A+B-]B REACTION FOR UNEQUAL REACTANT CONCENTRATIONS

We have studied the reaction A + B --> B ([A] << [B]) by computer simulations in 3-, 2-, and 1-dimensional lattices. We first reviewed the case of normal homogeneous lattices and then extended the study to lattice clusters below, at, and above the critical percolation threshold. The decay profiles of the minority species A were analyzed by a model of stretched exponentials of the form: I(t) approximate to exp(-C(l)t(f) + C(2)t(2f)-...). The corresponding reaction rate is then time-dependent. The analysis of the simulated decay profile was better when a higher number of terms of the series were employed. Higher-order terms are necessary when the reaction domain is more restricted. The choice of the approximation order mainly affects the calculated value of the reaction rate at long times. The exponent f was smaller when the reaction domain was more restricted, i.e., below the percolation threshold or at smaller dimensionalities. The above reaction is a model for time-correlated fluorescence quenching analyses. We compared these results with experimental data from time-resolved fluorescence measurements on pyrene decanoate incorporated in lipid vesicles (recorded with the photon counting technique), and we found that only two terms in the above stretched-exponential expression suffice to satisfactorily describe the fluorescence decay profile. The present work is useful for applications to fluorescence probing of organized molecular assemblies.