Highly compressed water structure observed in a perchlorate aqueous solution

Abstract

The discovery by the Phoenix Lander of calcium and magnesium perchlorates in Martian soil samples has fueled much speculation that flows of perchlorate brines might be the cause of the observed channeling and weathering in the surface. Here, we study the structure of a mimetic of Martian water, magnesium perchlorate aqueous solution at its eutectic composition, using neutron diffraction in combination with hydrogen isotope labeling and empirical potential structure refinement. We find that the tetrahedral structure of water is heavily perturbed, the effect being equivalent to pressurizing pure water to pressures of order 2 GPa or more. The Mg2+ and ClO4 − ions appear charge-ordered, confining the water on length scales of order 9 Å, preventing ice formation at low temperature. This may explain the low evaporation rates and high deliquescence of these salt solutions, which are essential for stability within the low relative humidity environment of the Martian atmosphere.

Hydration of sulfobetaine dizwitterions as a function of alkyl spacer length

“…The DSB : water ratio in these samples, 1 : 30, corresponds to 15 water molecules per zwitterionic unit and so, in the solutions, all the water molecules contribute to primary solvation of the DSB molecules. This is reflected in the reduction in the waterwater N coord that show a compressed structure of bound water, similar to that recorded for liquid metal salt hydrates, 42 rather than that of bulk water usually observed because few solutes produce significant perturbation of the water structure. 18,40,41,43 Therefore, the solubilised zwitterions cause a clear rearrangement in the water present in these solutions.…”

Temperature-Dependent Segregation in Alcohol–Water Binary Mixtures Is Driven by Water Clustering

“…EPSR has previously been used to study a wide range of biologically-relevant molecules in aqueous solution. [27][28][29][30][31][32] In this paper we refer to the different atomic constituents of methanol and ethanol according to the chemical structures shown in Figure 1. Simulated boxes of molecules were constructed at the same concentration, temperature and atomic number density as the experimentally measured samples.…”

Solution structure of propane and propene dissolved in the ionic liquid 1-butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide from neutron diffraction with H/D substitution and empirical potential structure refinement modelling

“…Neutron scattering combined with isotopic substitution has become well established as a tool to study liquid structure at the atomistic scale [13][14][15]. As systems of interest become increasingly complex (including biomolecules and drugs [16], surfactant solutions [17], electrolytes and solvents [18,19], and metal-amine liquids [20]) the Empirical Potential Structure Refinement (EPSR) approach to fit models to the experimental scattering data first introduced by Soper in the mid 1990s [21], and advanced since then [22], has made it possible to routinely study structurally complex systems.…”