The heterogeneous nucleation of pimelic acid under the effect of a template: experimental research and molecular simulation

Abstract

The nucleation experiments of pimelic acid were investigated in the absence and presence of a template. The results show that the template, malonamide, can selectively induce the nucleation of metastable form II of pimelic acid, while only stable form I of pimelic acid crystallizes under blank conditions. Furthermore, the nucleation of pimelic acid induced by a single crystal template was carried out and the induced crystals were characterized by Fourier transform infrared and micro-Raman spectroscopy. The lattice parameters and functional groups of the template and pimelic acid were analyzed, and it is inferred that functional groups play a critical role in the selective nucleation of pimelic acid. In addition, the surface structure of the template crystal was analyzed, and the result shows that the amide groups at both ends of the template molecules are exposed on the (111) and (011) faces, making these faces more likely to induce the nucleation of pimelic acid. The interaction energy, adsorption energy and mean square displacement analysis further verified the induction effect of the template faces on the pimelic acid molecules. The simulation results show that the interaction between the (111)/(011) faces and pimelic acid molecules is obviously stronger than that for other crystal faces. This study investigates the mechanism of heterogeneous nucleation at the molecular level, especially from the perspective of the effective faces, which may provide guidance about the control of polymorphs and selection of templates.