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Eric J. Munson, Principal Investigator

Modeling Structures of Organic Molecules in Crystals

Understanding molecular conformations in crystalline organic compounds such as pharmaceuticals is important because drugs can exist in two or more crystalline phases that differ in the arrangement and/or conformation of the molecules in the crystal lattice. These researchers need to be able to relate calculated nuclear magnetic resonance (NMR) chemical shifts of crystalline organic compounds such as drugs to molecular structure. The motivation for this is twofold. First, the researchers would like to use theory to assist in the assignment of resonances in solid-state NMR spectra. This is a significant problem, as peaks are often shifted by 10 ppm or more from their solution-state values, and there may be several peaks for each nucleus due to several different conformations present in the crystal lattice. Second, the researchers would like to determine the crystal structure of a drug from the solid-state NMR spectrum. An integral part of this strategy is to use chemical shift calculations to predict torsion angles and bond distances for compounds based on the isotropic and anisotropic chemical shifts in the solid state. By using a combination of single-crystal XRD, PXRD, chemical shift calculations, and solid-state NMR, these researchers hope to develop a robust method for determining the crystal structure of pharmaceutically-relevant solids for which no single-crystal data is available. This work is currently using the cerius2 program at the Supercomputing Institute's Basic Sciences Computing Laboratory and Medicinal Chemistry-Supercomputing Institute Visualization/Workstation Laboratory to model molecular structures and to predict PXRD patterns.Understanding molecular conformations in crystalline organic compounds such as pharmaceuticals is important because drugs can exist in two or more crystalline phases that differ in the arrangement and/or conformation of the molecules in the crystal lattice. These researchers need to be able to relate calculated nuclear magnetic resonance (NMR) chemical shifts of crystalline organic compounds such as drugs to molecular structure. The motivation for this is twofold. First, the researchers would like to use theory to assist in the assignment of resonances in solid-state NMR spectra. This is a significant problem, as peaks are often shifted by 10 ppm or more from their solution-state values, and there may be several peaks for each nucleus due to several different conformations present in the crystal lattice. Second, the researchers would like to determine the crystal structure of a drug from the solid-state NMR spectrum. An integral part of this strategy is to use chemical shift calculations to predict torsion angles and bond distances for compounds based on the isotropic and anisotropic chemical shifts in the solid state. By using a combination of single-crystal XRD, PXRD, chemical shift calculations, and solid-state NMR, these researchers hope to develop a robust method for determining the crystal structure of pharmaceutically-relevant solids for which no single-crystal data is available. This work is currently using the cerius2 program at the Supercomputing Institute's Basic Sciences Computing Laboratory and Medicinal Chemistry-Supercomputing Institute Visualization/Workstation Laboratory to model molecular structures and to predict PXRD patterns.

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