XAS structural comparisons of reversibly interconvertible oxo- and hydroxo-bridged heme-copper oxidase model compounds
XAS structural comparisons of reversibly interconvertible oxo- and hydroxo-bridged heme-copper oxidase model compounds
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DOI：
10.1021/ja951686b
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发表时间：
1996-01-10
影响因子：
15
通讯作者：
Blackburn, NJ
中科院分区：
文献类型：
--
作者：
Fox, S;Nanthakumar, A;Blackburn, NJ
在血红素铜氧化酶铁铜双核中心模型化合物的研究中，我们（i）详细研究了μ-氧代和μ-羟基配合物[（F-8-TPP）Fe-III-（OH-）-Cu-II（TMPA）]（+）（1）和[（F-8-TPP）Fe-III-（OH-）-Cu-II（TMPA）]（2+）（2）[F-8-TPP =四（O-）-Cu-II（TMPA（2，6-二氟苯基）-卟啉（2-），TMPA =三[（2-吡啶基甲基）胺];（ii）比较它们的物理性质;（iii）使用XAS确定2的结构（X射线吸收光谱），一种新的应用三体两边缘多重散射（MS）分析配体连接;和（iv）将2的XAS与1和酶制剂的XAS进行比较。配合物1通过[（TMPA）Cu-II（CH 3CN）]（2+）（3）和[（F-8-TPP）Fe-III-OH]（4）与三乙胺在乙腈中反应来制备（>70%产率）。通过3与4在二氯乙烷中的加成反应或1与三氟甲磺酸的质子化反应合成了2-（ClO_4）_2和2-（CF_3SO_3）（2）（产率>60%）。在用三氟甲磺酸进行的H-1-NMR光谱滴定（298 K）中，1的吡咯65 ppm共振逐渐转化为接近70 ppm的共振（三氟甲磺酸盐为71.5，高氯酸盐为68.5），诊断2。质子化-去质子化速率在NMR时间尺度上是缓慢的，H-1-NMR光谱性质与反铁磁耦合的高自旋铁（III）和Cu（II）离子（S = 2基态）一致，并且2中的相互作用较弱（2，5.5 +/- 0.1 mu（B）; 1，5.1 +/- 0.1 mu（B），Evans方法）。W-vis光谱也用于监测使用Et（3）N的2（Soret，410 nm）到1（434 nm）的转化。2去质子化的水溶液pK（a）估计为8 +/- 2.5。Fe和Cu的K-edge XAS分别在1、2和μ-过氧配合物[{（TMPA）Cu}（2）（O-2）]（2+）（5）上进行。在1的EXAFS中观察到的强MS相互作用是由于接近线性的Fe-O-Cu部分。最小二乘精化的铜K-EXAFS的1给出铜…Fe = 3.56 +/- 0.03埃，角Cu-O-Fe = 176 +/- 5度，Cu-O = 1.83 +/- 0.02埃; Fe K-EXAFS分析给出Fe-O = 1.72 +/- 0.02埃，Fe... Cu = 3.54 +/- 0.05埃，角度Fe-O-Cu = 172 +/- 10度。强烈的Fe-Cu（或Cu-Fe）特征在2中缺乏，但铁边光谱确实揭示了归因于Fe-Cu相互作用的较弱MS。Cu-O（H）和Fe-O（H）键在2中伸长（分别为1.89 +/- 0.02埃和1.87 +/- 0.02埃），Fe... Cu = 3.66 +/- 0.03埃。该质子化络合物是弯曲的;角Fe-O（H）-Cu = 157 +/- 5度。EXAFS与来自枯草芽孢杆菌的醌醇氧化酶aa（3）-600的酶制剂的比较支持以下观点：μ-OH-复合物2可能是用于静息状态和/或周转中间体的良好血红素-Cu酶模型。
In this study on model compounds for the iron-copper dinuclear center in heme-copper oxidases, we (i) detail the synthesis and reversible acid-base interconversion of mu-oxo and mu-hydroxo complexes [(F-8-TPP)Fe-III-O2-)-Cu-II(TMPA)](+) (1) and [(F-8-TPP)Fe-III-(OH-)-Cu-II(TMPA)](2+) (2) [F-8-TPP = tetrakis(2,6-difluorophenyl)-porphyrinate(2-), TMPA = tris[(2-pyridylmethyl)amine]; (ii) compare their physical properties; (iii) establish the structure of 2 using XAS (X-ray absorption spectroscopy), a novel application of a three-body two-edge multiple-scattering (MS) analysis of ligand connectivity; and (iv) compare the XAS of 2 with those of 1 and an enzyme preparation. Complex 1 was prepared by reaction of [(TMPA)Cu-II(CH3CN)](2+) (3) and [(F-8-TPP)Fe-III-OH] (4) with triethylamine in acetonitrile (>70% yield). Salts 2-(ClO4)2 and 2-(CF3SO3)(2) were synthesized (>60% yield) by addition of 3 with 4 in dichloroethane or by protonation of 1 with triflic acid. In a H-1-NMR spectroscopic titration (298 K) with triflic acid, the pyrrole 65 ppm resonance for 1 progressively converts to one near 70 ppm (71.5 for triflate, 68.5 for perchlorate), diagnostic of 2. The protonation-deprotonation rate is slow on the NMR time scale, the H-1-NMR spectral properties are consistent with antiferromagnetically coupled high-spin iron(III) and Cu(II) ions (S = 2 ground state), and the interaction is weaker in 2 (2, 5.5 +/- 0.1 mu(B); 1, 5.1 +/- 0.1 mu(B), Evans method). W-vis spectroscopy was also used to monitor the conversion of 2 (Soret, 410 nm) to 1 (434 nn) using Et(3)N. The aqueous pK(a) for deprotonation of 2 is estimated as 8 +/- 2.5. Both Fe and Cu K-edge XAS was performed on 1, 2, and mu-peroxo complex [{(TMPA)Cu}(2)(O-2)](2+) (5). The strong MS interaction observed in the EXAFS of 1 is due to the nearly linear Fe-O-Cu moiety. Least-squares refinement of the Cu K-EXAFS of 1 gives Cu ... Fe = 3.56 +/- 0.03 Angstrom, angle Cu-O-Fe = 176 +/- 5 degrees, Cu-O = 1.83 +/- 0.02 Angstrom; the Fe K-EXAFS analysis gives Fe-O = 1.72 +/- 0.02 Angstrom, Fe ... Cu = 3.54 +/- 0.05 Angstrom, angle Fe-O-Cu = 172 +/- 10 degrees. The intense Fe-Cu (or Cu-Fe) feature is lacking in 2, but the iron-edge spectra do reveal a weaker MS ascribed to the Fe-Cu interaction. The Cu-O(H) and Fe-O(H) bonds are elongated in 2 (1.89 +/- 0.02 Angstrom and 1.87 +/- 0.02 Angstrom, respectively), with Fe ... Cu = 3.66 +/- 0.03 Angstrom. This protonated complex is bent; angle Fe-O(H)-Cu = 157 +/- 5 degrees. An EXAFS comparison with an enzyme preparation of the quinol oxidase aa(3)-600 from Bacillus subtilis supports the notion that mu-OH- complex 2 may be a good heme-Cu enzyme model for the resting state and/or turnover intermediate.