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A model of primitive cation MZ+ in water is introduced in order to clarify the influence of ion charge on the hydration structure and dynamic properties of highly charged cations in aqueous solutions. A flexible nonconstrained model for water molecules is used. The considered model in the case of monovalent cation M+ reduces to the realistic model for the hydration structure of Na+. It is shown that for divalent ion M2+ the strong cation-water electrostatic interaction leads to the formation of stable structures constituted by six water molecules octahedrally arranged around the cation. The cation-oxygen attraction and cation-hydrogen repulsion modify the octahedral hydration configuration of the model cations M3+ and M4+ and additional water molecules can join the hydration shell. The increase of cation charge results in the increase of O–H bond length of water molecules in the cation hydration shell. Further increase of ion-water electrostatic interaction causes the loss of some protons from the hydration shell of cations M4+, M5+, and M6+ that is interpreted as a cation hydrolysis effect. For a correct description of this phenomenon the considered model is improved by modeling the effects of the charge redistribution between hydrolysis products, which essentially modified and stabilized the hydrated-hydrolyzed structure of cation. The influence of cation charge on dynamical properties of cation MZ+ and oxygens in its hydration shell was investigated and analyzed. [ABSTRACT FROM AUTHOR]

Abstract: Ab initio molecular dynamics simulations are applied to a study of hydration structure of a chain-like molecule containing vinyl alcohol groups -[CH2-CHOH] n - with n =4. Partial pair distribution functions and angle distributions are analyzed in order to estimate the features of the hydration shell. It is shown, that hydration process causes essential changes of mutual orientation of hydrophilic groups having on average less than two neighbor water molecules. A tendency of the hydrated poly(vinyl alcohol) chain fragment to backbone torsion is observed. [Copyright &y& Elsevier]

Abstract: Molecular dynamics calculations were carried out in order to investigate the hydration structure of uranyl in aqueous solution. The CF1 model of flexible water molecules is used. This model allows one to investigate a hydrolysis reaction for water molecules in the first uranyl hydration shell. Charge redistribution effects on hydrolysis products are also taken into account. We found five ligands in uranyl hydration shell, which is of bipyramidal pentacoordinated structure. The charge redistribution effects resulted in ligands of four water molecules and one hydroxyl, which was found closer to uranium than the other ligands. [Copyright &y& Elsevier]

Abstract: A molecular dynamics study of the influence of ion charge on hydrated–hydrolyzed structure and dynamical properties of multivalent cations in aqueous solutions is discussed. Such a study based on a model of primitive cation M Z+ in water was introduced by us in previous papers. Our investigation demonstrates a wide variety of hydrated–hydrolyzed forms of primitive cation, including aquo, hydroxo-aquo, hydroxo, oxo-hydroxo and oxo forms. The transition between these forms is defined by a value of cation charge. The influence of cation hydrolysis effects on self-diffusion coefficients and spectral densities of hindered translation motions of primitive cations and oxygens in first hydration shells of these cations is investigated and discussed. [Copyright &y& Elsevier]

Abstract: A model of a primitive cation M Z+ in aqueous solution is introduced in order to clarify the influence of ion charge on hydration structure of cations. A molecular dynamics study for this purpose was performed using a flexible non-constrained model of water molecules. It is shown that the increase of cation charge stabilized an octahedral arrangement of cation and significantly modified the intramolecular geometry of water molecules in hydration shell. For highly charged cations M4+ and M5+ the effect of deprotonation of some water molecules in hydration shell was observed. This phenomenon was treated as a cation hydrolysis. For correct description of this phenomenon the considered model was improved by introducing the effects of charge redistribution between hydrolysis products, which essentially modified and stabilized the hydrated–hydrolyzed structure of cation. [Copyright &y& Elsevier]

We made an attempt to clarify effects of the presence of high valence cations on the structure and dynamics of water molecules in aqueous solution. It is shown that the strong cation–water electrostatic interaction leads to formation of very stable structures constituted preferably by six water molecules octahedrally arranged around cation. The increase of cation charge and/or decrease of ionic size results in increase of O&z.sbnd;H bond length for molecules in cation hydration shell. Further increase of ion–water electrostatic interaction causes the loss of some protons from hydration shell, which is interpreted as hydrolysis effect. As a result of charge redistribution between the hydrolysis products the structure of cation hydration shell is essentially modified. New characteristic high frequencies are observed in spectral density of the hindered translational motion for highly charged cation and oxygens in hydration shell. [Copyright &y& Elsevier]