Investigation of the Effect of Oxy Bridging Groups in Dinuclear Zn(II) Complexes that Catalyze the Cleavage of a Simple Phosphate Diester RNA Analogue
Investigation of the Effect of Oxy Bridging Groups in Dinuclear Zn(II) Complexes that Catalyze the Cleavage of a Simple Phosphate Diester RNA Analogue
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DOI：
10.1021/ic9015965
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发表时间：
2009-12-07
影响因子：
4.6
通讯作者：
Brown, R. Stan
中科院分区：
文献类型：
--
作者：
Mohamed, Mark F.;Neverov, Alexei A.;Brown, R. Stan
制备了两组双核Zn（II）配合物，以确定金属中心之间存在的氧阴离子桥连基团对RNA类似物2-羟丙基-4-硝基苯磷酸（HPNPP，2）甲醇分解的催化活性的影响。本文报道了双金属锌配合物的合成、结构和性质。（二-（2-吡啶基甲基）氨基）-间二甲苯（6）和2，6-双（二-（2-吡啶基甲基）氨基）-4-甲基苯酚（7）的Zn（II）（2）络合物，以评估桥接酚盐配体的作用，而1，3-双-N-1-（2-吡啶基甲基）氨基）-4-甲基苯酚（7）的Zn（II）（2）络合物，制备（1，5，9-三氮杂环十二烷基）-丙-2-醇（8）以确定2-丙氧基与先前研究的1，3-双-N-1-（1，5，9-三氮杂环十二烷基）-丙烷（4）的络合物相比的作用。2的裂解的详细动力学研究，包括k（obs）VS [催化剂]图和（s）（s）pH-速率曲线，对每个系统进行沿着电位滴定实验，以确定催化相关基团的酸解离常数。结果表明，在7：Zn（11）2中包含苯氧基桥连基团使2裂解的二级催化速率常数（k（2）（cat））相对于6：Zn（II）（2）降低了160倍，而在8：Zn（II）（2）中引入丙氧基基团使其效力相对于4：Zn（II）（2）降低了3.7 × 10（4）倍。能量学计算表明，6：Zn（II）（2）比7：Zn（II）（2）提供了3.7 kcal/mol更高的反应过渡态稳定性，4：Zn（II）（2）比8：Zn（II）（2）提供了6.5 kcal/mol更高的过渡态稳定性。分析表明，具有永久桥接含氧阴离子基团的络合物经历的过渡态稳定的减少几乎完全源于磷酸盐和催化剂的较弱结合，以及降低的催化速率常数。这些结果表明，存在的金属中心之间的桥接含氧阴离子配体，一个共同的结构元素所需的成功形成的许多小分子双核催化剂，显示在水中的合作活动，显着损害裂解的催化效率2。
Two sets of dinuclear Zn(II) complexes were prepared to determine the effect of the presence of oxyanionic bridging groups between the metal centers on the catalytic activity toward the methanolysis of the RNA analogue 2-hydroxypropyl-4-nitrophenyl phosphate (HPNPP, 2). The Zn(II)(2) complexes of bis(di-(2-pyridylmethyl)amino)-m-xylene (6) and 2,6-bis(di-(2-pyridylmethyl)amino)-4-methylphenol (7) were compared to assess the effect of a bridging phenoxide ligand, while the Zn(II)(2) complex of 1,3-bis-N-1-(1,5,9-triazacyclododecyl)-propan-2-ol (8) was prepared to determine the effect of the 2-propoxy group compared to the previously studied complex of 1,3-bis-N-1-(1,5,9-triazacyclododecyl)-propane (4). Detailed kinetic studies of the cleavage of 2 including k(obs) VS [catalyst] plots and (s)(s)pH-rate profiles were performed for each system along with potentiometric titration experiments to determine the acid dissociation constants for the catalytically relevant groups. The results show that inclusion of the phenoxy bridging group in 7:Zn(11)2 reduces the second-order catalytic rate constant (k(2)(cat)) for cleavage of 2 by a factor of 160 relative to that of 6:Zn(II)(2), while the incorporation of a propoxy group in 8:Zn(II)(2) reduces its efficacy by 3.7 x 10(4) times relative to 4:Zn(II)(2). Energetics calculations reveal that 6:Zn(II)(2) offers a 3.7 kcal/mol greater stabilization of the reaction transition state for the cleavage of 2 than does 7:Zn(II)(2) and that 4:Zn(II)(2) affords 6.5 kcal/mol greater transition state stabilization than does 8:Zn(II)(2). The analyses show that the reduction in the transition state stabilization experienced with the complexes having permanently bridging oxyanion groups stems almost entirely from a weaker binding of the phosphate and catalyst, and a reduced catalytic rate constant. These results indicate that the presence of a bridging oxyanion ligand between the metal centers, a common structural element required for the successful formation of many small molecule dinuclear catalysts that show cooperative activity in water, significantly impairs the catalytic efficiency for cleavage of 2.