Shake‐up and shake‐off excitations with associated electron losses in X‐ray studies of proteins
Shake‐up and shake‐off excitations with associated electron losses in X‐ray studies of proteins
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DOI：
10.1110/ps.ps.26201
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发表时间：
2001-10
期刊：
影响因子：
8
通讯作者：
P. Persson;S. Lunell;Abraham Szöke;B. Ziaja;J. Hajdu
中科院分区：
文献类型：
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作者：
P. Persson;S. Lunell;Abraham Szöke;B. Ziaja;J. Hajdu
X射线对原子的光致电离通常会从原子中移除一个内层电子，留下一个扰动的“中空离子”，它的弛豫可能会采取不同的途径。在轻元素中，俄歇电子的发射是很常见的。然而，从原子中释放出的能量和电子总数可能会受到抖动和抖动效应的影响。当内层电子离开时，外层电子可能会发现自己处于一种不是周围原子本征态的状态。由此产生的集体激发称为震荡。如果这个过程还包括从外壳释放低能电子，那么这个过程被称为抖动。目前尚不清楚重组和重组对蛋白质等生物材料的整体电离有多大贡献。特别是，出射电子与剩余体系之间的相互作用取决于原子的化学环境，这可以用量子化学方法来研究。在这里，我们提供了对模型化合物的计算，以表示蛋白质中最常见的化学环境。结果表明，挥发和挥发过程对∼的影响占氮气排放总量的20%，碳排放的30%，氧气排放的40%，硫排放的23%。碳、氮和氧的三重电离和更高的电离很少见，但硫的电离很频繁。这一发现与新兴X射线自由电子激光的生物实验设计有关。
Photoionization of an atom by X‐rays usually removes an inner shell electron from the atom, leaving behind a perturbed “hollow ion” whose relaxation may take different routes. In light elements, emission of an Auger electron is common. However, the energy and the total number of electrons released from the atom may be modulated by shake‐up and shake‐off effects. When the inner shell electron leaves, the outer shell electrons may find themselves in a state that is not an eigen‐state of the atom in its surroundings. The resulting collective excitation is called shake‐up. If this process also involves the release of low energy electrons from the outer shell, then the process is called shake‐off. It is not clear how significant shake‐up and shake‐off contributions are to the overall ionization of biological materials like proteins. In particular, the interaction between the outgoing electron and the remaining system depends on the chemical environment of the atom, which can be studied by quantum chemical methods. Here we present calculations on model compounds to represent the most common chemical environments in proteins. The results show that the shake‐up and shake‐off processes affect ∼20% of all emissions from nitrogen, 30% from carbon, 40% from oxygen, and 23% from sulfur. Triple and higher ionizations are rare for carbon, nitrogen, and oxygen, but are frequent for sulfur. The findings are relevant to the design of biological experiments at emerging X‐ray free‐electron lasers.