Understanding the Salt-Dependent Outcome of Glycine Polymorphic Nucleation

Autor: Guangjun Han, Pui Shan Chow, Reginald B. H. Tan
Jazyk: angličtina
Rok vydání: 2021
Předmět:
Zdroj: Pharmaceutics, Vol 13, Iss 2, p 262 (2021)
Druh dokumentu: article
ISSN: 1999-4923
DOI: 10.3390/pharmaceutics13020262
Popis: The salt-dependent polymorphs of glycine crystals formed from bulk solutions have been a longstanding riddle. In this study, in order to shed fresh light, we studied the effects of seven common salts on primary nucleation of the metastable α-glycine and the stable γ-glycine. Our nucleation experiments and in-depth data analyses enabled us to reveal that (NH4)2SO4, NaCl and KNO3, in general, promote γ-glycine primary nucleation very significantly while simultaneously inhibiting α-glycine primary nucleation, thereby explaining why these three salts induce γ-glycine readily. In comparison, Ca(NO3)2 and MgSO4 also promote γ-glycine and inhibit α-glycine primary nucleation but not sufficiently to induce γ-glycine. More interestingly, Na2SO4 and K2SO4 promote not only γ-glycine but also α-glycine primary nucleation, which is unexpected and presents a rare case where a single additive promotes the nucleation of both polymorphs. As a result, the promoting effects of Na2SO4 and K2SO4 on γ-glycine do not enable γ-glycine nucleation to be more competitive than α-glycine nucleation, with γ-glycine failing to appear. These observations help us to better understand salt-governed glycine polymorphic selectivity.
Databáze: Directory of Open Access Journals
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