The effect of salt additives on the glycine crystallization pathway revealed by studying one crystal nucleation at a time

• 成果类型: Article
• 署名作者: Cotting, Gabriel; Urquidi, Oscar; Besnard, Celine; Brazard, Johanna; Adachi, Takuji B. M.
• 署名单位: University of Geneva; University of Geneva
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-12251
• DOI: 10.1073/pnas.2419638122
• 发表日期: 2025-03-04
• 关键词: molecular-dynamics; polymorphic transformation; aqueous-solutions; gamma-glycine; temperature; solvent; GROWTH

摘要

Molecular-level understanding of the early stage of crystallization remains a significant challenge. For a wide range of fundamental research and applications, it is of great importance to understand the mechanism of crystal polymorph selections in different solvents or in the presence of additives. We studied glycine crystallization in aqueous solution with or without the addition of sodium chloride (NaCl), one crystal nucleation at a time, using the recently developed single-crystal nucleation spectroscopy (SCNS). It has been reported that glycine forms gamma-glycine when salt is added to aqueous solution, and the mechanism has been considered as a classical nucleation where gamma-glycine forms directly as a crystal nucleus. Our study shows that metastable polymorph beta- glycine forms first in aqueous solution both with or without NaCl through a nonclassical nucleation pathway. NaCl can stabilize the metastable beta- glycine over several hours and also prevent it from converting to alpha- glycine. Eventually gamma-glycine nucleates on the surface of beta- glycine and then grows while dissolving the mother beta- glycine. The crystal habit of beta- glycine suggests that the stabilization by NaCl occurs at its polar face. SCNS provides crucial information to accelerate the investigation of the early stage of crystallization toward the rational control of polymorphisms.