Resolving the longstanding riddle of pH-dependent outcome of glycine polymorphic nucleation

Abstract

We have experimentally studied the nucleation of acidic and basic glycine aqueous solutions using in situ Raman spectroscopy and hence resolved the longstanding riddle of pH-dependent polymorphic outcome. We have found that typical inorganic acids and bases accelerate the nucleation rates of both α- and γ-glycine, with γ-glycine promoted to a greater extent hence formed preferentially over α-glycine. We hypothesize that glycine ions, readily formed in an acidic or basic environment, induce head-to-tail molecular ordering which structurally matches γ-glycine and primarily directs nucleation path from α-glycine to γ-glycine.