The mixing of protein solutions with that of precipitating agents is very important in protein crystallization experiments. In this work, the interferometry images were recorded during the mixing of two proteins with different molecular weights： lysozyme of -14.6 kDa, trypsin of -23.3 kDa and pepsin of -34.8 kDa were placed in a Mach-Zehnder interferometer. The protein mo- lecular weight dependence on the competition of the transport process and kinetics at the interface was studied. The concentra- tion profiles of protein solutions were calculated to analyze the mass transfer during the mixing process. It was observed that the mass transfer process is more efficient during the mixing of proteins with higher molecular weights. In addition, the more rapid concentration changes above the interface suggest that convection may dominate the diffusion. The phenomenon of con- vection is higher in the protein solutions with higher molecular weight.
We use non-equilibrium molecular dynamics simulations to calculate the self-diffusion coefficient, D, of a Lennard Jones fluid over a wide density and temperature range. The change in self-diffusion coefficient with temperature decreases by increasing density. For density ρ＊ = ρσ3 = 0.84 we observe a peak at the value of the self-diffusion coefficient and the critical temperature T＊ = kT/ε = 1.25. The value of the self-diffusion coefficient strongly depends on system size. The data of the self-diffusion coefficient are fitted to a simple analytic relation based on hydrodynamic arguments. This correction scales as N-α, where α is an adjustable parameter and N is the number of particles. It is observed that the values of a 〈 1 provide quite a good correction to the simulation data. The system size dependence is very strong for lower densities, but it is not as strong for higher densities. The self-diffusion coefficient calculated with non-equilibrium molecular dynamic simulations at different temperatures and densities is in good agreement with other calculations fronl the literature.
