J. Phys. Chem. A 2010, 114, 6811–6817
6811
Temperature Effect on the Vibrational Dynamics of Cyclodextrin Inclusion Complexes: Investigation by FTIR-ATR Spectroscopy and Numerical Simulation Vincenza Crupi, Domenico Majolino, and Valentina Venuti Dipartimento di Fisica, UniVersita` degli Studi di Messina, CNISM, UdR Messina, C. da Papardo, S. ta Sperone 31, P.O. Box 55, 98166 S. Agata, Messina, Italy
Graziano Guella, Ines Mancini, Barbara Rossi,* Paolo Verrocchio, and Gabriele Viliani Dipartimento di Fisica, UniVersita` degli Studi di Trento, Via SommariVe 14, 38123 PoVo, Trento, Italy
Rosanna Stancanelli Dipartimento Farmaco-Chimico, UniVersita` degli Studi di Messina, Viale Annunziata, 98168, Messina, Italy ReceiVed: March 02, 2010; ReVised Manuscript ReceiVed: April 29, 2010
The vibrational dynamics of solid inclusion complexes of the nonsteroidal anti-inflammatory drug Ibuprofen (IBP) with β-cyclodextrin (β-CD) and methyl-β-cyclodextrin (Me-β-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 βCDs in the solid phase. By comparing these results, Me-β-CD has been shown to be the most effective carrier for IBP. Introduction Inclusion or host-guest complexes are supramolecular systems where one chemical compound (the host) has a cavity, in which molecules of a second compound (the guest) are located.1-4 The study of noncovalent forces involved in the formation of host-guest complexes is of paramount importance for the design of synthetic inclusion compounds, of new drugs and materials, of enzyme-analogue catalysts, and for many other applications. Ibuprofen (IBP, 2-[4-(2-methylpropyl)phenyl]propanoic acid, see Figure 1) is a nonsteroidal anti-inflammatory drug (NSAID) largely used for relief of symptoms of arthritis, primary dysmenorrhea, fever, and also as an analgesic, especially where there is an inflammatory component.5,6 It also has been shown to protect neurons from glutamate toxicity (implicated in Alzheimer’s, Parkinson’s, and other neurodegenerative diseases) in vitro.7 Again, its potential antifungal activity, in particular against dermatophytes8 and against several Candida species,9 has been the focus of interest. It exhibits lower toxicity with respect to other anti-inflammatory agents such as indomethacin and diclofenac sodium, which allows this drug to be used without prescription. Nevertheless, at the same time, side effects on the mucous membrane of the stomach usually accompany treatment with this drug.10 Beside this, IBP is practically insoluble in water (
