Oxygenated cobalt

Although no direct evidence was found in the cobalt-N-hydroxyethylethyl-enediamine reaction that an oxygen-cobalt addition complex was formed, it seems reasonable to postulate that such an intermediate is present in the reaction. An oxygen-cobalt complex intermediate appears to afford the most logical method of explaining the evidence that the oxidation of cobalt (II) to cobalt (III) occurs in conjunction with the oxidative cleavage of the carbon-carbon bond of the hydroxyethyl group and the formation of ethylenediamine. 

Based upon the existence of this oxygen-cobalt intermediate, a reaction sequence is proposed for the cobalt (II)-catalyzed conversion of N-hydroxyethyl-ethylenediamine to ethylenediamine, which is consistent with the experimental results. The mechanism is a speculation based on the nature of the end products. The stoichiometry of the proposed reaction is ... 

ESR studies also show the similarity between oxycoboglobin and oxygenated cobalt porphyrin, and suggest that the protein does not measurably influence the electronic structure of the heme group, although the protein does control the extent to which dioxygen is bound. 

General Properties of Compounds of Cobalt—Cobalt and the Halogens—Oxy-Halogon Derivatives—Cobalt and Oxygen—Cobalt and Sulphur—The Alums—Cobalt and Selenium, Tellurium, Chromium, and Molybdenum—... 

The initiation step was proposed to proceed via the formation of the oxygenated adduct, like Co -0-0, which reacts with aldehyde in the rate-determining step [26]. However, the fact that the induction time is more for CoPc as compared to C0W12 (the latter is unable to form any adducts), shows that species different from oxygenated cobalt adducts may promote the chain initiation. We believe that for most cobalt catalysts studied these species are Co(III) forms of the catalyst produced by one-electron oxidation of Co(II) initial forms with peroxy acid, which in turn is produced in the course of aldehyde autoxidation. Usually, the end of the induction period coincides with the change of the reaction mixture colour expected for Co(III) appearance. 

Brunschwig BS, Chou MH, Creutz C, Ghosh P, Sutin N (1983) Mechanisms of water oxidation to oxygen cobalt(IV) as an intermediate in the aquocobalt(II)-catalyzed reaction. J Am Chem Soc 105 4832-4833... 

Phthalocyanine complexes within zeolites have also been prepared by the ship-in-a-bottle method (see Section 6.6), and have subsequently been investigated as selective oxidation catalysts, where their planar metal-N4 centres mimic the active sites of enzymes such as cytochrome P450, which is able to oxidize alkanes with molecular oxygen. Cobalt, iron and ruthenium phthalocyanines encapsulated within faujasitic zeolites are active for the oxidation of alkanes with oxygen sources such as iodosobenzene and hydroperoxides. Following a similar route, Balkus prepared Ru(II)-perchloro- and perfluorophthalocyanines inside zeolite X and used these composites for the selective catalytic oxidation of alkanes (tert-butylhydroperoxide). The introduction of fluorinated in place of non-fluorinated ligands increases the resistance of the complex to deactivation. 

The Co(II) azomethine chelates (III, VI, VII) have been found to absorb in dimethylformamide, giving rise to adducts, in which the oxygen - cobalt ratio is 1 2. The compounds in this study are presented in Table 1, together with their analytical and magnetic data. 

The oxygen-cobalt ratio was checked not only by direct elemental analysis, but also by gas-volumetric measurements of oxygen absorbed. 

Oxygen carriers would presumably not have been needed at a very early stage in the evolution of cells. Models of reversible complexes of iron and oxygen have been difficult to find. The only two clear examples are ferrous PROTO (or meso-) porphyrinimidazole in dry pyridine 178), and ferrous dimethylgloxime with amines 179). Many reversible oxygen-cobaltous complexes are known 180). 

A detailed structural study has also been made of oxygenated cobalt(II) heme model systems and oxygenated Co(II) corrin complexes. " These used a combination of X-, Q- and W-band CW and pulsed EPR, X- and Q-band ENDOR, X-band HYSCORE and S-band ESEEM to determine the g and A tensors and investigate the proton and nitrogen hyperfine interactions. Both studies are excellent examples of the power of multi-frequency CW and pulsed ESR and ENDOR in determining the full electronic structure of metallo-complexes. 

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