Conformational Changes of trans-1,2-Dichlorocyclohexane Adsorbed in Zeolites Studied by FT-Raman Spectroscopy and Molecular QM/MM Simulations

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• 作者：Andrei Buin ; Jianrong Ma ; Yining Huang ; Styliani Consta ; Zhang Hui
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：April 19, 2012
• 年：2012
• 卷：116
• 期：15
• 页码：8608-8618
• 全文大小：561K
• 年卷期：v.116,no.15(April 19, 2012)
• ISSN：1932-7455

文摘

The conformational behavior of trans-1,2-dichlorocyclohexane (T12D) adsorbed inside zeolites with Faujasite structure (FAU) including sodium Y (Na鈥揧) and siliceous Y (Si鈥揧) was investigated by FT-Raman spectroscopy and molecular simulations. The results have clearly shown that the conformational and dynamic properties of T12D strongly depend on the presence of charge-balancing cations as well as Si/Al ratio. Upon loading into Na鈥揧, the population of the diequatorial (ee) conformer increases compared with pure T12D liquid due to the strong interaction with the extra-framework Na⁺ ions. Molecular simulations of T12D in Na鈥揧 and Si鈥揧 have also been carried out. The T12D molecule was modeled by quantum and semiempirical quantum chemistry methods and embedded in a zeolite framework that was described by empirical force field. Conformational changes were sampled using quantum mechanics/molecular mechanics molecular dynamics and replica exchange molecular dynamics. Molecular simulations revealed that the ee conformer is preferable versus the diaxial (aa) conformer in both Na鈥揧 and Si鈥揧 frameworks. However, in the Na鈥揧 supercage environment, the Na⁺ ions polarize the ee conformer stronger than in Si鈥揧. This leads to a larger shift of the conformational equilibrium in favor of the ee component in Na鈥揧 relative to Si鈥揧. Computations of the equilibrium population of aa and ee conformers using the dihedral Cl鈥揅鈥揅鈥揅l angle distributions of aa and ee showed good quantitative agreement with the experimental findings with respect to the dominant ee conformer in both Na鈥揧 and Si鈥揧.