Effect of multiple and adjacent cage occupancies on host-guest interaction and NMR chemical shifts in gas hydrates

The encapsulation of H-2, CO2 and CH4 in various single and fused water cages is studied using dispersion corrected density functional B97-D with cc-pVTZ basis set. Single and double occupancies of the cages are considered and the host-guest interaction is correlated to size of the guest. Although an adjacent cage or guest species in that did not show appreciable change in interaction energy for small guests, it is slightly changed for relatively large guests. The chemical shifts of guest species in free and encapsulated states indicated a deshielding of magnetic nuclei inside the cages. The deshielding increased with double occupancy of a cage. It is also revealed that the chemical shift of a trapped molecule is not significantly changed due to the presence of a neighboring cage or the guest species in the latter. (C) 2016 Elsevier B.V. All rights reserved.