Nuclear Magnetic Resonance Parameters for Methane Molecule Trapped in Clathrate Hydrates

作者：Siuda Pawel; Sadlej Joanna^*

来源：Journal of Physical Chemistry A, 2011, 115(5): 612-619.

DOI：10.1021/jp110587x

The calculations of the nuclear shielding and spin-spin coupling constants were carried out for two models of clathrate hydrates, 5(12) and 5(12)6(8), using the density functional theory three-parameter Becke-Lee-Yang-Parr method with the basis set aug-cc-pVDZ (optimization) and HuzIII-su3 (NMR parameters). Particular attention has been devoted to evaluate the influence of a geometrical arrangement, the effect of long-range interactions on the NMR shielding of methane molecule, and to predict whether C-13 and H-1 chemical shifts can distinguish between guests in two clathrate hydrates cages. The correlation of the changes in the 70 shielding constants depend strongly on the hydrogen-bonding topology. The intermolecular hydrogen-bond transmitted (1h)J(OH) spin-spin coupling. constants are substantial. The increase of their values is connected with the elongation of the intramolecular O-H bond and the shortening of the intermolecular 0 center dot center dot center dot H distance. These data suggests that hydrogen bonds between double donor-single acceptor (DDA)-type water molecules acting as a proton acceptor from single donor-double acceptor (DAA)-type water molecules are stronger than ones formed by DAA-type water molecules acting as an acceptor for a DDA water proton. These state-of-the-art calculations confirmed the earlier experimental findings of the cage-dependency of C-13 chemical shift of methane.

• 出版日期2011-2-10