Crystalline cob(II)alamin (vitamin B12r) and its solutions in various liquids react reversibly with 02 to yield a complex which is shown by epr spectroscopy to be mononuclear. In accord with the known shielding of the cobalt atom of the cobalamin against collision with large molecules, the mononuclear product of oxygenation does not combine with a second cob(II)alamin molecule to give a dicobalt complex. Eight hyperfine lines are found in the spectrum of methanolic solutions of oxygenated cob(II)alamin at temperatures close to the melting point. The coupling constant due to the cobalt nucleus is 12 G. At about 159°K there is a transition attributed to cessation of tumbling to give a spectrum different in over-all shape and in having an additional set of eight hyperfine lines. Superhyperfine structure due to the coordinated nitrogen atom of dimethylbenzimidazole is lost on oxygenation. Comparison with the hyperfine coupling constants of related binuclear complexes indicates that oxygenated cob(II)alamin may be regarded as superoxocobalamin, most of the unpaired spin density being concentrated at the coordinated 02 •" group. Detection of a reversibly formed mononuclear product of oxygenation establishes the first reaction step in the autoxidation of Bi2r and indicates the likelihood of transient occurrence of mononuclear superoxo complexes during autoxidation of hemoproteins. When cob(II)inamides are oxygenated the epr signals obtained resemble those from superoxocobalamin at temperatures below 159°K. The hyperfine coupling constants may be larger or smaller than for superoxocobalamin, depending upon whether the strength of bonding of the fifth ligand is less or greater than that for the nucleotide in the cobalamin.

By spectrophotometric scanning of reacting solutions, we have studied the processes which can occur when Oz is admitted to aqueous solutions containing the Ion [CoII(CN)5]3- in the concentration range 0.0002-0.4M, at 0�. A scheme is given to explain the formation of and inter-relations between [(CN)5CoIII-O-O-CoIII(CN)5]6-; [(CN)5CoIII-O-O-CoIV(CN)5]5-; [(CN)5CoIIIOH2]2- ; [CoIII(CN)6]3-, and a complex believed to be [(CN)5CoIII-O-OH]3-, which absorbs at 272 mp Preparative methods are described for obtaining several of the oxidation products in the crystaline state. Hydrolysis of [(CN)5CoIII-O-O-CoIII(CN)5]6- to [(CN)5CoIIIOH2]2- takes place via the 272 mμ complex, which is fairly stable in alkaline solution and is resistant to oxidation. The same 272 mμ complex can be formed more directly by oxygenation of the hydrido complex [(CN)5CoIIIH]3-, which is present in aged or hydrogenated solutions of pentacyanocobaltate(II). All of the pentacyano oxidation products can be reduced by sodium borohydride to [(CN)5CoIIIH]3-, which is further reduced by excess borohydride to an insoluble green compound and finally to metallic cobalt. We have briefly examined the reactions of ammonia and CN- with [(CN)5CoIIIOH2]2-, and the reaction of [(CN)5CoIII-O-O-CoIV(CN)5]5- with reducing agents, including [CoII(CN)5]3-.

When the oxidation of metmyoglobin or methaemoglobin by H 20 2 is carried out at pH 5 or less the principal product absorbs at 525 m!'-. It is taken to be the conjugate acid of the ferrylmyoglobin or ferrylhaemoglobin which is the main oxidation product at neutral pH and which absorbs at 545 m!'-. It appears to be susceptible to further attack by H202, yielding an inert ferric complex which absorbs at 586 m!'-, and which cannot be reduced to an oxygen carrier. Formation of the 586 m!,- complex could be a minor factor in the aging of erythrocytes. Whale metmyoglobin differs from that of horse in not being oxidized to the ferryl state by chloroiridate ion if the pH is less than 6�5.

Three detailed mechanisms are considered for the catalatic decomposition of H,O,. I t is shown that the first of these, akin to the earlier hypotheses for catalase action, cannot satisfy the magnetic, titrimetric, and kinetic evidence. The second mechanism involves oxidation of the FeIII porphyrin to the equivalent of FeV. The electron deficiency is distributed over the ligands so that even in the most oxidized complex the iron is in the FeIV or possibly even the FeIII state. I n the third scheme it is suggested that the reduction step (in which 0, is liberated) takes place a t a carbon atom, while the site of the oxidation is the metal atom as commonly supposed.The liberation of 0, from H,O, can be catalysed by 6-coordinate ruthenium I1 complexes. I n the catalytic cycle, the metal appears to be oxidized to R d v , then reduced to RuII. Ethanol or ascorbic acid can substitute for H,O, in the reduction. Evidence for H,O, attack on the ligands is suggestive but not conclusive.A brief comment is made on the bonding of oxygen to haemoglobin and myoglobin. The accumulated evidence for the structures of catalase, peroxidase, and myoglobin complexes is utilized in a scheme for the uptake of oxygen by cytochrome oxidase.

A preliminary study has been made of the oxidation of four octahedral RuII complexes in aqueous solution, particularly by H2O2. Kinetic measurements and simple experiments such as electrolytic oxidation followed by reduction with H2O2 have been used to obtain evidence for the mechanism of H2O2 decomposition when catalysed by the ruthenium complexes. The main course of the catalysis appears to consist in oxidation of RuII to RuIV with a corresponding reduction of H2O2 to hydroxyl ions, followed by a "electron reduction of RuIV to RuII with oxidation of H2O2 to O2 and hydrogen ions.