MXAN analysis of the XANES energy region of a mononuclear copper complex: Applications to bioinorganic systems

The near edge XAS spectra of the mononuclear copper complex [Cu(TMPA)(OH2)](CIO4)(2) (1) have been simulated using the multiple scattering edge simulation package MXAN (or Minuit XANes). These simulations, which employ the muffin-tin (MT) approximation, have been compared to simulations generated using the finite-difference method (FDM) to evaluate the effect of MT corrections. The sensitivity of the MXAN method was tested using structural models that included several different variations on the bond angles and bond distances for the first-shell atoms of 1. The sensitivity to small structural changes was also evaluated by comparing MXAN simulations of 1 and of structurally modified [Cu(TMPA)(L)](n+) complexes [where L = -O-(F8TPP)Fe-III, -F, -OPO2(O-p-nitrophenyl)Zn-II-(TMPA), and -NCMe] to the experimental data. The accuracy of the bond distances obtained from the MXAN simulations was then examined by comparison to the metrics of the crystal structures. The results show that MXAN can successfully extract geometric information from the edge structure of an XAS spectrum. The systematic application of MXAN to 1 indicates that this approach is sensitive to small structural changes in the molecule that are manifested in the XAS edge spectrum, These results represent the first step toward the application of this methodology to bioinorganic and biological systems.