Electron Properties of pharmaceutical molecules

International audienceBeyond the conventional crystal structures, electron and electrostatic properties can be derived experimentally from high resolution X-ray diffraction data. For more than thirty years, this experimental approach has been successfully applied to different kinds of compounds. Results are comparable to those obtained from high standard quantum mechanics methods. When a molecule crystallizes in different forms (polymorphism), it gives the opportunity to study the subtle re-arrangement of the electron distribution in relation with the crystal environment and the intermolecular interactions. In the presentation, we will focuse on a small and flexible pharmaceutical molecule, piracetam (2-oxo-1-pyrrolidineacetamide) which is the first nootropic agent discovered. The characterization of physical and chemical properties of polymorphs is of considerable importance particularly for the pharmaceutical research and development. It deals with therapeutic treatments based on the solid drug formulations which largely dominate all other galenic preparations. Polymorphism has a great impact not only on the industrial processing (powder formulations, tablets) but also on the drug bioavailability in relation with solubility, permeability etc. The crystallographic studies are pertinent in this field of research since they reveal the arrangement of the molecules in the crystal lattice. The electrostatic interactions, from which the macroscopic properties (both thermodynamically stable and metastable states) originate, are related to the molecular arrangements, packing, hydrogen bonding and contacts.[1] Several properties as electron density, atomic charges, electrostatic potential and forces will be presented and discussed. [1] Chambrier M.H., Bouhmaida N., Bonhomme F., Lebègue S., Gillet J.M., Jelsch C. & Ghermani N.E. Electron and Electrostatic Properties of Three Crystal Forms of Piracetam. Crystal Growth & Design. 2011, 11, 2528–2539