Exploiting solid-state dynamic nuclear polarization NMR spectroscopy to establish the spatial distribution of...

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) Spectroscopy
• Materials Science
• Chemical Crystallography

Background:

• Heterogeneous materials often contain minor solid phases that are difficult to detect.
• Polymorphism, the existence of multiple crystal forms, is common in pharmaceuticals and other chemical compounds.
• Early detection of minor polymorphic phases is crucial for quality control and understanding material properties.

Purpose of the Study:

• To demonstrate the utility of NMR contrast based on DNP-enhanced polarization transport for detecting minor polymorphic phases.
• To quantitatively assess the spatial distribution of two polymorphs in a heterogeneous mixture.
• To apply this method to the specific case of detecting polymorph III of m-aminobenzoic acid within polymorph I.

Main Methods:

• Utilizing solid-state Dynamic Nuclear Polarization (DNP) NMR.
• Exploiting NMR contrast derived from DNP-enhanced polarization transport.
• Employing 1H spin diffusion simulations based on proposed spatial distribution models.
• Comparing simulated NMR data with experimental data.

Main Results:

• Successful detection of a minor amount (<4%) of polymorph III of m-aminobenzoic acid within polymorph I.
• Quantitative information on the spatial distribution of the two polymorphs was obtained.
• Established the best-fit model for polymorph spatial distribution by comparing simulated and experimental NMR data.

Conclusions:

• Solid-state DNP NMR is effective for the early detection and characterization of minor polymorphic phases in heterogeneous materials.
• NMR contrast from DNP-enhanced polarization transport provides quantitative insights into polymorph distribution.
• This approach offers a powerful tool for analyzing complex solid-state systems.