ELECTRONIC AND RAMAN-SPECTROSCOPIC PROPERTIES OF OXO-BRIDGED DINUCLEAR IRON CENTERS IN PROTEINS AND MODEL COMPOUNDS
ELECTRONIC AND RAMAN-SPECTROSCOPIC PROPERTIES OF OXO-BRIDGED DINUCLEAR IRON CENTERS IN PROTEINS AND MODEL COMPOUNDS
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DOI：
10.1021/ja00203a003
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发表时间：
1989-10-11
影响因子：
15
通讯作者：
LOEHR, TM
中科院分区：
文献类型：
--
作者：
SANDERSLOEHR, J;WHEELER, WD;LOEHR, TM
氧桥双核Fe(III)络合物在激发到氧基fwdarw中时，其共振拉曼光谱表现出强烈的增强的Fe-O-Fe对称伸缩振动。Fe(III)变化转移带。从Fe-O-Fe模式的强度、~(18)O取代后的位移、频率与Fe-O-Fe角的关系等方面，已在蛋白质杂色菊酯和核糖核苷酸还原酶以及一些单桥和三桥模型化合物中确定了Fe-O-Fe模式。蛋白质和模型化合物的共振拉曼激发谱表明，Fe-O-Fe增强峰倾向于对应于少量氧。吸收光谱中的Fe(III)CT谱带。NU_s(Fe-O-Fe)相对于nU_1(SO_4)的摩尔散射强度为a_apprx。蛋白质(取值300-1200)比模型络合物(取值10-90)大10倍。唯一被发现具有与蛋白质中一样大的增强作用的模型化合物是三桥Fe2O(HBpz3)2(OAc)2和[Fe2O(Tmip)2(OPR)2]2+络合物(值分别为320和380)。这些配合物的结构与杂氰菊酯中已知的双核铁中心最相似。提高Fe-O-Fe对称伸展强度的因素是(I)多个桥基(增强2-4倍)，(Ii)顺式到氧基的不饱和氮配体(进一步增强2-4倍)，和(Iii)反式到氧基的不饱和氮配体(比顺式配体增加3-8倍)。在核糖核苷酸还原酶中，Fe-O-Fe模式的强散射强度表明有一个或两个咪唑配体转移到氧代桥位，如在杂氰菊酯中。与对称模型络合物相比，这两种蛋白质都具有更强的αAs(Fe-O-Fe)，这表明两个双核铁中心中的两个金属原子并不相等。
Oxo-bridged dinuclear Fe(III) complexes generally exhibit a storngly enhanced Fe-O-Fe symmetric stretching vibration in their resonance Raman spectra upon excitation into an oxo .fwdarw. Fe(III) change-transfer band. The Fe-O-Fe mode has been identified in the proteins herythrin and ribonucleotide reductase, as well as in a number of monobridged and tribridged model compounds, from its intensity, its shift upon 18O substitution, and its frequency dependence with respect to the Fe-O-Fe angle. Resonance Raman excitation profiles for the proteins and model compounds show that the Fe-O-Fe enhancement maxima tend to correspond to minor oxo .fwdarw. Fe(III) CT bands inthe absorption spectra. The molar scattering intensity of .nu.s(Fe-O-Fe) relative to .nu.1(SO4) is .apprx. 10 times greater for the proteins (with values of 300-1200) than for the model complexes (with values of 10-90). The only model compounds that were found to exhibit as great a .nu.s(Fe-O-Fe) enhancement as in the prot eins were the tribridged Fe2O(HBpz3)2(OAc)2 and [Fe2O(tmip)2(OPr)2]2+ complexes (with values of 320 and 380, respectively). These complexes have the closest structural similarity to the known dinuclear iron site in hemerythrin. Factors which elevate the intensity of the Fe-O-Fe symmetric stretch are (i) multiple bridging groups (2- to 4-fold enhancement), (ii) unsaturated nitrogen ligands cis to the oxo group (a further 2- to 4-fold enhancement), and (iii) unsaturated nitrogen ligands trans to the oxo group (additional 3- to 8-fold enhancement compared to cis ligands). The strong scattering intensity of the Fe-O-Fe mode in ribonucleotide reductase is indicative of one or two imidazole ligands trans to the oxo bride, as in hemerythrin. Both protiens exhbiit a more intense .nu.as (Fe-O-Fe) than is observed with symmetric model complexes; this suggests that the tow metal atoms in each dinuclear iron center are not equivalent.