Sanche Léon
Group of the Canadian Institutes of Health Research in the Radiation Sciences, Faculté de médecine, Université de Sherbrooke, Canada J1H 5N4.
Mass Spectrom Rev. 2002 Sep-Oct;21(5):349-69. doi: 10.1002/mas.10034.
Low-energy electrons (LEEs) are produced in large quantities in any type of material irradiated by high-energy particles. In biological media, these electrons can fragment molecules and lead to the formation of highly reactive radicals and ions. The results of recent experiments performed on biomolecular films bombarded with LEEs under ultra-high vacuum conditions are reviewed in the present article. The major type of experiments, which measure fragments produced in such films as a function of incident electron energy (0.1-45 eV), are briefly described. Examples of the results obtained from DNA films are summarized along with those obtained from the fragmentation of elementary components of the DNA molecule (i.e., thin solid films of H(2)O, DNA bases, sugar analogs, and oligonucleotides) and proteins. By comparing the results of these different experiments, it is possible to determine fundamental mechanisms that are involved in the dissociation of biomolecules and the production of single- and double-strand breaks in DNA, and to show that base damage is dependent on the nature of the bases and on their sequence context. Below 15 eV, electron resonances (i.e., the formation of transient anions) play a dominant role in the fragmentation of all biomolecules investigated. These transient anions fragment molecules by decaying into dissociative electronically excited states or by dissociating into a stable anion and a neutral radical. These fragments usually initiate other reactions with nearby molecules, causing further chemical damage. The damage caused by transient anions is dependent on the molecular environment.
在任何被高能粒子辐照的材料中都会大量产生低能电子（LEEs）。在生物介质中，这些电子会使分子碎片化，并导致形成高反应性的自由基和离子。本文综述了近期在超高真空条件下用低能电子轰击生物分子薄膜所进行实验的结果。简要描述了主要类型的实验，这些实验测量了此类薄膜中产生的碎片作为入射电子能量（0.1 - 45电子伏特）的函数。总结了从DNA薄膜以及从DNA分子基本成分（即H₂O、DNA碱基、糖类似物和寡核苷酸的固体薄膜）和蛋白质的碎片化中获得的结果示例。通过比较这些不同实验的结果，可以确定生物分子解离以及DNA中单链和双链断裂产生所涉及的基本机制，并表明碱基损伤取决于碱基的性质及其序列背景。在15电子伏特以下，电子共振（即瞬态阴离子的形成）在所有研究的生物分子碎片化中起主导作用。这些瞬态阴离子通过衰变为解离电子激发态或解离为稳定阴离子和中性自由基来使分子碎片化。这些碎片通常会引发与附近分子的其他反应，从而造成进一步的化学损伤。瞬态阴离子造成的损伤取决于分子环境。
