THE DEPENDENCE OF QUININE FLUORESCENCE QUENCHING ON IONIC-STRENGTH

The Stern-Volmer constant for the quenching of quinine fluorescence by chloride ions has been Found to be markedly dependent on acid concent ration. Steady-stale and time-resolved fluorescence measurements under different acid and salt concentrations have further shown that the de crease in quenching arises from the influence of increasing ionic stre ngth on the diffusion-controlled rate constant for the bimolecular que nching process. Two possible mechanisms for this dependence are discus sed: a decrease in the intrinsic rate constant for the reaction due to the kinetic salt effect, and a decrease in the effective encounter di stance due to screening of the charges on the reactants. (C) 1996 John Wiley & Sons, Inc.