Glycine’s pH-Dependent Polymorphism: A Perspective from Self-Association in Solution Weiwei Tang Huaping Mo Mingtao Zhang Junbo Gong Jingkang Wang Tonglei Li 10.1021/acs.cgd.7b00969.s001 https://acs.figshare.com/articles/journal_contribution/Glycine_s_pH-Dependent_Polymorphism_A_Perspective_from_Self-Association_in_Solution/5406982 As a simple amino acid, glycine (Gly)’s polymorphism is pH-dependent. The α form is typically obtained from aqueous solution between pH of 4 and 9, while the γ is produced at either lower or higher pH. Formation of cyclic, hydrogen-bonded dimer in water is debated as a possible cause for the formation of the α form. To further understand the pH-dependent polymorphism, our current study examined the self-association of Gly in aqueous solutions under a wide range of pH, utilizing NMR, FTIR, and electronic calculation. The results indicate that glycine molecules form open, not cyclic, hydrogen-bonded dimers in water. It is revealed that the dimerization becomes significant between pH of 4 and 8 but remains trivial at the two pH extremes. The apparent connection between the pH-dependent polymorphism and self-association in solution implies that formation of the α form is driven by the dimerization, and moreover, charged molecular species at the extreme pH facilitate stabilization of γ nuclei. 2017-09-11 00:00:00 FTIR pH-dependent polymorphism formation glycine molecules form NMR α form solution