MEASURING AGGREGATION IN AQUEOUS ADIPIC ACID-SOLUTIONS USING A LOCK-AND-KEY PROBE MOLECULE

We report on the measurement of molecular scale self-organization of a queous adipic acid solutions near and above their saturation concentra tions. We use the steady-state and time-resolved fluorescence response s of the probe molecule 1-pyrenecarboxylic acid to elucidate informati on on precrystalline adipic acid aggregates in solution. We have used this probe molecule to ensure the proximity of the fluorescent moiety to the solution phase aggregation events of interest. Steady-state flu orescence data demonstrate the pH dependence of the chromophore respon se, with an acid dissociation constant of K-a = 1.64 x 10(-5). The flu orescence lifetime of protonated I-pyrenecarboxylic acid (HPCA) exhibi ts a discontinuous change at the saturation concentration of adipic ac id, although there is Little structural information contained in such data. The rotational diffusion behavior of HPCA reveals the presence o f aggregates of adipic acid with the fluorophore. We discuss these dat a in the context of solute local organization and the limits these dat a place on the lifetime of the aggregates.