Ab Initio Molecular Dynamics Study on the Interactions between Carboxylate Ions and Metal Ions in Water

Abstract

The interaction between a carboxylate anion (deprotonated propanoic acid) and the divalent Mg(2+), Ca(2+), Sr(2+), Ba(2+) metal ions is studied via ab initio molecular dynamics. The main focus of the study is the selectivity of the carboxylate-metal ion interaction in aqueous solution. The interaction is modeled by explicitly accounting for the solvent molecules on a DFT level. The hydration energies of the metal ions along with their diffusion and mobility coefficients are determined and a trend correlated with their ionic radius is found. Subsequently, a series of 16 constrained molecular dynamics simulations for every ion is performed, and the interaction free energy is obtained from thermodynamic integration of the forces between the metal ion and the carboxylate ion. The results indicate that the magnesium ion interacts most strongly with the carboxylate, followed by calcium, strontium, and barium. Because the interaction free energy is not enough to explain the selectivity of the reaction observed experimentally, more detailed analysis is performed on the simulation trajectories to understand the steric changes in the reaction complex during dissociation. The solvent dynamics appear to play an important role during the dissociation of the complex and also in the observed selectivity behavior of the divalent ions.

Hydration Mimicry by Membrane Ion Channels

“…Radial distributions (RDFs: Figure 4) of O (water) obtained from AIMD simulations for eight metal ions in water define inner-shell structures for alkali metal ions and alkaline earth metal ions. Those AIMD results are consistent with the accurate experimental determinations of peak positions (Table 1), and with alternative studies of particular cases (136,137,138). These ions are often compared to investigate effects of the ion charges and sizes on channel behavior.…”

Ab initiomolecular dynamics studies of hydroxide coordination of alkaline earth metals and uranyl

“…Various CPMD 41,42,62,63 studies of the hydration structure of Ca 2+ calculated CN in the range 5.9 41 to 7.2 62 and Ca-O distances of 2.36 41 to 2.45 Å. 63 A BOMD study by Mehandzhiyski et al 64 found a CN of 7 with a Ca-O distance of 2.45 Å, in agreement with earlier CPMD studies.…”

“…71 Various computational methods have been used to evaluate the first shell solvation structure of Sr 2+ including DFT, 73 Quantum Mechanical/Molecular Mechanics (QMMM), 74 QMSTAT 58 as well as MD and AIMD. 41,64,75 A Sr CN of around 8 40,56,64,[76][77][78][79] is typically identified within a range of CNs between 6.7 41 and 9.8 47 and Sr-O distances of 2.58 40 to 2.69. 58 A recent paper by D'Angelo et al 79 combined experimental and computational techniques to investigate the coordination shell of Sr 2+ using X-ray absorption near-edge spectroscopy (XANES) of [Sr(H 2 O) 8 ](OH) 2 , MD and CPMD.…”

“…The authors concluded that a CN of 8 with a first shell Sr-O distance of 2.6 Å was the most accurate description, reporting that the 2.72 Å bond length calculated with CPMD was inaccurate compared to their classical simulations and other AIMD literature. 41,75 A BOMD study by Mehandzhiyski et al 64 included a DFT-D2 dispersion correction to better model the interactions of the water molecules, something absent from earlier investigations and found a CN of 7.6 with 2.60 Å Sr-O first shell distance. 64 EXAFS, 80,81 High Energy X-ray Scattering (HEXS), 82 High Field NMR, 83 XAFS, 84,85 X-Ray Scattering 86 and XANES 87 have been used to probe the solvation structure of aquo complexes of UO 2…”

Computer simulations of alkali-acetate solutions: Accuracy of the forcefields in difference concentrations

“…Ab initio molecular dynamics of ions in solutions can be performed, and many such studies have been reported (e.g., [48][49][50][51][52] ). Unfortunately, such simulations are limited to small systems and short periods.…”