Solvent effects on glycine II. Water-assisted tautomerization

The water‐assisted tautomerization of glycine has been investigated at the B3LYP/6‐31+G** level using supermolecules containing up to six water molecules as well as considering a 1:1 glycine–water complex embedded in a continuum. The conformations of the tautomers in this mechanism do not display an...

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Bibliographic Details
Published in:Journal of computational chemistry 2004-04, Vol.25 (5), p.690-703
Main Authors: Balta, Bülent, Aviyente, Viktorya
Format: Article
Language:English
Subjects:
Algorithms
DFT
Energy Transfer
glycine
Glycine - chemistry
hydrogen bond
Hydrogen Bonding
Models, Molecular
Molecular Conformation
Protons
solvation energy
Solvents - chemistry
Thermodynamics
Water - chemistry
water-mediated proton transfer
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Summary:The water‐assisted tautomerization of glycine has been investigated at the B3LYP/6‐31+G** level using supermolecules containing up to six water molecules as well as considering a 1:1 glycine–water complex embedded in a continuum. The conformations of the tautomers in this mechanism do not display an intramolecular H bond, instead the functional groups are bridged by a water molecule. The replacement of the intramolecular H bond by the bridging water reduces the polarity of the NH bond in the zwitterion and increases that of the OH bond in the neutral, stabilizing the zwitterion. Both the charge transfer effects and electrostatic interactions stabilize the nonintramolecularly H‐bonded zwitterion conformer over the intramolecularly hydrogen bonded one. The nonintramolecularly H‐bonded neutral is favored only by charge transfer effects. Although there is no strong evidence whether the intramolecularly hydrogen bonded or non hydrogen bonded structures are favored in the bulk solution represented as a dielectric continuum, it is likely that the latter species are more stable. The free energy of activation of the water‐assisted mechanism is higher than the intramolecular proton transfer channel. However, when the presumably higher conformational energy of the zwitterion reacting in the intramolecular mechanism is taken into account, both mechanisms are observed to compete. The various conformers of the neutral glycine may form via multiple proton transfer reactions through several water molecules instead of a conformational rearrangement. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 690–703, 2004
ISSN:0192-8651
1096-987X
DOI:10.1002/jcc.10422