Shape and size of simple cations in aqueous solutions: A theoretical reexamination of the hydrated ion via computer simulations

Abstract

The simplest representation of monoatomic cations in aqueous solutions by means of a sphere with a radius chosen on the basis of a well-defined property ͑that of the bare ion or its hydrate͒ is reexamined considering classical molecular dynamics simulations. Two charged sphere-water interaction potentials were employed to mimic the bare and hydrated cation in a sample of 512 water molecules. Short-range interactions of trivalent cations were described by Lennard-Jones potentials which were fitted from ab initio calculations. Five statistically independent runs of 150 ps for each of the trivalent spheres in water were carried out in the microcanonical ensemble. A comparison of structural and dynamical properties of these simple ion models in solution with those of a system containing the Cr 3ϩ hydrate ͓͑Cr͑H 2 O͒ 6 ] 3ϩ) is made to get insight into the size and shape definition of simple ions in water, especially those that are highly charged. Advantages and shortcomings of using simple spherical approaches are discussed on the basis of reference calculations performed with a more rigorous hydrated ion model ͓J. Phys. Chem. B 102, 3272 ͑1998͔͒. The importance of nonspherical shape for the hydrate of highly charged ions is stressed and it is paradoxically shown that when spherical shape is retained, the big sphere representing the hydrate leads to results of ionic solution worse than those obtained with the small sphere. A low-cost method to generate hydrated ion-water interaction potentials taking into account the shape of the ionic aggregate is proposed.

Quantum Mechanical and Molecular Dynamical Simulations on Thorium(IV) Hydrates in Aqueous Solution

“…In this case, the bare ion−water interaction potential is replaced by the hydrated ion−water one. The Pappalardo et al have successfully used this method to develop ab initio hydrated ion−water potentials for small and highly charged cations including Be 2+ , Mg 2+ , Al 3+ , Cr 3+ , and Zn 2+ . The validity of this approach has also been demonstrated by Bleuzen et al…”

Structure of the 70S ribosome from human pathogenStaphylococcus aureus

“…In order to locate metal ion binding sites, we calculated a difference map in Chimera by subtracting a map we simulated at 4.0 Å using our metal-free model (CC = 0.88 Å) from the original density map. Partially or fully hydrated metal ions were placed according to stereochemistry and geometry in Coot (78,79). Final minimization of coordinates, including refinement of atomic displacement parameters, were carried out in Phenix v. dev-2341 (global minimization for 7–10 macro-cycles with hydrogen atoms, with secondary structure restraints (search_method = cablam) and restraints on metal ions that were not fully hydrated).…”

Geometry, Energy, and Vibrational Frequencies of the Bis(dicyanomethylene)squarilium Dianion

“…Since our samples are necessarily macroscopic, we must accept at least the perturbations due to the presence of many other anions and of the number of cations sufficient to obtain electrical neutrality. No known BCSQ 2- salt has appreciable vapor pressure; thus, such perturbations could be minimized by choosing a bulky and univalent cation, and examining the salt in solution. There, due to the interaction of the dianion also with the solvent molecules, the long-range interactions with the other ions are less strong and regular than in a crystal.…”