FLUORESCENCE QUENCHING KINETICS OF PHENANTHRENE COVALENTLY BOUND TO SODIUM POLY(ACRYLATE-CO-ACRYLAMIDE) - EFFECTS OF IONIC-STRENGTH AND COUNTERION

Steady-state and time-resolved fluorescence quenching experiments were performed on a series of random terpolymers comprising sodium acrylat e, acrylamide, and a phenanthrene (Phen) derivative. The polymers in t his series had a fixed Phen loading (4 mol %) and differed in the rela tive composition of the acrylate and acrylamide monomers. Fluorescence quenching by Tl+ and Cs+ was measured as a function of ionic strength in basic aqueous solutions. The apparent bimolecular rate constant fo r quenching (k(q)) is on the order of 10(12) M(-1) s(-1) at low ionic strength and diminishes by approximately 1 order of magnitude at 14 mM added ionic strength. This behavior is independent of the particular group 1A counterion salt but does depend on the polyelectrolyte linear charge density. At relatively high quencher concentration both Tl+ an d Cs+ display negative curvature in their I-0/I Stem-Volmer plots. ''D isplacement'' experiments were carried out in which K+ is added to a s olution of the polyelectrolyte with a fixed concentration of Tl+, ther eby decreasing the fluorescence quenching. These data and membrane dia lysis imply preferential binding of the Tl+ to the polyelectrolyte (co mpared to Na+ and K+). A restricted geometry model based on Manning co ndensation theory is presented that captures many of the features of a Poisson-Boltzmann reaction-diffusion calculation of the quenching dyn amics.