Solubility of xenon in n-alkanes and cycloalkanes by computer simulation. Towards the perfect anaesthetic

Abstract

The solubility (Henry’s constant) of xenon in a series of n-alkanes (n-heptane, n-octane, n-nonane, ndodecane and n-hexadecane) and in two cycloalkanes (cyclopentane and cyclohexane) has been obtained by Monte Carlo computer simulations as a function of temperature, at a reference pressure of 100 kPa and compared with experimental results from literature. The n-alkanes and cycloalkanes were modelled with the united atom TraPPE force field, using optimized non-bonded parameters in a transferable fashion for each solvent family. Standard enthalpies of solvation were calculated from the temperature dependence of the Henry’s constants. Solute-solvent interaction energies were also estimated for all systems by Molecular Dynamics. The agreement between the simulated Henry’s constants and experimental data from the literature is excellent in all cases. For all systems involving n-alkanes, the temperature dependence of the standard enthalpies of solvation displays a maximum at very similar reduced temperatures, 0.51 < TR < 0.55. These results confirm the behaviour previously observed experimentally for n-pentane and n-hexane. Furthermore, the simulation results provide a large coherent set of data that allows extending the analysis to a large number of longer n-alkanes, including those for which no experimental data is available. Structural details of the solutions were also studied calculating the radial distribution functions xenon/ CHn for all the systems at similar thermodynamic states. The results confirm the enrichment of methyl groups within xenon’s first coordination sphere relatively to methylene groups. The effect is more pronounced the longer the n-alkane chain.