A comparative ab initio Study of the Isomerizations and Hydrolyses of neutral and anionic M-Pyrophosphate Complexes, with M = Ca, Zn
In this work ab initio calculations were performed onanhydrous and monohydrated gas-phase calcium and zinc dicationschelated with various anionic pyrophosphate species: H2P2O72,HP2O73 and P2O74. The cleavage of the M-pyrophosphate into a metaphosphateand an orthophosphate coordinated by the dicat...
| Autores: | , , , |
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| Tipo de recurso: | artículo |
| Estado: | Versión publicada |
| Fecha de publicación: | 2002 |
| País: | México |
| Institución: | Universidad Nacional Autónoma de México |
| Repositorio: | Redalyc-UNAM |
| OAI Identifier: | oai:redalyc.org:47546213 |
| Acceso en línea: | https://www.redalyc.org/articulo.oa?id=47546213 |
| Access Level: | acceso abierto |
| Palabra clave: | Química metal cations ab initio calculations coordination properties Pyrophosphate hydrolysis nucleophilic substitution |
| Sumario: | In this work ab initio calculations were performed onanhydrous and monohydrated gas-phase calcium and zinc dicationschelated with various anionic pyrophosphate species: H2P2O72,HP2O73 and P2O74. The cleavage of the M-pyrophosphate into a metaphosphateand an orthophosphate coordinated by the dication wasalso investigated. The studied isomerization reactions were [M ·HNP2O7](2-N) ® [HNPO4·M·PO3](2-N) where N = 0, 1, 2, and M = Ca,Zn. These reactions were also studied in the presence of one watermolecule and also with a continuum model to mimic the solvationeffects. It was found that the interaction with a water molecule stabilizesthe pyrophosphates relative to their metaphosphate isomers.Moreover, upon interacting with the dianionic complexes, the watermolecule readily breaks and produces a hydroxide anion: H2O + [M ·P2O7]2 ® [HO · M · HP2O7]2. The latter dianionic complexes resultedvirtually isoenergetic with the hydrolyzed [M · (HPO4)2]2 complexes.The results were compared to previous data of magnesiumcontainingcomplexes. This comparative analysis shows that the differencesin the structures imposed by the various cations may play animportant role in the allosteric transformations of the substrate, thatultimately promote the hydrolysis. Though not conclusive, evidencewas found that Zn2+ has a similar oxidizing power on M-pyrophosphatesas Mg2+, whereas the oxidizing power of Ca2+ is significantlylower. Nevertheless, the electronic density on the M-pyrophosphatesand on the M-phosphates turned out to be very similar for the threecations, and thus the main difference in their biochemical role wheninteracting with phosphates stems from their different coordinationproperties, that could even lead to the presence of a hydroxide anionin the first hydration shells of Mg- and Zn-pyrophosphates. |
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