Interactions in systems with short-range attractions and applications to protein crystallisation

The problem of phase behaviour of solutions of globular proteins is approached by means of a Hard Core Yukawa fluid model with short-ranged attractions. We have determined the phase behaviour of this model system for different well widths, using a variety of high quality methods. The essential phase behaviour of systems with short-ranged attractions is reproduced. The typical phase behaviour of solutions of globular proteins is well represented by the Hard Core Yukawa fluid with short-ranged attractions. The formation of amorphous precipitates in protein crystal growth experiments is identified on our model phase diagram with the formation of an attractive glass. As the range of attraction is decreased, the formation of an attractive glass state dominates the phase behaviour in the meta-stable regime above the critical point. We show how the addition of a long-ranged attraction, in the Two-Yukawa model, has the effect of eliminating the formation of attractive glass, while preserving the equilibrium features of the short-ranged attractive system. This opens the possibility of using attractive long-range interactions to avoid the formation of an attractive glass state.