摘要/Abstract
生物体内，蛋白质中二硫键的自由基损伤会影响蛋白结构与功能，与细胞的衰老也有重要联系.因此研究自由基与二硫键相互作用机理，理解自由基与二硫键作用过程，对二硫键的断裂与保护有着重要意义.采取液体辅助的表面解吸常压化学电离技术，搭建在线监测（H2O）n+·与双（2-羟乙基）二硫醚（HEDS）相互作用装置，制备高丰度的水自由基阳离子（H2O）n+·（n=2~4），通过线性离子阱质谱仪，结合密度泛函理论方法，对（H2O）n+·与HEDS作用的质谱行为及热力学过程进行研究.结果表明，（H2O）n+·与HEDS发生相互作用，形成自由基复合物（M+H2O）+·（m/z 172）.其中（M+H2O）+·中H2O是来源于（H2O）n+·.热力学计算显示，HEDS结构中β位羟基上的H与S以分子内五元环的形式形成弱氢键；反应过程中，（H2O）n+·与HEDS中的羟基优先结合，形成（M+H2O）+·复合物后，二硫键将难以断裂.因此，在水自由基阳离子作用的过程中β位羟基对HEDS的二硫键有保护作用.
关键词: 水自由基阳离子, 二硫键, 自由基损伤, 常压化学电离
In vivo, free radical damage of disulfide bonds in proteins affects the structure and function of proteins, and has an important relationship with cell aging. Therefore, studying the mechanism of the interaction between free radicals and disulfide bonds, and understanding the interaction process between free radicals and disulfide bonds, is important for the cleavage or proteciton of disulfide bond. In this paper, liquid-assisted surface desorption atmospheric pressure chemical ionization technology is adopted (LA-DAPCI), to construct a two-channel ion source device, obtaining high abundance water radical cations (H2O)n+· (n=2~4). Using linear ion trap mass spectrometer, combining with Density Functional Theory, the interaction process between (H2O)n+· and bis(2-hydroxyethyl) disulfide (HEDS) in mass spectrometer and thermodynamic process of the interaction were studied. The results indicated that (H2O)n+· interacted with HEDS, forming a radical complex (M+H2O)+· (m/z 172) without covalent bond, and H2O in complex (M+H2O)+· (m/z 172) is derived from (H2O)n+·, not from the H2O of sample solution. Furthermore, thermodynamic theoretical calculation results demonstrated that H on the β-hydroxyl group of HEDS structure forms a weak hydrogen bond with S in the form of an intramolecular five-membered ring. During the interaction process, (H2O)n+· preferentially binds to the hydroxyl group of HEDS, forming a radical complex (M+H2O)+·, whose disulfide bond will be difficult to be cleaved. In conclusion, the β-hydroxyl group has a protective effect on the disulfide bond of HEDS during the interaction with water radical cations.
Key words: water radical cations, disulfide bonds, radical damage, atmospheric pressure chemical ionization
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