Abstract
The nucleation of glycine from aqueous supersaturated solution has been studied using non-photochemical laser-induced nucleation (NPLIN), ultrasound (sonocrystallization), and mechanical shock of sample vials. It was found that at higher supersaturation, samples were more susceptible to nucleation and produced more of the γ-glycine polymorph. The results are described in terms of a mechanism common to all three nucleation methods, involving the induction of cavitation events and pressure shockwaves. The switch in preference from α- to γ-glycine was observed to occur over a narrower range of supersaturation values for NPLIN. We attribute this to induction of cavitation events with higher energies, which result in higher localized pressures and supersaturations. Experiments on NPLIN using circularly versus linearly polarized light showed no evidence for binary polarization switching control of glycine polymorphism.
Highlights
From a fundamental scientific viewpoint, polymorphism in solids can pose a challenge
Samples exposed to sonocrystallization and mechanical shock show similar nucleation fractions, and these methods were more effective than nonphotochemical laser-induced nucleation (NPLIN) at S = 1.4
We focus on two observations that stand out from the results: (1) the results for sonocrystallization, nucleation by mechanical shock, and NPLIN show similar trends in fractions of samples nucleated as a function of supersaturation, they are not identical; (2) the results do not reproduce the polarization switching effect for glycine as reported by Garetz and co-workers
Summary
From a fundamental scientific viewpoint, polymorphism in solids can pose a challenge. Predicting different structural forms and their relative thermodynamic stabilities by computational methods is difficult. Each polymorph has different physical properties, e.g., morphology and solubility. There is the puzzle of so-called disappearing polymorphs, i.e., solid forms that once synthesised, are difficult or impossible to reproduce.[1] Polymorphs are complicated from an economic perspective. For prospective active pharmaceutical ingredients, industry puts significant resources into gathering physical data and finding polymorphs, to obtain ideal formulations and to protect intellectual property
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