Efeito do solvente aquoso sobre os parâmetros geométricos do íon tripolifosfato e do tripolifosfato de sódio usando dinâmica molecular de Car-parrinello

Abstract

The sodium tripolyphosphate (STP) is a salt of the anion pentavalent (P3O105-), characterized structurally by daisy thread of connections P-O-P-O-P and by molecular formula Na5P3O10. The study of the ion STP and STP in solution constitutes a valuable information, given the importance of these compounds in phosphate biochemical processes, in the kidnap of metallic cations, the ability to form complex and the versatility of formation of organic and inorganic polymers. Here, was investigated the effect of aqueous solvent on the geometric parameters of the ion STP and STP using the Car-Parrinello Molecular Dynamics (CPMD), the wave functions were expanded in terms of plane wave basis set and ultrasoft pseudopotentials of Vanderbilt with energy cutoff of 25 Ry and energy of 280 Ry was used for the expansion of the augmented charge, the temperature of ionic and electronic systems were controlled to around 300 (K) by Nosé-Hoover thermostat. The CPMD reveals that the process of aqueous solvation has influence over the bond lengths , interatomic angles and dihedral from both structures. It was observed that the water strongly interacts with these phosphatic compounds by means of hydrogen bonds, changing its physical-chemical properties. The presence of five structures of the resonance and electrostatic repulsion confers to these compounds thermodynamic instability, however, it was observed that the negative charge on the phosphate group repels eventual nucleophilic attack by water and hinders the hydrolysis, thereby giving them a great kinetics stability in aqueous solution. It was also found that the presence of the metal Na+ gives the STP a greater tendency to hydration in relation to its ion tripolyphosphate. Although the time of simulation of CPMD has been relatively short in aqueous phase, this method was effective to simulate the translation of molecular phenomena that occur in solution, since it was possible to verify the occurrence of chemical reactions, transfer of protons and the existence of strong interactions of the hydrogen bond.