Conformational polymorphism of a zinc complex with enalapril antihypertensive drug

Abstract

The crystal structure of an enalapril-Zn complex was determined by X-ray diffraction at various temperatures. The complex consisted of the drug enalapril coordinated to a Zn2+ ion by the oxygen atom of the carboxylate group in the monodentate mode. The metal ion produced a tetrahedral geometry, indicating that the enalapril complexation with a Zn2+ ion in vitro is similar to that suggested in vivo. The crystal structure of the enalapril-Zn complex showed an irreversible order–disorder structural phase transition in the temperature range of 150–200K during the cooling process. A symmetry change from C222 at room temperature (Phase I) to P212121 at 150K (Phase II) was observed. Phase I presented pronounced occupational disorder, whereas Phase II was slightly disordered.