Further Insights into the Spectroscopic Properties, Electronic Structure, and Kinetics of Formation of the Heme-Peroxo-Copper Complex [(F8TPP)FeIII-(O22
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文摘
In the further development and understanding of heme-copper O2-reduction chemistry inspired by the active-sitechemistry in cytochrome c oxidase, we describe a dioxygen adduct, [(F8TPP)FeIII-(O22-)-CuII(TMPA)](ClO4) (3),formed by addition of O2 to a 1:1 mixture of the porphyrinate-iron(II) complex (F8TPP)FeII (1a) {F8TPP = tetrakis(2,6-difluorophenyl)porphyrinate dianion} and the copper(I) complex [(TMPA)CuI(MeCN)](ClO4) (1b) {TMPA = tris(2-pyridylmethyl)amine}. Complex 3 forms in preference to heme-only or copper-only binuclear products, is remarkablystable {t1/2 (RT; MeCN) ntities/ap.gif"> 20 min; max = 412 (Soret), 558 nm; EPR silent}, and is formulated as a peroxocomplex on the basis of manometry {1a/1b/O2 = 1:1:1}, MALDI-TOF mass spectrometry {16O2, m/z 1239 [(3 +MeCN)+]; 18O2, m/z 1243}, and resonance Raman spectroscopy {nu.gif" BORDER=0 >(O-O) = 808 cm-1; 16O2/18O2 = 46 cm-1;16O2/16/18O2 = 23 cm-1}. Consistent with a ntities/mgr.gif">-2:1 bridging peroxide ligand, two metal-O stretching frequenciesare observed {nu.gif" BORDER=0 >(Fe-O) = 533 cm-1, nu.gif" BORDER=0 >(Fe-O-Cu) = 511 cm-1}, and supporting normal coordinate analysis is presented.2H and 19F NMR spectroscopies reveal that 3 is high-spin {also ntities/mgr.gif">B = 5.1 ± 0.2, Evans method} with downfield-shifted pyrrole and upfield-shifted TMPA resonances, similar to the pattern observed for the structurally characterizedntities/mgr.gif">-oxo complex [(F8TPP)FeIII-O-CuII(TMPA)]+ (4) (known S = 2 system, antiferromagnetically coupled high-spinFeIII and CuII). Mössbauer spectroscopy exhibits a sharp quadrupole doublet (zero field; = 0.57 mm/s, ntities/verbar.gif">EQntities/verbar.gif"> =1.14 mm/s) for 3, with isomer shift and magnetic field dependence data indicative of a peroxide ligand and S =2 formulation. Both UV-visible-monitored stopped-flow kinetics and Mössbauer spectroscopic studies reveal theformation of heme-only superoxide complex (S)(F8TPP)FeIII-(O2-) (2a) (S = solvent molecule) prior to 3. Thermaldecomposition of ntities/mgr.gif">-peroxo complex 3 yields ntities/mgr.gif">-oxo complex 4 with concomitant release of ~0.5 mol O2 per mol3. Characterization of the reaction 1a/1b + O2 ntities/rarr.gif"> 2 ntities/rarr.gif"> 3 ntities/rarr.gif"> 4, presented here, advances our understanding andprovides new insights to heme/Cu dioxygen-binding and reduction.

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