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.

中文翻译：

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甘氨酸的pH依赖性多态性：溶液中自缔合的视角

甘氨酸（Gly）作为一种简单的氨基酸，其多态性是pH依赖性的。通常从pH在4到9之间的水溶液中获得α形式，而在较低或较高的pH下产生γ。人们争论在水中形成环状的氢键二聚体可能是形成α形式的可能原因。为了进一步了解pH依赖的多态性，我们当前的研究利用NMR，FTIR和电子计算方法研究了宽pH范围内水溶液中Gly的自缔合。结果表明，甘氨酸分子在水中形成开放的，非环状的氢键二聚体。揭示了二聚化在pH为4和8之间变得显着，但是在两个pH极限下仍然微不足道。