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Glycine’s pH-Dependent Polymorphism: A Perspective from Self-Association in Solution
journal contribution
posted on 2017-09-11, 00:00 authored by Weiwei Tang, Huaping Mo, Mingtao Zhang, Junbo Gong, Jingkang Wang, Tonglei LiAs
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.