Conductance stopped-flow study of the association reactions of anionic colloidal spheres with cationic spheres and with bovine serum albumin molecules

Abstract

The equilibrium and kinetic parameters of the association reactions of anionic spheres with cationic spheres and with bovine serum albumin (BSA) are evaluated using the conductance stopped-flow technique. The forward rate constants (k_f) of the binary association between spheres of opposite charge are close to the theoretical values for the diffusion-controlled association process of neutral species. The k_f values of association between the colloidal spheres and BSA molecules are much smaller than those corresponding to diffusion-controlled rates. k_f and k_b decrease and the association constant (k_f/k_b) increases as the sphere size increases. k_f increases sharply, whereas k_b remains constant as the pH values of the mixtures decrease. These kinetic features are discussed.