TAAM Refinement for 3D ED/MicroED Data Improves Model Fitting for Organic Molecules

What is it about?

The article discusses the use of 3D electron diffraction (3D ED) or microcrystal electron diffraction (MicroED) to determine the crystal structures of compounds from sub-micron-sized crystals. The authors collected high-resolution 3D ED data on L-alanine, α-glycine, and urea and compared independent atom model (IAM) and transferable aspherical atom model (TAAM) kinematical refinement against experimental and simulated data. TAAM refinement improved the model fitting statistics compared to IAM refinement, indicating that TAAM better represents the experimental electrostatic potential of organic crystals. The study suggests that with the current experimental setup, it is possible to observe details of electrostatic potential deformations due to chemical bonding in organic crystals.

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Photo by FlyD on Unsplash

Photo by FlyD on Unsplash

Why is it important?

This research is important because it presents a comparison of two kinematical refinement models, IAM and TAAM, against experimental and simulated data for determining high-resolution crystal structures of organic compounds using 3D electron diffraction (3D ED). The study provides insights into the strengths and weaknesses of these two models and highlights the importance of using a more accurate model (TAAM) for better fitting of the model to the experimental data. The research demonstrates the potential of 3D ED as an alternative technique for determining crystal structures, particularly for compounds that are difficult to crystallize for X-ray diffraction methods. Key Takeaways: 1. The study collected high-resolution 3D ED data on L-alanine, α-glycine, and urea single crystals and determined their crystal structures using the kinematical approach. 2. The IAM refinements against 3D ED data led to satisfactory accurate non-H-atom bond lengths, while the TAAM refinements had the potential to further improve the accuracy of these bonds. 3. The TAAM refinements visibly improved all fitting statistics compared to IAM, showing that TAAM is a better physical model than IAM for representing the experimental electrostatic potential of organic crystals. 4. The study highlights the importance of using special protocols correcting for geometrical distortions during 3D ED data reduction specific for particular electron microscopes.