramagnetic with one unpaired electron per dimer unit and shows a typical axially symmetric e.p.r. spectrum in non-polar solvents at liquid N2 temperature (g⊥=2.126, g‖=2.001), with well-resolved superhyper-fine splitting resulting from the μ-nitrido bridge (A⊥N=2.48mT, A‖N=2.60mT).

Liberation of the superoxide anion from the dioxygen-Co(II)-tetrasulfophthalocyanine adduct in dimethyl sulfoxide

The present work originated from the finding that Co(II)-tetrasulfophthalocyanine forms reversible dioxygen adducts in both non-aqueous and aqueous solutions. The aim was to elucidate if and how the dioxygen adduct formation is connected with the generation of free superoxide ion and how it can be affected

Cationic rhodium(I) and iridium(I) complexes with phosphorus-sulfur bidentate ligands. Formation of dioxygen adducts

Synthese des complexes [M(PSR) 2 ]Y avec PSR=(C 6 H 5 ) 2 P(CH 2 ) 2 SR. Spectre RMN de 31 P

Dioxygen adducts of low-valent titanium porphyrins. prospects for the selective binding and activation of molecular oxygen

A five coordinate paramagnetic fluorotitanium(III) tetraphenylporphyrin complex, TiF(TPP), was prepared by zinc amalgam reduction of the corresponding difluorotitanium(IV) complex. The benzenethiolatotitanium(III) analog, Ti(SC 6H 5)(TPP), was obtained by metathesis with sodium benzenethiolate. Both complexes exhibit the features that are essential for dioxygen adduct formation, and indeed, they undergo fast autoxidation in the presence of dioxygen. Autoxidation mechanisms are proposed on the basis of the observed oxidation end-products and of the ability of the coordinated benzenethiolate to act as a one-electron reductant. Implication on the function of the axial thiolate ligand during cytochrome P-450 catalytic cycle is presented.

Formation of dioxygen adducts of cobalt(II) amine complexes in a cation exchange resin

The formation of monomeric dioxygen adducts of cobalt(II) complexes with ammonia, methylamine and ethylenediamine in an Amberlyst A-15 cation exchange resin is demonstrated by EPR. The EPR spectra are compared with those of the corresponding adducts formed in zeolite Y. The enhanced stability of the monomeric adducts in Amerlyst is attributed to the interaction of the complexes with sulfonate anion sites in the resin. The total amounts of oxygen adsorbed are greater than the spin concentrations of the monomeric adducts and this discrepancy is attributed to the formation of diamagnetic μ-peroxodicobalt adducts as well as a slow irreversible oxidation of the Co(II) to Co(III). A paramagnetic μ-superoxodicobalt adduct is observed only with methylamine and then only in very low concentrations.