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Issue 8, 2013
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Comprehensive studies on the tautomerization of glycine: a theoretical study

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Abstract

The tautomerization process of glycine between the neutral (NE) and zwitterionic (ZW) forms in aqueous solution was explored theoretically using the conductor-like polarizable continuum model (CPCM) by adopting the PAULING cavity model at the B3LYP, MP2 and CCSD levels with the 6-311+G(d,p) basis set. The tautomerization of glycine is unable to be predicted satisfactorily within the equilibrated framework of the CPCM method. Instead, in this study, three plausible non-equilibrated solvation situations were assumed: (S-1) one water molecule attached to the transferring proton in the ZW moves together with the transferring proton; (S-2) one water molecule attached to the transferring proton in the ZW remains motionless at a fixed position near the NH2 fragment at the TS structure; and (S-3) proton transfer occurs without changing the position of the surrounding water molecules from their initial state, the ZW form, in the eight water clusters. Although the calculation of (S-3) failed, the Gibbs free energies of activation for tautomerization from the ZW to NE, ΔG(ZW → NE), was well consistent with the experimental findings in the hypothetical non-equilibrated solvation states of (S-1) and (S-2). This suggests that non-equilibrium solvation is essential to explain the observed experimental data.

Graphical abstract: Comprehensive studies on the tautomerization of glycine: a theoretical study

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Publication details

The article was received on 14 Aug 2012, accepted on 26 Dec 2012 and first published on 03 Jan 2013


Article type: Paper
DOI: 10.1039/C2OB26602D
Citation: Org. Biomol. Chem., 2013,11, 1407-1413
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    Comprehensive studies on the tautomerization of glycine: a theoretical study

    C. K. Kim, B. Park, H. W. Lee and C. K. Kim, Org. Biomol. Chem., 2013, 11, 1407
    DOI: 10.1039/C2OB26602D

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