Temperature Effect on the Vibrational Dynamics of Cyclodextrin Inclusion Complexes: Investigation by FTIR-ATR Spectroscopy and Numerical Simulation

The vibrational dynamics of solid inclusion complexes of the nonsteroidal anti-inflammatory drug Ibuprofen (IBP) with beta-cyclodextrin (beta-CD) and methyl-beta-cyclodextrin (Me-beta-CD) has been investigated by using attenuated total reflection-Fourier transform infrared FTIR-ATR spectroscopy, in order to monitor the changes induced, as a consequence of complexation, on the vibrational spectrum of IBP, in the wavenumber range 600-4000 cm-1. Quantum chemical calculations were performed on monomeric and dimeric structures of IBP, derived from symmetric hydrogen bonding of the two carboxylic groups, in order to unambiguously assign some characteristic IR bands in the IBP spectrum. The evolution in temperature from 250 to 340 K of the CdO stretching vibration, described by a best-fit procedure, allowed us to extract the thermodynamic parameter ∆H associated to the binding of IBP with betaCDs in the solid phase. By comparing these results, Me-beta-CD has been shown to be the most effective carrier for IBP.