FLUORESCENCE QUENCHING IN CETYLTRIMETHYLAMMONIUM CHLORIDE MICELLES AND DIOCTADECYLDIMETHYLAMMONIUM CHLORIDE GIANT VESICLES - A COMPARISON

Fluorescence quenching experiments were carried out in cetyltrimethylammonium chloride (CTAC) micelles and in dioctadecyldimethylammonium chloride (DODAC) giant unilamellar vesicles employing a wide variety of quenchers and a series of pyrene derivatives whose fluorophores can be considered to be located at different positions within the microaggregates. The quenchers employed comprise ionic (I-) and zwitterionic compounds (tryptophan at pH 6-7) and neutral compounds (oxygen, acrylamide, hydrogen peroxide, dimethylaniline, di-tertbutyl-peroxide, tert-butylhydroperoxide, desferrioxamine, and carbon tetrachloride) of widely different hydrophobicities, and the quenching rates were measured at temperatures below (293 K) and above (323 K) the vesicles' phase transition temperature. Quenching rate constants in DODAC vesicles, both above and below the phase transition temperature of the vesicles, are very slightly dependent on the employed probe, particularly when ionic or highly polar quenchers are considered. The measured quenching rates are rather similar in CTAC micelles and DODAC vesicles. These results imply that either the quenchers readily reach all parts of the bilayer of the vesicles and/or that there is very little relationship between the structure of the probe, its average location, and/or its diffusion time towards the interface. The most noticeable differences between micelles and vesicles, as well as the largest effect of temperature in DODAC vesicles, are observed for uncharged, nonpolar quenchers. These differences, as well as the increase in deactivation rate by oxygen observed in the presence of hydrophobic additives, can be related to significant changes in the extent of incorporation of neutral solutes when the temperature increases or when the bilayer is perturbed by solute incorporation. © 1992.