Add time:07/20/2019         Source:sciencedirect.com

Cocrystal-salt continuum study is important to pharmaceutical industry, for which the empirical ΔpKa rules are not always applicable and a deep understanding is still required. In this present study, multicomponent crystals of ibuprofen (IBU) were screened and investigated based on pyridine-containing systems. Amino group was introduced in pyridine ring to examine its effect on salt/cocrystal formation. 4 new salts of IBU with 4-aminopyridine (4AP), 2-amino-5-methylpyridine (2A5MP), 3-methyl-4-aminopyridine (3M4AP) and 2,6-diaminopyridine (26DAP) were synthesized and characterized by X-ray diffraction (XRD), differential Scanning Calorimetry (DSC), Thermo gravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FT-IR). The crystal packing diagrams of three salts (S-IBU•4AP, 1:1; S-IBU•2A5MP, 1:1; RS-IBU•26DAP, 1:1) and one salt hydrate (S-IBU•3M4AP•H2O, 2:2:3) showed that the introduced amino groups are not involved in the proton transfer but play an important role in the hydrogen bond network. The ortho and para-amino groups of coformers can form ring motif to stabilize the structures. Meanwhile, the amino groups were found to enhance the electronegativity of pyridine nitrogen, to which the proton is easier to be transferred. The Hirshfeld surfaces analysis of the four new salts revealed that the structures are mainly stabilized by O⋯H, H⋯H and C⋯H interactions.

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