Supramolecular Design Research Articles

Supramolecular crafting of cell adhesion

The supramolecular design of bioactive artificial extracellular matrices to control cell behavior is of critical importance in cell therapies and cell assays. Most previous work in this area has focused on polymers or monolayers which preclude control of signal density and accessibility in the nanoscale filamentous environment of natural matrices. We have used here self-assembling supramolecular nanofibers that display the cell adhesion ligand RGDS at van der Waals density to cells. Signal accessibility at this very high density has been varied by changes in molecular architecture and therefore through the supramolecular packing of monomers that form the fibers. We found that branched architectures of the monomers and the consequent lower packing efficiency and additional space for epitope motion improves signaling for cell adhesion, spreading, and migration. The use of artificial matrices with nanoscale objects with extremely high epitope densities could facilitate receptor clustering for signaling and also maximize successful binding between ligands and receptors at mobile three-dimensional interfaces between matrices and cells. Supramolecular design of artificial bioactive extracellular matrices to tune cell response may prove to be a powerful strategy in regenerative medicine and to study biological processes.

Supramolecular photocurrent-generating systems using porphyrin composite materials

Supramolecular design principles for a porphyrin-sensitized, wet-type solar cell are described. To construct efficient organic photocurrent-generating systems, the following two important targets exist: (i) kinetic control of photoinduced electron-transfer processes by spatial, three-dimensional alignment of photo-functional molecules (sensitizers, electron donors, acceptors, and mediators) and (ii) highly dense deposition of composites of the photo-functional molecules on an electrode. These objectives can be achieved by tailoring a photoactive multilayer using supramolecular interactions, such as molecular adsorption, inclusion, coordination, and recognition. Using these interactions, it is expected that the reduction of the costs of synthesis and the combinational fabrication of a simplified-molecular device will become possible. In addition, recent approaches toward the construction of supramolecular porphyrin-sensitized photovoltaic cells are introduced.

Recent Advances in Synthetic Membrane Transporters

It is 25 years since the first report of a synthetic ion channel transporter. Today, dozens of molecular and supramolecular designs have been developed to facilitate ion and small molecule transport across a bilayer membrane. Presented here is a concise summary of the advances made over the past four years. The transporters are grouped into three mechanistic classes: mobile carrier, monomeric channel, and self-assembled pore. Common building blocks are crown ethers, steroids, cyclodextrins, peptides, curcubiturils, and calixarenes. The eventual goal is to produce functional supramolecular devices such as sensors, enzyme assays, and lead candidates for pharmaceutical development.

Supramolecular design in biopolymers and biomimetic polymers for advanced mechanical properties

AbstractThis mini review uses two examples to illustrate the importance of supramolecular chemistry in natural and biomimetic polymers for advanced mechanical properties. In the first example, dragline silk, one of the strongest and toughest natural fibers, uses intermolecular weak forces to self‐assemble into nanocomposites composed of β‐sheet nanocrystals imbedded in an amorphous matrix. In the second example, a load‐bearing protein, the sarcomere muscle protein titin, uses intramolecular weak forces to fold into repetitive modules for combined strength, toughness, and elasticity. Both examples show vividly that many natural polymers can combine important mechanical properties through programming supramolecular weak interactions into covalently formed biopolymers. This mini review attempts to summarize the current understanding of the molecular mechanisms that contribute to the exceptional mechanical properties for each natural polymer. Following that, the efforts from others and the author's own laboratory on developing synthetic polymers to mimic these natural counterparts are discussed. Copyright © 2007 Society of Chemical Industry

The Effect of Multiple Substituents on Sandwich and T‐Shaped π–π Interactions

Sandwich and T-shaped configurations of substituted benzene dimers were studied by second-order perturbation theory to determine how substituents tune pi-pi interactions. Remarkably, multiple substituents have an additive effect on the binding energy of sandwich dimers, except in some cases when substituents are aligned on top of each other. The energetics of substituted T-shaped configurations are more complex, but nevertheless a simple model that accounts for electrostatic and dispersion interactions (and direct contacts between substituents on one ring and hydrogen atoms on the other), provides a good match to the quantum mechanical results. These results provide insight into the manner by which substituents csan be utilized in supramolecular design.

Recent Advances in Supramolecular Design and Assembly of Silver(I) Coordination Polymers

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Self-assembled antimony-thiolate Sb2L3and Sb2L2Cl2complexes

The synthesis and single crystal X-ray structures of two new self-assembled antimony(III)-thiolate complexes are described: Sb2 L 3 (1) and “anti”-Sb2 L 2Cl2 (2), where H2 L is α,α′-dimercaptoxylene. The Sb(III) ions in both complexes exhibit tripodal coordination geometries with stereochemically-active lone pairs. The extended structure of 1 in the crystalline state reveals numerous C[sbnd]H···S interactions, while the packing in 2 is dominated by numerous antimony-sulfur and antimony-chlorine secondary bonding interactions. These structures demonstrate that a supramolecular design strategy can be developed to prepare self-assembled structures based on the coordination geometry of Sb(III) and the reversible formation of antimony-thiolate bonds in solution. This strategy offers promise in the specific chelation of toxic ions such as antimony, a contaminant of increasing environmental concern.

Recent Advances in Supramolecular Design and Assembly of Silver(I) Coordination Polymers

The supramolecular chemistry of Ag(i) coordination assemblies continues to attract attention due to their versatile structural diversity and potential physical and chemical functions. This article provides a short review of recent advances in the design and construction of Ag(i) coordination polymers with special emphasis on the Ag(i) ion coordination geometry, ligand functionality, and supramolecular interactions. The potential functions of Ag(i) coordination polymers are briefly summarized.

Reversible Penta- and Hexacoordination Motifs in [Co(TMPP)] Resulting in Interchange of 1D and 2D Supramolecular Designs

meso-Tetrakis(3,4,5-trimethoxyphenyl)cobalt(II) porphyrin [Co(TMPP)] (1) is synthesized by a new method. The X-ray structure of 1 grown in dichloromethane shows square-pyramidal coordination around the Co(II) ion, displaying a 1D polymeric network. When grown in chloroform, 1 displays an octahedral coordination around Co(II), resulting in a 2D coordination network. This solvent-dependent variation in ligation of the O-donor atom(s) of the 4-methoxy groups of the meso-phenyl rings in the axial position(s) of the central Co(II) is reversible, as shown by electronic spectroscopy. The magnetic and electron paramagnetic resonance (EPR) data of these two crystalline forms are dependent on the nature of the axial interaction. Increased axial coordination showed increased splitting between the e and a1 orbitals, resulting in further separation between 2A1 and 2E. The EPR data are consistent with this result. The difference in energy levels in these two forms is in agreement with the magnetic and spectroscopic data.

The Chemistry of Organic Nanomaterials

The development of nanotechnology using organic materials is one of the most intellectually and commercially exciting stories of our times. Advances in synthetic chemistry and in methods for the investigation and manipulation of individual molecules and small ensembles of molecules have produced major advances in the field of organic nanomaterials. The new insights into the optical and electronic properties of molecules obtained by means of single-molecule spectroscopy and scanning probe microscopy have spurred chemists to conceive and make novel molecular and supramolecular designs. Methods have also been sought to exploit the properties of these materials in optoelectronic devices, and prototypes and models for new nanoscale devices have been demonstrated. This Review aims to show how the interaction between synthetic chemistry and spectroscopy has driven the field of organic nanomaterials forward towards the ultimate goal of new technology.

Testing the reliability of the self-complementary noncovalent interactions: supramolecular implications and supramolecular design

Testing the reliability of the self-complementary noncovalent interactions: supramolecular implications and supramolecular design

Supramolecular blueprint approach to metal-coordinated capsules

An important problem in designing any large network is the assembly of systems that are resilient to change. From a chemical point of view, an analogy can be used where one requires supramolecular assemblies to maintain their dimensionality combined with limited structural perturbation in response to variation in its intermolecular framework. The identification of hydrogen-bonded framework patterns within experimentally known supramolecular assemblies that are structurally robust to disruption and selective hydrogen substitution are envisioned to act as a supramolecular blueprint or template for metal-ion retroinsertion. Here, we report the formation of a large neutral discrete pseudo-spherical coordination capsule assembled from 6 pyrogallol[4]arene ligands and 24 Cu(II) metal ions. Amazingly, this coordination capsule is structurally analogous to its hydrogen-bonded counterpart. This result shows a robust ability of pyrogallol[4]arene molecules to self-assemble into large hexameric cage structures from either the hydrogen-bonding or metal-ligand coordination process. The identification of robust supramolecular assemblies that conserve their structure in response to interchangeability between hydrogen-bonded networks for metal coordination, or inversely, represents an important advancement in supramolecular design.

Supramolecular design of a porphyrin–[60]fullerene photocurrent generation system on a DNA scaffold fabricated by a conjugate polymer film

DNA which binds monocationic [60]fullerene ( 1 ) and tetracationic porphyrin (TMPyP) was readily fabricated by electrochemical oxidative polymerization of 3.4-ethylenedioxythiophene (EDOT) and the resultant poly(EDOT) composite was deposited on an ITO electrode as a stable thin film. Spectral and CV analyses established that one 1 and one TMPyP are bound per 57 nucleobase units, that is, every three pitches of DNA. Photoirradiation of this 1 /TMPyP/DNA-poly(EDOT) film generated a photocurrent in 3.8% quantum yield, which was much higher than those obtained from 1 /DNA and TMPyP/DNA systems. One can conclude, therefore that the photoexcited energy of TMPyP is transferred to 1 , which is collected by the electron-conducting poly(EDOT) film. The present paper shows that DNA is useful as a scaffold to arrange redox-active couples in a one-dimensional matrix.

Complementarity in the Supramolecular Design of Arenaviruses and Retroviruses Revealed by Electron Cryomicroscopy and Image Analysis

Arenaviruses are rodent-borne agents of diseases, including potentially lethal human hemorrhagic fevers. These enveloped viruses encapsidate a bisegmented ambisense single-stranded RNA genome that can be packaged in variable copy number. Electron cryomicroscopy and image analysis of New World Pichinde and Tacaribe arenaviruses and Old World lymphocytic choriomeningitis virus revealed pleomorphic enveloped particles ranging in diameter from approximately 400 to approximately 2,000 A. The surface spikes were spaced approximately 100 A apart and extended approximately 90 A from the maximum phospholipid headgroup density of the outer bilayer leaflet. Distinctive stalk and head regions extended radially approximately 30 and approximately 60 A from the outer bilayer leaflet, respectively. Two interior layers of density apposed to the inner leaflet of the viral lipid bilayer were assigned as protein Z and nucleoprotein (NP) molecules on the basis of their appearance, spacing, and projected volume. Analysis of en face views of virions lacking the GP-C spikes showed reflections consistent with paracrystalline packing of the NP molecules in a lattice with edges of approximately 57 and approximately 74 A. The structural proteins of retroviruses and arenaviruses assemble with similar radial density distributions, using common cellular components.

Supramolecular electronics; nanowires from self-assembled π-conjugated systems

The conditions required for supramolecular electronics, e.g. nano-sized optoelectronic devices, will be illustrated on the basis of the programmed self-assembly of pi-conjugated systems into individual nanosized wires. Using the supramolecular design rules nanowires can be created from almost any polymeric and oligomeric pi-conjugated system. In the case of oligomers it is even possible to construct individual wires having a uniform diameter of one molecule thickness. The construction of wires on a substrate is possible by self-assembly in solution or during the deposition. The transfer of the supramolecular stacks from solution to a solid support is a very delicate process. A comprehensive knowledge of all intermolecular interactions gives rise to controlled transfer of pi-conjugated assemblies to specific surfaces. There are a large number of very appealing targets that should be reached before supramolecular electronics can serve as an attractive alternative in between single molecule electronics and bulk devices. Nevertheless, the combination of exciting scientific results and intriguing technological challenges creates an interesting future for supramolecular electronics.

Progress Toward Understanding the Nature and Function of C-H...O Interactions

Recent studies confirm that C-H...O hydrogen bonds have many, if not all, of the spectroscopic and physical earmarks of “traditional” H-bonds. Only more recently have we come to understand that these contacts are operative not only in protein-protein recognition, but enzyme-substrate interactions (with implications for drug design), biological and nonbiological transition state stabilization and have, in some circumstances, a strength and geometric predictability to make them useful in the construction of materials and supramolecular assemblies. Forays into each of these areas have come largely due to advances in computational protocols and spectroscopic instrumentation. This review discusses the most recent findings related to the nature (i.e. strength, geometrical preferences, and spectroscopic features) and function (i.e. in supramolecular design and synthesis, conformational control, enantioselective synthesis, and biology) of C-H...O interactions in a variety of chemical and biological systems. An understanding of the key features of these interactions should promote their deployment in target areas like medicinal chemistry and materials science.

Structure and excited state properties of multiporphyrin arrays formed by supramolecular design

Structurally defined nanoscale self-assembled multiporphyrin arrays of variable geo-metry and composition (up to eight tetrapyrrole macrocycles) have been formed via two-fold extra-ligation in solutions at 77-293 K. The array formation is based on non-covalent binding interactions of the phenyl bridged Zn octaethylporphyrin chemical dimers or trimers, ( ZnOEP )2Ph or ( ZnOEP )3Ph2, with di- and tetrapyridyl substituted tetrapyrrole extra-ligands (porphyrin, pentafluorophenyl substituted porphyrin, Cu porphyrin, tetrahydroporphyrin). Using steady-state and time-resolved measurements, spectral properties as well as pathways and dynamics of non-radiative relaxation processes (energy migration, photoinduced electron transfer, exchange d-π effects, realized in nano-femtosecond time scale) have been studied in these complexes upon variation of the composition, mutual geometry, redox and photophysical properties of interacting subunits as well as on the tempera-ture and polarity of surrounding.

Crystal Engineering of “Porphyrin Sieves” Based on Coordination Polymers of Pd- and Pt-tetra(4-carboxyphenyl)porphyrin

Targeted solid-state synthesis of supramolecular porphyrin networks with palladium- and platinum-tetra(4-carboxyphenyl)porphyrins as building blocks, in different reaction environments, afforded a series of new extended coordination polymers sustained by sodium, potassium, and copper metal ion cluster auxiliaries. Formulation of open channel-type architectures in these materials has been confirmed by X-ray crystallography at low temperature. Open, 0.50−0.65 nm wide, channels were found to propagate throughout the corresponding crystals. These channels are accessible to other guest/solvent molecules for inclusion in the crystalline lattice. The structural features of the analyzed materials resemble those of common molecular sieve solids, and represent a successful realization of the crystal engineering concepts of porphyrin-based supramolecular design evaluated in this laboratory.

Derivatives of tetraphenylmethane and tetraphenylsilane: Synthesis of new tetrahedral building blocks for molecular construction

Useful derivatives of tetraphenylmethane and tetraphenylsilane have been synthesized by efficient methods that give crystalline products without chromatographic purification. New compounds include tetrakis(4-hydroxyphenyl)methane (21), tetrakis(4-formylphenyl)methane (22), tetrakis[(4-hydroxymethyl)phenyl]methane (23), tetrakis(4-bromophenyl)silane (24), tetrakis(4-iodophenyl)silane (25), tetrakis(4-hydroxyphenyl)silane (26), tetrakis[(4-hydroxymethyl)phenyl]silane (27), and tetrakis[(4-chloromethyl)phenyl]silane (28). These compounds are valuable precursors for the construction of complex molecules with tetrahedral geometries.Key words: organic synthesis, molecular and supramolecular design and construction, tetraphenylmethane, tetraphenyl silane, tetrahedral building blocks.

Supramolecular Design of Coordination Complexes of Silver(I) with Polyimine Ligands: Synthesis, Materials Characterization, and Structure of New Polymeric and Oligomeric Materials

A series of new coordination polymers and oligomers of polyimine ligands with silver(I) ions have been synthesized and characterized by single-crystal X-ray diffraction studies, elemental analysis, IR, UV−Vis, and NMR spectroscopy. They represent discrete dinuclear Ag(I) complexes, one-dimensional polymers, and two-dimensional polymeric assemblies, depending on the chosen type, functionality, and denticity of the bridging ligands. Trigonal, tetrahedral, and pseudo-tetrahedral, as well as the more common linear coordination motifs of the silver(I) ions, have been observed, demonstrating the high versatility in the supramolecular design of such hybrid organic−inorganic materials.