Supramolecular Building Blocks Research Articles

Reciprocal Self-Assembly of Peptide-DNA Conjugates into a Programmable Sub-10-nm Supramolecular Deoxyribonucleoprotein.

To overcome the limitations of molecular assemblies, the development of novel supramolecular building blocks and self-assembly modes is essential to create more sophisticated, complex, and controllable aggregates. The self-assembly of peptide-DNA conjugates (PDCs), in which two orthogonal self-assembly modes, that is, β-sheet formation and Watson-Crick base pairing, are covalently combined in one supramolecular system, is reported. Despite extensive research, most self-assembly studies have focused on using only one type of building block, which restricts structural and functional diversity compared to multicomponent systems. Multicomponent systems, however, suffer from poor control of self-assembly behaviors. Covalently conjugated PDC building blocks are shown to assemble into well-defined and controllable nanostructures. This controllability likely results from the decrease in entropy associated with the restriction of the molecular degrees of freedom by the covalent constraints. Using this strategy, the possibility to thermodynamically program nano-assemblies to exert gene regulation activity with low cytotoxicity is demonstrated.

Reciprocal Self‐Assembly of Peptide–DNA Conjugates into a Programmable Sub‐10‐nm Supramolecular Deoxyribonucleoprotein

AbstractTo overcome the limitations of molecular assemblies, the development of novel supramolecular building blocks and self‐assembly modes is essential to create more sophisticated, complex, and controllable aggregates. The self‐assembly of peptide–DNA conjugates (PDCs), in which two orthogonal self‐assembly modes, that is, β‐sheet formation and Watson–Crick base pairing, are covalently combined in one supramolecular system, is reported. Despite extensive research, most self‐assembly studies have focused on using only one type of building block, which restricts structural and functional diversity compared to multicomponent systems. Multicomponent systems, however, suffer from poor control of self‐assembly behaviors. Covalently conjugated PDC building blocks are shown to assemble into well‐defined and controllable nanostructures. This controllability likely results from the decrease in entropy associated with the restriction of the molecular degrees of freedom by the covalent constraints. Using this strategy, the possibility to thermodynamically program nano‐assemblies to exert gene regulation activity with low cytotoxicity is demonstrated.

A Partially Fluorinated, Water-Stable Cu(II)-MOF Derived via Transmetalation: Significant Gas Adsorption with High CO2 Selectivity and Catalysis of Biginelli Reactions.

A partially fluorinated, angular tetracarboxylic acid linker (H4L) incorporating a pendant amine moiety forms a three-dimensional Zn(II) framework, 1. The structure consists of paddle-wheel Zn2(CO2)4 secondary building units (SBUs) and Zn12(CO2)24 supramolecular building blocks (SBBs). Thermal stability of 1 is found to be low. However, it undergoes transmetalation reaction with Cu(II) at room temperature without losing crystallinity affording an isostructural framework, 1Cu. Framework 1Cu is thermally robust and allows generation of the solvent-free porous framework 1Cu' upon activation with coordinatively unsaturated metal centers. Framework 1Cu' exhibits water stability and at 77 K, adsorbs 2.56 wt % of H2 up to 1 bar that significantly increases to 4.01 wt % at 13 bar. Also, this framework gives a high adsorption of 164.70 cc/g of CH4 (11.7 wt %) at 303 K and 60 bar. The channel surfaces decorated with -NH2 group and unsaturated metal centers in 1Cu' allow a promising 36.4 wt % of CO2 adsorption at 1 bar and 273 K. Moreover, it exhibits pronounced selectivity of CO2 adsorption over N2 and H2 at 273 K. Finally, the versatility of 1Cu' is shown by its excellent heterogeneous catalytic activity in the Biginelli coupling reactions involving an aldehyde, urea, and ethylacetoacetate to afford dihydroprimidinones.

A Polyhedral Metal–Organic Framework Based on Supramolecular Building Blocks: Catalysis and Luminescent Sensing of Solvent Molecules

A multifunctional polyhedral metal–organic framework with a pcu network topology based on supramolecular building blocks can be constructed by the reaction of Eu(NO3)3 and pyridine-3,5-dicarboxylic acid (H2PDC). The basic EuIII paddlewheel nodes as secondary building units (SBUs) are connected by PDC ligands to generate nanosized metal–organic cuboctahedra (MOCs), which are further connected by sharing the paddlewheel SBUs to give rise to a three-dimensional primitive cubic network arrangement. The obtained metal–organic frameworks (MOFs) exhibit excellent catalytic activity toward the cyanosilylation of aromatic aldehydes and could be reused without loss of activity. In addition, they can also be considered as a fluorescent probe for nitrobenzene sensing based on luminescence quenching effects arising from host–guest interactions. This porous MOF combining catalytic and fluorescent properties could further meet the requirement as a multifunctional material.

Influence of acidic media on the supramolecular aggregation of iso-tellurazole N-oxides

Iso-tellurazole N-oxides are promising supramolecular building blocks. While in neutral solutions, they form tetra- and hexameric macrocyclic aggregates linked by Te···O secondary bonding (σ hole interactions or chalcogen bonds), protonation of the oxygen atom in acidic media disrupts such supramolecular association. The process is reversible and, consequently, can be used to switch on and off the self-assembly process. Hammett acidity measurements gave pKa values of –3.2 for the protonated molecules. Adducts with HCl and HBr were isolated and structurally characterized. Protonation in solution led to the crystallization of a new polymorph of 3-methyl-5-phenyl-1,2-tellurazole N-oxide, which features a unique polymeric arrangement.

(Invited) Controlled Assembly of C60 Using Supramolecular Scaffolds

Spontaneous molecular assembly in solution usually proceeds under thermodynamic control and thus provides a reliable approach to creating materials with high positional and/or orientational order of the constituent molecules. If supramolecular building blocks could be purposely designed, one may control the alignment of functional molecular units so that the resulting assembly can take full advantage of the inherent properties of the functional units. This presentation will focus on the controlled assembly of C60 using several supramolecular building blocks. When C60 is attached to a particular type of hexabenzocoronene capable of forming a nanotubular assembly, a coaxial nanotube results, where the wall consists of hole-transporting hexabenzocoronene arrays, while inner and outer surfaces are covered by an electron-transporting monolayer of C60 [1]. We have also shown that an amphiphilic design of an oligothiophene-C60 dyad provides a rational strategy for tailoring bicontinuous electron donor and acceptor arrays [2]. We recently found that a tripodal triptycene self-assembles into a 2D hexagonal structure by nested packing. The interpenetration of the triptycene part may suppress structural fluctuation, thus enabling the formation of organic films with a remarkably long-range structural order [3]. Using this tripodal triptycene as a supramolecular building block, a C60 unit can be assembled into a two-dimensional sheet-like structure. The synthesis and properties of these materials with controlled C60assemblies will be discussed.

ChemInform Abstract: Heterometallic Rings: Their Physics and Use as Supramolecular Building Blocks

AbstractReview: [86 refs.

Direct Observation of Highly Ordered Dendrimer Soft Building Blocks over a Large Area.

Developing large-area, single domain of organic soft-building blocks such as block copolymers, colloids, and supramolecular materials is one of the most important issues in the materials science and nanotechnology. Owing to their small sizes, complex molecular architectures, and high mobility, supramolecular materials are not well-suited for building large area, single domain structures. In the described study, a single domain of supramolecular columnar dendrimers was created over large area. The columnar structures in these domains have smaller (4.5 nm) diameters, higher area densities (ca. 36 Tera-dots/in(2)) and larger domains (>0.1 × 0.1 mm(2)) than those of all existing BCP and colloidal assemblies. By simply annealing dendrimer thin films between two flat solid surfaces, single domains of hexagonal columnar structures are created over large macroscopic areas. Observations made in this effort should serve as the foundation for the design of new routes for bottom-up lithography based on supramolecular building blocks.

Heterometallic Rings: Their Physics and use as Supramolecular Building Blocks.

An enormous family of heterometallic rings has been made. The first were Cr7 M rings where M = Ni(II), Zn(II), Mn(II), and rings have been made with as many as fourteen metal centers in the cyclic structure. They are bridged externally by carboxylates, and internally by fluorides or a penta-deprotonated polyol. The size of the rings is controlled through templates which have included a range of ammonium or imidazolium ions, alkali metals and coordination compounds. The rings can be functionalized to act as ligands, and incorporated into hybrid organic-inorganic rotaxanes and into molecules containing up to 200 metal centers. Physical studies reported include: magnetic measurements, inelastic neutron scattering (including single crystal measurements), electron paramagnetic resonance spectroscopy (including measurements of phase memory times), NMR spectroscopy (both solution and solid state), and polarized neutron diffraction. The rings are hence ideal for understanding magnetism in elegant exchange-coupled systems.

Distinct Packings of Supramolecular Building Blocks in Metal-Organic Frameworks Based on Imidazoledicarboxylic Acid.

When the supramolecular building block packings (face-centered, body-centered, and primitive cubic) with different interactions (hydrogen and coordination bonding) were controlled, four new structures based on octahedral M(II) (M = Zn, Ni, Mn) and imidazoledicarboxylate were constructed. The interaction modes between the supramolecular building blocks affect the water stability of the structures. Furthermore, with uncoordinated carboxylate O atoms in the structures, these compounds demonstrate a strong capability of capturing metal ions in the solution.

ChemInform Abstract: Arylene Ethynylene Macrocycles: From Molecular Hosts to Components of High‐Performance Supramolecular Architectures

AbstractReview: [22 refs.

New ruthenium(II) complexes of 2,2′:6′,2″-terpyridine derivatives as supramolecular building blocks

Eight new heteroleptic ruthenium(II) complexes of 2,2′:6′,2″-terpyridine derivatives are reported and characterized by multinuclear NMR and electrospray mass spectrometry. Complexes featuring pendant aryl bromide or pyridyl groups in the 4′ position of terpyridine are suitable for palladium(0) coupling reactions to form large metallo-supramolecular ligands. Aryl boronic ester derivatives were found to be unstable with respect to hydroxylation.

Long-range energy transport in single supramolecular nanofibres at room temperature.

Efficient transport of excitation energy over long distances is a key process in light-harvesting systems, as well as in molecular electronics. However, in synthetic disordered organic materials, the exciton diffusion length is typically only around 10 nanometres (refs 4, 5), or about 50 nanometres in exceptional cases, a distance that is largely determined by the probability laws of incoherent exciton hopping. Only for highly ordered organic systems has the transport of excitation energy over macroscopic distances been reported--for example, for triplet excitons in anthracene single crystals at room temperature, as well as along single polydiacetylene chains embedded in their monomer crystalline matrix at cryogenic temperatures (at 10 kelvin, or -263 degrees Celsius). For supramolecular nanostructures, uniaxial long-range transport has not been demonstrated at room temperature. Here we show that individual self-assembled nanofibres with molecular-scale diameter efficiently transport singlet excitons at ambient conditions over more than four micrometres, a distance that is limited only by the fibre length. Our data suggest that this remarkable long-range transport is predominantly coherent. Such coherent long-range transport is achieved by one-dimensional self-assembly of supramolecular building blocks, based on carbonyl-bridged triarylamines, into well defined H-type aggregates (in which individual monomers are aligned cofacially) with substantial electronic interactions. These findings may facilitate the development of organic nanophotonic devices and quantum information technology.

Synthesis, characterization and comparative study of a series of fluorinated Schiff bases containing different orientation [sbnd]CH[dbnd]N[sbnd] spacers

Investigation of the crystal structures of three pairs of multi-fluorinated compounds with bridge-flipped isomeric character, which on the molecular level differ only in the orientation of the bridging bond CHN connecting two larger parts of the molecule, offers a useful context for the examination and evaluation of supramolecular assembly in the case. The results show that the orientation of the bridging bond CHN determines the conformation of six organic molecules 1a–b, 2a–b and 3a–b, thus further influencing intermolecular weak interactions and final supramolecular arrangements. Accordingly, each molecule of six multi-fluorinated compounds as supramolecular building block unit, via strong intermolecular interactions, including interactions between fluorine atoms and aromatic ring hydrogen atoms, between fluorine atoms, and between hydroxyl groups and fluorine atoms, as well as interaromatic π⋯π stacking interactions etc., constructs a series of different and attractive crystal packings. These results demonstrate that by changing CHN orientation, we can obtain different hydrogen-bonded supramolecular structures through different interactions.

Proteins as supramolecular building blocks: Nterm-Lsr2 as a new protein tecton.

Proteins hold great promise in forming complex nanoscale structures which could be used in the development of new nanomaterials, devices, biosensors, electronics, and pharmaceuticals. The potential to produce nanomaterials from proteins is well supported by the numerous examples of self-assembling proteins found in nature. We have explored self-assembling proteins for use as supramolecular building blocks, or tectons, specifically the N-terminal domain of Lsr2, Nterm-Lsr2. A key feature of this protein is that it undergoes self-assembly via proteolytic cleavage, thereby allowing us to generate supramolecular assemblies in response to a specific trigger. Herein, we report the effects of pH and protein concentration on the oligomerization of Nterm-Lsr2. Furthermore, via protein engineering, we have introduced a new trigger for oligomerization via enteropeptidase cleavage. The new construct of Nterm-Lsr2 can be activated and assembled in a controlled fashion and provides some ability to alter the ratio of higher ordered structures formed.

Synthesis of cobalt cluster-based supramolecular triple-stranded helicates.

A cobalt cluster-based triple-stranded helicate, Co8(PDA)6(PTA)3(DMF)3(H2O)3 () (PDA = 2,6-pyridinedicarboxylate, PTA = benzene-1,3-dicarboxylate, DMF = dimethylformamide) was successfully synthesized and fully characterized. Complex can be used as a supramolecular building block in constructing a higher-order helix-of-helix structure, [Co8(PDA)6(PTA)3(DMF)2(H2O)4-0.51(Co(OHn)2)] (n = 1 or 2) ().

Exocyclic self-assembly behavior of carboxylic acid and lariat ether macrocyclic hosts: regulation by pendent arm

An exocyclic supramolecular building block through O–H⋯N hydrogen bonding interaction for the assembly of di-sidearm dibenzo-diazacrown ethers bearing a flexibility sidearm with PTA acid.

Self-assembly of channel type β-CD dimers induced by dodecane.

Cyclodextrins (CDs) can hardly self-assemble into well-defined structures. Here we report if they preassemble into channel type dimers assisted by dodecane, well-defined vesicles and bricks can be formed. Unlike the traditional self-assembly of amphiphilic molecules driven by hydrophobic effect, the self-assembly of the channel type dodecane@2β-CD supramolecular building block is predoninantly driven by hydrogen-bonds. More water molecules are found in the lyophilized vesicles than in the bricks, suggesting water molecules play an important role in the self-assembly of the channel-type dimers of β-CD. The amount of structural water in the self-assembly is closely related to the curvature of the final self-assembled structures. Our work reveals that the channel-type dimer of β-CD may represent a new sort of building block for advanced structures.

A Macrocyclic 2,2′‐Bibenzimidazole Ruthenium(II) Chromophore as a Versatile Building Block for Supramolecular Devices

AbstractWe present the synthesis of a macrocyclic ruthenium(II) complex that combines the versatile photophysics and supramolecular chemistry of biimidazole ruthenium(II) chromophores with a macrocyclic geometry that allows for its introduction into mechanically interlocked frameworks. Structural information on the core framework was gained from a solid‐state structure. The new supramolecular building block shows that the principal photophysics of the ruthenium chromophore, that is, the cation‐driven light‐switch effect, are retained during the formation of the macrocycle.

Synthesis and solid-state supramolecular chemistry of a series of pyridinium-derived zwitterions

A new class of potential supramolecular building blocks is presented. The synthesis and crystal structures of seven novel pyridinium-derived zwitterionic compounds are discussed, as well as two related pyridinium salts. The synthesis of these compounds was achieved by simple solution methods using mild conditions, and the products were isolated as single crystals with no further purification required. Hydrogen-bonded chains were found to be prevalent in all of the crystal structures of the zwitterions and due to the robust nature of this motif, these compounds have the potential to be exploited in future supramolecular studies. There is a large scope for the synthesis of related zwitterionic compounds using a range of pyridyl substituents with varied functional groups. These zwitterionic compounds show great potential as a new class of supramolecular building block in the formation of ionic- as well as metal–organic frameworks.