Submitted to: Journal of Chemical Crystallography
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2004
Publication Date: 8/1/2004
Citation: Dowd, M.K., Stevens, E.D. 2004. The (-)-gossypol-2,4-pentanedione (1:2) inclusion complex. Journal of Chemical Crystallography. 34(8):559-564
Interpretive Summary: Low temperature x-ray diffraction was used to study the structure of a new crystalline solvate of (-)-gossypol, a natural product of the cotton plant. In this structure, the (-)-gossypol and solvent molecules are in a 1:2 ratio and the structure is unusual in many features. The results will be of interest to scientists working to develop products based on gossypol unusual ability to form inclusion complexes with small molecular weight molecules.
Technical Abstract: (-)-Gossypol and 2,4-pentanedione form an inclusion complex in a one-to-two molar ratio. The compound crystallizes in the tetragonal P41212 space group and has unit cell dimensions of a = b = 10.9966(7) Å and c = 60.213(4) Å. Both solvent molecules are in the enol form and occupy two distinct cavities within the structure. The first cavity is formed between pairs of gossypol naphthalene rings and contains a pair of symmetry related solvent molecules that each accepts a hydrogen bond from one of the surrounding gossypol molecules. The four molecules together form a wedged-shape assembly that is repeated throughout the cell. The assemblies stack to form columns with adjacent columns aligned parallel to form layers. Neighboring layers are oriented at 90 degree angles, which accounts for the four-fold symmetry of the space group. The second solvent cavity is located in isolated pockets that form between the layers. These solvent molecules also accept hydrogen bonds from the surrounding gossypol molecules. Although many gossypol solvates have been reported, this structure is unusual in a number of features. It is the second example of a chiral gossypol solvate and the first example of a non-conglomerate form to crystallize from a solution of chiral gossypol. It is also the first example of gossypol crystallizing in a tetragonal system and the first example of a chiral gossypol inclusion form that does not lose appreciable amounts of solvent when exposed to ambient conditions.