Characterization of the fluorescence emission properties of 7-azatryptophan in reverse micellar environments

The amino acid analogue 7-azatryptophan has attracted significant recent attention as a novel optical probe for protein structure, function and dynamics. We report here, for the first time, its fluorescence emission behavior in a membrane mimetic model system, namely reverse micelles of aerosol-OT in n-heptane, containing varying amounts of added H2O or D2O. Upon increase in the water/surfactant molar ratio from 0.5 to 50 the emission maximum undergoes a pronounced red shift (by 20 nm), which is accompanied by dramatic quenching of the fluorescence emission and sharp decrease in its average lifetime. These data are used to infer the microenvironments of the fluorophore in the reverse micelles. Furthermore, the highly sensitive dependence of the fluorescence emission parameters of 7-azatryptophan on the water content of the reverse micelles highlights its suitability as a probe for water restricted environments, with possible applications to interfacial regions of biomembranes.