X-ray absorption spectroscopic studies of the blue copper site: Metal and ligand K-edge studies to probe the origin of the EPR hyperfine splitting in plastocyanin

摘要: X-ray absorption spectra for the oxidized blue copper protein plastocyanin and several Cu(II) model complexes have been measured at both Cu K-edge ligand K-edges (Cl S) in order to elucidate source of small parallel hyperfine splitting EPR centers. Assignment analysis a feature spectrum [approximately]8,987 eV as 1s [yields] 4p + ligand-to-metal charge-transfer shakedown transition has allowed quantitation mixing into ground-state wave function reflected [yields]3d (+4p) intensity [approximately]8,979 eV. The results show that distorted tetrahedral (D[sub 2d])CuCl[sub 4][sup 2[minus]] is characterized by <4% 4p[sub z] mixing, while only xy] mixing. Thus, D[sub 2d]CuCl[sub cannot be explained 12% 3d[sub x[sup 2]-y[sup 2]] orbital had previously postulated. Data collected Cl CuCl[sub pre-edge [approximately]2,820 reflects degree covalency between metal half-occupied ligands.more » data not unusually covalent. discussed. Experiments S ([approximately]2,470 eV) highly covalent Cu-S(cysteine) bond relative cupric-thiolate complex [Cu(tet b)(o-SC[sub 6]H[sub 4]CO[sub 2])][center dot]H[sub 2]O. XAS demonstrate sites high copper-thiolate bond. 34 refs., 12 figs., 3 tabs.« less