Krishnamurthy Divya, Kasper Gary D, Namuswe Frances, Kerber William D, Narducci Sarjeant Amy A, Moënne-Loccoz Pierre, Goldberg David P
Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA.
J Am Chem Soc. 2006 Nov 8;128(44):14222-3. doi: 10.1021/ja064525o.
The synthesis of a mononuclear, five-coordinate ferrous complex ([15]aneN4)FeII(SPh) (1) is reported. This complex is a new model of the reduced active site of the enzyme superoxide reductase (SOR), which is comprised of a [(NHis)4(Scys)FeII] center. Complex 1 reacts with alkylhydroperoxides (tBuOOH, cumenylOOH) at low temperature to give a metastable, dark red intermediate (2a: R = tBu; 2b: R = cumenyl) that has been characterized by UV-vis, EPR, and resonance Raman spectroscopy. The UV-vis spectrum (-80 degrees C) reveals a 526 nm absorbance (epsilon = 2150 M-1 cm-1) for 2a and a 527 nm absorbance (epsilon = 1650 M-1 cm-1) for 2b, indicative of alkylperoxo-to-iron(III) LMCT transitions, and the EPR data (77 K) show that both intermediates are low-spin iron(III) complexes (g = 2.20 and 1.97). Definitive identification of the Fe(III)-OOR species comes from RR spectra, which give nu(Fe-O) = 612 (2a) and 615 (2b) cm-1, and nu(O-O) = 803 (2a) and 795 (2b) cm-1. The assignments for 2a were confirmed by 18O substitution (tBu18O18OH), resulting in a 28 cm-1 downshift for nu(Fe-18O), and a 46 cm-1 downshift for nu(18O-18O). These data show that 2a and 2b are low-spin FeIII-OOR species with weak Fe-O bonds and suggest that a low-spin intermediate may occur in SOR, as opposed to previous proposals invoking high-spin intermediates.
报道了单核五配位亚铁配合物([15]aneN4)FeII(SPh) (1)的合成。该配合物是超氧化物还原酶(SOR)还原活性位点的新模型，其由[(NHis)4(Scys)FeII]中心组成。配合物1在低温下与烷基过氧化氢(tBuOOH、异丙苯过氧化氢)反应，生成一种亚稳的深红色中间体(2a: R = tBu; 2b: R = 异丙苯基)，该中间体已通过紫外可见光谱、电子顺磁共振光谱和共振拉曼光谱进行了表征。紫外可见光谱(-80℃)显示2a在526 nm处有吸收峰(ε = 2150 M-1 cm-1)，2b在527 nm处有吸收峰(ε = 1650 M-1 cm-1)，表明存在烷基过氧-铁(III)配体到金属中心的电子转移跃迁，电子顺磁共振数据(77 K)表明两种中间体均为低自旋铁(III)配合物(g = 2.20和1.97)。Fe(III)-OOR物种的确切鉴定来自共振拉曼光谱，其给出ν(Fe-O) = 612 (2a)和615 (2b) cm-1，以及ν(O-O) = 803 (2a)和795 (2b) cm-1。通过18O取代(tBu18O18OH)证实了2a的归属，导致ν(Fe-18O)下移28 cm-1，ν(18O-18O)下移46 cm-1。这些数据表明2a和2b是具有弱Fe-O键的低自旋FeIII-OOR物种，并表明SOR中可能出现低自旋中间体，这与之前提出的涉及高自旋中间体的观点相反。
