Ion Hydration under Pressure

Abstract

The pressure dependence of the radial distribution of water oxygen atoms around Rb+ and Br- ions in a diluted RbBr aqueous solution has been investigated by means of x-ray absorption spectroscopy at the Br and Rb K edges up to 2.8 GPa, using a large-volume high-pressure setup developed at a third generation synchrotron radiation facility. Dramatic effects in the anion hydration structure, in particular, are observed, indicating that upon increasing pressure water undergoes a structural transformation which involves considerable molecular reorientation.

Octa-Coordination and the Aqueous Ba2+ Ion

“…Barium ion directly coordinates with n=8 waters in aqueous solution, in contrast to lower hydration numbers reported earlier in experimental and theoretical studies of K + 37-39,41-44 and its analogue, Rb + . 40,[45][46][47] An interesting observation is that octa-coordinated ion binding sites in K channels appear to mimic the local hydration structure of Ba 2+ , a blocking ion, not the permeant ions, K + and Rb + .…”

Structural and electronic evolution of the As(OH)3 molecule in high temperature aqueous solutions: An x-ray absorption investigation

“…In the former case, the study of ion hydration-shell structures under high temperature and high pressure conditions gives information on the molecular reorientation taking place in the solvent, 2 and on the evolution of solvent permittivity ⑀ that controls coulombic interactions. 3 The present study belongs to the latter case where the solute under consideration is a neutral complex.…”

“…1,2 The growing interest in these processes stems from both the fundamental and applied insights that their understanding brings to the geochemical, ͑bio͒chemical, and industrial communities. It must be emphasized in the case of aqueous solutions that the interparticle interactions under elevated temperature and pressure conditions are very sensitive to the structure of the solvent and, in particular, to the hydrogen bonding strength.…”

“…Thus many studies using this tool have been dedicated to the structural characterization of the hydration of cations and anions of metals and nonmetallic elements at elevated pressure and temperature conditions. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Although the extended x-ray Absorption Fine Structure ͑EXAFS͒ analysis is widely used to get information on the structure of molecular aqueous complexes ͑see Ref. 21 and references therein͒, quantitative analysis of the x-ray Absorption Near Edge Structure ͑XANES͒ is rather new for aqueous systems.…”

Ion Hydration Under Pressure: A Molecular Dynamics Study

“…Sarma and Paul [9] performed a molecular dynamics (MD) study of the high pressure (0.8 GPa) effect on neopentane hydration and noticed an increase of hydration numbers and a reduction of hydrophobe association. One should also mention two recent investigations of the influence of pressure on ionic hydration by extended X-ray absorption fine structure (EXAFS) measurements for an RbBr aqueous solution under pressures up to 2.8 GPa [10] and for the hydration of Zn 2+ in aqueous solutions under pressures up to 2.85 GPa (by means of EXAFS combined with MD simulations) [11]. These studies have shown structural changes in the ionic hydration shells, appearing in the ion-water radial distribution functions (RDFs) by a decrease of the height of the first peak and a shift toward smaller distances.…”