Abstract

We present an experimental study on the stability of cluster cations formed by the assembly of tryptophan or serine moelcules inside charged helium droplets and subsequent droplet evaporation. The stability is probed via collision induced dissociation and mass spectrometry. We focus on the neutral loss of 18 Da that was previously proposed to result in the formation of an amide bond in amino acid clusters. We show that the cluster cations formed by the neutral loss of 18 Da from protonated parent cluster ion precursors are softly, presumably van der Waals, bound similar to the parent and protonated parent cluster cations. Cluster cations formed after neutral loss of 18 Da from the parent cluster cations are strongly bound, indicating the formation of new covalent bonds. Even though we observe a signal at m/z corresponding to dipeptide cations, their collision induced dissociation fragmentation does not allow unambiguous identification of their structure, particularly the amide bond. Our study at cryogenic conditions of He droplets demonstrates that peptide formation by the cluster ion polymerization is not a barrierless process and the formation of amide bonds may depend on activation methods and available catalysts.

Graphical abstract

中文翻译：

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丝氨酸和色氨酸的团簇离子聚合，失水通道

摘要

我们提出了由色氨酸或丝氨酸分子在带电的氦气小滴内组装以及随后的小滴蒸发形成的簇状阳离子稳定性的实验研究。通过碰撞诱导解离和质谱法来探测稳定性。我们专注于18 Da的中性损失，该损失先前被提议导致氨基酸簇中酰胺键的形成。我们表明，从质子化母体簇离子前体中性损失18 Da所形成的簇阳离子是柔软的，大概是范德华斯，与母体和质子化母簇阳离子结合相似。从母簇阳离子中性损失18 Da后形成的簇阳离子牢固结合，表明形成了新的共价键。即使我们观察到m / z的信号对应于二肽阳离子，它们的碰撞诱导的解离断裂不能明确鉴定其结构，特别是酰胺键。我们在He液滴的低温条件下的研究表明，簇离子聚合形成的肽不是无障碍过程，酰胺键的形成可能取决于活化方法和可用的催化剂。

图形概要