Guest–Host Hydrogen Bonding in Structure H Clathrate Hydrates

Abstract

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 (1)H and (13)C 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 CH(2) 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.

Inter-cage dynamics in structure I, II, and H fluoromethane hydrates as studied by NMR and molecular dynamics simulations

“…It was expected that the relatively rapid intercage dynamics may have some contributions from specific guesthost interactions, in particular related to the hydrogen bonding of TBME with the water lattice, as was the case for CO 2 dynamics in the binary THF sII clathrate hydrates. 4 Recent work, 30,38,39 after initial suggestions made many years ago, 40 has shown that guest molecules capable of accepting hydrogen bonds can introduce Bjerrum L-defects 41 in the water lattice by forming transient hydrogen bonds with a water molecule. Migration of L and D Bjerrum defects in the hydrate lattice occurs through water molecule reorientation.…”

Water molecular reorientation in ice and tetrahydrofuran clathrate hydrate from lineshape analysis of 17O spin-echo NMR spectra

“…10,15 Recent molecular dynamics (MD) simulation studies on nanosecond timescales have in fact observed the existence of both transient and persistent guest-host hydrogen bonds for oxygencontaining guests [53][54][55] . In the simplest cases, this corresponds exactly to the injection of an L-defect as there is indeed a misdirected H-bond, leaving a hydrogen vacancy in the water lattice.…”

A molecular dynamics study of ethanol–water hydrogen bonding in binary structure I clathrate hydrate with CO2

“…The NMR relaxation times strongly supported the interpretation of hydrogen bonding in the case of the tert-butylmethylether guests and the absence of such hydrogen bonding in the isoelectronic neo-hexane guest in the sH clathrate hydrate. 10 The single crystal x-ray diffraction showed the direct observation of hydrogen bonding for the pinacolone (sH) and tert-butyl amine (sII) guests. 8 Buch, Devlin, and co-workers 11 performed IR experiments and MD simulations of binary sII clathrate hydrates of HCN or SO 2 with ethylene oxide and observed evidence of guest-host hydrogen bonding in these materials.…”

“…Many aspects of their work is complementary to the discussion of the present work and Refs. [8][9][10].…”

“…Parallel to MD simulations, we performed NMR relaxation time and single crystal x-ray diffraction experiments 8,10 on the clathrate hydrates systems where MD simulations showed the presence of hydrogen bonding. The NMR relaxation times strongly supported the interpretation of hydrogen bonding in the case of the tert-butylmethylether guests and the absence of such hydrogen bonding in the isoelectronic neo-hexane guest in the sH clathrate hydrate.…”