Download Solid-solid phase transitions in amino

Solid-solid phase transitions in amino-acid crystals
Polymorphism is the ability of molecules to crystallize in different crystal structures. The properties of
crystals are related to their structure and therefore they can be different for different polymorphs. For
example, the bioavailability of pharmaceuticals can change depending on the polymorph. We aim to
understand transitions between polymorphs that occur in the solid phase with the ultimate goal to induce
or inhibit these transitions. We use amino-acid crystals, in particular DL-norleucine, as model system.
The three polymorphs of DL-norleucine consist of hydrogen-bonded bilayers, which is a characteristic of
alpha amino acids with linear side chains. The hydrogen bonds connect the amino and acid groups of
opposing molecules. The butyl-side chains of the molecules are connected through Van-der-Waals bonds
and are therefore much more weakly bound. It is in this region that the polymorphs are different. When
DL-norleucine undergoes a polymorphic transition, the bilayers shift with respect to each other. We apply
Molecular Dynamics (MD) simulations as a computational microscope to study these processes at the
molecular level.