Crystal Growth in Gels from the Mechanisms of Crystal Growth to Control of Polymorphism: New Trends on Theoretical and Experimental Aspects

Mayra Cuéllar-Cruz,Vivian Stojanoff,Nuria Esturau-Escofet,Andrea Flores-Ibarra,Camila Campos-Escamilla,Roberto Arreguin-Espinosa,Omar Velásquez-González,Abel Moreno

doi:10.3390/cryst9090443

Abstract

A gel can be considered to be a two-phase (liquid and solid) system, which lacks flow once it reaches a stationary state. The solid phase is usually a tridimensional polymeric mesh, while the liquid phase is usually found in three forms: contained in great cavities, retained in the capillary pores between micelles, or adsorbed on the surface of a micelle. The influence of the use of gels in crystal growth is diverse and depends on the type of gel being used. A decrease in solubility of any solute in the liquid may occur if the solvent interacts extensively with the polymeric section, hence, the nucleation in gels in these cases apparently occurs at relatively low supersaturations. However, if the pore size is small enough, there is a possibility that a higher supersaturation is needed, due to the compartmentalization of solvents. Finally, this may also represent an effect in the diffusion of substances. This review is divided into three main parts; the first evaluates the theory and practice used for the obtainment of polymorphs. The second part describes the use of gels into crystallogenesis of different substances. The last part is related to the particularities of protein crystal polymorphism, as well as modern trends in gel growth for high-resolution X-ray crystallography.

Highlights

Instituto de Química, Universidad Nacional Autónoma de Mexico, Av
X-ray scattering (SAXS), and increasingly, cryo-electron microscopy may be made with nuclear magnetic resonance (NMR), small-angle X-ray scattering (SAXS), and increasingly, cryo-electron
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Summary

Introduction

Instituto de Química, Universidad Nacional Autónoma de Mexico, Av. Universidad 3000, Ciudad Universitaria, Ciudad de Mexico 04510, Mexico. If the pore size is small enough, there is a possibility that a higher supersaturation is needed, due to the compartmentalization of solvents This may represent an effect in the diffusion of substances. The aim of this review is to describe how the use of gels affects the polymorphism of a crystalline substance. A simple and straightforward definition could describe it as a solid-state phenomenon in which more than one crystalline form can be obtained for a single compound. This definition, may result ambiguous, given that a “crystalline form” could refer either to the network, to the crystal structure, or even to an allotrope. Crystals 2019, 9, x FOR PEER REVIEW could probably probably emerge emerge from the effects effects of polymorphism

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