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14:55
Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
Published on: September 17, 2017
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Electrostatic Constraints Assessed by 1H MAS NMR Illuminate Differences in Crystalline Polymorphs
Joshua T Damron1, Kortney M Kersten1, Manoj Kumar Pandey2
1Department of Chemistry, University of Michigan , 930 North University Avenue, Ann Arbor, Michigan 48109-1055, United States.
The Journal of Physical Chemistry Letters
|August 22, 2017
Summary
This study uses advanced 1H NMR MAS to measure chemical shift anisotropy (CSA) tensors, revealing intermolecular forces and hydrogen bonding in acetaminophen polymorphs. These findings offer deeper insights beyond traditional crystal structure analysis.
Area of Science:
- Solid-state chemistry
- Crystallography
- Nuclear Magnetic Resonance (NMR) spectroscopy
Background:
- Atomically resolved crystal structures often struggle with precise hydrogen atom localization and fail to fully explain the forces driving structure formation.
- Understanding intermolecular forces, particularly the role of hydrogen atoms, is crucial for predicting and controlling crystalline solid structures.
- Novel techniques are needed to complement diffraction methods by illuminating these structure-enabling forces.
Purpose of the Study:
- To apply novel 1H NMR MAS methodology to measure chemical shift anisotropy (CSA) tensors.
- To utilize 1H CSA tensors to investigate the structure-driving intermolecular forces between acetaminophen polymorphs.
- To elucidate the specific roles of hydrogen bonding and aromatic interactions in acetaminophen polymorphism.
Main Methods:
- Solid-state 1H NMR Magic Angle Spinning (MAS) experiments were performed to measure 1H CSA tensors.
- Density Functional Theory (DFT) calculations were employed to characterize the measured 1H CSA tensors.
- The study focused on comparing the two known polymorphic forms of acetaminophen (paracetamol).
Main Results:
- Robust measurements of 1H CSA tensors were achieved, demonstrating their high sensitivity to electrostatic interactions.
- The 1H CSA tensors successfully differentiated between the two acetaminophen polymorphs.
- Key differences in hydrogen bonding and aromatic interactions contributing to structural stability were identified.
Conclusions:
- 1H CSA tensors provide valuable insights into intermolecular forces that are not apparent from static crystal structures alone.
- This NMR approach complements diffraction data, offering a dynamic view of structure-enabling forces in rigid molecules.
- The study highlights the utility of 1H CSA in understanding polymorphism and molecular interactions in crystalline solids.
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