Solvent Effects on Catechol Crystal Habits and Aspect Ratios: A Combination of Experiments and Molecular Dynamics Simulation Study

Dan Zhu,Chang Wang,Pingping Cui,Lina Zhou,Qiuxiang Yin,Hongxun Hao,Ling Zhou,Shihao Zhang,Baohong Hou,Jiayu Dai,Yaohui Huang

doi:10.3390/cryst10040316

Abstract

This work could help to better understand the solvent effects on crystal habits and aspect ratio changes at the molecular level, which provide some guidance for solvent selection in industrial crystallization processes. With the catechol crystal habits acquired using both experimental and simulation methods in isopropanol, methyl acetate and ethyl acetate, solvent effects on crystal morphology were explored based on the modified attachment energy model. Firstly, morphologically dominant crystal faces were obtained with the predicted crystal habit in vacuum. Then, modified attachment energies were calculated by the molecular dynamics simulation to modify the crystal shapes in a real solvent environment, and the simulation results were in agreement with the experimental ones. Meanwhile, the surface properties such as roughness and the diffusion coefficient were introduced to analyze the solvent adsorption behaviors and the radial distribution function curves were generated to distinguish diverse types of interactions like hydrogen bonds and van der Waals forces. Results show that the catechol crystal habits were affected by the combination of the attachment energy, surface structures and molecular interaction types. Moreover, the changing aspect ratios of catechol crystals are closely related to the existence of hydrogen bonds which contribute to growth inhibition on specific faces.

Highlights

Crystal size and shape have essential effects on downstream processing such as filtration, washing and drying for solution crystallization [1,2,3]
This study aimed to describe the solvent effects on crystal habits from the perspective of crystal–solvent interactions and surface properties, which may favor a better understanding of crystal habit distinctions, especially the aspect ratio changes of crystal shapes in solvents
The Bravais–Friedel–Donnay–Harker (BFDH) model [27] is one of the models which are initially applied to predict crystal habits, but the model lacks precision because it simulates possible crystal facets merely according to geometric factors without considering the actual chemical environment, so it was soon developed into the attachment energy (AE) model by Hartman and Bennema [28,29,30], taking into account the energies of the system on the basis of the period bond chain (PBC) theory [31]

Summary

Introduction

Crystal size and shape have essential effects on downstream processing such as filtration, washing and drying for solution crystallization [1,2,3]. Crystal properties such as flowability and bulk density [4,5] are closely associated with crystal morphology. The effect of solvents is one of the most primary factors that affects final crystal habits. In order to obtain desired crystal shapes, it is necessary to investigate solvent effects on crystal habits and aspect ratio changes

Objectives

Methods

Results

Discussion

Conclusion