Oxygen-Bridged Iron—Copper Assemblies Pertinent to Heine-Copper Oxidases: Synthesis and Structure of an [Fe~Ⅲ-(OH)-Cu~Ⅲ] Bridge and EXAFS Multiple-Scattering Effects of Linear Oxo and Nonlinear Hydroxo Bridges

摘要

In the course of our development of molecular bridged assemblies relevant to the binuclear Fe/Cu (heme a—Cu_B) site of heme—copper oxidases,1 we have prepared the bridges [Fe~Ⅲ— X-Cu~Ⅱ] with X = O~(2-) and CN~-. The species [(OEP)Fe-O-Cu(Me_6tren)]~(+2) (1) with ground state S = 2 is a plausible representation of the oxidized binuclear site in the resting state of the enzymes, while [(py)(OEP)Fe-CN-Cu(Me_6tren)]~(2+) and related assemblies delineate the cyanide-inhibited form of the oxidized enzymes. These and other bridged species, whose bridge angles can deviate from linearity, provide especially challenging cases for multiple-scattering (MS) EXAFS analysis. Recently, we have reported the successful use of the GNXAS analysis package to determine reliable metric information (including angles) beyond the first coordination sphere. Of particular present relevance is the significant amplitude enhancement when a backscatterer and an intervening atom form a linear or near-linear relationship, such as might occur in an [Fe-X-Cu] bridge.