Selective Covalent Chemistry via Gas-Phase Ion/ion Reactions: An Exploration of the Energy Surfaces Associated with N-Hydroxysuccinimide Ester Reagents and Primary Amines and Guanidine Groups
Selective Covalent Chemistry via Gas-Phase Ion/ion Reactions: An Exploration of the Energy Surfaces Associated with N-Hydroxysuccinimide Ester Reagents and Primary Amines and Guanidine Groups
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DOI：
10.1007/s13361-016-1359-3
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发表时间：
2016-06-01
影响因子：
3.2
通讯作者：
McLuckey, Scott A.
中科院分区：
文献类型：
--
作者：
Bu, Jiexun;Fisher, Christine M.;McLuckey, Scott A.
选择性共价键形成反应（简称共价反应）可以在气相离子/离子反应中发生，并通过形成长寿命的化学复合物而发生。通过DFT计算和复杂解离率测量，研究了磺酰- n -羟基琥珀酰亚胺（磺酰- nhs）酯试剂阴离子和含有伯胺或胍基团的肽阳离子之间的气相离子/离子反应性。结果揭示了有关复杂的竞争过程的障碍的作用的见解。当共价反应是放热反应时，由能面性质决定的两种典型情况是明显的。当共价反应的过渡态势垒较高（例1）时，产物在共价反应和长寿命配合物解离后的简单质子转移之间的分配对活化条件敏感，而当过渡态势垒较低（例2）时，产物分配对活化条件不敏感。在第二种情况下，共价反应的效率非常高，比如反应位点是胍，阴离子附着位点是胍离子。共价反应的效率是可变的，通常在情况1的情况下是低的，例如当胺是反应位点而铵离子是阴离子附着的位点时。然而，在情况1的情况下，在复杂解离步骤之前相对较长的缓慢加热步骤可以显著提高共价反应的产率。
Selective covalent bond forming reactions (referred to as covalent reactions) can occur in gas-phase ion/ion reactions and take place via the formation of a long-lived chemical complex. The gas-phase ion/ion reactivity between sulfo-N-hydroxysuccinimide (sulfo-NHS) ester reagent anions and peptide cations containing a primary amine or guanidine group has been examined via DFT calculations and complex dissociation rate measurements. The results reveal insights regarding the roles of the barriers of competing processes within the complex. When the covalent reaction is exothermic, two prototypical cases, determined by the nature of the energy surface, are apparent. The product partitioning between covalent reaction and simple proton transfer upon dissociation of the long-lived complex is sensitive to activation conditions when the transition state barrier for covalent reaction is relatively high (case 1) but is insensitive to activation conditions when the transition state barrier is relatively low (case 2). Covalent reaction efficiencies are very high in case 2 scenarios, such as when the reactive site is a guanidine and the anion attachment site is a guanidinium ion. Covalent reaction efficiencies are variable, and generally low, in case 1 scenarios, such as when an amine is the reactive site and an ammonium ion is the site of anion attachment. A relatively long slow-heating step prior to the complex dissociation step, however, can dramatically increase covalent reaction yield in case 1 scenarios.