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Effect of amino group protonation on the carboxyl group in aqueous glycine observed by O 1s X-ray emission spectroscopy

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Abstract

The valence electronic structures of the amino acid glycine in aqueous solution were investigated in detail through X-ray emission spectroscopy at O 1s excitation under selective excitation conditions of the C[double bond, length as m-dash]O site in the carboxyl group. The X-ray emission spectra of glycine were similar to that of acetic acid (CH3COOH), suggesting a resemblance between the molecular orbitals associated with the carboxyl groups in the two molecules. The changes of O 1s X-ray emission spectra as a function of pH were investigated in detail. In addition to spectral changes due to protonation/deprotonation of the carboxyl group for lower pH-values around the pKa value (∼2.3), the spectra of glycine exhibited further changes in the higher-pH region near the pKb value of glycine (dissociation constant of amino group ∼9.5). These results show the effects of amino group protonation on the electronic state around the carboxyl group. X-ray emission spectroscopy might be a tool to investigate intramolecular interactions between functional groups in a molecule.

Graphical abstract: Effect of amino group protonation on the carboxyl group in aqueous glycine observed by O 1s X-ray emission spectroscopy

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Publication details

The article was received on 12 Dec 2017, accepted on 11 Jul 2018 and first published on 11 Jul 2018


Article type: Paper
DOI: 10.1039/C7CP08305J
Citation: Phys. Chem. Chem. Phys., 2018, Advance Article
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    Effect of amino group protonation on the carboxyl group in aqueous glycine observed by O 1s X-ray emission spectroscopy

    Y. Horikawa, T. Tokushima, O. Takahashi, Y. Harada, A. Hiraya and S. Shin, Phys. Chem. Chem. Phys., 2018, Advance Article , DOI: 10.1039/C7CP08305J

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