MULTIPLE-EDGE XAS STUDIES OF CYANIDE-BRIDGED IRON-COPPER MOLECULAR ASSEMBLIES RELEVANT TO CYANIDE-INHIBITED HEME-COPPER OXIDASES USING 4-BODY MULTIPLE-SCATTERING ANALYSIS

A pair of cyanide-bridged iron-copper molecular assemblies relevant to cyanide-inhibited heme-copper oxidases has been studied by X-ray abso rption spectroscopy at both Fe and Cu K-edges. These two complexes, [( py>(OEP>Fe-CN-Cu(Me(6)tren)](2+) (2) and [(py)(OEP)Fe-CN-Cu(TIM)](2+) (3), contain a unique four-body Fe-C-N-Cu bridge with an Fe-C-N angle of 179 degrees. They, however, differ significantly in the Cu-N-C angl e (174 degrees in 2 and 147 degrees in 3). These two complexes provide the opportunity to study long-range multiple scattering CMS) interact ions between the Fe and the Cu centers. We have calculated theoretical four-body MS signals for the bridge configuration and other four-body pathways in the structures, and performed least-squares fittings of t he theoretical signals to the experimental data using;the GNXAS progra ms. A strong long-range Fe Cu interaction (4.94 Angstrom) has been obs erved from both the Fe and Cu K-edge data for 2. GNXAS analysis shows that this long-range interaction is attributed to the MS amplitude enh ancement from the linear four-body Fe-C-N-Cu configuration. This inter action is not observable from the Fe and Cu K-edge data for 3 where th e angle deviates significantly from linearity. An angle-dependence stu dy of MS effects on the Cu-N-C angle shows that there is a large enhan cement of MS intensity when the angle approaches linearity, and that t his MS effect is negligible when the angle is below similar to 160 deg rees. Essentially no Fe-Cu interaction is detectable for a configurati on with such an angle. Comparisons with three-body MS effects found in Fe-O/O(H)-Cu bridged systems are made. The significance of the findin gs of this study to the structural definition of the binuclear center in the cyanide-inhibited heme-copper oxidases is discussed.