Atomic Partitioning of the Dissociation Energy of the P-O(H) Bond in Hydrogen Phosphate Anion (HPO42-): Disentangling the Effect of Mg2+

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• 作者：Ché ; rif F. Matta ; Alya A. Arabi ; Todd A. Keith
• 刊名：Journal of Physical Chemistry A
• 出版年：2007
• 出版时间：September 13, 2007
• 年：2007
• 卷：111
• 期：36
• 页码：8864 - 8872
• 全文大小：239K
• 年卷期：v.111,no.36(September 13, 2007)
• ISSN：1520-5215

文摘

This paper has three goals: (1) to provide a first step in understanding the atomic basis of the role of magnesiumin facilitating the dissociation of the P-O bond in phosphorylated biochemical fuel molecules (such as ATPor GTP), (2) to compare second-order Mller-Plesset perturbation theory (MP2) results with those obtainedat the more economical density functional theory (DFT) level for a future study of larger more realisticmodels of ATP/GTP, and (3) to examine the calculation of atomic total energies from atomic kinetic energieswithin a Kohn-Sham implemention of DFT, as compared to ab initio methods. A newly described methodbased on the quantum theory of atoms in molecules (QTAIM), which is termed the "atomic partitioning ofthe bond dissociation energy" (APBDE), is applied to a simple model of phosphorylated biological molecules(HPO₄^2-). The APBDE approach is applied in the presence and in the absence of magnesium. It is found thatthe P-O(H) bond in the magnesium complex is shorter, exhibits a higher stretching frequency, and has ahigher electron density at the bond critical point than in the magnesium-free hydrogen phosphate anion. Thoughthese data would seem to suggest a stronger P-O(H) bond in the magnesium complex compared to themagnesium-free case, the homolytic breaking of the P-O(H) bond in the complex is found to be easier, i.e.,has a lower BDE. This effect is the result of the balance of several atomic contributions to the BDE inducedby the magnesium cation, which stabilizes the dissociation product more than it stabilizes the intact modelmolecule.