Spectroscopic characterization and photochemical behavior of host-guest complexes between beta-cyclodextrin and drugs containing a biphenyl-like chromophore

The effects of the addition of beta -cyclodextrin (beta -CD) on the light absorption and emission properties and on the photoreactivity of two non-steroidal anti-inflammatory drugs, diflunisal (DF) and fenbufen (FB), containing a biphenyl skeleton, have been investigated in aqueous media. The formation of host-guest inclusion complexes with 1:1 stoichiometry was indicated by steady state absorption, induced circular dichroism, NMR and fluorescence spectroscopy. The emitting properties of DF and FB were changed by beta -CD complexation in a well-differentiated manner, in agreement with a particular sensitivity of the respective fluorescent states to the microenvironment. The interaction with the host cage is also responsible for remarkable changes in the photoreactivity of both drugs. The encapsulated molecules exhibit a significantly higher photochemical stability if compared to the free drugs. Moreover, in the case of DF, the beta -CD microenvironment influences the distribution of the stable photoproducts by controlling the fate of the photogenerated radical intermediates. A rationale for the beta -CD induced photochemical changes is proposed.