603 research outputs found
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That's No Moon: It's a Molecular Capsule
In this issue of Chem, Fujita et al. have produced the largest synthetic self-assembled capsule to date through subtle modification of the flexibility and geometry of its constituent ligands.This is the author accepted manuscript. The final version is available from Cell Press via http://dx.doi.org/10.1016/j.chempr.2016.06.00
Pathway-Dependent Post-assembly Modification of an Anthracene-Edged M Tetrahedron
Fe tetrahedral cage undergoes post-assembly modification (PAM) via a Diels-Alder cycloaddition of the anthracene panels of the cage with tetracyanoethylene (TCNE). The modified cage possesses an enclosed cavity suitable for encapsulation of the fullerene C, whereas original cage forms a unique covalent adduct through a Diels-Alder cycloaddition of three of its anthracene ligands with C. This adduct undergoes further PAM via reaction of the remaining three ligands with TCNE, enabling the isolation of two distinct products depending on the order of addition of C and TCNE. Modified cage was also able to bind an anionic guest, [Co(CBH)], which was not encapsulated by the original cage, demonstrating the potential of PAM for tuning the binding properties of supramolecular hosts.Engineering and Physical Sciences Research Council, University of Cambridge (Herchel Smith Research Fellowship), Corpus Christi College (Cambridge; Fellowship
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Directed Phase Transfer of an FeL Cage and Encapsulated Cargo
Supramolecular capsules can now be prepared with a wide range of volumes and geometries. Consequently, many of these capsules encapsulate guests selectively by size and shape, an important design feature for separations. To successfully address practical separations problems, however, a guest cannot simply be isolated from its environment; the molecular cargo must be removed to a separate physical space. Here we demonstrate that an FeL coordination cage 1 can transport a cargo spontaneously and quantitatively from water across a phase boundary and into an ionic liquid layer. This process is triggered by an anion exchange from 1[SO] to 1[BF]. Upon undergoing a second anion exchange, from 1[BF] to 1[SO], the cage, together with its encapsulated guest, can then be manipulated back into a water layer. Furthermore, we demonstrate the selective phase transfer of cationic cages to separate a mixture of two cages and their respective cargoes. We envisage that supramolecular technologies based upon these concepts could ultimately be employed to carry out separations of industrially relevant compounds.This work was supported by the European Research Council (695009). A.B.G. also acknowledges the Cambridge Trusts for Ph.D. funding
Guest Encapsulation within Surface-Adsorbed Self-Assembled Cages
Coordination cages encapsulate a wide variety of guests in the solution state. This ability renders them useful for applications such as catalysis and the sequestration of precious materials. A simple and general method for the immobilization of coordination cages on alumina is reported. Cage loadings are quantified via adsorption isotherms and guest displacement assays demonstrate that the adsorbed cages retain the ability to encapsulate and separate guest and non-guest molecules. Finally, a system of two cages, adsorbed on to different regions of alumina, stabilizes and separates a pair of Diels-Alder reagents. The addition of a single competitive guest results in the controlled release of the reagents, thus triggering their reaction. This method of coordination cage immobilization on solid phases is envisaged to be applicable to the extensive library of reported cages, enabling new applications based upon selective solid-phase molecular encapsulation
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Separation and Selective Formation of Fullerene Adducts within an ML Cage.
The self-assembly of 4-fold-symmetric porphyrins with Fe or Zn gave a new cubic ML cage framework with electron-deficient walls. This cage bound C-indene or C-anthracene bisadducts selectively, whereas unfunctionalized fullerenes and monoadducts were not encapsulated. The FeL cage also enabled the reaction of C and anthracene to yield the bisadducts selectively under conditions where no reaction was observed in the absence of the cage. These findings have relevance in the context of polymer solar cells, where C bisadducts have found use as electron acceptors, because these adducts currently require laborious and time-consuming syntheses and purification
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Self-Assembly of Conjugated Metallopolymers with Tunable Length and Controlled Regiochemistry
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Sequence-selective encapsulation and protection of long peptides by a self-assembled FeL cubic cage
Self-assembly offers a general strategy for the preparation of large, hollow high-symmetry structures. Although biological capsules, such as virus capsids, are capable of selectively recognizing complex cargoes, synthetic encapsulants have lacked the capability to specifically bind large and complex biomolecules. Here we describe a cubic host obtained from the self-assembly of Fe and a zinc-porphyrin-containing ligand. This cubic cage is flexible and compatible with aqueous media. Its selectivity of encapsulation is driven by the coordination of guest functional groups to the zinc porphyrins. This new host thus specifically encapsulates guests incorporating imidazole and thiazole moieties, including drugs and small proteins. Once encapsulated, the reactivity of a peptide is dramatically altered: Encapsulated peptides are protected from trypsin hydrolysis, whereas physicochemically similar peptides that do not bind are cleaved.This work was supported by the UK Engineering and Physical Sciences Research Council (EPSRC EP/M008258/1). The authors thank the Department of Chemistry NMR facility (University of Cambridge), Balasubramanian Group for use of the HPLC, and Dr. J. A. Foster for providing 5-hydroxypicolinaldehyde employed in the initial experiments of the project. J. M. acknowledges postdoctoral fellowship support from Fundación Ramón Areces
Subcomponent Exchange Transforms an Fe(II)4L4 Cage from High- to Low-Spin, Switching Guest Release in a Two-Cage System
Subcomponent exchange transformed new high-spin Fe(II)4L4 cage 1 into previously-reported low-spin Fe(II)4L4 cage 2: 2-formyl-6-methylpyridine was ejected in favor of the less sterically hindered 2-formylpyridine, with concomitant high- to low-spin transition of the cage's Fe(II) centers. High-spin 1 also reacted more readily with electron-rich anilines than 2, enabling the design of a system consisting of two cages that could release their guests in response to combinations of different stimuli. The addition of p-anisidine to a mixture of high-spin 1 and previously-reported low-spin Fe(II)4L6 cage 3 resulted in the destruction of 1 and the release of its guest. However, initial addition of 2-formylpyridine to an identical mixture of 1 and 3 resulted in the transformation of 1 into 2; added p-anisidine then reacted preferentially with 3 releasing its guest. The addition of 2-formylpyridine thus modulated the system's behavior, fundamentally altering its response to the subsequent signal p-anisidine.This work was funded by the European Research Council
(695009) and EPSRC (EP/M01083X/1
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