(438c) Investigating Solute Incorporation into Crystal Kink Sites from Organic Solvents with Molecular Simulation

Crystallization from solution is ubiquitous. Solvents play a crucial role in the determination of the crystal habit and solvent-surface interactions lead to distinct morphologies for a crystal. During crystallization, solvents structured on the solute as well as growth sites are removed. Therefore, solvent structure and dynamics at the crystal-solvent interface, which depends on crystal-surface interactions, become essential for understanding the growth mechanisms. Experiments have been crucial in understanding the crystal growth from the solution, but the molecular perspective of the fundamental thermodynamics and kinetics which drive these growth mechanisms still evade the community. We employ atomistic molecular dynamic (MD) simulations and advanced sampling techniques to investigate the structure, dynamics, and energetics that determine the growth mechanism of the molecular crystals. We studied the crystallization of organic crystals from the organic solvents which recently attracted a lot of attention to obtain better crystals for pharmaceutical and fine chemicals. We also addressed the growth mechanism of etioporphyrin-I, an organic semiconductor candidate, from pure organic solvents. We found that irrespective of the solvents used the incorporation of the etioporphyrin-I happens in two steps through an intermediate state and this intermediate state is stabilized by the solvent-solute as well as solvent-crystal interaction. The proposed two-step scheme of molecular incorporation presents a new paradigm for solution crystallization that may contribute to understanding crystallization in nature and expedite the selection of solutes and solvents in the crystallization process design of organic pharmaceuticals and advanced materials.