Li Xifeng, Sevilla Michael D, Sanche Léon
Group of the Canadian Institutes of Health Research in the Radiation Sciences, Faculty of Medicine, Université de Sherbrooke, Quebec, J1H 5N4, Canada.
J Am Chem Soc. 2003 Nov 12;125(45):13668-9. doi: 10.1021/ja036509m.
The discovery of DNA strand breaks induced by low energy secondary electrons sparks a necessity to elucidate the mechanism. Through theoretical studies based on a sugar-phosphate-sugar model that mimics a backbone section of the DNA strand, it is found that bond cleavages at 3' or 5'C-O sites after addition of an electron are possible with a ca. 10 kcal/mol activation barrier. Moreover, the potential energy surfaces show that dissociation at both sites is highly favorable thermodynamically. Although the phosphate group in DNA is not a favored site for electron attachment because of competitive electron transfer to the bases, any electrons which attach to phosphates on first encounter may induce strand breaks even when the electron energy is near zero eV. These findings have profound implication as low energy secondary electrons are abundantly generated in all types of ionization radiation.
低能二次电子诱导DNA链断裂的发现引发了阐明其机制的必要性。通过基于模拟DNA链主干部分的磷酸-糖-磷酸模型的理论研究，发现电子添加后3'或5' C-O位点的键断裂是可能的，活化能垒约为10 kcal/mol。此外，势能面表明两个位点的解离在热力学上非常有利。尽管由于电子向碱基的竞争性转移，DNA中的磷酸基团不是电子附着的有利位点，但首次附着在磷酸上的任何电子即使在电子能量接近零电子伏特时也可能诱导链断裂。这些发现具有深远的意义，因为在所有类型的电离辐射中都会大量产生低能二次电子。
