Factors Affecting the Polymorphic Outcome of Glycine Crystals Constrained on Patterned Substrates

Abstract

The primary goal of crystallization process is to generate particles with controlled size, shape and solid form, and the desired chemical purity. Many different types of approaches including molecular level strategies have been devised and employed to control the final structure of crystals. One promising approach is the utilization of self-assembled monolayers (SAMs) as templates. Recently, we reported that single glycine crystals can nucleate on patterned metallic square islands, with the size and morphology of the particles controlled by the dimensions of the islands or the concentration of the solution. Herein, the effect of the solution concentration on the polymorphic outcome of glycine crystals confined to hydrophilic metallic islands is investigated. Furthermore, we examine how variations in the solvent evaporation rate can impact the polymorph distribution of glycine.

Crystallization on Self Assembled Monolayers

“…As shown in previous reports (Lee, A.Y. et al, 2005(Lee, A.Y. et al, , 2006, metastable forms ( -glycine) were consistently more frequently observed with smaller islands.…”

Concomitant Polymorphism in Confined Environment

“…With small square metallic islands (25 mm), the unstable b-form was obtained, whereas for larger islands, the solid state outcome favored the a-form. The bias toward the bform was attributed to the rapid solvent evaporation which lead to high supersaturation that favored the formation of the higher energetic metastable phase (17). Surprisingly, the gform is also observed in several instances for the different island dimensions together with the other two polymorphs as this particular modification only nucleates under acidic or basic conditions (18).…”

“…Recently, we demonstrated that multiple forms of glycine simultaneously nucleated on patterned metallic gold islands (16,17). Moreover, it was observed that the polymorph distribution was dependent on the size of aqueous glycine droplets.…”

Controlling Polymorphism in Pharmaceutical Compounds Using Solution Shearing

“…32 The evaporation rate has reportedly allowed for selection of polymorphic forms with controllable change in the crystal shape and size. 33 Confinement has been shown to be a parameter that influences polymorphism and crystallization, however confinement is a surface dominated phenomenon that cannot be effectively accomplished in a bulk crystallization system. 19 If we wish to utilize the fundamental information that polymorphism arises from confinement, then we must use a surface dominant (as opposed to volumetric) approach to crystallization.…”