Effect of beta-cyclodextrin complexation on the photochemical and photosensitizing properties of tolmetin: A steady-state and time-resolved study

The effects of P-cyclodextrin complexation on the photochemical and photose nsitizing properties of tolmetin have been investigated. Absorption, emissi on, circular dichroism and NMR measurements were used to characterize the h ost-guest complex. Nanosecond laser flash photolysis and steady-state photo lysis experiments were performed to clarify the photoreactivity of the drug in the macrocycle. The decarboxylation of the drug is markedly reduced upo n inclusion and the rate constants of the decay of the transient intermedia tes involved in tolmetin photodecomposition were slowed down due to their i ncorporation in the hydrophobic cavity. This also influenced the distributi on of the stable photoproducts. A remarkable cyclodextrin-mediated protecti on against the tolmetin-photoinduced damage on biological substrates was ob served. A rationale for these biological effects is provided.