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Galactose Oxidase Models: Solution Chemistry, and Phenoxyl Radical Generation Mediated by the Copper Status
Author(s) -
Michel Fabien,
Thomas Fabrice,
Hamman Sylvain,
SaintAman Eric,
Bucher Christophe,
Pierre JeanLouis
Publication year - 2004
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200400099
Subject(s) - chemistry , disproportionation , galactose oxidase , copper , comproportionation , ligand (biochemistry) , radical , redox , photochemistry , polymer chemistry , stereochemistry , medicinal chemistry , inorganic chemistry , organic chemistry , enzyme , electrochemistry , catalysis , biochemistry , receptor , electrode
Galactose oxidase (GO) is an enzyme that catalyzes two‐electron oxidations. Its active site contains a copper atom coordinated to a tyrosyl radical, the biogenesis of which requires copper and dioxygen. We have recently studied the properties of electrochemically generated mononuclear Cu II ‐phenoxyl radical systems as model compounds of GO. We present here the solution chemistry of these ligands under various copper and dioxygen statuses: N 3 O ligands first chelate Cu II , leading, in the presence of base, to [Cu II (ligand)(CH 3 CN)] + complexes ( ortho ‐ tert ‐butylated ligands) or [(Cu II ) 2 (ligand) 2 ] 2+ complexes ( ortho ‐methoxylated ligands). Excess copper( II ) then oxidizes the complex to the corresponding mononuclear Cu II ‐phenoxyl radical species. N 2 O 2 tripodal ligands, in the presence of copper( II ), afford directly a copper( II )‐phenoxyl radical species. Addition of more than two molar equivalents of copper( II ) affords a Cu II –bis(phenoxyl) diradical species. The donor set of the ligand directs the reaction towards comproportionation for ligands possessing an N 3 O donor set, while disproportionation is observed for ligands possessing an N 2 O 2 donor set. These results are discussed in the light of recent results concerning the self‐processing of GO. A path involving copper( II ) disproportionation is proposed for oxidation of the cross‐linked tyrosinate of GO, supporting the fact that both copper( I ) and copper( II ) activate the enzyme.