Gauche conformation of acyclic guest molecules appearing in the large cages of structure-H clathrate hydrates |
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Authors: | Kyuchul Shin Youngjune Park Jung Hoon Hong Huen Lee |
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Affiliation: | (1) Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon, 305-701, Korea |
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Abstract: | In the present study, measurements and analyses were made of the High-Power Decoupling (HPDEC) solid-state 13C NMR spectra of structure-H (sH) methane hydrates with isopentane, one of the simplest and smallest acyclic large guest molecules,
and methylcyclohexane (MCH), a commonly used cyclic guest molecule that is larger than isopentane. From the spectroscopic
information, clear and definite evidence for the molecular conformation of acyclic guest molecules that are sufficiently small
so as to be entrapped into the structure-H large cage (sH-L) was expected. The 13C NMR chemical shift change was additionally checked through the use of a hydrogen-hydrogen steric perturbation model. From
the overall results, we concluded that one of the smallest acyclic guest molecules, isopentane, participating in the formation
of a structure-H clathrate hydrate is encaged, confirming the gauche conformation in large cavities. The present results strongly
suggest that the guest position and structure in hydrate cages are greatly influenced by both short-range interactions between
guest molecules and cage frameworks and long-range interactions between small and large guests. Accordingly, cage dynamics
must be carefully considered when a specific sH hydrate is designed and synthesized for the purpose of tuning material properties. |
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Keywords: | Structure-H Clathrate Hydrate Large Guest Molecule Substance |
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