A Lennard-Jones plus Coulomb potential for Al3+ ions in aqueous solutions

Abstract

We developed a simple pair-additive Lennard-Jones plus Coulomb potential for molecular simulations of the trivalent cation Al(3+) in water which accounts reasonably well for the behavior of aluminum aqueous solutions. The model predicts an octahedral first hydration shell containing 6 water molecules and a trigonal second shell with 12 molecules on average, in good agreement with the available experimentally determined structure. The peak positions of the cation-oxygen radial distribution function are only slightly compressed compared to the x-ray structure, the hydration enthalpy is 10% too low, and the cation self-diffusion coefficient and the single-particle second rank reorientational time are in excellent agreement with inelastic neutron scattering and NMR spectroscopy data, respectively. The model also captures the essential vibrational features of the hydrated [Al(H(2)O)(6)](3+) complex. It predicts the main O-Al-O bending mode frequency to within approximately 5%, but significantly overestimates the frequency of the totally symmetric Al-O stretching mode. Overall, the accuracy of the proposed model is as good as the best available classical potentials, if not better in some aspects, with a much simpler functional form, which makes it an attractive alternative for computer simulations of Al(3+) in more complex aqueous and biomolecular systems.

The structure of water in the hydration shell of cations from x-ray Raman and small angle x-ray scattering measurements

“…1, [66][67][68][69] The SAXS data of NaCl closely resemble that of bulk water indicating that no structures that give an additional density contrast are formed. The scattering curves for MgCl 2 and AlCl 3 , on the other hand, show strongly enhanced signals at low Q and prepeaks at intermediate Q regions arising from structures formed by the cations and water in the hydration shells.…”

“…1, [66][67][68][69] In combination with the short cation-oxygen distance, this allows a higher density of ordered water molecules to be present in the hydration shells without introducing interstitial spaces such as those found in LDL water and ice. In addition, whereas the proposed LDL and HDL species in bulk water should continuously interconvert, 45,52 the hydration shells of Mg 2+ and Al 3+ are stable on a long time scale albeit with exchange of water molecules occurring.…”

“…1, [66][67][68][69] At high concentrations, solvated ions are known to form ion pairs (see, e.g., Ref. 70 for Na-Cl ion pairing).…”

Understanding the cation specific effects on the aqueous solubility of amino acids: from mono to polyvalent cations

“…Water was described by the rigid SPC/E model, 52 while the OPLS all-atom potential was applied for the amino acids 53 and for the chloride, lithium, calcium and potassium ions. 53,54 For sulfate, the force eld parameters of the second (std2) model proposed by Cannon et al 55 were used, and for the aluminum cations the force eld parameters were taken from the work of Faro et al 56 The force elds selected for the ions in this work have provided accurate description of aqueous saline solutions of amino acids, 13,14 and it has been shown that although absolute degrees of binding are somehow affected by the choice of the model, relative changes along the Hofmeister series are unchanged. 13 Nevertheless, Heyda et al 57 demonstrated that the consideration of non-polarizable and polarizable models for describing the interaction of halides with basic amino acids (Arg, His and Lys) in water leads to similar conclusions, i.e., water densities around the charged regions and the ion-specic interactions for charged and apolar regions of those amino acids were qualitatively the same.…”

Slime coating mitigation on mineral surfaces in froth flotation by saline water

“…It was concluded that the addition of ions had no influence on the rotational dynamics of water molecules outside the first solvation shell which means the effect of ions on water structure is short range. The 2nd hydration shell is normally less than 1nm (Hitoshi, 1993;Martinez, 1999;Spå ngberg, 2004;Faro, 2010). This result was used to argue that the presence of ions does not lead to an enhancement or a breakdown of the hydrogen bond network in liquid water beyond the first hydration shell of the ions.…”