Selectivity in Gas Adsorption by Molecular Cucurbit[6]uril

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• 作者：Sudip Pan ; Ranajit Saha ; Subhajit Mandal ; Sukanta Mondal ; Ashutosh Gupta ; María A. Fernández-Herrera ; Gabriel Merino ; Pratim K. Chattaraj
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：July 7, 2016
• 年：2016
• 卷：120
• 期：26
• 页码：13911-13921
• 全文大小：727K
• 年卷期：0
• ISSN：1932-7455

文摘

The relative preference in adsorption among 19 common gas molecules, namely, C₂H₂, C₂H₄, C₂H₆, CH₄, X₂, HX (X = F, Cl, Br), CO₂, CS₂, CO, H₂, H₂O, H₂S, N₂, NO₂, and NO within the cavity of cucurbit[6]uril (CB[6]) is investigated via density functional theory computations. Energies associated with the dissociation of gas@CB[6] producing CB[6] and gas molecules show the order of the efficacy to be encapsulated within CB[6], C₂H₂@CB[6] being the most viable system. However, the dissociation free energy change implies that CB[6] is most efficient in accommodating Cl₂ followed by C₂H₂ among the considered gas molecules. In general, guest molecules having large surface contact with the host and/or high polarizability and/or having acidic hydrogen to make hydrogen bond with >C═O show larger propensity to be encapsulated within CB[6] cavitand. Functionalized CB[6] are better candidates for gas adsorption than CB[6]. However, the nature of functionalization needed to improve the adsorption ability varies with the change in the guest molecule. While full −C₂H₅ substitution improves C₂H₂ and CO₂ adsorption ability of CB[6] the most, the −CN functionalized CB[6] is the best candidate to encapsulate C₂H₄ and C₂H₆ among the studied −OH, −C₂H₅, and −CN substituted analogues. The interaction is mostly of van der Waals type, except in the cases of C₂H₂, H₂O, H₂S, and HX (X = F, Cl, Br), in which both the electrostatic and dispersion contributions are important owing to the interaction between acidic hydrogen of these guest molecules and oxygen centers of the host moiety.