Molecular Mechanisms of Hematin Crystallization from Organic Solvent

Abstract

Here, we employ n-octanol to elucidate the fundamental processes of hematin crystallization from an organic solvent, identify the operational mechanisms of growth, and determine the respective control parameters. The values of the enthalpy, entropy, and free energy of the crystal–solution equilibrium suggest that octanol may structure around the hematin solute molecules and along the crystal interface. Time-resolved in situ atomic force microscopy demonstrates that hematin crystal growth strictly follows classical layer growth mechanisms. Steps propagate by the attachment of solute molecules, described by a first-order chemical rate law. The molecules reach the steps via adsorption on the crystal surface, followed by surface diffusion, and the kinetic barriers of this pathway offer additional crystallization control strategies. Solute incorporation into steps from the adjacent lower and upper terraces is strongly asymmetric, with the lower terrace contributing the major solute amount. These findings provide a foundation for the rational design of hematin crystals that may find applications utilizing their high magnetic and optical anisotropy.