Abstract：
The emergence of a crystal nucleus from disordered states is a critical and challenging aspect of the crystallization process, primarily due to the extremely short length and timescales involved. Methods such as liquid-cell or low-dose focal-series transmission electron microscopy (TEM) are often employed to probe these events. In this study, we demonstrate that ion mobility spectrometry-mass spectrometry (IMS-MS) offers a complementary and insightful perspective on the nucleation process by examining the sizes and shapes of small clusters, specifically those ranging from n = 2 to 40. Our findings reveal the significant role of sulfate ions in the growth of adeninediium sulfate clusters, which are the precursors to the formation of single crystals. Specifically, sulfate ions stabilize adenine clusters at the 1:1 ratio. In contrast, guanine sulfate forms smaller clusters with varied ratios, which become stable as they approach the 1:2 ratio. The nucleation size is predicted to be between n = 8 and 14, correlating well with the unit cell dimensions of adenine crystals. This correlation suggests that IMS-MS can identify critical nucleation sizes and provide valuable structural information consistent with established crystallographic data. We also discuss the strengths and limitations of IMS-MS in this context. IMS-MS offers rapid and robust experimental protocols, making it a valuable tool for studying the effects of various additives on the assembly of small molecules. Additionally, it aids in elucidating nucleation processes and the growth of different crystal polymorphs.
摘要：
晶核从无序状态的出现是结晶过程的关键和挑战性的方面。主要是由于涉及的极短的长度和时间尺度。通常采用诸如液体电池或低剂量聚焦系列透射电子显微镜（TEM）之类的方法来探测这些事件。在这项研究中,我们证明了离子迁移谱-质谱（IMS-MS）通过检查小团簇的大小和形状，为成核过程提供了互补和有见地的观点，特别是那些范围从n=2到40。我们的发现揭示了硫酸根离子在硫酸腺嘌呤簇生长中的重要作用，它们是形成单晶的前体。具体来说,硫酸根离子以1:1的比例稳定腺嘌呤簇。相比之下,鸟嘌呤硫酸盐形成具有不同比例的较小簇，当它们接近1:2的比例时变得稳定。预计成核尺寸在n=8至14之间，与腺嘌呤晶体的晶胞尺寸密切相关。这种相关性表明IMS-MS可以识别临界成核尺寸并提供与已建立的晶体学数据一致的有价值的结构信息。在这种情况下，我们还讨论了IMS-MS的优势和局限性。IMS-MS提供快速和强大的实验协议，使其成为研究各种添加剂对小分子组装的影响的有价值的工具。此外,它有助于阐明成核过程和不同晶体多晶型物的生长。
