Phase solubility and FTIR-ATR studies of idebenone/sulfobutyl ether β-cyclodextrin inclusion complex

The favourable accessibility offered by sulfobutyl ether beta-cyclodextrin (SBE-beta-CD) for the complexation with idebenone (IDE) has been probed, as a function of temperature, in liquid state, by phase solubility study, and, in solid state, by FTIR-ATR technique. The phase solubility results indicated the formation of a IDE/SBE-beta-CD inclusion complex with 1:1 molar ratio (A(L) type diagram), whose apparent stability constants at T = 300, 310, and 320 K have been estimated according to the Higuchi-Connors method. The formation of the inclusion complex has been confirmed on a freeze-dried and a co-precipitated product by FTIR-ATR spectroscopy, monitoring the changes induced by complexation on some characteristic vibrational bands of IDE. Quantitative studies, performed in a wide T range, from T = 250 K to T = 340 K, allowed us to extract information on the effect of temperature on the different hydrogen-bonded environments involving host, guest, and crystallization water molecules. Again, complexation is proved to enhance the stability of the guest, at least in the explored T range.