Sasiene Zachary J, Mendis Praneeth M, Jackson Glen P
C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, WV 26506-6121, USA.
Department of Forensic and Investigative Science, West Virginia University, Morgantown, WV 26506-6121, USA.
Int J Mass Spectrom. 2021 Apr;462. doi: 10.1016/j.ijms.2021.116532. Epub 2021 Jan 27.
Charge transfer dissociation mass spectrometry (CTD-MS) has been shown to induce high energy fragmentation of biological ions in the gas phase and provide fragmentation spectra similar to extreme ultraviolet photodissociation (XUVPD). To date, CTD has typically employed helium cations with kinetic energies between 4-10 keV to initiate radical-directed fragmentation of analytes. However, as a reagent, helium has recently been listed as a critical mineral that is becoming scarcer and more expensive, so this study explored the potential for using cheaper and more readily available reagent gases. A model peptide, bradykinin, and a model oligosaccharide, κ-carrageenan with a degree of polymerization of 4, were fragmented using a variety of CTD reagent gases, which included helium, hydrogen, oxygen, nitrogen, argon and lab air. The CTD results were also contrasted with low-energy collision-induced dissociation (LE-CID), which were collected on the same 3D ion trap. Using constant reagent ion fluxes and kinetic energies, all five alterative reagent gases generated remarkably consistent sequence coverage and fragmentation efficiencies relative to He-CTD, which suggests that the ionization energy of the reagent gas has a negligible effect on the activation of the biological ions. The CTD efficiencies of all the gases ranged from 11-13% for bradykinin and 7-8% for κ-carrageenan. Within these tight ranges, the abundance of the CTnoD peak of bradykinin and the efficiency of CTD fragmentation of bradykinin both correlated with the ionization energy of the CTD reagent gas, which suggests that resonant charge transfer plays a small role in the activation of this peptide. The majority of the excitation energy for bradykinin and for κ-carrageenan comes from an electron stopping mechanism, which is described by long-range interactions between the reagent cations and electrons in the highest occupied molecular orbitals (HOMOs) of the biological ions. The CTD spectra do not provide any evidence for covalently bound products between the biological ions and the more-reactive gases like hydrogen, oxygen and nitrogen, which implies that the high kinetic energies of the reagent ions make them unavailable for covalent reactions. This work demonstrates that any of the substitute reagent gases tested are viable options for future CTD-MS experiments.
电荷转移解离质谱法（CTD-MS）已被证明能在气相中诱导生物离子发生高能碎片化，并提供与极紫外光解离（XUVPD）相似的碎片化光谱。迄今为止，CTD通常使用动能在4-10 keV之间的氦阳离子来引发分析物的自由基导向碎片化。然而，作为一种试剂，氦最近被列为一种关键矿物，其正变得越来越稀缺且价格昂贵，因此本研究探索了使用更便宜且更容易获得的试剂气体的可能性。使用包括氦、氢、氧、氮、氩和实验室空气在内的多种CTD试剂气体，对一种模型肽缓激肽和一种聚合度为4的模型寡糖κ-卡拉胶进行了碎片化处理。CTD结果还与在同一3D离子阱上收集的低能碰撞诱导解离（LE-CID）进行了对比。在使用恒定的试剂离子通量和动能的情况下，相对于He-CTD，所有五种替代试剂气体产生的序列覆盖率和碎片化效率都非常一致，这表明试剂气体的电离能对生物离子的活化影响可忽略不计。缓激肽的所有气体的CTD效率在11-13%之间，κ-卡拉胶的CTD效率在7-8%之间。在这些狭窄范围内，缓激肽的CTnoD峰丰度和缓激肽的CTD碎片化效率均与CTD试剂气体的电离能相关，这表明共振电荷转移在该肽的活化中起的作用较小。缓激肽和κ-卡拉胶的大部分激发能量来自电子阻止机制，这由试剂阳离子与生物离子最高占据分子轨道（HOMO）中的电子之间的长程相互作用来描述。CTD光谱没有提供任何证据表明生物离子与氢、氧和氮等反应性更强的气体之间存在共价结合产物，这意味着试剂离子的高动能使其无法进行共价反应。这项工作表明，所测试的任何一种替代试剂气体都是未来CTD-MS实验的可行选择。
