Nonclassical Nucleation Pathways and Growth Kinetics of Protein Crystallization

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While classical nucleation theory has been successful in many systems, recent studies of protein and colloid crystallization as well as biomineralization have shown nonclassical features in the early stage of nucleation. Instead of forming nuclei directly from the supersaturated solution, the nonclassical mechanism suggests an intermediate phase (clusters or a dense liquid phase) to exist between the initial solution and the final crystalline state. In practice, however, predicting the exact pathway followed by a specific system under specific conditions is still a challenge. Our recent study (Sauter, et al. J. Am. Chem. Soc. 2015, 137, 1485) serves as a proof of principle of a real-time study to identify the nucleation pathway by the details of growth kinetics. In this proposal, we aim to explore the nonclassical nucleation and growth pathway using a protein-salt model system. By performing a systematic real-time study of crystallization of several proteins in the presence of multivalent metal ions, we aim to provide systematic results on the nucleation kinetics, the role of various intermediates on nucleation and growth, and we expect to establish the relationship between the crystallization pathways and microscopic specific and nonspecific interactions.