Uncovering the Pathway of Serine Octamer Magic Number Cluster Formation during Electrospray Ionization: Experiments and Simulations,Journal of the American Chemical Society

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Uncovering the Pathway of Serine Octamer Magic Number Cluster Formation during Electrospray Ionization: Experiments and Simulations
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2024-09-17 , DOI: 10.1021/jacs.4c05760
Vida Alinezhad ₁ , Yuen Ki Ng ₁ , Sanvid Mehta ₁ , Lars Konermann ₁

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Electrospray ionization (ESI) of serine (Ser) solution generates Ser₈H⁺ as an abundant magic number cluster. ESI clustering of most other solutes yields nonspecific stoichiometries. It is unclear why Ser₈H⁺ dominates in the case of Ser, and how Ser₈H⁺ forms during ESI. Even the location of Ser₈H⁺ formation is contentious (in solution, in ESI droplets, or elsewhere). Here we unravel key aspects of the l-Ser₈H⁺ formation pathway. Harsh ion sampling conditions promote the collision-induced dissociation (CID) of regular ESI analytes. Unexpectedly, Ser₈H⁺ was seemingly resistant against CID during ion sampling, despite its extremely low tandem mass spectrometry (MS/MS) stability. This unusual behavior reveals that Ser₈H⁺ forms during ion sampling. We propose the following pathway: (1) Nonspecific Ser clusters are released when ESI droplets evaporate to dryness. These initial clusters cover a wide size range, from a few Ser to hundreds or thousands of monomers. (2) The clusters undergo dissociation during ion sampling, mostly via successive loss of neutral monomers. For any source activation voltage, there is a subpopulation of clusters for which this CID cascade tends to terminate at the octamer level, culminating in Ser₈H⁺-dominated product distributions. Mobile proton molecular dynamics simulations were used to model the entire pathway. Ser₈H⁺ structures formed in these simulations were consistent with ion mobility experiments. The most compact structures resembled the model of [Scutelnic, V. J. Am. Chem. Soc. 2018, 140, 7554–7560], with numerous intermolecular salt bridges and H-bonds. Our findings illustrate how the interplay of association and dissociation reactions across phase boundaries can culminate in magic number clusters.

中文翻译：

揭示电喷雾电离过程中丝氨酸八聚体魔数簇形成的途径：实验和模拟

丝氨酸（Ser）溶液的电喷雾电离（ESI）产生 Ser₈H⁺，是一个丰富的魔数簇。大多数其他溶质的 ESI 聚集产生非特异性化学计量。目前尚不清楚为什么 Ser₈H⁺ 在 Ser 的情况下占主导地位，以及 Ser₈H⁺ 在 ESI 期间是如何形成的。甚至 Ser₈H⁺ 形成的位置也是有争议的（在溶液中、在 ESI 液滴中或其他位置）。在这里，我们揭示了 l-Ser ₈H⁺ 形成途径的关键方面。苛刻的离子采样条件会促进常规 ESI 分析物的碰撞诱导解离（CID）。出乎意料的是，尽管 Ser₈H⁺ 的串联质谱（MS/MS）稳定性极低，但它在离子采样过程中似乎对 CID 具有抵抗力。这种不寻常的行为表明，Ser₈H⁺ 在离子采样过程中形成。我们提出以下途径：（1）当 ESI 液滴蒸发至干燥时，释放非特异性 Ser 簇。这些初始簇涵盖了广泛的尺寸范围，从几个 Ser 到数百或数千个单体。（2）离子簇在离子采样过程中发生解离，主要是通过中性单体的连续损失。对于任何源激活电压，都有一个簇的子群，其 CID 级联往往终止于八聚体水平，最终导致 Ser₈H⁺ 主导的乘积分布。移动质子分子动力学模拟用于对整个通路进行建模。在这些模拟中形成的 Ser₈H⁺ 结构与离子淌度实验一致。最紧凑的结构类似于 [Scutelnic， V.J. Am. 化学。 Soc 的。2018， 140， 7554–7560]，具有许多分子间盐桥和 H 键。我们的研究结果说明了跨相边界的缔合和解离反应的相互作用如何最终形成幻数簇。

更新日期：2024-09-17

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