TEMPERATURE-INDUCED STRUCTURAL AND PERMEABILITY CHANGES IN DIOCTADECYLDIMETHYLAMMONIUM BROMIDE (DODAB) VESICLES - A FLUORESCENCE INVESTIGATION USING AMINO)PHENYL]-3,3-DIMETHYL-5-CARBOETHOXY-3H-INDOLE AS A PROBE

An investigation of the temperature dependence of the fluorescence spe ctral characteristics of 2-[(p-methyl-amino) phenyl]-3,3-dimethyl-5-ca rboethoxy-3H indole (I) in aqueous micelles (sodium dodecyl sulfate (S DS), cetyltrimethylammonium bromide (CTAB)) and surfactant vesicles (d ioctadecyldimethylammonium bromide (DODAB)) is presented. The gel-to-l iquid crystalline phase transition temperature T(c), determined to be approximately 309 K (36-degrees-C) for DODAB vesicles, is in close agr eement with the values reported previously. A pretransition at 294 K ( 21-degrees-C) has also been obtained. The blue shift in the fluorescen ce maximum and the increase in bandwidth are accounted for by the disp lacement of molecule I towards the interior of the bilayer as a functi on of temperature. Arrhenius plots for the non-radiative decay process es competing with fluorescence as a function of temperature show relat ively high values for the activation energy above the phase transition temperature, indicating the displacement of molecule I to a new, more viscous, less polar site compared with its initial location in DODAB. The highest value of the activation energy in water indicates that th e decay dynamics of this molecule are different in water than in the o rganized media studied here.