| Résumé | Molecular dynamics simulations are used to study the guest–host hydrogen bonding and guest dynamics in the clathrate hydrate phases of trimethylene oxide (TMO), ethylene oxide (EO), and formaldehyde (FA) as polar guests. Two water models, the SPC/E and TIP4P/ice, were used in the simulations. Binary hydrates are constructed with these guests in the large 14-sided cages and methane placed in the small 12-sided cages of the structure sI clathrate hydrates. The results of these simulations are compared with the nonpolar guests with analogous structures, cyclobutane (CB), cyclopropane (CP), and ethane, respectively, for TMO, EO, and FA. These simulations show that oxygen atoms of the cyclic ethers and carbonyl oxygen of formaldehyde form hydrogen bonds to differing degrees with cage water hydrogen atoms. The TMO size is larger than that of the EO and FA molecules and the closer proximity of the atoms of this large guest to the cage water molecule enhances the probability of guest–host hydrogen bonding in the TMO clathrate. The TMO oxygen atom is tethered by a lattice water hydrogen atom by hydrogen bonding for longer times, which reduces the range of translational and rotational motions of the TMO guests in the cages compared to EO and FA. The effect of guest–host hydrogen bond formation is the insertion of Bjerrum L-defects in the clathrate water lattice. We consider guest dynamic properties such as velocity autocorrelation function (VACF) and orientational autocorrelation function (OACF) of the different guests in these hydrate phases and compare the hydrogen bonding and non-hydrogen bonding analogues. We discuss some other potential experimentally observable effects of the guest–host hydrogen bonding on the guest and water dynamics in the corresponding clathrate hydrates. |
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