FATTY-ACID INDOLE FLUORESCENT DERIVATIVES AS PROBES TO MEASURE THE POLARITY OF INTERFACES CONTAINING GANGLIOSIDES

The fluorescence emission properties of three indole derivative probes N-2-(3-indolyl)ethyl-tetradecanoyl carboxamide (N-myrTAM), 2-tetradec anoyl carboxamidyl-3-(3-indolyl)propanoic acid (N-myrTRP) and 11-N(2-[ 3-indolyl]ethylamino)-9-en-methyloxy carbonyldecenate (11-TAMundec) we re studied in solvents of different polarities in pure lysophosphatidy lcholine micelles (lysoPC) and in total brain gangliosides (TBG) micel les using steady-state and phase-modulation fluorometry. By comparing the fluorescence emission spectra in solvent mixtures with the spectra in lipid micelles it is concluded that the probes detect a more polar environment in TBG compared to lysoPC micelles. Quenching experiments with acrylamide indicate that the indole group of N-myrTRP and N-myrT AM are more exposed to the aqueous medium than the indole group of 11- TAMundec both in lysoPC and TBG micelles. Quenching of the indole fluo rescence with brominated fatty acid at the position 9-10 of the acyl c hain is in the following order: 11-TAMundec > N-MyrTAM > N-MyrTRP in l ysoPC micelles whereas in TBG micelles only 11-TAMundec fluorescence i s quenched. Based on the results of accessibility of the probes to the aqueous quencher and the dielectric constant calculated for their env ironment, we estimated the surface to core polarity gradient of the mi celles. The polarity gradient is higher in TBG micelles compared to ly soPC micelles.