Fractal Analysis of Aggregates Formed by Heating Dilute BSA Solutions Using Light Scattering Methods

Abstract

The structure of aggregates formed by heating dilute BSA solution was analyzed with the fractal concept using light scattering methods. BSA was dissolved in HEPES buffer of pH 7.0 and acetate buffer of pH 5.1 to 0.1% and 0.001% solutions, respectively, and heated at 95°C, varying the heating time t_a. The fractal dimension D_f of the aggregate in the solution was evaluated from static light scattering experiments. The polydispersity exponent τ and the average hydrodynamic radius <R_h> of the aggregates were calculated from dynamic light scattering experiments using master curves obtained by Klein et al. The values of D_f and τ of heat-induced aggregates of BSA at pH 7.0 were about 2.1 and 1.5, respectively, the values of which agreed with those predicted by the reaction-limited cluster-cluster aggregation (RLCCA) model. On the other hand, D_f of heat-induced aggregates at pH 5.1 was about 1.8, which agreed with that predicted by the diffusion-limited cluster-cluster aggregation (DLCCA) model. The dependence of <R_h> for the sample of pH 7.0 on t_a was similar to that of the polystyrene colloids reported previously.