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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Stabilization of Zwitterions in Solution:gamma-Aminobutyric Acid (GABA)
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Stabilization of Zwitterions in Solution:gamma-Aminobutyric Acid (GABA)

机译：溶液中两性离子的稳定化：γ-氨基丁酸（GABA）

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摘要

The stabilization of gamma-aminobutyric acid (GABA) zwitterions in aquyeous solution is investigated at the HF/6-31+G~*,B3LYP/6-31+G~*,and MP2/6-31+G~* levels of theory using explicitly bound water molecules to model short-range solvent effects and the conductor-like screening solvation model (COSMO) to estimate long-range solvent interactions.B3LYP and MP2 yield simialr structures,realtive energies and overall trends whereas HF theory does not provide a realistic description of GABA.The only approaches yielding zwitterionic structures consistent with experiment are the application of COSMO to GABA·2H_2O or GABA·5H_2O.An accurate description of aqueous phase GABA therefore requires both explicit interaction with at least two water molecules and long-range dielectric interactions with the solvent.Both types of interaction preferentially stabilize zwitterionic over neutral structures and stabilize extended zwitterions with respect to folded conformers.No stable neutral GABA·5H_2O tautomers are obtained,suggesting that only zwitterionic forms of GABA are likely to be present in water.The extended GABA·5H_2O zwitterions are postulated to be more stable in solution than the folded conformers and it is likely that a number of zwitterionic conformations are stable in water.
机译：研究了HF / 6-31 + G〜*，B3LYP / 6-31 + G〜*和MP2 / 6-31 + G〜*浓度下γ-氨基丁酸（GABA）两性离子在水溶液中的稳定性。 B3LYP和MP2产生相似的结构，真实能量和总体趋势，而HF理论则不能提供类似的理论，即使用明确结合的水分子对短程溶剂效应进行建模，并使用类似导体的筛选溶剂化模型（COSMO）来评估远程溶剂相互作用。生成与实验一致的两性离子结构的唯一方法是将COSMO应用于GABA·2H_2O或GABA·5H_2O。因此，准确描述水相GABA既需要与至少两个水分子的显式相互作用，又需要长距离的相对于中性结构，两种类型的相互作用都优先稳定两性离子，相对于折叠构象异构体，稳定两性延伸离子。没有稳定的中性GABA·5H_2O互变异构体rs的存在，表明水中仅可能存在两性离子形式的GABA。据推测，扩展的GABA·5H_2O两性离子在溶液中比折叠的构象异构体更稳定，并且许多两性离子构象在水中稳定。水。

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