Department of Chemistry, University of California, Riverside, California 92521, United States.
J Am Soc Mass Spectrom. 2023 Mar 1;34(3):452-458. doi: 10.1021/jasms.2c00326. Epub 2023 Feb 14.
Radical-directed dissociation (RDD) is a fragmentation technique in which a radical created by selective 213/266 nm photodissociation of a carbon-iodine bond is reisolated and collisionally activated. In previous RDD experiments, collisional activation was effected by ion-trap collision-induced dissociation (CID). Higher-energy collisional dissociation (HCD) differs from CID both in terms of how ions are excited and in the number, type, or abundance of fragments that are observed. In this paper, we explore the use of HCD for activation in RDD experiments. While RDD-CID favors fragments produced from radical-directed pathways such as a/z-ions and side chain losses regardless of the activation energy employed, RDD-HCD spectra vary considerably as a function of activation energy, with lower energies favoring RDD while higher energies favor products resulting from cleavage directed by mobile protons (b/y-ions). RDD-HCD therefore affords more tunable fragmentation based on the HCD energy provided. Importantly, the abundance of radical products decreases as a function of increasing HCD energy, confirming that RDD generally proceeds via lower-energy barriers relative to mobile-proton-driven dissociation. The dominance of b/y-ions at higher energies for RDD-HCD can therefore be explained by the higher survivability of fragments not containing the radical after the initial or subsequent dissociation events. Furthermore, these results confirm previous suspicions that HCD spectra differ from CID spectra due to multiple dissociation events.
自由基定向解离（RDD）是一种碎片化技术，其中通过对碳-碘键的选择性 213/266nm 光解产生的自由基被重新分离并进行碰撞激活。在之前的 RDD 实验中，通过离子阱碰撞诱导解离（CID）实现了碰撞激活。高能碰撞解离（HCD）在离子激发方式和观察到的碎片数量、类型或丰度方面与 CID 不同。在本文中，我们探讨了在 RDD 实验中使用 HCD 进行激活的方法。虽然 RDD-CID 有利于从自由基定向途径产生的碎片，例如 a/z-离子和侧链损失，而与所采用的激活能无关，但 RDD-HCD 光谱随激活能的变化相当大，较低的能量有利于 RDD，而较高的能量有利于由移动质子引导的裂解产物（b/y-离子）。因此，RDD-HCD 可以根据提供的 HCD 能量实现更可调节的碎片化。重要的是，随着 HCD 能量的增加，自由基产物的丰度降低，这证实了 RDD 通常通过相对较低的能量势垒进行，而不是由移动质子驱动的解离。因此，在更高的 RDD-HCD 能量下，b/y-离子的优势可以通过初始或后续解离事件后不包含自由基的碎片的更高存活率来解释。此外，这些结果证实了之前的怀疑，即 HCD 光谱与 CID 光谱不同是由于多个解离事件。
