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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 16, Number 5
BKCSDE 16(5)
May 20, 1995 

Determination of the Proton Transfer Energies of Glycine and Alanine and the Influence of Water Molecules
Oh Young Kwon, Su Yeon Kim, Kyoung Tai No*
The proton transfer energies of gas phase glycine and alanine and those of hydrated glycine and alanine were calculated both with Hartree-Fock and MΦller-Plesset ab initio molecular orbital (MO) calculations with 6-31G** basis set. The transition states of the proton transfer of gas phase glycine was also investigated. For zwitterions, both for glycine and alanine, the water bound to -NH3+ site stabilize the complex more compared with the water bound to -CO2-. The proton transfer energy, ΔEpt, of glycine, alanine, mono-hydrated glycine, mono-hydrated alanine, di-hydrated glycine and di-hydrated alanine were obtained as 30.78 (MP2: 22.57), 31.43, 23.99 (MP2: 17.00), 24.98, 22.87, and 25.63 kcal/mol, respectively. The activation energy for proton transfer from neutral (Nt) glycine to zwitterion (Zw) glycine, Ea, was obtained as 16.13 kcal/mol and that for reverse process, Ear, was obtained as 0.85 kcal/mol. Since the transition state of the proton transfer of gas phase glycine locate near the glycine zwitterion on the potential energy surface and the shape of the potential well of the zwitterion is shallow, the zwitterion easily changed to neutral glycine through the proton transfer.
410 - 416
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