The Structure of the Cyclodextrin Complex. IV. The Crystal Structure of α-Cyclodextrin–Sodium 1-Propanesulfonate Nonahydrate

Abstract α-Cyclodextrin, which is a cyclic oligosaccharide consisting of six d-glucose residues, forms a 1 : 1 complex with sodium 1-propanesulfonate. The crystal structure was determined by the X-ray method. The crystal is orthorhombic, and the space group is P21212 with cell dimensions of a=21.608(2), b=16.700(2), and c=8.302(1) Å, and Z=2. The structure was solved on the basis of 2219 diffractometer data and refined by the block-diagonal leastsquares method to the final R-value of 0.077. The α-cyclodextrin molecule is nearly hexagonal with diagonal distances of 8.40–8.59 Å between the glycosidic oxygen atoms. The framework of the crystal is built up of a stack of α-cyclodextrin rings along the c axis in head-to-tail arrangement, with channel-type structure. The adjacent α-cyclodextrin molecules along the channel are linked by six O(3)···O(6) hydrogen bonds. The guest 1-propanesulfonate anions are located in channels, having statistical disorder. The primary hydroxyl groups of α-cyclodextrin exhibit gauche-trans conformation, and they form hydrogen bonds with the sulfonato group resulting in oxygen-oxygen distances of 2.72–2.80 Å. The propyl group is in contact with the O(2), O(3) side of the α-cyclodextrin ring. The sodium ion is located outside the channel, and is surrounded by five oxygen atoms which form a distorted trigonal bipyramid.