Concomitant Crystallization of Glycine on Patterned Substrates: The Effect of pH on the Polymorphic Outcome

Abstract

This study demonstrates the effect of the solution pH on the polymorphic outcome of glycine by evaporation-driven crystallization from aqueous solution. More than 2000 solution droplets under identical conditions were generated using a patterned self-assembled monolayers (SAMs) substrate. Each droplet on the substrate serves as an independent crystallization trial. Glycine nucleated inside the droplets through solvent evaporation, and their polymorphic forms were identified via Raman microscopy. Three different polymorphic forms of glycine (α-, β-, and γ-forms) simultaneously crystallized at all conditions employed. The probability of producing the thermodynamically stable γ-glycine from acidic (pH 3.40) or basic solution (pH 10.10) droplets significantly increased when compared with neutral aqueous solution (pH ∼ 6.00) droplets.