The Crystal Structure of the Inclusion Complex of the Sodium Salt of Piroxicam with β-cyclodextrin

The structural characterization by X-ray diffraction analysis of the title compound is reported. Crystallographic details are: C 42 H 70 O 35 °C 15 H 12 N 3 O 4 SNa·8D 2 O, triclinic, space group P1, a = 14.767(3), b = 12.237(2), c = 11.537(2)Å, α = 79.49(1), β = 110.91-(1), c = 104.61(1)°, d calc = 1.460 g/cm 3 , Z = 1, R = 0.045 for 6635 observed reflections. The crystal structure consists of head-to-tail β-cyclodextrin molecules (β-CD) linked together by piroxicam anions in infinite polymeric chains running along the c axis. In a chain each β-CD molecule takes up simultaneously two guest molecules including on the secondary hydroxyl end the benzene ring and on the primary hydroxyl end the pyridine ring of two adjacent piroxicam anions. The piroxicam anion is located with its central hydrophilic moiety at the interface between two adjacent β-CD molecules, forming with them hydrogen bonds through the enolate and amide oxygen atoms. Conformation of piroxicam is different from those observed for its neutral and zwitterionic forms. It assumes the ZZE conformation expected for the enolate. The six-coordinated sodium cation acts as a bridge between adjacent polymeric chains linking them along the b axis. This results in the formation of hydrophilic channels filled by deuterium oxide molecules.