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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >To jump or not to jump? C_α hydrogen atom transfer in post-cleavage radical-cation complexes
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To jump or not to jump? C_α hydrogen atom transfer in post-cleavage radical-cation complexes

机译：跳还是不跳？ C_α氢原子在裂解后自由基-阳离子配合物中的转移

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摘要

Conventionally, electron capture or transfer to a polyprotonated peptide ion produces an initial radical-cation intermediate which dissociates "directly" to generate complementary c_n′ and z_m~? sequence ions (or ions and neutrals). Alternatively, or in addition, the initial radical-cation intermediate can undergo H~? migration to produce cn ? (or c_n - H~?) and z_m~′ (or z_m~? + H~?) species prior to complex separation ("nondirect"). This reaction significantly complicates spectral interpretation, creates ambiguity in peak assignment, impairs effective algorithmic processing (reduction of the spectrum to solely ~(12)C m/z values), and reduces sequence ion signal-to-noise. Experimental evidence indicates that the products of hydrogen atom transfer reactions are substantially less prevalent for higher charge state precursors. This effect is generally rationalized on the basis of decreased complex lifetime. Here, we present a theoretical study of these reactions in post N-C_α bond cleavage radical-cation complexes as a function of size and precursor charge state. This approach provides a computational estimate of the barriers associated with these processes for highly charged peptides with little charge solvation. The data indicate that the H~? migration is an exothermic process and that the barrier governing this reaction rises steeply with precursor ion charge state. There is also some evidence for immediate product separation following N-C_α bond cleavage at higher charge state.
机译：通常，电子捕获或转移到多质子化的肽离子上会产生一个初始的自由基阳离子中间体，该中间体会“直接”解离以生成互补的c_n'和z_m〜？序列离子（或离子和中性离子）。替代地或另外，初始自由基阳离子中间体可以经历H 2-。迁移产生cn？ （或c_n-H〜？）和z_m〜'（或z_m〜？+ H〜？）物种，然后进行复杂分离（“非直接”）。该反应显着复杂化了光谱解释，在峰分配中产生了歧义，损害了有效的算法处理（将光谱减少到仅〜（12）C m / z值），并降低了序列离子的信噪比。实验证据表明，对于较高电荷态的前体，氢原子转移反应的产物普遍较少。通常根据减少的复杂寿命来合理化此效果。在这里，我们目前对N-C_α键裂解自由基-阳离子络合物中这些反应的大小和前体电荷状态的函数进行理论研究。这种方法提供了与这些过程有关的障碍的计算估计，这些障碍涉及电荷少，溶剂化程度高的肽。数据表明H〜？迁移是一个放热过程，控制该反应的势垒会随着前体离子的电荷状态而急剧上升。也有一些证据表明在高电荷状态下N-C_α键断裂后立即分离出产物。

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