CD-MOF: A Versatile Separation Medium

Abstract

Porous metal-organic frameworks (MOFs) have been studied in the context of a wide variety of applications, particularly in relation to molecular storage and separation sciences. Recently, we reported a green, renewable framework material composed of γ-cyclodextrin (γ-CD) and alkali metal salts--namely, CD-MOF. This porous material has been shown to facilitate the separation of mixtures of alkylaromatic compounds, including the BTEX mixture (benzene, toluene, ethylbenzene, and the regioisomers of xylene), into their pure components, in both the liquid and gas phases, in an energy-efficient manner which could have implications for the petrochemical industry. Here, we report the ability of CD-MOF to separate a wide variety of mixtures, including ethylbenzene from styrene, haloaromatics, terpinenes, pinenes and other chiral compounds. CD-MOF retains saturated compounds to a greater extent than their unsaturated analogues. Also, the location of a double bond within a molecule influences its retention within the extended framework, as revealed in the case of the structural isomers of pinene and terpinine, where the isomers with exocyclic double bonds are more highly retained than those with endocyclic double bonds. The ability of CD-MOF to separate various mono- and disubstituted haloaromatic compounds appears to be controlled by both the size of the halogen substituents and the strength of the noncovalent bonding interactions between the analyte and the framework, an observation which has been confirmed by molecular simulations. Since CD-MOF is a homochiral framework, it is also able to resolve the enantiomers of chiral analytes, including those of limonene and 1-phenylethanol. These findings could lead to cheaper and easier-to-prepare stationary phases for HPLC separations when compared with other chiral stationary phases, such as CD-bonded silica particles.

Biologically derived metal organic frameworks

“…[215] In 2016, Stoddart et al further reported the ability to separate a wide variety of mixtures, including ethylbenzene from styrene, haloaromatics, terpinenes, pinenes, alkyl-, vinyl-and others, including chiral compounds, with CD-MOF-1. [230] The retention was influenced by i. the saturation of a compound, with those having a greater retention being saturated, ii. the placement of a double bond within the molecule, for example in the case of pinene and terpinine, isomers with an exocyclic double bond were more highly retained than their endocyclic counterparts.…”

“…the placement of a double bond within the molecule, for example in the case of pinene and terpinine, isomers with an exocyclic double bond were more highly retained than their endocyclic counterparts. [230] Separations between mono-and di-substituted haloaromatic compounds were influenced by the size of the halogen substituent, and the strength between the analyte and framework through noncovalent bonding interactions. [230] Enantiomers of chiral analytes, including limonene and 1-phenylethanol, could be resolved due to the homochiral framework.…”

“…[230] Separations between mono-and di-substituted haloaromatic compounds were influenced by the size of the halogen substituent, and the strength between the analyte and framework through noncovalent bonding interactions. [230] Enantiomers of chiral analytes, including limonene and 1-phenylethanol, could be resolved due to the homochiral framework. [230] With a wide variety of separation abilities, CD-MOF-1 is not only versatile, environmentally benign, and biocompatible, but it can be additionally used as a stationary-phase material for separations.…”

“…[230] Enantiomers of chiral analytes, including limonene and 1-phenylethanol, could be resolved due to the homochiral framework. [230] With a wide variety of separation abilities, CD-MOF-1 is not only versatile, environmentally benign, and biocompatible, but it can be additionally used as a stationary-phase material for separations.…”

Supramolecular Polymeric Materials Containing Cyclodextrins

“…Therefore there is a large gap between macroscopic self-assembly and molecular selfassembly. Although there are a large number of reports on molecular self-assembly, [13][14][15][16][17][18] few exist on macroscopic selfassembly directed by macroscopic forces, [19][20][21] and there have been no reports on macroscopic self-assembly through specific molecular recognition.…”