32 research outputs found

    Molecular assembly and encapsulation

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    Abstract Assemblies can emerge whenever more than one copy of a moleeule is present and it is frequently difficult to predict what will emerge without experimentation. Multiple copies of complementaq molecules can give rise to SupersmCNres with functions that are unique to the assembled states. The weak intermolecular forces that hold assemblies together endow them with dynamic, tempomy and even self-correcting qualities.' We give here an account of our recent experiments with minimalistic models for molecular assemblies. BASEBALLS Since twodimensional hydrogen bond arrays are plentiful in supramolecular chemistry, and even more elaborate assemblies have been characterized? our intent was to use the principles of molecular recognition and the moderately directional characteristics of hydrogen bonds to assemble three-dimensional structures that may be said to have a function. These were intended to form closed shells that could encapsulate smaller molecules. The first of these are reported elsewhere3 and involved a collaboration with Javier de Mendoza in Madrid

    Fluorescence resonance energy transfer across a mechanical bond of a rotaxane

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    Fluorescence transfer across a donor-acceptor tagged rotaxane was studied and a small conformational change of the rotaxane observed using fluorescent spectroscopy and ROESY NMR

    Molecular Assembly and Encapsulation Directed by Hydrogen-Bonding Preferences and the Filling of Space

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    Multiple copies of a molecule, held together in finite aggregates, give rise to properties and functions that are unique to their assembled states. Because these aggregates are held together by weak forces operating over short distances, a premium is placed on complementarity: The molecular surfaces must facilitate specific interactions that direct the assembly to one aggregate rather than another. Hydrogen-bonding preferences can be combined with molecular curvature to favor the assembly of four self-complementary subunits into a pseudo-spherical capsule. Filling the capsule with smaller, complementary molecules provides the final instruction for the assembly process.Peer reviewe

    Mechanically regulated rotation of a guest in a nanoscale host

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    The spinning rate of an encapsulated cyclophane guest is affected by the "size" of the coguests

    Chiral Spaces: Dissymmetric Capsules Through Self-Assembly

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    Molecules with self-complementary surfaces interact through weak intermolecular forces to form assemblies, and the assembled states frequently exhibit distinctive properties. Described here are systems in which symmetrical molecules assemble through hydrogen bonding to produce capsules with dissymmetric cavities. The capsules form and dissipate on a time scale that permits their direct observation by nuclear magnetic resonance measurements, and they act as hosts for smaller molecular guests. Molecular recognition of chiral guests, such as naturally occurring terpenes, determines which dissymmetric cavities are preferentially formed in the assembly process.Peer reviewe

    Chiral Softballs:  Synthesis and Molecular Recognition Properties

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    Studies on the different congeners of the softball were undertaken to explore structural variants for enantioselective encapsulation. Two different spacer elements in the monomeric subunit render the dimeric softball chiral although the monomer itself is achiral. The dimers represent capsules with dissymmetric cavities with volumes ranging from 190 to 390 Ã…3. The cavities are distorted spheres, and asymmetric guests, such as naturally occurring terpenes, generally prefer one enantiomer of the capsule to its mirror image. The selectivities are moderate (up to 4:1). The complexation studies show that the host capsules are flexible enough to arrange themselves comfortably around a guest but still maintain enough rigidity to be influenced by the occupancy of a chiral guest. The enantiomeric capsules can interconvert (racemize) by dissociation and recombination of their subunits.Peer reviewe

    Structural Rules Governing Self-Assembly Emerge from New Molecular Capsules

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    We thank the Skaggs Research Foundation and the National Institutes of Health for support. We also thank Dr. Tomas Szabo for advice on the synthesis of protected glycolurils. Administración de Fomento Económico of Puerto Rico provided fellowship support to J.M.R. The Ministerio de Educación y Cultura of Spain provided fellowship support to T.M.Peer reviewe

    Chiral Microenvironments in Self-Assembled Capsules

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    A nonracemic compound is synthesized and shown to assemble reversibly through hydrogen bonding to form a cyclic tetramer. The chiral arrangement of atoms in the individual pieces becomes amplified through self-assembly to yield multiple functional groups asymmetrically arranged within the cavity. The tetrameric capsule shows a special affinity for ketones and is able to discriminate between their enantiomers in solution.Peer reviewe

    Extended cavitands of nanoscale dimensions

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    New tetrabenzimidazole cavitands with upper rims extended by aromatic groups have been prepared and their X-ray structures were analyzed. The reversible encapsulation of a series of n-alkylammonium guests was studied by NMR spectroscopy and mass spectrometry. These guests showed different binding modes and unique interactions with the hydrophobic cavity. The trimethylammonium guests bearing n-butyl to n-hexyl substituents stabilize the C4v conformation of the cavitand by additional CH⋯π interactions with the aromatic upper part. The longest n-hexylammonium salt adopts a minimal gauche conformation to fit in the cavity
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