title: Comprehensive studies on the tautomerization of glycine: a theoretical study.
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 NH(2) 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.
authors: Department of Chemistry, Inha University, Incheon 402-751, Korea.
authors: Chang Kon
authors: CK
authors: Kim
authors: Byung-Ho
authors: BH
authors: Park
authors: Hai Whang
authors: HW
authors: Lee
authors: Chan Kyung
authors: CK
authors: Kim
mesh_terms: D005998:Glycine / Q000031:analogs & derivatives / Q000138:chemical synthesis* / Q000737:chemistry; D011789:Quantum Theory
chemical_list: D005998:Glycine