Raman and solid state C-13-NMR investigation of the structure of the 1 : 1 amorphous piroxicam :beta-cyclodextrin inclusion compound

摘要

The results of a Raman and solid state C-13-NMR spectroscopic investigation aimed at studying the conformation of piroxicam (P) and its interaction with beta-cyclodextrin (beta CD) in 1 : 1 amorphous P beta CD inclusion compound are reported. The 1700-1200 cm(-1) FT-Raman and the C-13 CP/MAS NMR spectra of 1 : 1 P beta CD inclusion compound are discussed and assigned in comparison with those of the three main modifications of piroxicam (alpha, beta, and monohydrate). The FT-Raman and C-13-NMR results show that in 1 : 1 PPCD inclusion compound piroxicam mainly assumes the zwitterionic structure typical of monohydrate, even if the presence of a different structure, that is, beta form, is not excluded. Piroxicam monohydrate, differently from alpha and beta forms, is characterized by a zwitterionic structure with an internal proton transfer and an increased charge delocalization, as shown by our spectroscopic results. The charge delocalization characteristic of this zwitterionic structure gives rise to the interaction with beta CD via electrostatic and hydrogen bonds. The possibility of a host-guest interaction between piroxicam and beta CD is not excluded; the guest molecule can be accommodated in beta CD cavity. by interaction via hydrophobic bonds. (C) 1999 John Wiley & Sons, Inc. [References: 27]