Department of Chemistry, Bagley Hall, Box 351700, University of Washington, Seattle, Washington 981195-1700, United States.
J Am Soc Mass Spectrom. 2022 Jun 1;33(6):1038-1047. doi: 10.1021/jasms.2c00098. Epub 2022 May 10.
We report unusual dissociations of protonated RNA nucleosides tagged with radical initiator groups at ribose 5'-O and furnished with a 2',3'--isopropylidene protecting group. The ions undergo collision-induced radical cascade dissociations starting at the radical initiator that break down the dioxolane ring and trigger the formation of nucleobase cations and cation radicals. The adenine cation radical that was formed by radical cascade dissociations was identified by MS UV-vis photodissociation action spectroscopy to be a higher-energy N-3-H tautomer of the canonical ionized nucleobase. The guanine cation radical was formed by radical cascade dissociations as the N-7-H tautomer. In contrast to adenosine and guanosine, radical cascade dissociations of the tagged ribocytidine ion produced protonated cytosine, whereas tagged ribothymidine showed yet different dissociations resulting in predominant thymine loss. Reaction mechanisms were suggested for the cascade dissociations that were based on Born-Oppenheimer molecular dynamics and density functional theory calculations that were used to map the relevant parts of the potential energy surfaces for adenosine, guanosine, and cytidine radical ions. The reported radical cascade dissociations represent a new, nonredox approach to nucleobase and nucleoside cation radicals that has the potential of being expanded to the generation of various oligonucleotide cation radicals.
我们报告了一些不寻常的质子化 RNA 核苷的离解，这些核苷在核糖 5'-O 上标记有自由基引发基团，并带有 2'、3'--异亚丙基保护基团。这些离子通过自由基引发的碰撞诱导自由基级联离解开始，破坏了二氧戊环并引发碱基阳离子和阳离子自由基的形成。通过 MS UV-vis 光解作用光谱鉴定，由自由基级联离解形成的腺嘌呤阳离子自由基是规范离子化碱基的高能 N-3-H 互变异构体。由自由基级联离解形成的鸟嘌呤阳离子自由基是 N-7-H 互变异构体。与腺苷和鸟苷不同，标记的核糖胞苷离子的自由基级联离解产生质子化胞嘧啶，而标记的胸苷则表现出不同的离解方式，导致胸腺嘧啶主要丢失。基于 Born-Oppenheimer 分子动力学和密度泛函理论计算，提出了用于描述腺苷、鸟苷和胞苷自由基离子相关势能面部分的反应机制，这些计算用于描述腺苷、鸟苷和胞苷自由基离子相关势能面部分的反应机制。报告的自由基级联离解代表了一种新的、非氧化还原的碱基和核苷阳离子自由基生成方法，有可能扩展到各种寡核苷酸阳离子自由基的生成。
