Magnetic circular dichroism study of a dicobalt(II) complex with mixed 5- and 6-coordination: a spectroscopic model for dicobalt(II) hydrolases.
Magnetic circular dichroism study of a dicobalt(II) complex with mixed 5- and 6-coordination: a spectroscopic model for dicobalt(II) hydrolases.
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DOI：
10.1021/ic901000d
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发表时间：
2009-09-21
影响因子：
4.6
通讯作者：
Volwiler, Adam S.
中科院分区：
文献类型：
--
作者：
Larrabee, James A.;Johnson, W. Rainey;Volwiler, Adam S.
用磁性圆二色谱研究了二苯并呋喃-4，6-二苯并呋喃-4，6-二苯并呋喃-4，6-双(二苯乙酸酯)[CO_2(μ-OH)(μ-Ph_4DBA)(TMEDA)_2(OTf)]的磁圆二色谱.该络合物是许多双钴(II)酶和蛋白质的极好的光谱模型，这些酶和蛋白质既有μ-羟基，μ-羧基桥联，也有不对称的6和5配位。模型络合物的低温MCD光谱显示了6坐标CoII上d-d跃迁产生的490、504和934 nm处的谱带，以及5坐标CoII上d-d跃迁产生的471、522、572、594和638 nm处的谱带。6-和5-配位CoII最强的MCD谱带分别位于504和572 nm，这两条谱带分别出现在大肠杆菌双钴(II)取代的蛋氨酸氨基肽酶(CoMetAP)、产气肠杆菌的甘油磷酸二酯酶(CoCoGpdQ)、蛋白溶解单胞菌的氨基肽酶(CoCoAAP)和兽疫杆菌的肌红蛋白(CoCoMyoHry)的MCD谱中。这些双钴(II)取代的蛋白质已知具有一个5配位和一个6配位的CoII，由一个或两个羧酸盐和一个水或氢氧化物桥联。桥接水的质子化状态的不确定性是有问题的，因为这可能是双金属水解酶中攻击亲核试剂的候选。变温可变场MCD数据的分析表明，模型络合物中的CoII离子是铁磁耦合的，J=3.0cM−1。所有双钴(II)络合物和双钴(II)取代的蛋白质活性中心与μ-羟基/水，μ-羧基桥联基序的比较表明，J在μ-水体系中为零或负(反铁磁性)，在μ-羟基体系中为正(铁磁性)。CoCoAAP和CoCoMyoHry中的CoII离子是铁磁耦合的，每个离子的J值为3.4 cm−1，这表明这些离子具有μ-羟基桥联配体。
The magnetic circular dichroism (MCD) study of [Co2(μ-OH)(μ-Ph4DBA)(TMEDA)2(OTf)], in which Ph4DBA is the dinucleating bis(carboxylate) ligand dibenzofuran-4,6-bis(diphenylacetate), is presented. This complex serves as an excellent spectroscopic model for a number of dicobalt(II) enzymes and proteins that have both the μ-hydroxo, μ-carboxylato bridging and asymmetric 6- and 5-coordination. The low-temperature MCD spectrum of the model complex shows bands at 490, 504, and 934 nm arising from d-d transitions on the 6-coordinate CoII and bands at 471, 522, 572, 594, and 638 nm arising from d-d transitions on the 5-coordinate CoII. The most intense MCD bands are at 504 and 572 nm for 6- and 5-coordinate CoII, respectively, and these two bands are found in the MCD spectra of dicobalt(II)-substituted methionine aminopeptidase from Escherichia coli (CoCoMetAP), glycerophosphodiesterase from Enterobacter aerogenes (CoCoGpdQ), aminopeptidase from Aeromonas proteolytica (CoCoAAP), and myohemerythrin from Themiste zostericola (CoCoMyoHry). These dicobalt(II)-substituted proteins are known to have one 5- and one 6-coordinate CoII bridged by one or two carboxylates and either a water or hydroxide. The uncertainty of the bridging water’s state of protonation is problematic, as this is a likely candidate for the attacking nucleophile in the dimetallohydrolases. Analysis of the variable-temperature variable-field (VTVH) MCD data determined that the CoII ions in the model complex are ferromagnetically coupled with a J of 3.0 cm−1. A comparison of all dicobalt(II) complexes and dicobalt(II)-substituted protein active sites with the μ-hydroxo/aqua, μ-carboxylato bridging motif reveals that J is either zero or negative (antiferromagnetic) in the μ-aqua systems and positive (ferromagnetic) in the μ-hydroxo systems. It was also determined that the CoII ions in CoCoAAP and CoCoMyoHry are ferromagnetically coupled, each with a J of 3.4 cm−1, which suggests that these ions have a μ-hydroxo bridging ligand.
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影响因子：
2.9
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