Solvation of arsenate anion: combined quantum mechanics and molecular dynamics based investigation

Abstract

ABSTRACTArsenate, a toxic chemical, is found in soil to drinking water and may interfere with the functions of phosphate in living organism. Despite enormous importance, its hydration is poorly understood. The calculated equilibrium radial distribution function between arsenate and water oxygen atom based on molecular dynamics simulation by employing mean-field polarisable water model is found to consist of three peaks. We also observe an extended hydration shell of 0.9 nm. Based on ωB97X-D/Aug-cc-pvtz level of theory, it is observed that the lower arsenate water clusters, AsO43−.nH2O (n = 1–8) are formed by various types of arsenate–water and water–water hydrogen bonding interactions. We observed that the decay of the arsenate–water hydrogen bond auto correlation function can be excellently fitted to double exponential curve. The calculated life times of arsenate–water hydrogen bonds are 366.09 and 181.63 ps at temperatures 298 and 310 K, respectively. The potential of mean force (PMF) is also constructed from well-tempered version of meta-dynamics simulation by considering coordination number as a collective variable and the most probable coordination number is observed to be 10. The calculated bulk vertical electron detachment energy (8.54 eV) is found to be very close (within 3%) to that of the experimentally measured one (8.30 eV). The coordination number is also calculated to be 11 based on solvent-berg and statistical mechanical modelling, and is observed to be very close to that obtained from the PMF profile.