Crystal structure of hydrated 6A,6C,6E-Tri-O-methylcyclohexaamylose and its conformation in solution

Abstract

The crystal structure of uncomplexed 6A,6C,6E-tri-O-methylcyclohexaamylose (CD-3OMe) has been determined by X-ray analysis. The structure was solved by molecular replacement methods and refined by the full matrix least-squares method to the R-value of 0.074. Cyclodextrin molecules are arranged in a herring-bone cage-type packing. Inside the cavity only two water molecules are found close to the primary hydroxyl rim. One O-methyl group of a molecule is inserted into a neighbouring host molecule from the secondary hydroxy side. The conformation of CD-3OMe was also studied in solution by NMR spectroscopy. In particular heteronuclear 3J13C–1H coupling constants through the glycosidic linkages were measured. The results obtained in deuteriated water and pyridine could be intepreted in terms of an averaged flexible conformation.