Interaction of UO₂²⁺ with sodium dodecyl sulfonate micelles based on fluorescence data

Summary

The interaction between the U(VI) and a sodium dodecyl sulfonate (SDS) micelle was studied for intensity and emission lifetime. The measurements of the uranyl ion were done in a 1M H₃PO₄ medium. The self quenching rate constant (k_sq) shows a larger value in micellar than in a SDS monomeric solution. This fact should be interpreted by micelles favoring the localized concentration of UO₂²⁺ species. Dynamic and static quenching was observed in the interaction between uranyl ion and the surfactant monomer before the induced critical micelle concentration (icmc) (1 mM) yielding a value of K_D = (134±2) ^. 10M^-1 and K_S= (16±2) ^. 10²M^-1 for the dynamic and static quenching constant, respectively. A quantitative description of the binding was obtained by monitoring the emission lifetime of the uranyl excited state as a function of the surfactant concentration (titration curve), assuming that the observed lifetime is related to a weighted fraction of rate constants for the bound and unbound species.