Use of additives to regulate solute aggregation and direct conformational polymorph nucleation of pimelic acid

• Published in: IUCrJ Vol. 8; no. Pt 2; pp. 161 - 167
• Main Authors: Shi, Peng, Xu, Shijie, Yang, Huaiyu, Wu, Songgu, Tang, Weiwei, Wang, Jingkang, Gong, Junbo
• Format: Journal Article
• Language: English
• Published: England International Union of Crystallography 01.03.2021
• Subjects: Additives; Agglomeration; Alkanes; Atomic properties; Carbon; conformational polymorphs; crystal engineering; crystal growth; crystal nucleation; Homology; hydrogen bonding; intermolecular interactions; Molecular chains; Molecular conformation; NMR spectroscopy; Nuclear magnetic resonance spectroscopy; Nucleation; polymorphism; Polymorphism (Crystallography); Research Letters; Self-assembly; Solvation; hydrogen bonding; self-assembly; additives; crystal nucleation; intermolecular interactions; polymorphism; crystal growth; crystal engineering; conformational polymorphs
• ISSN: 2052-2525; 2052-2525
• DOI: 10.1107/S2052252521000063

Understanding the nucleation pathway and achieving regulation to produce the desired crystals are mutually beneficial. The authors previously proposed a nucleation pathway of conformational polymorphs in which solvation and solute self-assembly could affect the result of the conformational rearrangement and further nucleation outcomes. Based on this, herein α,ω-alkanedi-carb-oxy-lic acids (DA , where represents the number of carbon atoms in the molecule, = 2-6, 8-11) were designed as homologous additives to interfere with the self-assembly of pimelic acid (DA7) to further induce the form II compound, which differs from form I only in conformation. Interestingly, longer-chain additives (DA6-11) have a stronger form II-inducing ability than short-chain ones (DA2-4). In addition, an apparent gradient of the degree of interference with solute self-assembly, consistent with form II-inducing ability, was detected by infrared and nuclear magnetic resonance spectroscopy. The calculated molecular electrostatic potential charges also clearly indicate that additive-solute electrostatic interactions gradually increase with increasing carbon chain length of the additives, reaching a maximum value with DA6-11. This novel use of additives demonstrates a direct link between solute aggregation and conformational polymorph nucleation.