Two Concomitant Polymorphs of a Supramolecular Model of the Asp···His···Ser Catalytic Triad

The supramolecular chemistry and crystal structures of two concomitant polymorphs (1 and 2) of a
1:2:2 complex between betaine, imidazole, and picric acid are reported. Cocrystallization of these complexes gives
discrete aggregates composed of five different molecules joined by four N−H···O and four C−H···O hydrogen bonds.
These interactions define a supramolecular unit with a unique composition, structure, and connectivity between
the molecular components that is common to both polymorphs despite considerable differences in crystal packing.
The network of hydrogen bonds between betaine, imidazole, and picric acid mimics the connectivity present in the
Asp···His···Ser catalytic triad and serves as a structural model for hydrogen bonding in the active site of serine
proteases.