Metal-organic frameworks (MOFs) represent [1] an extensive class of porous crystals in which organic struts link metalcontaining clusters. The success in controlling the functionality and structure of MOFs has led to numerous applications, [2] most notably gas adsorption, [3] storage of clean gas fuels, [4] catalysis, [5] separations, [6] and drug delivery. [7] However, the vast majority of MOFs described to date are composed of organic struts derived from non-renewable petrochemical feedstocks and transition metals. The challenge in preparing MOFs from natural products lies in the inherent asymmetry of the building units, which are not amenable to crystallization in the form of highly porous frameworks. Herein, we report a strategy to overcome this problem using g-cyclodextrin (g-CD), a symmetrical cyclic oligosaccharide that is mass-produced enzymatically from starch [8] and comprised of eight asymmetric a-1,4-linked dglucopyranosyl residues. These g-CD building units are then linked by potassium ions, in aqueous media at ambient temperature and pressure, to form a body-centered cubic structure, termed CD-MOF-1, which has the empirical formula [(C 48 H 80 O 40 )(KOH) 2 ] n . CD-MOFs can be prepared entirely from edible ingredients: combining food-grade g-CD with salt substitute (KCl) or potassium benzoate (food additive E212) in bottled water and Everclear grain spirit (EtOH) yields porous frameworks which constitute edible MOFs.While there have been a few reports of MOFs assembled from amino acids, [9] nucleobases, [7a, 10] peptides, [11] magnesium formates, [12] and metal glutarates, [13] examples of these materials are not common despite the rapidly growing desire to fabricate MOFs from naturally available building blocks. We suspect that the key to our success in assembling CD-MOFs lies in the symmetric arrangement (C 8 ) within the g-CD torus of eight asymmetric (C 1 ) a-1,4-linked d-glucopyranosyl residues and the ready availability of g-CD as a chiral molecular building block (Figure 1). CD-MOF-1 was prepared by combining 1.0 equiv of g-CD with 8.0 equiv of KOH in aqueous solution, followed by vapor diffusion of MeOH into the solution during 2-7 days, resulting in colorless, cubic, single crystals, suitable for X-ray crystallography, in approximately 70 % yield. Other CD-MOFs were readily obtained using salts of Na + , Rb + , and Cs + , giving rise to an extensive new family of porous materials. A complete list of metal salts employed to form CD-MOFs and the full synthesis of CDMOFs are provided in Section S2 of the Supporting Information.The X-ray crystal structure of CD-MOF-1 [14] reveals that eight-coordinate K + ions not only assist in the assembly of (g-CD) 6 cubes (Figure 2 a,b), wherein six g-CD units occupy the faces of a cube, but they also serve to link these cubes together in a three-dimensional array which extends throughout the crystal (Figure 2 c). The (g-CD) 6 repeating motifs adopt a body-centered cubic packing arrangement wherein each symmetrically equivalent K + ion links two co...

The efficient capture and storage of gaseous CO(2) is a pressing environmental problem. Although porous metal-organic frameworks (MOFs) have been shown to be very effective at adsorbing CO(2) selectively by dint of dipole-quadruple interactions and/or ligation to open metal sites, the gas is not usually trapped covalently. Furthermore, the vast majority of these MOFs are fabricated from nonrenewable materials, often in the presence of harmful solvents, most of which are derived from petrochemical sources. Herein we report the highly selective adsorption of CO(2) by CD-MOF-2, a recently described green MOF consisting of the renewable cyclic oligosaccharide γ-cyclodextrin and RbOH, by what is believed to be reversible carbon fixation involving carbonate formation and decomposition at room temperature. The process was monitored by solid-state (13)C NMR spectroscopy as well as colorimetrically after a pH indicator was incorporated into CD-MOF-2 to signal the formation of carbonic acid functions within the nanoporous extended framework.

The binding of alkali and alkaline earth metal cations by macrocyclic and diazamacrobicyclic polyethers, composed of ordered arrays of hard oxygen (and nitrogen) donor atoms, underpinned the development of host-guest supramolecular chemistry in the 1970s and 1980s. The arrangement of -OCCO- and -OCCN- chelating units in these preorganized receptors, including, but not limited to, crown ethers and cryptands, is responsible for the very high binding constants observed for their complexes with Group IA and IIA cations. The cyclodextrins (CDs), cyclic oligosaccharides derived microbiologically from starch, also display this -OCCO- bidentate motif on both their primary and secondary faces. The self-assembly, in aqueous alcohol, of infinite networks of extended structures, which have been termed CD-MOFs, wherein γ-cyclodextrin (γ-CD) is linked by coordination to Group IA and IIA metal cations to form metal-organic frameworks (MOFs), is reported. CD-MOF-1 and CD-MOF-2, prepared on the gram-scale from KOH and RbOH, respectively, form body-centered cubic arrangements of (γ-CD)(6) cubes linked by eight-coordinate alkali metal cations. These cubic CD-MOFs are (i) stable to the removal of solvents, (ii) permanently porous, with surface areas of ~1200 m(2) g(-1), and (iii) capable of storing gases and small molecules within their pores. The fact that the -OCCO- moieties of γ-CD are not prearranged in a manner conducive to encapsulating single metal cations has led to our isolating other infinite frameworks, with different topologies, from salts of Na(+), Cs(+), and Sr(2+). This lack of preorganization is expressed emphatically in the case of Cs(+), where two polymorphs assemble under identical conditions. CD-MOF-3 has the cubic topology observed for CD-MOFs 1 and 2, while CD-MOF-4 displays a channel structure wherein γ-CD tori are perfectly stacked in one dimension in a manner reminiscent of the structures of some γ-CD solvates, but with added crystal stability imparted by metal-ion coordination. These new MOFs demonstrate that the CDs can indeed function as ligands for alkali and alkaline earth metal cations in a manner similar to that found with crown ethers. These inexpensive, green, nanoporous materials exhibit absorption properties which make them realistic candidates for commercial development, not least of all because edible derivatives, fit for human consumption, can be prepared entirely from food-grade ingredients.

Metal-organic frameworks (MOFs) represent [1] an extensive class of porous crystals in which organic struts link metalcontaining clusters. The success in controlling the functionality and structure of MOFs has led to numerous applications, [2] most notably gas adsorption, [3] storage of clean gas fuels, [4] catalysis, [5] separations, [6] and drug delivery. [7] However, the vast majority of MOFs described to date are composed of organic struts derived from non-renewable petrochemical feedstocks and transition metals. The challenge in preparing MOFs from natural products lies in the inherent asymmetry of the building units, which are not amenable to crystallization in the form of highly porous frameworks. Herein, we report a strategy to overcome this problem using g-cyclodextrin (g-CD), a symmetrical cyclic oligosaccharide that is mass-produced enzymatically from starch [8] and comprised of eight asymmetric a-1,4-linked dglucopyranosyl residues. These g-CD building units are then linked by potassium ions, in aqueous media at ambient temperature and pressure, to form a body-centered cubic structure, termed CD-MOF-1, which has the empirical formula [(C 48 H 80 O 40 )(KOH) 2 ] n . CD-MOFs can be prepared entirely from edible ingredients: combining food-grade g-CD with salt substitute (KCl) or potassium benzoate (food additive E212) in bottled water and Everclear grain spirit (EtOH) yields porous frameworks which constitute edible MOFs.While there have been a few reports of MOFs assembled from amino acids, [9] nucleobases, [7a, 10] peptides, [11] magnesium formates, [12] and metal glutarates, [13] examples of these materials are not common despite the rapidly growing desire to fabricate MOFs from naturally available building blocks. We suspect that the key to our success in assembling CD-MOFs lies in the symmetric arrangement (C 8 ) within the g-CD torus of eight asymmetric (C 1 ) a-1,4-linked d-glucopyranosyl residues and the ready availability of g-CD as a chiral molecular building block (Figure 1). CD-MOF-1 was prepared by combining 1.0 equiv of g-CD with 8.0 equiv of KOH in aqueous solution, followed by vapor diffusion of MeOH into the solution during 2-7 days, resulting in colorless, cubic, single crystals, suitable for X-ray crystallography, in approximately 70 % yield. Other CD-MOFs were readily obtained using salts of Na + , Rb + , and Cs + , giving rise to an extensive new family of porous materials. A complete list of metal salts employed to form CD-MOFs and the full synthesis of CDMOFs are provided in Section S2 of the Supporting Information.The X-ray crystal structure of CD-MOF-1 [14] reveals that eight-coordinate K + ions not only assist in the assembly of (g-CD) 6 cubes (Figure 2 a,b), wherein six g-CD units occupy the faces of a cube, but they also serve to link these cubes together in a three-dimensional array which extends throughout the crystal (Figure 2 c). The (g-CD) 6 repeating motifs adopt a body-centered cubic packing arrangement wherein each symmetrically equivalent K + ion links two co...

Metal-organic frameworks (MOFs) are a class of coordination polymers, consisting of metal ions or clusters linked together by chemically mutable organic groups. In contrast to zeolites and porous carbons, MOFs are constructed from a building block strategy that enables molecular level control of pore size/shape and functionality. An area of growing interest in MOF chemistry is the synthesis of MOF-based composite materials. Recent studies have shown that MOFs can be combined with biomacromolecules to generate novel biocomposites. In such materials, the MOF acts as a porous matrix that can encapsulate enzymes, oligonucleotides, or even more complex structures that are capable of replication/reproduction (i.e., viruses, bacteria, and eukaryotic cells). The synthetic approach for the preparation of these materials has been termed "biomimetic mineralization", as it mimics natural biomineralization processes that afford protective shells around living systems. In this Perspective, we focus on the preparation of MOF biocomposites that are composed of complex biological moieties such as viruses and cells and canvass the potential applications of this encapsulation strategy to cell biology and biotechnology.

The chemical and photophysical properties of a fluorescent squaraine dye are greatly enhanced when it is mechanically encapsulated inside a tetralactam macrocycle. This feature article describes the synthesis, structure, and photophysical performance of first-generation squaraine rotaxanes, and shows how they can be used as fluorescent imaging probes and chemosensors.

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.

Millimeter-sized single MOF-5 crystals are used as "chromatographic columns" to effectively separate mixtures of organic dyes. Remarkably, owing to the nanoscopic pore dimensions and the molecular-level interactions between the migrating molecules and the MOF scaffold, the separations occur over a distance of only a few hundred micrometers which is unambiguously confirmed by fluorescence confocal microscopy.