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The aim of this study is to further the understanding of the mechanisms that govern the hydration behavior of neutral solutes, with respect to the ions' properties that are present in a solution. For that, a systematic volumetric study of saccharides (xylose, glucose and sucrose), in the presence of various electrolytes (LiCl, NaCl, KCl, Na 2 SO 4 , K 2 SO 4 , CaCl 2 , MgCl 2 , MgSO 4 ) has been carried out with density measurements at 298.15 K. From this data, the standard transfer molar volume of the saccharide Δ V ϕ , S 0 , which characterizes the hydration state of the solute, has been determined. Positive and increasing values of Δ V ϕ , S 0 with increasing electrolyte concentrations were obtained. This indicated the dehydration of the saccharide in the presence of the electrolyte, due to the predominance of saccharide/cation interactions. Concerning the influence of the cation, it was shown that saccharides are more dehydrated in the presence of divalent cations than in the presence of monovalent ones. This is because the interactions are stronger between saccharides and divalent cations, in comparison to those with monovalent cations. For a specific cation valence and molality, regardless of the anion, saccharide dehydration increases according to the following sequences: Li + < Na + < K + and Mg 2+ < Ca 2 + . These saccharide dehydration sequences have been explained by the Gibbs free energy of hydration of the cations, reflecting the cation/water interactions. For a specific cation valence, it was concluded that decreasing cation/water interactions induce the increase of saccharide dehydration. Concerning the influence of the anion, it was also observed that saccharides are more dehydrated in the presence of divalent anions than in the presence of monovalent ones. It was stated that saccharide/cation interactions are modulated by the nature of the anion. The anion impact was again attributed to its capacity to interact with water molecules. It was pointed out that anions with increasing values of Gibbs free energy of hydration cause an increase in saccharide/cation interactions or a decrease in saccharide/anion interactions. Therefore, saccharide dehydration increases. [ABSTRACT FROM AUTHOR]

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+, Mg2+, Ca2+). Conversely, the anion first hydration layer depends on the cation of the system. Unlabelled Image • Quantum mechanics is used to determine the hydration properties of ions. • The hydration properties of ions with and without counter-ions are compared. • Cl− or SO 4 2− doesn't change the first hydration layer of Li+, Na+, K+, Mg2+, Ca2+. • Conversely, the first hydration layer of Cl− or SO 4 2− depends on the cation. [ABSTRACT FROM AUTHOR]