Self-Aggregation of Sodium Ibuprofenate in Water. I. Deriving the Speciation Diagram from Ibuprofenate Fluorescence

The self-aggregation process of sodium ibuprofenate in water was fully characterized using both steady-state and time-resolved fluorescence techniques. Changes in the fluorescence properties of the amphiphilic ion in water were analyzed as a function of its analytical concentration, enabling the quantitative determination of the complete speciation diagram without needing external probes. The differential reabsorption model, introduced in a previous work as a key tool for the quantitative analysis of steady-state fluorescence, is here complemented by a newly developed kinetic model designed to interpret recent time-resolved fluorescence data. The integration of these two approaches enables the simultaneous retrieval of the speciation diagram and the photophysical properties of both free ibuprofenate and the micellar-like aggregates. This combined methodology offers a novel and powerful tool for analyzing the self-aggregation behavior of fluorescent amphipathic compounds.