Performance of Chiral Zeolites for Enantiomeric Separation Revealed by Molecular Simulation

Abstract

We used molecular simulations to test the adsorption selectivity for enantiomers in the chiral zeolites SOF, STW, and ITQ-37. This work is the first simulation study which demonstrates the chirality of SOF, STW, and ITQ-37. We obtain information at the molecular level that explains the nature of the chiral selectivity. We selected CHBrClF and 4-ethyl-4-methyloctane as the probe molecules for the study. We calculated pure component and racemic mixture adsorption isotherms, Henry coefficients, adsorption enthalpies, and radial distribution functions. While STW is enantioselective for the probe molecules studied, ITQ-37 is likely to be enantioselective for other chiral molecules, and SOF is not a candidate for chiral separation. Appropriate pore geometry, resulting in differences in the adsorption behavior between the two isomers, is required for observing chiral selectivity. We provide insight that could be used for the synthesis and characterization of new chiral structures aimed to separate specific isomers. Using the methodology described here, it could be possible to easily determine if a new zeolite structure would show adsorption selectivity for a given chiral molecule.

Exploring new methods and materials for enantioselective separations and catalysis

“…decreases with increasing fugacity, which suggests that only certain sites in the pores that are filled at low fugacities are enantioselective to DMA in MOF 1. This is qualitatively different from the results for chiral zeolites reported by Castillo et al [41]. Figure 8(c) shows the interaction energy DE between the sorbates and the MOF framework.…”

“…[41] The study was performed for CHBrClF and 4-ethyl-4-methyloctane isomers in pure silica STW, SOF and ITQ-37 zeolites. According to their simulation results, STW is enantioselective for the studied isomers, whereas ITQ-37 only showed adsorption selectivity when its unit cell was scaled in size by 30%.…”

Synthesis and characterization of chiral zeolite ITQ-37 by using achiral organic structure-directing agent

“…Such examples are germanosilicate ITQ-15 (zeotype UTL) with 14 Â 12R pore system [13][14][15], silicogermanate ITQ-33 with 18 Â 10 Â 10R pore system [16], silicogermanate ITQ-44 (IRR) with 18 Â 12 Â 12R pore system [17], and silicogermanate zeolite ITQ-43 with 28 Â 12 Â 12R hierachical mesopore-micropore system [2]. Chiral zeolites are highly desired since they would be able to perform shape-selective, asymmetric catalysis and separation [18][19][20] that could not be achieved by other materials. In 2008, Sun et al reported the first chiral germanosilicate zeolite ITQ-37 (-ITV) [21].…”

Enantioselective adsorption of ibuprofen and lysine in metal–organic frameworks

“…[9][10][11][20][21][22][23][24][25] However, to the best of our knowledge, enantioselective separation of more complex molecules in liquid phase has not yet been studied. The molecule of ibuprofen contains a chiral centre in the a-carbon of the propionate moiety.…”

“…It can also be found in other systems, since the effect is not directly related to enantioselectivity but to many other factors such as channel shape, pore size, steric fit, and interaction with the framework. 5,[7][8][9]25,29 To get a deep understanding of this behaviour we provide insights into the microscopic assembly in the systems. We evaluated the hydrogen bonding (HB) between guest molecules using a specific criterion for HB definition.…”