Inclusion complexation of sulfapyridine with α- and β-cyclodextrins: Spectral and molecular modeling study

• Inclusion complexes of SFP with α- and β-cyclodextrin were investigated.
• SFP drug formed 1:1 complex with α-CD and β-CD at pH ∼ 6.5.
• Complex formation was confirmed by FTIR, DSC, SEM, 1H NMR, XRD and PM3 methods.
• Part of pyridine ring of SFP is present inside the CD nanocavity.
• Nanoparticles were observed from drug–CD complex in the presence of water by TEM.

The inclusion complexes of sulfapyridine (SFP) with α-CD and β-CD were investigated by absorption, fluorescence, time-resolved fluorescence, FTIR, DSC, XRD, 1H NMR, SEM, TEM and molecular modeling methods. The normal fluorescence takes place from locally excited (LE) state while twisted intramolecular charge transfer (TICT) is responsible for highly Stokes shifted fluorescence. The enhancement of TICT emission in both CDs suggesting that the inclusion process plays the major role in this emission. The spectral shifts revealed that part of pyridine ring of SFP is entrapped in the CDs cavities. TEM images confirmed round shaped nanoparticles with the average size about 20–50 nm were observed in SFP with α-CD and β-CD inclusion complexes. PM3 calculations have suggested that the large stabilization of excited singlet state of SFP with twisted conformation occurring at the amide SN bond between the electron donor group (aniline ring) and the electron acceptor group (pyridine ring).