Dioxygen reduction intermediate species, spectroscopic

The EPR and ENDOR spectroscopy was used for studies of catalytic intermediates in native and mutant cytochrome P450cam in cryogenic temperatures (6 and 77K) (Davydov et al., 2001). The ternary complex of camphor, dioxygen, and ferrous-enzyme was irradiated with y-rays to inject the second electron. This process showed that the primary product upon reduction of the complex is the end -on intermediate. This species converts even at cryogenic temperatures to the hydroperoxo-ferriheme form and after brief annealing at a temperature around 200 K, causes camphor to convert to the product. In spite of conclusions derived from x-ray analysis (Schlichtich et al., 2000) no spectroscopic evidence for the buildup of a high-valance oxyferryl/porphyrin rc-cation radical intermediate during the entire catalytic circle has been obtained. 

Photolysis of [Co(CH2R)(L)(Hdmg)2] under oxygen proceeds by insertion of dioxygen into the cobalt carbon bond to provide a solution species for which nmr spectroscopic data is rq)orted. Reduction of this intermediate produces primary alcohols whereas thermolysis produces aldehydes and alcohols. Treatment of [Co oep)] with simple aldehydes and rm-butylhydroperoxide in the presence of sodium borohydride produces cobalt(III) acyls in 65-98% yields. In the absence of the borohydride the yield is reduced. The reaction is proposed to proceed by acyl radical trapping by the Co(n) centre. Methyl transfer in a protein free model of vitamin B12 dependent methyl transf enzymes has been studied. These systems convert homocysteine to methionine in nature. Trimethyl-phenylammonium icm reacts with the CoG) centre in cobalamin producing methylcobalamin. ... 

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