Exploiting solid-state dynamic nuclear polarization NMR spectroscopy to establish the spatial distribution of polymorphic phases in a solid material.

Cousin SF, Hughes CE, Ziarelli F, Viel S, Mollica G, Harris KDM, Pinon AC, Thureau P

Chem. Sci. 14 (37) 10121-10128 [2023-09-27; online 2023-06-23]

Solid-state DNP NMR can enhance the ability to detect minor amounts of solid phases within heterogenous materials. Here we demonstrate that NMR contrast based on the transport of DNP-enhanced polarization can be exploited in the challenging case of early detection of a small amount of a minor polymorphic phase within a major polymorph, and we show that this approach can yield quantitative information on the spatial distribution of the two polymorphs. We focus on the detection of a minor amount (<4%) of polymorph III of m-aminobenzoic acid within a powder sample of polymorph I at natural isotopic abundance. Based on proposed models of the spatial distribution of the two polymorphs, simulations of 1H spin diffusion allow NMR data to be calculated for each model as a function of particle size and the relative amounts of the polymorphs. A comparison between simulated and experimental NMR data allows the model(s) best representing the spatial distribution of the polymorphs in the system to be established.

Swedish NMR Centre (SNC) [Technology development]

PubMed 37772100

DOI 10.1039/d3sc02063k

Crossref 10.1039/d3sc02063k

pmc: PMC10530703
pii: d3sc02063k