Binding of cationic derivative of pyrene

pyrenemethylamine hydrochloride (PyMeA·HCl) to a polyanion

poly(2-(acrylamido)-2-methylpropanesulfonic acid) (PAMPS) in aqueous solutions was probed by the excimer fluorescence and simulated with a competitive binding equilibrium model．The relative emission intensity IE／IM of excimer to monomer displays a maximum with increasing PyMeA·HCl concentration and the binding stoichiometry for saturation binding is determined from the concentrations of PAMPS and PyMeA·HCl at the maximum．IE／IM obviously decreases with adding sodium chloride of about 10-4 mol／L into the solution due to the competitive binding of sodium and probe cations．In our binding equilibrium model

the binding of different cations on anionic polymer is considered as an equilibrated reversible process governed by the equilibrium constant．IE and IM are assumed to be proportional to the probe concentrations forming excimer and remaining individually

respectively．Calculated bound probe concentration cDL increases with total probe concentration cDO before binding saturation and the increasing rate becomes higher with higher value of the equilibrium constant．The simulated IE／IM

as the above probe concentration ratio

also shows a maximum with increasing cDO the same position as experimentally observed．By assuming a comparable binding equilibrium constant for the cation of added salt

the abrupt decrease in IE／IM observed with adding salt is reproduced by the simulation．These results indicate that the competitive binding of ionic pyrene probe on polyelectrolyte can be reasonably described by the binding equilibrium model.