(321ac) The Use of Hard-Core Two-Yukawa Potential in Imac for Prediction of Diffusion Coefficients

Dispersion systems such as micelle, colloid and microemulsion systems are of great importance in a variety of technological applications. Enzymes are charged macromo-lecular compounds that can be treated as colloid particles, and they play an important role in physiological reactions of human and animals. An increasingly important operation in biotechnology industry is the separation and purification of proteins, where the degree of separation, purity and yield of a particular protein is highly influenced by the media properties, and the diffusion coefficient plays a significant role in these properties. Moreover, it is crucial to have some knowledge of diffusion dependence on pH and concentration, because the biological fluids in such process are concentrated solutions under a wide range of pH values. However, the diffusion coefficients are studied much less than it is needed, due to the difficulty both in theory and experiment. In general, colloids are composed of solvent, dispersed particles and electrolytes. The dispersed particles immersed in the continuum are surrounded by an electric double layer, where one layer id formed by the charge in the surface of the particles and the other layer is formed by the excess of oppositely charged ions in the solution. Theoretically the diffusion coefficients of charged globular proteins in aqueous electrolyte solutions can be predicted by using the generalized Stokes-Einstein equation. In this method, the sedimentation coefficient and the osmotic pressure may be known in advance, but they can also be determined by several empirical correlations. The sedimenetation coefficient for completely ordered suspensions of spheres can be estimated, among others, by the correlations developed by Zick and Homsy [1] and by Happel and Brenner [2], both showing great accuracy. The osmotic pressure for proteins or other electrostatically stabilized colloids may be calculated accurately via use of the integral equation, Poisson-Boltzman (PB) cell model based on the Yukawa potentials [3], using the mean spherical approximation (MSA), which it can give an analytical solution and an explicit equation of state (EOS) . In the PB cell model, the osmotic pressure includes the contributions from electrostatic interactions, London-van der Waals forces and configurational entropy. In a previous work we determined the diffusion coefficient of dilute aqueous solutions of Catalase in IMAC at different pH values by dynamic methods. The results obtained shown that diffusion coefficient depends on pH. The purpose of this work is to establish a predictive method for the concentration and the pH dependence of the diffusion coefficient as a function of the main physicochemical conditions. We investigate the diffusion coefficient of Catalase in aqueous electrolyte solution by means of the generalized Stokes-Einstein equation, where the required concentration dependence of the osmotic pressure is described by the MSA solution of the hard-core two-Yukawa potential. REFERENCES [1] A.A. Zick and G.M. Homsy, ?Stokes flow through periodic arrays of spheres?, Journal of Fluid Mechanics, 1982, 115, 13-26 [2] J. Happel and H. Brenner, ?Flow relative to assemblages of particles?. In Low Rey-nolds number hydrodynamics. 1973, pp. 358-430. The Netherlands: Noordhoff Interna-tional Publishing [3] D.M. Duh and L. Mier-Y-Terán, ?An analytical equation of state for the hard-core Yukawa fluid?, Molecular Physics, 1996, 3, 373-379