Nucleation in a simple model for protein solutions with anisotropic interactions

Area of Science:

• Computational physics and chemistry
• Soft matter physics
• Biophysics

Background:

• Understanding protein crystallization is crucial for drug development and biomaterial design.
• Protein solutions exhibit complex phase behavior, including liquid-liquid and liquid-solid transitions.
• Anisotropic interactions, such as hydrogen bonding, play a key role in protein self-assembly.

Purpose of the Study:

• To investigate the structural and thermodynamic properties of critical nuclei in protein solutions.
• To explore the influence of anisotropic interactions on nucleus formation and shape.
• To elucidate the role of metastable fluid-fluid critical points in nucleation.

Main Methods:

• A lattice analog of density functional theory was employed.
• Model parameters were chosen to mimic protein-water interactions and phase behavior.
• The geometry and ordering within critical nuclei were analyzed.

Main Results:

• Critical nuclei of the solidlike phase were predicted to have nonspherical shapes.
• Molecule alignment differed in the core and interfacial regions of critical clusters.
• The interface width and structure were significantly affected by a metastable fluid-fluid critical point.
• Increasing interaction anisotropy reduced the nucleation barrier height.

Conclusions:

• Anisotropic interactions lead to nonspherical critical nuclei in protein solutions.
• Nucleation is initiated by ordered clusters with order-disorder transitions confined to the interface.
• The findings provide insights into the fundamental mechanisms of protein crystallization.