title: Influence of structure on the spectroscopic properties of the polymorphs of piroxicam.
abstract: The complete (13)C NMR chemical-shift tensors for the carbon sites of the two polymorphic forms (P(I) and P(II)) and the monohydrate form (PM) of the analgesic drug, piroxicam, are reported. The NMR parameters (isotropic chemical shifts, chemical-shielding anisotropies and asymmetries, and dipolar couplings), X-ray powder diffraction, and density functional calculations of piroxicam are analyzed in terms of hydrogen bonding and structure. The integration of all the data gives an improved model of the local solid-state structures of the polymorphs. In particular, the solid-state NMR spectra demonstrate that the asymmetric unit of the monohydrate, PM, contains two zwitterionic piroxicam molecules.
authors.affiliation: State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou, Gansu, 730000, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Liu
authors.forename: Wei David
authors.initials: WD
authors.lastname: Wang
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.forename: Shi
authors.initials: S
authors.lastname: Bai
authors.forename: Cecil
authors.initials: C
authors.lastname: Dybowski
mesh_terms: D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000737:chemistry; D006860:Hydrogen Bonding; D007477:Ions; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010894:Piroxicam / Q000737:chemistry* / Q000145:classification
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D007477:Ions; D010894:Piroxicam