Monitoring Crystallization Processes in Confined Porous Materials by Dynamic Nuclear Polarization Solid-State Nuclear Magnetic Resonance

Abstract

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.

Monitoring of CaCO3 Nanoscale Structuration through Real-Time Liquid Phase Transmission Electron Microscopy and Hyperpolarized NMR

“…The latter aspect allows one to record NMR spectra of frozen solutions and enables the quenching (or the strong reduction) of the dynamics in solution. As a result, it becomes possible to characterize by solid-state NMR transient dynamics solute species as shown recently for glycine precipitation. , Dynamic nuclear polarization (DNP) has recently emerged as an appealing technique to drastically enhance the sensitivity of solid-state NMR spectroscopy and, in particular, to amplify signals at surfaces in an approach called DNP SENS (DNP surface enhanced NMR spectroscopy) . If the first proofs of concepts were reported on model mesoporous silica matrixes of high surface area, recent applications of DNP SENS concern a large range of chemical systems such as high-performance organometallic heterogeneous catalysts, doped silicon surfaces, metal–organic frameworks, ligand-capped nanoparticles, cementitious materials, quantum dots, or active Sn-zeolites .…”

Solid-State Reaction Synthesis of Nanoscale Materials: Strategies and Applications

“…67,81,82 Moreover, NSC-SSRs enable the opportunity to observe, deconvolute, and control novel intricate nanoscale chemical phenomena that are impossible to investigate in bulk-scale systems. 67,83 Such a comprehensive mechanistic understanding of solid-state nanoscale chemistry can be utilized to advance SSRs toward synthesizing sophisticated multicomponent NMs and the possible isolation of stable intermediate nanostructures similar to the kinetically controlled products of solution-state syntheses. 84−86 Apart from synthesizing sintering-proof, simple mono-or intermetallic spherical shapes from embedded precursors, NSC-SSRs can offer greater morphological control (porous, hollow, concave, Janus, etc.)…”

Triplet Dynamic Nuclear Polarization of Guest Molecules through Induced Fit in a Flexible Metal–Organic Framework**

“…Another promising approach is to confine the polarization source and target molecules in the nanopores of porous materials, which is expected to enable hyperpolarization of a variety of guest molecules. Unique DNP systems based on various nanoporous materials have been developed, [8,[25][26][27][28] and our group has also reported triplet-DNP of metal-organic frameworks (MOFs). [29] target guest molecules in nanoporous materials at room temperature.…”