Organic Synthesis & Mass Spectrometry Laboratory, Interdisciplinary Center for Mass Spectrometry (CISMa), Center of Innovation and Research in Materials and Polymers (CIRMAP), University of Mons - UMONS, 23 Place du Parc, 7000, Mons, Belgium.
Department of General, Organic Biomedical Chemistry, NMR and Molecular Imaging Laboratory, University of Mons - UMONS, 23 Place du Parc, 7000, Mons, Belgium.
J Am Soc Mass Spectrom. 2019 Dec;30(12):2726-2740. doi: 10.1007/s13361-019-02342-z. Epub 2019 Nov 21.
Mass spectrometric techniques and more particularly collision-induced dissociation (CID) experiments represent a powerful method for the determination of the primary sequence of (bio)molecules. However, the knowledge of the ion fragmentation patterns say the dissociation reaction mechanisms is a prerequisite to reconstitute the sequence based on fragment ions. Previous papers proposed that protonated peptoids dissociate following an oxazolone-ring mechanism starting from the O-protonation species and leading to high mass Y sequence ions. Here we revisit this backbone cleavage mechanism by performing CID and ion mobility experiments, together with computational chemistry, on tailor-made peptoids. We demonstrated that the B/Y cleavages of collisionally activated O-protonated peptoids must involve the amide nitrogen protonated structures as the dissociating species, mimicking the CID behavior of protonated peptides. Upon the nucleophilic attack of the oxygen atom of the N-terminal adjacent carbonyl group on the carbonyl carbon atom of the protonated amide, the peptoid ions directly dissociate to form an ion-neutral complex associating an oxazolone ion to the neutral truncated peptoid residue. Dissociation of the ion/neutral complex predominantly produces Y ions due to the high proton affinity of the secondary amide function characteristic of truncated peptoids. Whereas the production of Y ions from acetylated peptoids also involves the B/Y pathway, the observation of abundant Y ions from non-acetylated peptoid ions is shown in the present study to arise from an A-Y mechanism. The consecutive and competitive characters of the A-Y and the B/Y mechanisms are also investigated by drift time-aligned CID experiments.
质谱技术，特别是碰撞诱导解离（CID）实验，代表了一种确定（生物）分子一级序列的强大方法。然而，要根据碎片离子重建序列，就必须先了解离子碎片化模式和离解反应机制。先前的论文提出，质子化肽类似物通过从 O-质子化物种开始的噁唑啉环机制解离，从而产生高质量的 Y 序列离子。在这里，我们通过对定制的肽类似物进行 CID 和离子淌度实验以及计算化学研究，重新审视了这种骨架断裂机制。我们证明，碰撞激活的 O-质子化肽类似物的 B/Y 裂解必须涉及酰胺氮质子化结构作为离解物种，模拟了质子化肽的 CID 行为。在质子化酰胺的氧原子对相邻羰基碳原子的羰基碳原子的亲核攻击下，肽类似物离子直接解离形成离子-中性复合物，将噁唑啉离子与中性截断的肽类似物残基结合。由于截断的肽类似物的二级酰胺官能团具有高质子亲和力，因此离子/中性复合物的解离主要产生 Y 离子。虽然乙酰化肽类似物的 Y 离子的产生也涉及 B/Y 途径，但本研究表明，非乙酰化肽类似物离子中大量 Y 离子的产生源自 A-Y 机制。通过与漂移时间对齐的 CID 实验还研究了 A-Y 和 B/Y 机制的连续和竞争特征。
