Enhancement of the nucleation of protein crystals by the presence of an intermediate phase: a kinetic model

The role of an intermediate state in the kinetics of the passage between an initial and a final state is analyzed using a generic model involving one-order parameter and a sixth-order Landau-type potential. Applied to the problem of nucleation of protein crystals the model shows that the rate of nucleation can be enhanced in a large part of the state diagram by the presence of an intermediate fluid phase. Some conditions under which this enhancement can be optimized are brought out. These predictions are compared to the results of recent experimental and theoretical investigations on protein crystallization.