| STUDY |
A stable complex that aims to model the activation of molecular oxygen by cytochrome P450 enzymes has been synthesized by researchers at Kyushu University, Fukuoka, Japan [Angew. Chem. Int. Ed., 39, 1989 (2000)]. These heme-thiolate enzymes are monooxygenases that metabolize lipophilic compounds via a process that first involves the addition of O2 to the cytochrome. Because this adduct is unstable, the molecular mechanism of O-O bond cleavage and the role of the cytochrome's peripheral groups are not fully understood. Chemistry professor Yoshinori Naruta and coworkers built their complex from a binaphthyl-bridged porphyrin that shelters a thiolate ligand. They showed that the adduct is stable at 0 C and postulated that a hydrogen bond between the bound oxygen and a hydroxyl group on the binaphthyl ring confers stability. Using Raman spectroscopy, they verified this hypothesis: When deuterium was substituted for hydrogen in the exchangeable protons, only the frequency of the O-O stretching mode shifted--there was no perturbation in the porphyrin skeleton. The work "shows the first direct evidence for a hydrogen bond between dioxygen and a thiolate-coordi-nated heme, which has significance for the dioxygen binding and activation in cytochrome P450," the team writes
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