Substituent effects on the thermodynamic stability of imines formed from glycine and aromatic aldehydes: implications for the catalytic activity of pyridoxal-5'-phosphate.
Substituent effects on the thermodynamic stability of imines formed from glycine and aromatic aldehydes: implications for the catalytic activity of pyridoxal-5'-phosphate.
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DOI：
10.1021/ja906230n
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发表时间：
2009-11-04
影响因子：
15
通讯作者：
Richard, John P.
中科院分区：
文献类型：
--
作者：
Crugeiras, Juan;Rios, Ana;Riveiros, Enrique;Richard, John P.
通过在D2 O中的1H NMR分析确定了甘氨酸与取代苯甲醛加成形成相应亚胺的平衡常数和亚胺离子电离的pKa。苯氧阴离子取代基引入苯甲醛的芳环导致亚胺离子的pKa从6.3大幅增加到10.2对羟基苯甲醛和水杨醛的12.1。邻位与对位取代的差异效应的分析表明，亚胺离子水杨醛是稳定的分子内氢键在水溶液中，与估计的能量ca。3 kcal/mol，比简单的静电相互作用大。通过比较邻-O −取代基对甘氨酸、苯甲醛和4-吡啶-甲醛亚胺离子酸性的影响，证明了吡哆醛5 '-磷酸（PLP）亚胺离子在水中存在强度相似的内部氢键。讨论了其它环上取代基对PLP亚胺离子稳定性的影响。
Equilibrium constants for addition of glycine to substituted benzaldehydes to form the corresponding imines and pKas for ionization of the iminium ions were determined by 1H NMR analysis in D2O. The introduction of a phenoxide anion substituent into the aromatic ring of benzaldehyde leads to a substantial increase in the pKa of the iminium ion from 6.3 to 10.2 for p-hydroxybenzaldehyde and to 12.1 for salicyaldehyde. An analysis of the differential effect of ortho- versus para-substitution shows that the iminium ion to salicylaldehyde is stabilized by an intramolecular hydrogen bond in aqueous solution, with an estimated energy ca. 3 kcal/mol larger than can be accounted for by a simple electrostatic interaction. A comparison of the o-O− substituent effect on the acidity of the iminium ions of glycine to benzaldehyde and 4-pyridine-carboxaldehyde provides evidence for the existence of an internal hydrogen bond of similar strength in pyridoxal 5'-phosphate (PLP) iminium ions in water. The effects of other ring substituents on the stability of PLP iminium ions are discussed.
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影响因子：
15
作者：
GILLI, G;BELLUCCI, F;BERTOLASI, V
通讯作者：
BERTOLASI, V
影响因子：
15
作者：
Crugeiras, Juan;Rios, Ana;Richard, John P.
通讯作者：
Richard, John P.
影响因子：
15
作者：
AULD, DS;BRUICE, TC
通讯作者：
BRUICE, TC
影响因子：
2.9
作者：
FRENCH, TC;AULD, DS;BRUICE, TC
通讯作者：
BRUICE, TC
影响因子：
15
作者：
Rios, A;Crugeiras, J;Richard, JP
通讯作者：
Richard, JP