When an ion is inserted into a network of water molecules, the structure of the hydrogen bonds changes. Water is a polar molecule. It tends to orientate so to face its opposite charge to the ion. The group of water molecules bound to the ion is called “first hydration shell”. The orientation of the molecules in the hydration shell results in a net charge on the outside of this shell, a charge of the same sign as that of the ion in the center. The charge on the outside of the hydration shell tends to orient water molecules in the vicinity, leading to a second hydration shell. The purpose of this work is to conduct a systematic study of ion solvation, comparing positive ions of different size, namely the divalent Ca2+, Pb2+ and Cd2+. In particular, the analysis focuses on the characterization of the structural reorganization of the solvent due to the presence of the ion. To this aim, we use first principles calculations within the framework of the Density Functional Theory (DFT), i.e. an investigation at an electronic and atomistic scale, accounting for electronic polarization as well as geometrical conformations. A metal ion in aqueous solution (aqua-ion) is a cation, dissolved in water, of chemical formula [M(H2O)n]z+. The n water molecules directly bonded to the metal ion are meant to belong to the first coordination sphere. The sistems considered are small clusters, from one water molecule to the cluster containing a number of molecules equal to the coordination number. This stepwise analysis allows for an accurate detection of the structural and energy changes due to each additional water in the first hydration shell. There are many experimental and theoretical reports on the hydration of ions. More specifically, calcium raises great interest due to its role in many biological fuctions, several industrial applications (paper, rubber, plastics, paint production, and the wide occurrence in works of art).
The solvation Structure of Ca (II), Pb (II), Cd (II) in dilute aqueous solution: A first principles study
GIACOPETTI, LAURA;
2013-01-01
Abstract
When an ion is inserted into a network of water molecules, the structure of the hydrogen bonds changes. Water is a polar molecule. It tends to orientate so to face its opposite charge to the ion. The group of water molecules bound to the ion is called “first hydration shell”. The orientation of the molecules in the hydration shell results in a net charge on the outside of this shell, a charge of the same sign as that of the ion in the center. The charge on the outside of the hydration shell tends to orient water molecules in the vicinity, leading to a second hydration shell. The purpose of this work is to conduct a systematic study of ion solvation, comparing positive ions of different size, namely the divalent Ca2+, Pb2+ and Cd2+. In particular, the analysis focuses on the characterization of the structural reorganization of the solvent due to the presence of the ion. To this aim, we use first principles calculations within the framework of the Density Functional Theory (DFT), i.e. an investigation at an electronic and atomistic scale, accounting for electronic polarization as well as geometrical conformations. A metal ion in aqueous solution (aqua-ion) is a cation, dissolved in water, of chemical formula [M(H2O)n]z+. The n water molecules directly bonded to the metal ion are meant to belong to the first coordination sphere. The sistems considered are small clusters, from one water molecule to the cluster containing a number of molecules equal to the coordination number. This stepwise analysis allows for an accurate detection of the structural and energy changes due to each additional water in the first hydration shell. There are many experimental and theoretical reports on the hydration of ions. More specifically, calcium raises great interest due to its role in many biological fuctions, several industrial applications (paper, rubber, plastics, paint production, and the wide occurrence in works of art).
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