| Summary: | Gradient diffusion coefficients of BSA were systematically determined up to much higher concentration than had been reported previously, which were found to be in accordance with the theoretical predictions based on the calculations of thermodynamic and hydrodynamic coefficients via different approaches. Dynamic light scattering experiments were also conducted with the commercially significantly protein, recombinant human lactoferrin, on which no gradient diffusion coefficients had been reported before. With the experimental results, a further development of the predictive method was made via applying the Watzlawek and Nägele's equation as well as the Zick and Homsy's data to the calculations of hydrodynamic coefficients. The refined model gives the greatly improved calculations of the gradient diffusion coefficients of lactoferrin. Experiments were extended from bio-colloids to inorganic colloids to more extensively test the model. Silica was chosen to carry out the measurements. Dilute limit calculations of gradient diffusion coefficients agreed well with the experiments. However, further work is required for the gradient diffusion model over a wide range of concentration studied. A theoretical analysis depending upon the calculations of thermodynamic and hydrodynamic coefficients has been applied. The thermodynamic coefficient was determined via (i) dilute limit calculations, (ii) solution of the Ornstein-Zernike equation or (iii) cell model calculations. Furthermore, the hydrodynamic coefficient was computed via (i) dilute limit calculations or (ii) a combination of perturbation theory and the results of an exact numerical solution for an ordered system. These coefficients were then combined, according to the generalized Stokes-Einstein equation, to allow comparison between theory and experiment.
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