TRIS(PYRAZOLYL)HYDROBORATOZINC HYDROXIDE COMPLEXES AS FUNCTIONAL MODELS FOR CARBONIC-ANHYDRASE - ON THE NATURE OF THE BICARBONATE INTERMEDIATE
TRIS(PYRAZOLYL)HYDROBORATOZINC HYDROXIDE COMPLEXES AS FUNCTIONAL MODELS FOR CARBONIC-ANHYDRASE - ON THE NATURE OF THE BICARBONATE INTERMEDIATE
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DOI：
10.1021/ja00064a033
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发表时间：
1993-06-02
影响因子：
15
通讯作者：
PARKIN, G
中科院分区：
文献类型：
--
作者：
LOONEY, A;HAN, R;PARKIN, G
本文研究了碳酸酐酶活性中心的结构模型化合物{η 3-HB（3-But-5-MePZ）3}ZnOH（3-But-5-Mepz = 3-But-5-MeC 3 N2 H）和{η 3-HB（3，5-Pri 2 pz）3}ZnOH（3，5-Pri 2C 3 N2 H）与CO2的反应。氢氧化物{eta 3-HB（3-But-5-Mepz）3}ZnOH立即与CO2反应，得到碳酸氢盐络合物{eta 3-HB（3-But-5-Mepz）3}Zn（OCO 2 H），其已通过IR光谱表征。1H-1 NMR研究表明，与CO2的反应是快速和可逆的NMR时间尺度在室温下。随后较慢的转变涉及碳酸盐络合物[{eta 3-HB（3-But-5-MePZ）3}Zn]2（mu-eta 1，eta 1-CO 3）的形成，其中碳酸盐配体以对称的单齿配位模式桥接两个锌中心。相比之下，空间位阻较小的氢氧化物{eta 3-HB（3，5-Pri 2 pz）3}ZnOH的相应反应迅速得到碳酸盐络合物[{eta 3-HB（3，5-Pri 2 pzZ）3}Zn]2（μ-eta 1，eta 2-CO 3），其中碳酸盐配体以不对称方式桥接两个锌中心，并且对一个锌中心是单齿的，但对另一个锌中心是双齿的。{Eta 3-HB（3-But-5-MePZ）3}ZnOH也是碳酸酐酶的功能模型，因为它有效地催化CO2和（H2O）-O-17之间的氧原子交换。单齿和双齿碳酸盐复合物的结构和反应性研究，以及一系列硝酸盐复合物的结构研究表明，容易获得单齿碳酸氢盐物种可能是碳酸酐酶活性的一个关键因素。
The reactions of (CO2 With the zinc hydroxide complexes {eta3-HB(3-But-5-MePZ)3}ZnOH (3-But-5-Mepz = 3-But-5-MeC3N2H) and {eta3-HB(3,5-Pri2pz)3}ZnOH (3,5-Pri2pz = 3,5-Pri2C3N2H), which are proposed to be structural models for the active site of the enzyme carbonic anhydrase, have been investigated. The hydroxide {eta3-HB(3-But-5-Mepz)3}ZnOH reacts immediately with CO2 to give a bicarbonate complex {eta3-HB(3-But-5-Mepz)3}Zn(OCO2H) that has been characterized by IR spectroscopy. H-1 NMR studies reveal that the reaction with CO2 is rapid and reversible on the NMR time scale at room temperature. A subsequent slower transformation involves the formation of the carbonate complex [{eta3-HB(3-But-5-MePZ)3}Zn]2(mu-eta1,eta1-CO3), in which the carbonate ligand bridges the two zinc centers with a symmetric unidentate coordination mode. In contrast, the corresponding reaction of the less sterically encumbered hydroxide {eta3-HB(3,5-Pri2pz)3}ZnOH rapidly gives the carbonate complex [{eta3-HB(3,5-Pri2pzZ)3}Zn]2(mu-eta1,eta2-CO3), in which the carbonate ligand bridges the two zinc centers in an asymmetric manner and is unidentate to one zinc center but bidentate to the other. {Eta3-HB(3-But-5-MePZ)3}ZnOH is also a functional model for carbonic anhydrase, since it effectively catalyzes the exchange of oxygen atoms between CO2 and (H2O)-O-17. Structural and reactivity studies on the unidentate and bidentate carbonate complexes, together with structural studies on a series of nitrate complexes, suggest that facile access to a unidentate bicarbonate species may be a critical factor for carbonic anhydrase activity.