Comparative study of the behaviour of fisetin in homogrneous medium and in reverse micelles

M. FUNES; N. M. CORREA; J. J. SILBER; M. ALICIA BIASUTTI

Lisbon-Portugal

Congreso; MAF9 9th Internacional Conference on Methods and Applications of Fluorescence Spectroscopy, Imaging and Probes; 2005

The 3,3’, 4’,7 tetrahydroxiflavon (Fisetin) is a fluorescent molecule which has inhibitory action with protein kinase and the HIV1 proteinase. Even when reverse micelles (RM) constitute an oversimplified model for biological membranes, the amphipatic essence is present in this systems. In this sense, the investigation of this probe in organized medium constitutes an important topic in order to understand its behaviour in biological media. The study has been done in homogeneous media with special emphasis in water and in benzene, which are the polar core and the organic pseudofase in the RM, respectively. The surfactants utilized were the anionic sodium 1, 4 bis (2-ethylhexyl) sulfosuccinate (AOT) and  the cationic benzyl n-hexadecyl dimethyl ammonium chloride (BHDC). The studies have been done by using absorption spectroscopy, flurescence and fluorescence anisotropy as well single photon counting techniques. The emission spectrum of fisetin shows two bands, the normal one (N) from S1 ®S0 and the other one called T, generated from proton transfer in the excited state. The possibility that the proton transfer occurs also in the ground state as well the possible interactions or association was investigated in water and in benzene. Likewise, temperature effects, which can give aditional information related with hydrogen bond interactions in the ground state, have been performed. The behaviour by varying fisetin was different in water as compared with benzene. An association process between fisetin molecules was found in benzene which does not occurs in water. In RM the experiments were done by varying the [surfactant] at W(=[H2O]/[Surfactant]) and changing W at constant [surfactant]. In AOT micelles, from the fluorescence results an interaction between fisetin and the polar head group of AOT can be propoused. From single photon counting measurements the monoexponential fit obtained in water allows as to assign the fluorescence lifetime to the N specie. Depending on the [fisetin], monoexponential or biexponential behaviour was obtained in benzene. In the later case, the fluorescence decay times can be assigned to the two species present in this solvent. In the RM the fitting are always biexponential but the fluorescence decay times contributions depend on the surfactant concentration, W, as well the charge of the surfactant. In all systems fluorescence anisotropy were used in order to relate the anisotropy values with the microviscocity of the medium as well the volume of the rotating unit in each media.