Guest-Host Hydrogen Bonding in Structure H Clathrate Hydrates

The formation of guest-host hydrogen bonds in structure H (sH) clathrate hydrates is studied herein. We contrast the structure and guest dynamics of the tert-butylmethylether (TBME) and neohexane (NH) sH clathrates by performing molecular dynamics simulations on these two clathrates and measuring H-1 and C-13 NMR relaxation times of the guests. These two guests are isoelectronic and differ with respect to the presence of the ether oxygen atom in TBME and a CH2 group in NH. The TBME guest forms long-lived hydrogen bonds with water molecules in the equatorial region of the large sH clathrate cage. These hydrogen bonds effectively tether the TBME guest to the side of the cage and restrict its rattling and rotational motions in the cage compared to NH, which does not become hydrogen bonded to the cage's water molecules.