Magnetic circular dichroism spectroscopy as a probe of geometric and electronic structure of Cobalt(II)- substituted proteins: Ground-state zero-field splitting as a coordination number indicator
Magnetic circular dichroism spectroscopy as a probe of geometric and electronic structure of Cobalt(II)- substituted proteins: Ground-state zero-field splitting as a coordination number indicator
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DOI：
10.1021/ja963555w
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发表时间：
1997-05-07
影响因子：
15
通讯作者：
Volkert, TL
中科院分区：
文献类型：
--
作者：
Larrabee, JA;Alessi, CM;Volkert, TL
用变温磁性圆二色谱(VT MCD)研究了Co(II)取代的肝醇脱氢酶、碳酸酐酶、羧基肽酶及其底物和抑制剂络合物以及四配位和五配位的Co(Li)模型络合物的基态电子结构。用VT MCD确定了这些样品中基板零场分裂(ZFS)的大小。四坐标Co(II)物种的ZFS范围从2.3到30厘米(-1)，五坐标物种的ZFS范围从2.7到98厘米(-1)，这些值超出了先前建议的区分四坐标和五坐标Co(Li)的范围(Makinen，M.W.；Kuo，L.C.；Yim，M.B.；Wells，G.B.；Fukuyama，J.M.；Kim，J.E.J.Am化学。秒。1985、107、5245-5255)。ZFS的大小对配体的异质性不是很敏感，但可以对键角非常敏感。由于蛋白质活性中心通常从理想的四配位或五配位几何构型高度角度扭曲，ZFS作为配位数Rn Co(II)取代的蛋白质的唯一指示剂变得毫无用处。在角度重叠法(AOM)计算中使用了蛋白质和模型化合物的MCD光谱和吸收(或漫反射)光谱以及ZFS值，这些计算支持了四配位和五配位Co(II)化合物的ZFS值存在显著重叠的结论。
Variable-temperature magnetic circular dichroism (VT MCD) is used as a probe of the ground-state electronic structure in Co(II)-substituted liver alcohol dehyrogenase, carbonic anhydrase, carboxypeptidase, substrate and inhibitor complexes of these enzymes, and four- and five-coordinate Co(LI) model complexes. VT MCD was used to determine the magnitude of the ground-slate zero-field splitting (ZFS) in these samples. The four-coordinate Co(II) species had ZFS's that ranged from 2.3 to 30 cm(-1) and the five-coordinate species had ZFS's that ranged from 2.7 to 98 cm(-1), values which fall outside of the ranges previously suggested for distinguishing 4-coordinate and 5-coordinate Co(LI) (Makinen, M. W.; Kuo, L. C.; Yim, M. B.; Wells, G. B.; Fukuyama, J. M.; Kim, J. E. J. Am. Chem. Sec. 1985, 107, 5245-5255). The magnitude of the ZFS is not very sensitive to ligand heterogeneity but can be very sensitive to bond angles. Since protein active sites are in general highly angularly distorted from ideal four- or five-coordinate geometries, ZFS is rendered useless as a sole indicator of coordination number rn Co(II)-substituted proteins. The MCD and absorption (or diffuse reflectance) spectra and the values of the ZFS for the proteins and model compounds are used in angle overlap method (AOM) calculations, These calculations support the conclusion that there is significant overlap in the ranges of ZFS for four- and five-coordinate Co(II) compounds.