The crystal structure of the inclusion complex of the sodium salt of piroxicam with beta-cyclodextrin

The structural characterization by X-ray diffraction analysis of the title compound is reported. Crystallographic details are: C42H70O35. C15H12N3O4 S Na . 8D(2)O, triclinic, space group pi, a=14.767(3), b = 12.237(2), c=11.53 7(2) Angstrom, alpha = 79.49(1), beta = 110.91-(1), c=104.61(1)degrees, d(c alc)=1.460g/cm(3) Z=1, R=0.045 for 6635 observed reflections. The crystal s tructure consists of head-to-tail beta-cyclodextrin molecules (beta-CD) lin ked together by piroxicam anions in infinite polymeric chains running along the c axis. In a chain each beta-CD molecule takes up simultaneously two g uest molecules including on the secondary hydroxyl end the benzene ring and on the primary hydroxyl end the pyridine ring of two adjacent piroxicam an ions. The piroxicam anion is located with its central hydrophilic moiety at the interface between two adjacent beta-CD molecules, forming with them hy drogen bonds through the enolate and amide oxygen atoms. Conformation of pi roxicam is different from those observed for its neutral and zwitterionic f orms. It assumes the ZZE conformation expected for the enolate. The six-coo rdinated sodium cation acts as a bridge between adjacent polymeric chains l inking them along the b axis. This results in the formation of hydrophilic channels filled by deuterium oxide molecules.