S. Sudalai Kumar’s favorite structure is:

Clonixin (BIXGIY)

Clonixin (BIXGIY)

Source: S. Sudalai Kumar and A. Nangia, Cryst. Growth Des., 2014, 14 (4), 1865–1881

Why?

This is the first polymorphic system reported for neutral and zwitterionic polymorphism in the crystal structure data base. These zwitterionic polymorphs are rare in ampholytes and have pharmaceutical importance of high solubility and stability compared to neutral polymorphs. Several drugs are amphoteric in nature. This structural-cum-solubility study of neutral and zwitterionic polymorphs provides methods for their preparation and a comparison of solubility–stability characteristics. Normally solubility and stability are inversely related for drug polymorphs. We show that the twin characteristics of high solubility and good stability may be jointly optimized in the same zwitterionic polymorph for amphoteric drugs. The high polarity and ionic nature of acidic/ basic groups promote hydrogen bonding with water (for higher solubility) as well as a tighter crystal lattice of ionized molecules (polymorph stability). All the crystal structures were fully characterized by FT-IR, Raman and ss-NMR as well as powder X-ray diffraction line pattern. The thermodynamic relationships and phase transition between the neutral and zwitterionic polymorphs was analyzed by DSC and VT-PXRD. This study provides a new direction to crystallize ionic polymorphs of amphoteric drugs for solubility enhancement. The selective crystallization of zwitterionic forms could be possible through crystallization promoter additives.—S. Sudalai Kumar

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