Synthetic Models of the Inactive Copper(II)-Tyrosinate and Active Copper(II)-Tyrosyl Radical Forms of Galactose and Glyoxal Oxidases
详细信息 查看全文
- 作者：Jason A. Halfen ; Brian A. Jazdzewski ; Samiran Mahapatra ; Lisa M. Berreau ; Elizabeth C. Wilkinson ; Lawrence Que ; Jr. ; and William B. Tolman
- 刊名：Journal of the American Chemical Society
- 出版年：1997
- 出版时间：September 3, 1997
- 年：1997
- 卷：119
- 期：35
- 页码：8217 - 8227
- 全文大小：430K
- 年卷期：v.119,no.35(September 3, 1997)
- ISSN：1520-5126
文摘
A series of CuII and ZnIIcomplexes with new ligands having either one or two substitutedphenolatesappended to the 1,4,7-triazacyclononane frame were prepared andcharacterized by optical absorption, EPR, NMR,and/or resonance Raman spectroscopy, cyclic voltammetry, and, in eightcases, X-ray crystallography. Features ofthe active site geometries of the CuII-tyrosinate formsof galactose and glyoxal oxidases (GAO and GLO) weremodeled by these complexes, including the binding of a redox-activephenolate and an exogenous ligand (Cl-,CH3CO2-, orCH3CN) in a cis-equatorial position of asquare pyramidal metal ion. The role of the uniqueorthoS-C covalent bond between a cysteine (C228) and theequatorial tyrosinate (Y272) in the proteins was probedthrough an examination of the optical absorption and electrochemicalproperties of sets of similar complexes comprisedof phenolate ligands with differing ortho substituents,including thioether groups. The o-alkylthio unitinfluencesthe PhO- 
CuII LMCT transition and theMII-phenolate/MII-phenoxyl radical redoxpotential, but to a relativelysmall degree. Electrochemical and chemical one-electron oxidationsof the CuII and ZnII complexes of ligandshavingtert-butyl protecting groups on the phenolates yielded newspecies that were identified as novel MII-phenoxylradicalcompounds analogous to the active CuII-tyrosyl radicalforms of GAO and GLO. The MII-phenoxyl radicalspecieswere characterized by optical absorption, EPR, and resonance Ramanspectroscopy, as well as by their stoichiometryof formation and chemical reduction. Notable features of theCuII-phenoxyl radical compounds that are similartotheir protein counterparts include EPR silence indicative of magneticcoupling between the CuII ion and the boundradical, a band with 
max 
410 nm (
3900M-1 cm-1) inUV-vis spectra diagnostic for the phenoxyl radical,and a feature attributable to the phenoxyl radical C-O vibration(
7a) in resonance Raman spectra. SimilarRamanspectra and electrochemical behavior for the ZnII analogs,as well as an isotropic signal at g = 2.00 in theirX-bandEPR spectra, further corroborate the formulations of theMII-phenoxyl radical species.
CuII LMCT transition and theMII-phenolate/MII-phenoxyl radical redoxpotential, but to a relativelysmall degree. Electrochemical and chemical one-electron oxidationsof the CuII and ZnII complexes of ligandshavingtert-butyl protecting groups on the phenolates yielded newspecies that were identified as novel MII-phenoxylradicalcompounds analogous to the active CuII-tyrosyl radicalforms of GAO and GLO. The MII-phenoxyl radicalspecieswere characterized by optical absorption, EPR, and resonance Ramanspectroscopy, as well as by their stoichiometryof formation and chemical reduction. Notable features of theCuII-phenoxyl radical compounds that are similartotheir protein counterparts include EPR silence indicative of magneticcoupling between the CuII ion and the boundradical, a band with max 410 nm ( 3900M-1 cm-1) inUV-vis spectra diagnostic for the phenoxyl radical,and a feature attributable to the phenoxyl radical C-O vibration(7a) in resonance Raman spectra. SimilarRamanspectra and electrochemical behavior for the ZnII analogs,as well as an isotropic signal at g = 2.00 in theirX-bandEPR spectra, further corroborate the formulations of theMII-phenoxyl radical species.