MOLECULAR-INTERACTIONS IN CRYSTALLIZING LYSOZYME SOLUTIONS STUDIED BY PHOTON-CORRELATION SPECTROSCOPY

The concentration dependence of the diffusion coefficient of particles suspended in solution depends primarily on the occupied volume fraction and on repulsive and attractive forces. This dependency is expressed by the interaction parameter that can be assessed experimentally by light scattering measurements. In the present work we have determined the interaction parameter for the diffusion coefficient of hen egg white lysozyme under nonstationary crystallization conditions. The hydrated lysozyme monomer has a free-particle diffusion coefficient D-0 - 102 +/- 4 mu m(2) s(-1) that corresponds to a hydrodynamic radius a = 2.09 nm. It also bears a net charge of +6.4 and has a Hamaker constant, A(H) = 7.7 k(B)T, for the crystallization conditions employed. At an intermediate degree of screening, Van der Waals forces become dominant, and the behavior of lambda can be correlated with the onset of fractal cluster formation. The latter is employed as a useful index for predicting the fate of the lysozyme solution under examination.