Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2008
Publication Date: 1/24/2009
Citation: Talipov, S.A., Mamadrakhimov, A.A., Tiljakov, Z.G., Dowd, M.K., Ibragimov, B.T., Xonkeldieva, M.T. 2009. Zeolite-Like Crystal Structure of Dianhydrogossypol. Journal of the American Oil Chemists' Society. 86:207-213.
Interpretive Summary: NMR spectroscopy and X-ray diffraction was used to study the structure dianhydrogossypol, which is formed from gossypol by dehydration. Like gossypol, a natural product of the cotton plant, this related compound forms appears to form complexes with low molecular weight organic molecules. However, by crystallizing the compound from dichloromethane, a structure is formed that appears to have large open channels. The channels in this structure might be useful to scavenge or carry low molecular weight organic compounds. 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: Dianhydrogossypol (4,4'-dihydroxy-5,5'-diisopropyl-7,7'-dimethyl-bis(3H-naphtho[1,8-bc]furan-3-one)) was made by refluxing gossypol in m-xylene. Proton NMR confirmed that complete conversion was achieved over several hours. Single crystals were obtained by slow evaporation of the product from dichloromethane. The crystals are tetragonal with a I41/a space group, and the unit cell dimensions are a = b = 33.8265(4) Å, c = 9.1497(2) Å, V=10469.4(3) Å3, Z=16, dcalc.=1.224 g/cm3 at 100 K. The crystal structure was solved by direct methods and was refined to an R1 value of 0.0415 on 6408 reflections. Through a symmetrical 41 operation, repeating groups of four enantiomeric dianhydrogossypol molecules form helical structures that are supported by carbon and oxygen hydrogen bonds. Each helix is surrounded by four neighboring helices that are composed of molecules of the opposite enantiomer. The helices form the walls of open channels that are 5–6 Å wide and extend parallel to the cell’s c-axis. As has been found for some gossypol crystal forms, this “zeolite-like” structure might be useful for scavenging or carrying small molecules. Additional NMR studies confirm that dianhydrogossypol can be converted directly to gossypol lactol ethers in the presence of alcohols.