Insight into the morphology and crystal growth of DL-methionine in aqueous solution with presence of cellulose polymers

Abstract

Cellulose derivatives such as hydroxyethyl cellulose (HEC), methylcellulose (MC) and hydroxypropyl methycellulose (HPMC) were employed to modify the morphology and growth of DL-methionine crystals. The methodology involved a systematic study through batch cooling crystallization, slow solvent evaporation, seeded single crystal growth, solid-state characterization, and molecular simulation. The presence of the polymeric additive, at very low concentrations (1–100 ppm), has modified the crystal shape from elongated leaf-like crystals to hexagonal plates or blocks with smaller aspect ratio. All three polymers exhibited strong retardation on crystal growth along the b-axis (length) and c-axis (width) direction. The growth inhibition degree depends on the types and concentrations of the additives, which can be ranked as HPMC > MC > HEC at same concentration. To further explore the mechanism of polymeric additives on morphology modulation and growth inhibition, Hirshfeld surface analysis, molecular electrostatic potential surface calculations, and molecular dynamic simulations of additive-crystal surface system as well as aqueous solution-crystal surface system were carried out. The molecular modeling revealed surface adsorption of additives on crystal faces via electrostatic interactions, van der Waals interactions, and hydrogen bonds. Other factors like hydrophobic interactions and steric hindrance effect of polymers also have significant impact on crystal growth inhibition.