Differentiating impact of the AOT-stabilized droplets of water-in-octane microemulsions as examined using halogenated fluoresceins as molecular probes

The stepwise ionization H2R ⇄ HR− ⇄ R2 − of six halogenated fluorescein dyes was studied by vis spectroscopy. The 'apparent' pKaa values were determined in the reversed Aerosol OT (AOT) microemulsion in n-octane at a water:surfactant ratio W = 20 and ionic strength of the dispersed aqueous phase at 0.05 M. An expressed shift of the tautomeric equilibria of a neutral (molecular) H2R form of dyes toward colorless lactone was registered on going from water to the reversed AOT microemulsions. The consideration of the Ka1a/Ka2a ratios of fluorescein dyes in dispersed water pools against those in an aqueous solution allowed the revelation of the essential differentiation impact of the interior of AOT-stabilized droplets on acidity strength. This phenomenon is caused by the peculiarities of the location of the dye species in water pools and by the specific state of dispersed water inside the microdroplets.