Comparative Study of the Photophysical Behaviour of Fisetin in Homogeneous Media and in Anionic and Cationic Reverse Micelles Media

MATIAS FUNES; N. MARIANO CORREA; JUANA J. SILBER; M. A. BIASUTTI

PHOTOCHEMISTRY AND PHOTOBIOLOGY

Blackwell Publishing USA

Año: 2007 vol. 83 p. 486 - 493

0031-8655

Abstract  The 3,3?, 4?,7 tetrahydroxiflavon (fisetin) is a natural therapeutically active and  fluorescent polyhydroxyflavone, with important spectroscopic and biological behaviour. Fisetin shows dual emission, with a normal band (N) from the S1 ®S0 transition and the one generated in the excited state (PT) from the intramolecular proton transfer (ESIPT) process. The influence of different interfaces on the ESIPT process of fisetin, was investigated in reverse micelles media (RMs) made of the anionic sodium 1, 4 bis (2-ethylhexyl) sulfosuccinate (AOT) and cationic benzyl n-hexadecyl dimethyl ammonium chloride (BHDC) surfactants, in benzene. The studies were carried out by absorption, emission spectroscopy, steady-state anisotropy and time resolved fluorescence measurements. Fisetin behaviour was also investigated in homogeneous media with special emphasis in water and benzene, which are the polar core and the organic pseudofase in the RMs, respectively. In addition, the effect of concentration in benzene and the variation of the pH in water were studied. Fluorescence lifetime measurements show that, in water the ESIPT process is independent on the concentration, while in benzene it was possible to detect fluorescent aggregate species (Nas) formed in the ground state. The effect of the pH in water allowed us to identify the anionic fisetin (A-) emission. The studies in RMs show that fisetin interacts specifically with the head of the surfactants which always results in diminishing the emission of the PT. Also the formation of A- is detected particurlarly at W0 > 0. Appreciable high anisotropy values are obtained in RMs, as compared with those get in fluid homogeneous media, which are independent of the water content confirming that fisetin molecules are anchored in the anionic as well as in the cationic interfaces.