Investigation of ions hydration using molecular modeling

Abstract

Ion hydration phenomena are of great interest in the fields of physics, chemistry, biology, geochemistry and environment. However, few studies using identical calculation methods to characterize the hydration properties of ions in water and in electrolytic systems are available. Hence, it is difficult to compare the hydration properties of ions when they come from different methods. The objective of this work is, therefore, to use a unique approach to compare the hydration properties of ions in pure water and in presence of counter-ion using a quantum mechanical method, the Density Functional Theory (DFT). For this purpose, a methodology based on the decomposition of the system's energy is described and implemented in this study. In the first part, quantum mechanics calculations are used to determine the hydration properties of ions, without counter-ion, in presence of water molecules. In the second part, the hydration characteristics of solutes in systems containing ions, counter-ions and water molecules are studied. Results show that the presence of an anion (Cl − or SO 4 2−) does not cause structural and energetic changes in the cation first hydration layer (Li + , Na + , K + , Mg 2+ , Ca 2+). Conversely, the anion first hydration layer depends on the cation of the system.

Intrinsic Contributions of 2′‐Hydroxyl to the Hydration of Nucleosides at the Monomeric Level

“…As shown in Figure 5 f, perhaps this is due to the decreased chain–chain interactions that fail to be arranged in order, such as those in 1 in H 2 O, and form numerous spiny and fibril structures, as observed in Figure 5 a. The above results further confirm the effects of ion hydration, which modifies water molecules around the ions and plays a broad role in many natural processes, [23] especially because 2 and 3 , without hydration in the crystals, fail to display any special superstructures. Previous studies have revealed that slight adjustments to the water molecules, especially the three water molecules highlighted in Figure 5 g, are triggered by Na + , [24] which suggests that, in PBS, with Na + as the dominant cation, the trihydrol is undoubtedly modified by Na + .…”

Advances in the Understanding of the Transfer of Saccharides through NF Membranes in the Presence of Electrolytes by Coupling Quantum Mechanics and Thermodynamic Methods

“…In our previous works, the solute hydration properties (ions and saccharides) in pure water and in mixture were studied via a full geometry optimization using the DFT method [ 24 , 25 , 26 ]. First, the ion coordination number, CN , which is defined as the number of water molecules directly bonded to the central ion in its solvation first layer, was determined [ 25 ]. Then, the number of interactions between the cation and the oxygen, n inter S/C+ , defined as the number of oxygen belonging to the saccharide in direct interaction with the ion, was calculated [ 26 ].…”

“…Then, the number of interactions between the cation and the oxygen, n inter S/C+ , defined as the number of oxygen belonging to the saccharide in direct interaction with the ion, was calculated [ 26 ]. Results concerning the ion coordination number and the number of interactions between glucose and different cations are given in Table 5 [ 25 , 26 ]. In saccharide/cation/water systems, results showed that saccharides are all the more dehydrated as the number of saccharide/cation interactions increases, n inter S/C+ [ 26 ].…”

“…More recently, the interactions in saccharide/electrolyte systems were also determined at the microscopic scale using a theoretical method (DFT, theory of density functionality). First, the computation of the ion hydration properties in water confirmed that the presence of an anion (Cl − or SO 4 2− ) does not lead to a change in the first cation hydration layer (Na + , K + , Mg 2+ and Ca 2+ ) [ 25 ]. Considering this last point, the saccharide/electrolyte interactions have been characterized in saccharide/cation/water systems showing that in such systems, cations and saccharides are both dehydrated [ 26 ].…”

“…The envisaged methodology is based on the comparison of the hydration properties obtained by experimental and theoretical approaches (volumetric properties from a thermodynamic method and quantum mechanics data) with the mass transfer of saccharides through an NF membrane. Thus, correlations between the solute hydration properties obtained at different scales [ 23 , 24 , 25 , 26 ] and the mass transfer parameters, which characterize the impact of the electrolyte on the saccharide transfer, are investigated to improve the understanding of the impact of the nature (cation, anion, size, valence, etc.) and the concentration of the ions.…”