Protonation, phenoxyl radical coordination

The catalytic mechanism of GOase has been extensively studied (Fig. 8) 63,64). The primary alcohol first coordinates to the active species A, leading to the formation of the metal-phenoxyl radical complex B. This species undergoes proton abstraction from the substrate by the axial tyrosinate (Tyr495), followed by a rapid intramolecular electron transfer from the intermediate ketyl radical anion with reduction of Cu to Cul The copper(I) species C reacts with dioxygen to form the hydroperoxo copper(II) complex D with the liberation of the aldehyde. Finally, dihydrogen peroxide is released to give back the active form of the enzyme. 

The formation of the phenoxyl radical was proposed to occur in the presence of acetic acid by coupling the two-electron, two-proton reduction of molecular oxygen to H2O2 [85]. In some way this process is reminiscent of the half reaction observed in GAO. The unusual aspect, however, was its identification in the activated HKR reaction system, although there was no evidence for its involvement in the hydrolysis of epoxides [85]. As Wieghardt noted in earlier works, bulky substituents are required for stabilization of metal-coordinated phenolate radicals [66]. We confirmed this by activation of a Co-salen derivative, [Co(12)] (Fig. 3). In the absence... 

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