Molecular Dynamics Study of Guest–Host Hydrogen Bonding in Ethylene Oxide, Trimethylene Oxide, and Formaldehyde Structure I Clathrate Hydrates

Abstract

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.

“Liquid-like” Water in Clathrates Induced by Host–Guest Hydrogen Bonding

“…We attribute the peak at 6.5 ppm to reorienting H-bonded water molecules in the host structure induced by the H-bonding defects originating from temporary host–guest H-bonding. The formation of water–THF H-bonding was predicted by molecular dynamics simulations. − Ethereal oxygen atom(s) on the polar guest molecules can form temporary H-bonds with water molecules in the host framework. − However, every water molecule is fully coordinated to their neighbors. The formation of temporary additional host–guest H-bonding therefore induces a local breakage of the intrinsic H-bonding between water molecules, which can be seen as L-type Bjerrum defects (red ovals in Figure d,e).…”

“…Classical understanding of clathrates is based on nonpolar guest molecules, for which structural defects are not considered since nonpolar guest molecules do not interfere the host lattice strongly. For polar guest molecules such as THF, temporary host–guest H-bonds can be sufficient to interfere the intrinsic water–water H-bonds − and create H-bonding defects in the host lattice, known as Bjerrum defects. − …”

Distortion of the Large Cages Encapsulating Cyclic Molecules and Empty Small Cages of Structure II Clathrate Hydrates

“…From a physico-chemical point of view, occurrence of hydrogen bonding between the host water molecule and guest molecule of ether oxygen atoms of such as THF or trimethylene oxide (TMO: C 3 H 6 O) hydrate were observed. − It is proposed that these hydrates containing hydrogen bonding guests are rich in host-lattice water lattice point defects which promote the effective water transport through the low-temperature hydrate crystal lattice. To date, spectroscopic measurements have been performed to clarify the guest dynamics of cyclic molecules. − On the other hand, crystalline data of these hydrates are not enough for simulating and understanding their thermodynamic properties .…”

Surface Science in the Research and Development of Hydrate-Based Sustainable Technologies

“…These inclusion structures are sustained by a three-dimensional hydrogen-bonded network of water molecules (i.e., the host lattice). This means that the hydrogen bonding between water molecules is a determining factor of the hydrate stability even though the properties of guest molecules play certain roles. − In the bulk of a hydrate structure, every water molecule typically forms four hydrogen bonds to their nearest neighbors that create a periodic, tetrahedrally symmetric, and relatively permanent host lattice. This tetrahedral symmetry ensures the balance of intermolecular interaction and standard coordination of water molecules in the bulk phase (Figure a).…”