Aix Marseille Univ, CNRS, ICR, 13397 Marseille, France.
Aix Marseille Univ, CNRS, Centrale Marseille, FSCM, 13397 Marseille, France.
J Am Chem Soc. 2021 Apr 28;143(16):6095-6103. doi: 10.1021/jacs.0c12982. Epub 2021 Apr 15.
Establishing mechanistic understanding of crystallization processes at the molecular level is challenging, as it requires both the detection of transient solid phases and monitoring the evolution of both liquid and solid phases as a function of time. Here, we demonstrate the application of dynamic nuclear polarization (DNP) enhanced NMR spectroscopy to study crystallization under nanoscopic confinement, revealing a viable approach to interrogate different stages of crystallization processes. We focus on crystallization of glycine within the nanometric pores (7-8 nm) of a tailored mesoporous SBA-15 silica material with wall-embedded TEMPO radicals. The results show that the early stages of crystallization, characterized by the transition from the solution phase to the first crystalline phase, are straightforwardly observed using this experimental strategy. Importantly, the NMR sensitivity enhancement provided by DNP allows the detection of intermediate phases that would not be observable using standard solid-state NMR experiments. Our results also show that the metastable β polymorph of glycine, which has only transient existence under bulk crystallization conditions, remains trapped within the pores of the mesoporous SBA-15 silica material for more than 200 days.
在分子水平上建立对结晶过程的机械理解具有挑战性，因为它既需要检测瞬态固相，又需要监测液相和固相随时间的演化。在这里，我们展示了动态核极化 (DNP) 增强 NMR 光谱在纳米受限条件下研究结晶的应用，揭示了一种可行的方法来探究结晶过程的不同阶段。我们专注于在经过修饰的介孔 SBA-15 硅材料的纳米孔（7-8nm）内甘氨酸的结晶，该材料的壁中嵌入了 TEMPO 自由基。结果表明，使用这种实验策略可以直接观察到结晶的早期阶段，其特征是从溶液相到第一晶相的转变。重要的是，DNP 提供的 NMR 灵敏度增强允许检测到使用标准固态 NMR 实验无法观察到的中间相。我们的结果还表明，甘氨酸的亚稳β多晶型物在大块结晶条件下仅存在短暂存在，在介孔 SBA-15 硅材料的孔中仍被捕获超过 200 天。
