Molecular Simulation Study of Tetraalkylammonium Halides. 1. Solvation Structure and Hydrogen Bonding in Aqueous Solutions

Abstract

The hydration structure in aqueous solutions of three tetraalkylammonium halides (TAAX), tetramethylammonium chloride (TMACl), tetrapropylammonium bromide (TPABr), and tetrabutylammonium bromide (TBABr) at concentrations of 2.2, 1.4, and 1.0 m, respectively, is studied via molecular dynamics (MD) simulation at ambient conditions. The results are compared directly with neutron diffraction with isotopic substitution (NDIS) experimental results for the same systems. In agreement with the NDIS results, we find evidence of a small enhancement of water structure around the apolar solutes, based on water H−H radial distribution functions. Decomposition of the water−water O−H radial distribution function into hydrogen-bonded and non-hydrogen-bonded components, using the geometric criterion for hydrogen bonding of Mezei and Beveridge (1981), allowed us to calculate the hydrogen-bonded (HB) contribution to the total O−H radial distribution function, both in the bulk solution and in the first solvation shell of the ...