Department of Chemistry, Purdue University, West Lafayette, IN, USA.
J Am Soc Mass Spectrom. 2013 Apr;24(4):534-42. doi: 10.1007/s13361-012-0548-y. Epub 2013 Jan 26.
In this study, we demonstrated the formation of gas-phase peptide perthiyl (RSS•) and thiyl (RS•) radical ions besides sulfinyl radical (RSO•) ions from atmospheric pressure (AP) ion/radical reactions of peptides containing inter-chain disulfide bonds. The identity of perthiyl radical was verified from characteristic 65 Da (•SSH) loss in collision-induced dissociation (CID). This signature loss was further used to assess the purity of peptide perthiyl radical ions formed from AP ion/radical reactions. Ion/molecule reactions combined with CID were carried out to confirm the formation of thiyl radical. Transmission mode ion/molecule reactions in collision cell (q2) were developed as a fast means to estimate the population of peptide thiyl radical ions. The reactivity of peptide thiyl, perthiyl, and sulfinyl radical ions was evaluated based on ion/molecule reactions toward organic disulfides, allyl iodide, organic thiol, and oxygen, which followed in order of thiyl (RS•) > perthiyl (RSS•) > sulfinyl (RSO•). The gas-phase reactivity of these three types of sulfur-based radicals is consistent with literature reports from solution studies.
在这项研究中，我们证明了在含有链间二硫键的肽的大气压（AP）离子/自由基反应中，除了亚磺酰基自由基（RSO•）离子外，还形成了气相肽过硫基（RSS•）和硫基（RS•）自由基离子。过硫基自由基的特征是在碰撞诱导解离（CID）中丢失 65 Da（•SSH）。该特征丢失进一步用于评估从 AP 离子/自由基反应形成的肽过硫基自由基离子的纯度。结合 CID 的离子/分子反应用于确认硫基自由基的形成。碰撞室（q2）中的传输模式离子/分子反应被开发为快速估计肽硫基自由基离子的种群的方法。基于有机二硫化物、烯丙基碘、有机硫醇和氧气的离子/分子反应评估了肽硫基、过硫基和亚磺酰基自由基离子的反应性，其顺序为硫基（RS•）>过硫基（RSS•）>亚磺酰基（RSO•）。这三种类型的基于硫的自由基在气相中的反应性与来自溶液研究的文献报道一致。
