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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >A minimalist approach to understanding the efficiency of mononuclear Zn(II) complexes as catalysts of cleavage of an RNA analog
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A minimalist approach to understanding the efficiency of mononuclear Zn(II) complexes as catalysts of cleavage of an RNA analog

机译：理解单核锌（II）配合物作为裂解RNA类似物的催化剂的效率的极简方法

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摘要

Mononuclear complexes between Zn2+ and the following four macrocycles were prepared: 1,4,7,10-tetraazacyclododecane ( 1), 1-oxa-4,7,10-triazacyclododecane ( 2), 1,5,9-triazacyclododecane ( 3) and 1-hydroxyethyl-1,4,7-triazacyclononane ( 4). The pH rate profiles of values of the observed second-order rate constant log ( k(Zn)) (app) for Zn( X)(OH2)-catalyzed cleavage ( X = 1, 2, 3 and 4) of 2-hydroxypropyl-4-nitrophenyl phosphate ( HpPNP) show downward breaks centered at the pK(a) for ionization of the respective zinc bound water. At low pH, where the rate acceleration for the catalyzed reaction is largest, the stabilizing interaction between the catalyst and the bound transition state is 5.7, 7.4, 7.4 and 5.9 kcal mol(-1) for the reactions catalyzed by Zn( 1)( OH2), Zn( 2)( OH2), Zn( 3)( OH2) and Zn( 4)( OH2), respectively. The interactions between the metal cation and the macrocycle cause either a modest increase or reduction in transition state stabilization compared with 6.6 kcal mol(-1) stabilization for catalysis by Zn( OH2)(6). The best Zn( II)-macrocycle catalysts are those for which the interactions between the metal ion and macrocycle are the weakest. Inhibition studies show that each of the four catalysts form complexes with phosphate and oxalate dianions with a much higher affinity than diethyl phosphate monoanion, consistent with stronger interaction of the catalysts with the transition state dianion compared with the substrate monoanion HpPNP. The pH-dependence of methyl phosphate inhibition of Zn( 2) catalyzed cleavage of HpPNP shows that only the Zn( 2)( OH2) species binds the inhibitor. This result is consistent with a mechanism that has Zn( 2)( OH2) as the active catalytic species.
机译：制备了Zn2 +与以下四个大环之间的单核络合物：1,4,7,10-四氮杂十二烷（1），1-oxa-4,7,10-三氮杂十二烷（2），1,5,9-三氮杂十二烷（3）和1-羟乙基-1,4,7-三氮杂环壬烷（4）。 pH值分布图，观察到的2-羟基丙基的Zn（X）（OH2）催化裂解（X = 1，2，3和4）的二阶速率常数log（k（Zn））（app）的值-4-硝基苯基磷酸酯（HpPNP）显示出以pK（a）为中心的向下断裂，以使各个结合锌的水电离。在低pH值下，催化反应的速率加速最大，对于Zn（1）催化的反应，催化剂与键合过渡态之间的稳定相互作用为5.7、7.4、7.4和5.9 kcal mol（-1）（ OH2），Zn（2）（OH2），Zn（3）（OH2）和Zn（4）（OH2）。与通过Zn（OH2）（6）催化的6.6 kcal mol（-1）稳定相比，金属阳离子与大环之间的相互作用导致过渡态稳定的增加或减少。最佳的Zn（II）-大环催化剂是那些金属离子与大环之间的相互作用最弱的催化剂。抑制研究表明，四种催化剂中的每一种与磷酸盐和草酸二价阴离子形成络合物的亲和力均高于磷酸二乙酯单阴离子，这与底物单阴离子HpPNP相比，催化剂与过渡态二价阴离子的相互作用更强。 pH依赖性的磷酸锌对HpPNP的Zn（2）催化裂解的抑制作用表明只有Zn（2）（OH2）种类与抑制剂结合。此结果与具有Zn（2）（OH2）作为活性催化物质的机理是一致的。

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