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

Abstract

The crystal structure of uncomplexed 6^A,6^C,6^E-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 ³J_¹³C–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.