Collision cross-section values, which can be determined using ion mobility experiments, are sensitive to the structures of protein ions and useful for applications to structural biology and biophysics. Protein ions with different charge states can exhibit very different collision cross-section values, but a comprehensive understanding of this relationship remains elusive. Here, we review cation-to-anion, proton-transfer reactions (CAPTR), a method for generating a series of charge-reduced protein cations by reacting quadrupole-selected cations with even-electron monoanions. The resulting CAPTR products are analyzed using a combination of ion mobility, mass spectrometry, and collisional activation. We compare CAPTR to other charge-manipulation strategies and review the results of various CAPTR-based experiments, exploring their contribution to a deeper understanding of the relationship between protein ion structure and charge state.

中文翻译：

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电荷对蛋白质离子结构的影响：从阳离子到阴离子、质子转移反应的经验教训

碰撞截面值可以使用离子淌度实验确定，对蛋白质离子的结构敏感，可用于结构生物学和生物物理学的应用。具有不同电荷状态的蛋白质离子可以表现出非常不同的碰撞截面值，但对这种关系的全面理解仍然难以捉摸。在这里，我们回顾了阳离子到阴离子的质子转移反应（CAPTR），这是一种通过四极选择的阳离子与偶数电子单阴离子反应生成一系列电荷减少的蛋白质阳离子的方法。使用离子淌度、质谱和碰撞激活相结合的方式对所得 CAPTR 产品进行分析。我们将 CAPTR 与其他电荷操纵策略进行比较，并回顾各种基于 CAPTR 的实验的结果，探索它们对更深入地理解蛋白质离子结构和电荷状态之间关系的贡献。