Probing potential medium effects on phosphate ester bonds using 18O isotope shifts on 31P NMR.
Probing potential medium effects on phosphate ester bonds using 18O isotope shifts on 31P NMR.
复制标题
使用 31P NMR 上的 18O 同位素位移探测介质对磷酸酯键的潜在影响。
DOI：
10.1021/jo051090z
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
Hengge,AlvanC
中科院分区：
文献类型：
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作者：
Sorensen-Stowell,Kerensa;Hengge,AlvanC
偶极非质子型助溶剂，如DMSO和乙腈，加快了磷酸单酯二阴离子的水解率。有人推测，速率加速是由于磷酰基的氢键被破坏所致。水溶剂化壳层可以通过与磷酰氧基形成氢键来稳定双阴离子磷酰基，而DMSO等溶剂不能形成这样的键。有人提出，失去稳定性可能会导致P-−或酯键减弱，从而导致观察到的较快的水解率。计算结果支持这一观点。我们利用18O对31P化学位移的扰动来确定溶剂的变化是否会导致P−O(R)键的变化。我们研究了16O18O标记的甲基、乙基、苯基、对硝基苯基、二乙基对硝基苯基、三苯基和二叔丁基乙基磷酸酯在水、甲醇、氯仿、乙腈、二氧六环和二甲基亚砜中的反应。结果表明，在所测试的任何溶剂中，没有明显的溶剂诱导的磷酸酯键的减弱，这不太可能是在混合溶剂中加速水解的重要来源。
Dipolar aprotic cosolvents, such as DMSO and acetonitrile, accelerate the rates of hydrolysis of phosphate monoester dianions. It has been speculated that the rate acceleration arises from the disruption of hydrogen bonding to the phosphoryl group. An aqueous solvation shell can stabilize the dianionic phosphoryl group by forming hydrogen bonds to the phosphoryl oxygens, whereas solvents such as DMSO are incapable of forming such bonds. It has been proposed that the loss of stabilization could result in a weakened P−OR ester bond, contributing to the observed faster rate of hydrolysis. Computational results support this notion. We have used the18O-induced perturbation to the31P chemical shift to ascertain whether solvent changes result in alterations to the P−O(R) bond. We have studied16O18O-labeled methyl, ethyl, phenyl,p-nitrophenyl, diethylp-nitrophenyl, triphenyl, and di-tert-butyl ethyl phosphate in the solvents water, methanol, chloroform, acetonitrile, dioxane, and DMSO. The results suggest no significant solvent-induced weakening of the phosphate ester bonds in any of the solvents tested, and this is unlikely to be a significant source for the acceleration of hydrolysis in mixed solvents.