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

✍ Scribed by Enrico Redenti; Margherita Zanol; Paolo Ventura; Giovanni Fronza; Angiolina Comotti; Paola Taddei; Alessandro Bertoluzza

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 176 KB
• Volume: 5
• Category: Article
• ISSN: 1075-4261
• DOI: 10.1002/(sici)1520-6343(1999)5:4<243::aid-bspy5>3.0.co;2-c

✦ Synopsis

The results of a Raman and solid state 13 C-NMR spectroscopic investigation aimed at studying the conformation of piroxicam (P) and its interaction with ␤-cyclodextrin (␤CD) in 1 : 1 amorphous P␤CD inclusion compound are reported. The 1700 -1200 cm Ϫ1 FT-Raman and the 13 C CP/MAS NMR spectra of 1 : 1 P␤CD inclusion compound are discussed and assigned in comparison with those of the three main modifications of piroxicam (␣, ␤, and monohydrate). The FT-Raman and 13 C-NMR results show that in 1 : 1 P␤CD inclusion compound piroxicam mainly assumes the zwitterionic structure typical of monohydrate, even if the presence of a different structure, that is, ␤ form, is not excluded. Piroxicam monohydrate, differently from ␣ and ␤ 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 ␤CD via electrostatic and hydrogen bonds. The possibility of a hostguest interaction between piroxicam and ␤CD is not excluded; the guest molecule can be accommodated in ␤CD cavity by interaction via hydrophobic bonds.