Effect of the chiral recognition process on the vibrationalproperties of (R)-, (S)- and (R,S)-ibuprofen/beta-cyclodextrins inclusion complexes

Cyclodextrins are supramolecular host systems able to encapsulate molecules in their hydrophobic cavity via noncovalent interactions. Their chiral recognition properties, not fully characterized yet, are of great relevance in pharmaceutical industry. Here, we studied how the vibrational properties are affected by the chiral recognition process, upon selection of the non-steroidal anti-inflammatory drug Ibuprofen (IBP) in its chiral (R)- and (S)-, and racemic (R, S)- forms, as model guest, and native and modified beta-cyclodextrins (beta-CyDs) as model host. The usefulness of beta-CyDs to form inclusion complexes with IBP has been investigated, in pure water, by UV absorption. Phase-solubility diagrams allowed the determination of the stoichiometry and the association constant between IBP and beta-CyDs. The changes induced, as a consequence of complexation, on the vibrational spectrum of IBP, have been studied, in solid phase, by attenuated total reflection Fourier transform i nfrared FTIR-ATR and Raman spectroscopies. The recorded spectra have been compared with the wavenumbers and IR and Raman intensities as obtained by simulation for the free and complexed guest molecule. This combined experimental-numerical approach gave crucial information on the expected different "host-guest" interactions that drive the chiral recognition process, helpful to put into evidence differences in the conformational properties of the complexes, that are retained a prerequisite for chiral recognition.