Aqueous solvation of As(OH)3: A Monte Carlo study with flexible polarizable classical interaction potentials

Abstract

A theoretical study of the hydration of arsenious acid is presented. This study included ab initio calculations and Monte Carlo simulations. The model potentials used for the simulations were ab initio derived and they include polarizability, nonadditivity, and molecular relaxation. It is shown that with these refined potentials it is possible to reproduce the available experimental evidence and therefore permit the study of clusters, as well as of the hydration process in solution. From the study of stepwise hydration and the Monte Carlo simulation of the condensed phase it is concluded that As(OH)(3) presents a hydration scheme similar to an amphipathic molecule. This phenomenon is explained as due to the existence of both a positive electrostatic potential and a localized lone pair in the vicinity of As. These results are used to rationalize the known passage of As(OH)(3) through aqua-glyceroporines.

Hydration of arsenic oxyacid species

“…Testemale et al performed an X-ray absorption investigation on As(OH) 3 in aqueous solution, confirming the covalence within the As-O bonds and showing that a temperature increase opens up the O-As-O angles, following a decrease in hydrogen bonding strength. 31 A computer simulation by Hernandez-Cobos et al predicts that As(OH) 3 hydration occurs mainly at the hydroxyl groups, while the lone pair on arsenic(III) rather being surrounded by a clathrate like structure, 32 in a similar way as recently described for the hydrated sulfite ion. 33 It has been proposed that this type of hydration is the reason why As(OH) 3 has the ability to pass through aqua-glyceroporines-membrane proteins for the transportation of glycerol and urea.…”

“…33 It has been proposed that this type of hydration is the reason why As(OH) 3 has the ability to pass through aqua-glyceroporines-membrane proteins for the transportation of glycerol and urea. 32 A computer simulation of AsO(OH) 2 -by Tossel predicts one As-O distance of 1.647 Å and two distances of 1.815 Å, mean 1.759 Å, while a simulation of AsO 2 OH 2-did predict one longer distance of 1.940 Å and two shorter averaging at 1.684 Å, mean 1.769 Å, and As-O-As angles of 97-99°. 34 The same author also opens up the possibility for the formation of As 4 3 3-.…”

Theoretical study of the solvation of HgCl2, HgClOH, Hg(OH)2 and HgCl3−: a density functional theory cluster approach

“…The difference of solvation energies between both orientations is only 3.1 kcal mol À1 , thus, the formation of both structures are nearly equally favorable. This fact allows us to think that HgCl 2 may have a non-negligible dipole moment in water due to the presence of This could account for the ability of HgCl 2 to easily cross membranes, as reported for As(OH) 3 by Herna´ndez-Cobos et al 24 In order to check the validity of this cluster approach, a Born-Oppenheimer molecular dynamics simulation was carried out at the DFT level (B3PW91) starting from the most stable HgCl 2 -(H 2 O) 24 structure imposing a rather high temperature of 1000 K to check for the thermodynamic stability of this solvated structure in the gas phase. After 5 ps of thermalization, a 10 ps trajectory has been computed with the Geraldyn code to obtain the radial distribution function (g(r)) (Fig.…”

“…Both the equatorial and apical orientations previously observed for HgCl 2 were found as stable structures for the two molecules. Globally, structural and energetic differences between HgCl 2 -(H 2 O) 24 and HgClOH-(H 2 O) 24 are small. The Hg-OH bond is found to be mainly covalent in HgClOH in the gas phase, as the Hg-Cl one, and same trends appear during the solvation (i.e., bond elongations).…”

“…A Nose´-Hoover chain of thermostats 36,37 was used to control the temperature at 1000 K. Electronic structure as well as the energy gradient calculations were performed at the same level of theory (B3PW91, RECPs and basis sets) as that used in the static approach. The trajectory was simulated starting from the optimized equilibrium structure of HgCl 2 -(H 2 O) 24 without any preferred velocity vector other than the thermal energy. The 15 ps simulation took 70 days on a QuadCore dual-processor@2.8GHz running the Linux versions of Geraldyn2.1-G03.…”