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.

The free primary hydroxyl groups in the metal-organic framework of CDMOF-2, an extended cubic structure containing units of six γ-cyclodextrin tori linked together in cube-like fashion by rubidium ions, has been shown to react with gaseous CO2 to form alkyl carbonate functions. The dynamic covalent carbon-oxygen bond, associated with this chemisorption process, releases CO2 at low activation energies. As a result of this dynamic covalent chemistry going on inside a metal-organic framework, CO2 can be detected selectively in the atmosphere by electrochemical impedance spectroscopy. The "as-synthesized" CDMOF-2 which exhibits high proton conductivity in pore-filling methanolic media, displays a ∼550-fold decrease in its ionic conductivity on binding CO2. This fundamental property has been exploited to create a sensor capable of measuring CO2 concentrations quantitatively even in the presence of ambient oxygen.

Although complexation of hydrophilic guests inside the cavities of hydrophobic hosts is considered to be unlikely, we demonstrate herein the complexation between γ- and β-cyclodextrins (γ- and β-CDs) with an archetypal polyoxometalate (POM)--namely, the [PMo12O40](3-) trianion--which has led to the formation of two organic-inorganic hybrid 2:1 complexes, namely [La(H2O)9]{[PMo12O40]⊂[γ-CD]2} (CD-POM-1) and [La(H2O)9] {[PMo12O40]⊂[β-CD]2} (CD-POM-2), in the solid state. The extent to which these complexes assemble in solution has been investigated by (i) (1)H, (13)C, and (31)P NMR spectroscopies and (ii) small- and wide-angle X-ray scattering, as well as (iii) mass spectrometry. Single-crystal X-ray diffraction reveals that both complexes have a sandwich-like structure, wherein one [PMo12O40](3-) trianion is encapsulated by the primary faces of two CD tori through intermolecular [C-H···O═Mo] interactions. X-ray crystal superstructures of CD-POM-1 and CD-POM-2 show also that both of these 2:1 complexes are lined up longitudinally in a one-dimensional columnar fashion by means of [O-H···O] interactions. A beneficial nanoconfinement-induced stabilizing effect is supported by the observation of slow color changes for these supermolecules in aqueous solution phase. Electrochemical studies show that the redox properties of [PMo12O40](3-) trianions encapsulated by CDs in the complexes are largely preserved in solution. The supramolecular complementarity between the CDs and the [PMo12O40](3-) trianion provides yet another opportunity for the functionalization of POMs under mild conditions by using host-guest chemistry.

Although ibuprofen is one of the most widely used nonsteroidal anti-inflammatory drugs (NSAIDs), it exhibits poor solubility in aqueous and physiological environments as a free acid. In order to improve its oral bioavailability and rate of uptake, extensive research into the development of new formulations of ibuprofen has been undertaken, including the use of excipients as well as ibuprofen salts, such as ibuprofen lysinate and ibuprofen, sodium salt. The ultimate goals of these studies are to reduce the time required for maximum uptake of ibuprofen, as this period of time is directly proportional to the rate of onset of analgesic/anti-inflammatory effects, and to increase the half-life of the drug within the body; that is, the duration of action of the effects of the drug. Herein, we present a pharmaceutical cocrystal of ibuprofen and the biocompatible metal-organic framework called CD-MOF. This metal-organic framework (MOF) is based upon γ-cyclodextrin (γ-CD) tori that are coordinated to alkali metal cations (e.g., K ions) on both their primary and secondary faces in an alternating manner to form a porous framework built up from (γ-CD) cubes. We show that ibuprofen can be incorporated within CD-MOF-1 either by (i) a crystallization process using the potassium salt of ibuprofen as the alkali cation source for production of the MOF or by (ii) absorption and deprotonation of the free-acid, leading to an uptake of 23-26 wt % of ibuprofen within the CD-MOF. In vitro viability studies revealed that the CD-MOF is inherently not affecting the viability of the cells with no IC value determined up to a concentration of 100 μM. Bioavailability investigations were conducted on mice, and the ibuprofen/CD-MOF pharmaceutical cocrystal was compared to control samples of the potassium salt of ibuprofen in the presence and absence of γ-CD. From these animal studies, we observed that the ibuprofen/CD-MOF-1 cocrystal exhibits the same rapid uptake of ibuprofen as the ibuprofen potassium salt control sample with a peak plasma concentration observed within 20 min, and the cocrystal has the added benefit of a 100% longer half-life in blood plasma samples and is intrinsically less hygroscopic than the pure salt form.

Metal−organic frameworks (MOFs) are known to facilitate energy-efficient separations of important industrial chemical feedstocks. Here, we report how a class of green MOFsnamely CD-MOFsexhibits high shape selectivity toward aromatic hydrocarbons. CD-MOFs, which consist of an extended porous network of γ-cyclodextrins (γ-CDs) and alkali metal cations, can separate a wide range of benzenoid compounds as a result of their relative orientation and packing within the transverse channels formed from linking (γ-CD) 6 body-centered cuboids in three dimensions. Adsorption isotherms and liquid-phase chromatographic measurements indicate a retention order of ortho-> meta-> para-xylene. The persistence of this regioselectivity is also observed during the liquid-phase chromatography of the ethyltoluene and cymene regioisomers. In addition, molecular shape-sorting within CDMOFs facilitates the separation of the industrially relevant BTEX (benzene, toluene, ethylbenzene, and xylene isomers) mixture. The high resolution and large separation factors exhibited by CD-MOFs for benzene and these alkylaromatics provide an efficient, reliable, and green alternative to current isolation protocols. Furthermore, the isolation of the regioisomers of (i) ethyltoluene and (ii) cymene, together with the purification of (iii) cumene from its major impurities (benzene, n-propylbenzene, and diisopropylbenzene) highlight the specificity of the shape selectivity exhibited by CD-MOFs. Grand canonical Monte Carlo simulations and single component static vapor adsorption isotherms and kinetics reveal the origin of the shape selectivity and provide insight into the capability of CD-MOFs to serve as versatile separation platforms derived from renewable sources. ■ INTRODUCTIONWith the expanding global demand for petrochemical feedstocks, the development of novel, low-cost materials that reduce the impact of chemical processing on the environment is critically important. Improving the efficiency of the refinement and separation of aromatic hydrocarbons is of particular importance, given the large volumes on which these compounds are produced. The sustained interest in metal− organic frameworks 1 (MOFs) as adsorbents and sequestering agents for industrially important gases, 2−4 e.g., H 2 , CH 4 , CO 2 and N 2 , as well as for the liquid-phase separation of larger molecular compounds, which include (1) constitutional isomers, 5 (2) chiral compounds, 6 (3) aliphatic hydrocarbons, 3b,5b,7 and (4) pharmaceuticals, 8 is leading to MOFs being investigated as alternatives to zeolites 9 and activated carbon 10 as separation media. The improvements 5−7 in separation efficiencies using MOFs over traditional size-and shape-selective materials can be attributed primarily to (i) the physiochemical properties imbedded in their diverse building blocks, (ii) their higher surface areas, and (iii) their larger adsorption capacities, which reduce the amount of adsorbent required for industrial processes. 7a,11 Consequently, MOFs represent emergent materials f...

We report the template-directed synthesis of BlueCage(6+), a macrobicyclic cyclophane composed of six pyridinium rings fused with two central triazines and bridged by three paraxylylene units. These moieties endow the cage with a remarkably electron-poor cavity, which makes it a powerful receptor for polycyclic aromatic hydrocarbons (PAHs). Upon forming a 1:1 complex with pyrene in acetonitrile, however, BlueCage⋅6 PF6 exhibits a lower association constant Ka than its progenitor ExCage⋅6 PF6. A close inspection reveals that the six PF6(-) counterions of BlueCage(6+) occupy the cavity in a fleeting manner as a consequence of anion-π interactions and, as a result, compete with the PAH guests. This conclusion is supported by a one order of magnitude increase in the Ka value for pyrene in BlueCage(6+) when the PF6(-) counterions are replaced by much bulkier anions. The presence of anion-π interactions is supported by X-ray crystallography, and confirms the presence of a PF6(-) counterion inside its cavity.

The syntheses of several 3,6-dihalopyromellitic diimides have been achieved. Two-point intermolecular halogen–oxygen interactions—reminiscent of carboxylic acid dimers—are observed in the solid-state superstructures of (i) these molecules and (ii) their charge-transfer complexes with electron-rich naphthalenes.

Eight compounds of Co, Ni and Cu with mellitate ligands display a wide variety of structures with metal-mellitate coordination polymer dimensionality 0-3. Usually mellitate is fully deprotonated (mel 6− ), but there is one example of Hmel 5− and one of H 2 mel 4− . [M 3 (mel)(OH 2 ) 12 ]•6H 2 O (M = Co or Ni) are chain polymers with octahedral M, while [Cu 7 (OH 2 ) 19 (OH) 2 (mel) 2 ]•9H 2 O has a 2D polymer sheet structure with square-based pyramidal Cu. Addition of KOH produces different compounds. Two incorporate K + in the structures: K + 2 (OH 2 ) 5 [{Ni(OH 2 ) 5 } 2 (mel)] 2 •2H 2 O contains discrete nickel-mellitate anionic units, and K + 2 (OH 2 ) 6 [{Cu(OH 2 ) 3 } 2 (mel)] 2 •H 2 O has a copper-mellitate 2D polymeric anion. For Co the product is [Co(OH 2 ) 6 ] 2+ [{Co(OH 2 ) 4 } 5 (mel) 2 ] 2 •4H 2 O, with a 2D polymeric anion and discrete cations. A gel-supported synthesis leads to [Cu 3 (OH 2 ) 10 (Hmel)][Cu 2 (OH 2 ) 6 (Hmel)]•7H 2 O, with two different copper-mellitate polymeric sheets arranged alternately in a stack. [{Cu(OH 2 )(EtOH)(4,4-bipy)} 2 (H 2 mel)] contains a 3D copper-mellitate network with hexagonal channels, occupied by 4.4-bipyridyl molecules coordinated to Cu at one end and hydrogen bonded to H 2 mel 4− at the other. While some of these features are familiar from other structures, 4 some are new, raising the question of how far design principles can be applied to the synthesis of mellitate complexes Full crystallographic details for complexes 1-8 in cif format and in conventional tabulated form together with displacement ellipsoid plots; observed and calculated powder X-ray diffraction patterns. This material is available free of charge via the Internet at http://pubs.acs.org. CCDC numbers 1009817-1009824 contain the supplementary crystallographic data. These data can also be obtained free of charge, upon request, at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, U.K.