Department of Chemistry , LMU München , Butenandtstrasse 5-13 , 81377 München , Germany.
J Phys Chem B. 2018 Sep 27;122(38):8880-8890. doi: 10.1021/acs.jpcb.8b07485. Epub 2018 Sep 18.
We explored the influence of external electric fields (EEFs) on the stability of a glycine dipeptide model radical using high-level quantum chemical methods. Remotely located ions (Cl/Na) are used to implement EEF effects. The effects of these ions are reproduced using background point charges and oriented EEFs. Remote charges as far as 900 pm from the C radical center can be significantly stabilizing or destabilizing as a function of their relative orientation. The magnitude of these effects is also strongly dependent on the distance between the radical center and the charge location. After examining the strengths and weaknesses of some frequently used quantum mechanics methods in describing these effects properly, a comparison is made on the stability of dipeptide radicals bearing protonable or deprotonable side chains. In this group, the stability of the respective C radicals mainly depends on the preferred orientation of the charge-carrying side chain.
我们使用高级量子化学方法探讨了外加电场（EEF）对甘氨酸二肽模型自由基稳定性的影响。使用远程离子（Cl/Na）来实现 EEF 效应。通过背景点电荷和定向 EEF 来再现这些离子的影响。远程电荷距离 C 自由基中心最远可达 900 pm，其稳定性会随相对取向显著增强或减弱。这些影响的幅度也强烈依赖于自由基中心与电荷位置之间的距离。在检查了一些常用量子力学方法在正确描述这些效应方面的优缺点之后，我们比较了带有可质子化或去质子化侧链的二肽自由基的稳定性。在这一组中，各自 C 自由基的稳定性主要取决于带电荷侧链的优选取向。
