Metal-catalyzed phosphodiester cleavage: secondary 18O isotope effects as an indicator of mechanism.
Metal-catalyzed phosphodiester cleavage: secondary 18O isotope effects as an indicator of mechanism.
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DOI：
10.1021/ja065931a
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发表时间：
2006-12
影响因子：
15
通讯作者：
J. Rawlings;W. Cleland;A. Hengge
中科院分区：
文献类型：
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作者：
J. Rawlings;W. Cleland;A. Hengge
通过测定同位素对水解反应的影响，获得了有关模型磷酸盐化合物金属催化水解反应过渡态的信息。已发现金属络合显着改变碱性水解反应的过渡态，并且过渡态很大程度上取决于所使用的特定金属离子。对于二酯，对硝基苯基磷酸乙酯，由 Co(III) 1,5,9-三氮杂环壬烷和 Eu(III) 催化的水解反应的非桥 18O 效应分别为 1.0006 和 1.0016，表明与非桥氧的键合有轻微缔合过渡态和很少的净变化。 Zn(II) 1,4,7,10-四氮杂环十二烷催化的反应的18O非桥IE为1.0108，表明该反应与非络合二酯的反应显着不同，并且与三酯的反应相似。与 Co(III) 1,4,7,10-四氮杂环十二烷的反应显示出 0.9948 的反向效应，反映了二酯与 Co(III) 的键合效应。已观察到镧系元素催化的水解具有异常大的 15N 效应。为了进一步研究这种效应，在 pH 8 下，Ce(IV) 双-Tris 丙烷溶液催化反应的 15N 效应被确定为 1.0012。还测量了磷酸单酯对硝基苯酯与 Ce(IV) 双-Tris 丙烷 (1.0014) 和 Eu(III) 双-Tris 丙烷 (1.0012) 反应的 15N 效应。 pH 8 时这些较小的影响表明在水解反应过程中氮上产生较小的负电荷。
Information about the transition states of metal-catalyzed hydrolysis reactions of model phosphate compounds has been obtained through determination of isotope effects (IEs) on the hydrolysis reactions. Metal complexation has been found to significantly alter the transition state of the reaction from the alkaline hydrolysis reaction, and the transition state is quite dependent on the particular metal ion used. For the diester, ethyl p-nitrophenyl phosphate, the nonbridge 18O effect for the hydrolysis reactions catalyzed by Co(III) 1,5,9-triazacyclononane and Eu(III) were 1.0006 and 1.0016, respectively, indicative of a slightly associative transition state and little net change in bonding to the nonbridge oxygen. The reaction catalyzed by Zn(II) 1,4,7,10-tetraazacyclododecane had an 18O nonbridge IE of 1.0108, showing the reaction differs significantly from the reaction of the noncomplexed diester and resembles the reactions of triesters. Reaction with Co(III) 1,4,7,10-tetraazacyclododecane showed an inverse effect of 0.9948 reflecting the effects of bonding of the diester to the Co(III). Lanthanide-catalyzed hydrolysis has been observed to have unusually large 15N effects. To further investigate this effect, the 15N effect on the reaction catalyzed by Ce(IV) bis-Tris propane solutions at pH 8 was determined to be 1.0012. The 15N effects were also measured for the reaction of the monoester p-nitrophenyl phosphate by Ce(IV) bis-Tris propane (1.0014) and Eu(III) bis-Tris propane (1.0012). These smaller effects at pH 8 indicate that a smaller negative charge develops on the nitrogen during the hydrolysis reaction.