Microhydration of Protonated Glycine: An ab initio Family Tree

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• 作者：Catherine Michaux ; Johan Wouters ; Eric A. Perpè ; te ; Denis Jacquemin
• 刊名：Journal of Physical Chemistry B
• 出版年：2008
• 出版时间：February 28, 2008
• 年：2008
• 卷：112
• 期：8
• 页码：2430 - 2438
• 全文大小：195K
• 年卷期：v.112,no.8(February 28, 2008)
• ISSN：1520-5207

文摘

The incremental hydration of the glycine cation is investigated using an ab initio approach fully correctingfor basis set superposition errors and explicitly incorporating electron-correlation effects. Structures withzero to four surrounding water molecules have been determined. It is demonstrated that the successiveaggregates follow a Darwinian family tree, the most stable complexes systematically belonging to the samebranch of the tree. In strong contrast with neutral glycine, the direct hydrogen bonding to the glycine cationis favored over bridging water structures. The agreement between experimental and theoretical hydrationenthalpies and Gibbs free energies is impressive, as ab initio estimates almost systematically fit the experimentalerror bars. For GlyH⁺-(H₂O) and GlyH⁺-(H₂O)₃, we show that two structures are generated by theexperimental setup. The present approach also resolves most of the previous theory/experiment discrepanciesand provides patterns for the evolution of the vibrational spectra: a decrease of the hydrogen-bond stretchingfrequency indicating second-shell water molecules. Additionally, the impact of bulk solvent solvation isinvestigated, as four discrete water molecules still do not fully hydrate the protonated glycine.