pH Jump: Kinetic Analysis and Determination of the Diffusion-Controlled Rate Constants

Excitation of proton-emitter Compounds such as 8-hydroxypyrene-l,3,6-trisulfonate or sulfonated β-naphthol derivatives by short, intensive laser pulses discharges protons into the Solution. These protons are readily detected by their reaction with pH indicators. The kinetics are followed by transient light absorption techniques with a time resolution of 100 ns. The observed proton cycle, protonation and relaxation of the indicator, is a sum of simultaneous \first- and second-order reactions between the various reactants. This dynamic is a complex function of all rate constants and reactant concentrations. In the present study, we employed a numerical Solution of nonlinear differential rate equations to simulate the dynamics of the observed proton cycle. This analysis permite a direct determination of the diffusion-controlled rate constants of all participating reactions with an accuracy better than 20%.