Design and construction of supramolecular and macromolecular architectures by tandem interactions

The self-assembling behaviour of several molecular building blocks are used to construct a variety of chiral and nonchiral supra-molecular and macromolecular architectures. These structures can be finely tuned by slight changes in e.g. the shape of the building blocks, the pH and by the addition of guest molecules.     

Combination of orthogonal supramolecular interactions in polymeric architectures

Supramolecular polymers represent a highly interesting approach towards new "smart materials". A recent strategy includes the combination of different "orthogonal" non-covalent binding sites within one polymer system. Different functionalities can be introduced in a highly defined way by controlled self-assembly processes. This feature article presents highlights in the supramolecular polymer chemistry of multiple hydrogen-bonding, metal complexation (especially of bi- and terpyridines) and host-guest interactions as well as recent advances in combining these interactions in novel polymers.     

Pillar[5]arene-based polymeric architectures constructed by orthogonal supramolecular interactions

Ureidopyrimidinone functionalized pillar[5]arene (UPyP5) was synthesized and employed to complex with a bisparaquat derivative (G) to form supramolecular polymers at relatively high concentration. The orthogonal binding interactions including quadruple hydrogen bonding and host-guest interaction should play vital roles in the construction of this linear assembly.     

Asymmetrical supramolecular interactions as basis for complex responsive macromolecular architectures

Intrigued by natural responsive systems based on a combination of macromolecules and non-covalent interactions, polymer scientists have mimicked such systems by the formation of supramolecular polymers based on ionic interaction, hydrogen bonding and metal coordination. In recent years, the focus has shifted from rather simple non-directional and self-complementary interactions to the use of asymmetrical directional supramolecular interactions that allow the formation of complex responsive macromolecular architectures such as block copolymers, star-shaped polymers and graft copolymers. This feature article covers these recent developments on the use of asymmetrical supramolecular interactions in polymer science. Special attention is given to the formation of complex macromolecular architectures using directional supramolecular interactions. In addition, the responsiveness of the resulting macromolecular systems is discussed based on the assembly and/or disassembly that can be triggered by changes in external conditions.     

Organic semi-conducting architectures for supramolecular electronics

The properties of organic electronic materials in the solid-state are determined not only by those of individual molecules but also by those of ensembles of molecules. The ability to control the architectures of these ensembles is thus essential for optimizing the properties of conjugated materials for use in electronic devices (light emitting diodes, field effect transistors, solar cells, …) and is primordial for potential technological applications in nanoelectronics.Here, we report on the observation by atomic force microscopy (AFM) of 1D and 2D nanoscale architectures obtained in the solid-state from solutions of molecularly-dissolved conjugated block copolymers or oligomers, and demonstrate that the conjugated molecules can organize onto a surface over lengthscales from nanometers to several microns, forming semiconducting fibrils or bi-dimensional organizations (monolayers) by π-stacking processes (by changing the sample preparation conditions).     

Interrogation of cobaloxime-based supramolecular photocatalyst architectures

This perspective provides a discussion of recent work focused on elucidating the fundamental interactions of artificial photosynthesis in newly developed supramolecular photocatalysts composed of linked chromophore and catalyst modules. Supramolecular photocatalyst architectures are of particular interest because of their potential to overcome many of the limitations of molecular or multimolecular systems and amenability to conventional and emerging physical characterization techniques. As such, changes to the oxidation state and/or physical structure of either chromophore or catalyst modules in response to light excitation is readily monitored with high spatial and temporal resolution. To illustrate this approach, the design evolution of photocatalysts based on Ru(II)poly(pyridyl) chromophores linked to cobaloxime-based H₂ catalysts is discussed. In this work, new synthesis, transient optical spectroscopy, and X-ray scattering were combined to develop next generation photocatalysts capable of ultrafast charge transfer and identification of a key intermediate for hydrogen photocatalysis. Recent and upcoming advances in light source capabilities are ideally suited to monitor light-generated transient structures and well-poised to dramatically impact the drive toward technologically relevant systems for artificial photosynthesis.     

Hierarchical supramolecular fullerene architectures with controlled dimensionality

Self-assembly of a fullerene derivative with long alkyl chains in different solvents results in the formation of hierarchically-ordered supramolecular assemblies with well-defined 1, 2 and 3D architectures such as vesicles, fibers, discs and cones, whose fundamental structural sub-unit consists of bilayers.     

New supramolecular architectures based on hydrogen bonding

Heterocyclic compounds containing two and three adjacent hydrogen bond donor and acceptor sites in all possible arrangements were synthesized (see generalized structures shown below) to study and use their “base-pairing” capabilities. With two adjacent donor and acceptor groups there are three possible arrangements and these form two types of complexes (DA·AD and AA·DD). Three adjacent hydrogen bond donor and acceptor sites can be arranged in six different ways and these form three different complexes (ADA·DAD, AAD·DDA, and AAA·DDD).     

Towards tobacco mosaic virus-like self-assembled supramolecular architectures

This paper discusses the molecular design of selected examples of structural units containing taper shaped exo-receptors and various crown ether, oligooxyethylenic, and H-bonding based endo-receptors, which self-assemble into cylindrical channel-like architectures via principles resembling those of tobacco mosaic virus (TMV). The ability of these structural units to self- assemble via a delicate combination of exo-and endo-recognition processes will be presented. A comparison between various supramolecular (generated via H-bonding, ionic, and electrostatic interactions) and molecular “polymer backbones” will be made. The present limitations concerning the ability to engineer the structural parameters of these supramolecular channel-like architectures and some possible novel material functions derived from them will be briefly mentioned.     

Self-assembly of supramolecular architectures and polymers by orthogonal metal complexation and hydrogen-bonding motifs

A modular construction kit with two orthogonal noncovalent binding sites for self-assembly of supramolecular architectures is presented. The heteroditopic building blocks contain a terpyridine (tpy) unit for coordination of metal ions and a Hamilton receptor for multiple H-bonding of cyanuric acid derivatives. The association constants of ligand binding of M(II) complexes (M=Ru, Zn, Fe, and Pt) with a dendritic end cap were determined to be in the range of 10(2) and 10(4) L mol(-1) in chloroform. The capabilities for binding of metal ions were investigated by (1)H NMR and UV/Vis spectroscopy. The Fe complexes are most appropriate for the generation of discrete and high-ordered architectures due to their strong tendency to form FeL(2) complexes. Superstructures are readily formed in a one-pot procedure at room temperature. No mutual interactions between the orthogonal binding motifs were observed, and this demonstrates the highly specific nature of each binding process. Decomplexation experiments were carried out to examine the reversibility of Fe-tpy coordination. Substitution of the terminal end cap with a homoditopic bis-cyanurate linkage leads to formation of an iron-containing supramolecular strand. Formation of coordination polymers was confirmed by viscosity measurements. The supramolecular polymer strands can be reversibly cleaved by addition of a terminating cyanuric acid building block, and this proves the dynamic nature of this noncovalent polymerization process.     

Two-dimensional supramolecular self-assembly probed by scanning tunneling microscopy

Supramolecular chemistry has a very large impact on chemistry of current interest and the use of non-covalent but directional forces is appealing for the construction of 'supramolecular architectures'. The invention of scanning probe microscopy techniques has opened new doorways to study these concepts on surfaces. This review deals with recent progress in the study of two-dimensional supramolecular self-assembly on surfaces probed by scanning tunneling microscopy, with a special emphasis on structure, dynamics and reactivity of hydrogen bonded systems.     

Novel silver-containing supramolecular frameworks constructed by combination of coordination bonds and supramolecular interactions

The hydrothermal reactions of AgNO(3), 4,4'-bipy, and carboxylate ligands gave rise to three supramolecular architectures, namely [Ag(bipy)].H(2)SIPA.1/2bipy.H(2)O (1), [Ag(bipy)].1/2H(2)btec.H(2)O (2), and [Ag(bipy)](2).H(2)dpstc.2H(2)O (3) (H(3)SIPA = 5-sulfoisophthalic acid, bipy = 4,4'-bipyridine, H(4)btec = 1,2,4,5-benzenetetracarboxylic acid, H(4)dpstc = 3,3',4,4'-tetracarboxydiphenyl sulfone). All complexes are extended from Ag-bipy linear chains by the combination of coordination bonds and supramolecular interactions in two different approaches. Complexes 1 and 3 comprise two-dimensional frameworks. In the two complexes, a one-dimensional ladderlike structure is first formed by the connection of a Ag-bipy chain through hydrogen bonding between a free carboxylate/bipy ligand and weak coordinative interactions between a free carboxylate ligand and silver ion. The ladderlike structure is then extended to a two-dimensional layer architecture by pi...pi interactions between bipy ligands of the Ag-bipy chains. Complex 2 possesses a three-dimensional framework. The free H(2)btec(2)(-) ligands form a two-dimensional layer network by hydrogen-bonding interactions between protonated and deprotonated carboxylate groups; meanwhile, pi.pi interactions between bipy ligands of Ag-bipy chains also result in a two-dimensional layer. The two layers are further connected by weak Ag-O interactions to generate a three-dimensional supramolecular structure.     

Interfacial recognition reactions as seen by fluorescence-, surface plasmon-and atomic force microscopies

We report on various microscopic investigations of the specific recognition and binding reaction between a biotinylated lipid layer and streptavidin. First, we present fluorescence microscopic evidence for the preferential adsorption of the protein to only the fluid matrix of a monolayer at the water-air interface if the latter is compressed to the phase transition region where crystalline domains coexist with expanded phase. Surface plasmon microscopy shows that this selectivity is preserved also if the monofilm is first transferred to a solid support (but still in contract with the aqueous phase) and then exposed to a streptavidin-containing solution. Finally, atomic force microscopic pictures taken at the monolayer-electrolyte interface are presented that confirm this preferential binding.     

Chiral supramolecular polymers formed by host-guest interactions

alpha-Cyclodextrin with a p-t-butoxyaminocinnamoylamino group in the 3-position (3-p-(t)()BocCiNH-alpha-CD) has been found to form a supramolecular polymer in an aqueous solution. The degree of polymerization of the supramolecular polymer is higher than 15 at 20 mM, as proved by VPO (vapor pressure osmometry) measurements and turbo ion spray TOF MS measurements. The existence of substitution/substitution interactions between adjacent monomers of the supramolecular polymer have been confirmed by the observation of positive and negative Cotton bands in circular dichroism spectra. The mechanism for the induction of the chirality was confirmed using model compounds. The substituents were found to exist as a left-handed anti configuration in supramolecular polymers. The supramolecular polymer was found to take a helical structure. The structure of the supramolecular polymer was observed by STM measurements.     

Photoregulated supramolecular hydrogels driven by polyradical interactions

Organic radical as a powerful tool has been extensively applied in synthetic chemistry. However, harnessing radical-mediated noncovalent interactions to fabricate soft materials remains elusive. Here we report a new category of supramolecular hydrogel system held by multiple radical-radical (polyradical) interactions, and its photosensitive cross-linking structure. A simple polyacrylamide with triarylamine (TAA) pendants is designed as the precursor. The TAA units in polymer can be converted into active TAA^•⁺ radical cations with light and further associate each other via TAA^•⁺‒TAA^•⁺ stacking interactions to form stable supramolecular network. Temporal control of the light irradiation dictates the degree of radical stacks, thus regulating the mechanical performance of the resulting hydrogel materials on-demand. Moreover, the reversible collapse of this hydrogels can be promoted by adding radical scavenger or exerting reduction voltage.     

Chiral supramolecular metal-organic architectures from dinuclear copper complexes

Two new chiral dinuclear Cu(II) complexes [Cu₂(μ-Cl)₂(HL¹)₂] · C₂H₅OH (1) and [Cu₂(μ-Cl)₂(HL²)₂] · CH₃OH (2), have been synthesized and structurally characterized, where the chiral ligands H₂L¹ and H₂L² are derived from the chiral amino alcohols (S)-(−)-2-amino-3-phenyl-1-propanol and (S)-(+)-2-phenylglycinol. Single-crystal X-ray crystallographic analyses revealed that in these complexes, the dominant hydrogen bonding property of metal bound chloride anion directs the self assembly of complex molecules through C–H···Cl hydrogen bonding interactions leading to the formation of intriguing hydrogen bonded metallo-supramolecular architectures in their respective crystal lattices. The supramolecular systems described here belong to the rare class of metal-organic architectures that are formed as a result of metal directed hydrogen bonding interactions among chiral complex molecules. Complexes 1 and 2 are further characterized by IR, ESR, UV–Vis and CD spectroscopy.     

Noncovalent synthesis of supramolecular dendritic architectures in water

Water‐soluble guest–host complexes are prepared in a two‐step process. For this a new, polydisperse ethylene glycol containing guest molecule is synthesized that is soluble in both chloroform and water. This guest is able to bind to urea–adamantyl‐modified poly(propylene imine) dendrimers in chloroform in a noncovalent manner. When the chloroform is slowly evaporated and D₂O is added, the hydrophobic dendrimer is solubilized in water. This is not possible when the hydrophobic dendrimer is directly added to the hydrophilic guests in water. When the unmodified poly(ethylene glycol) starting material is used, no solubilization occurs, and this indicates that the urea–acetic acid head group is necessary to solubilize the dendrimer. Approximately 26 guests are required for solubilization of the dendrimer. A lower number of guests results in aggregation and precipitation of the dendrimer. A monodisperse guest molecule has been used in NMR studies to show that the guest molecule binds with its acidic head group to the periphery of the dendrimer. This methodology opens the way to functional dendrimer aggregates in aqueous media. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6431–6437, 2005     

Structural characterization of modular supramolecular architectures in solution

Structures of modular supramolecular architectures consisting of a hexameric, diphenylethyne-linked porphyrin macrocyclic array and the corresponding host-guest complex formed by inclusion of a tripyridyl guest molecule were characterized in solution using high-angle X-ray scattering. Scattering measurements made to 6 A resolution coupled with pair distance function (PDF) analyses demonstrated that (1) the porphyrin architectures are not rigid but are distributed across a conformational ensemble with a mean diameter that is 1.5 A shorter than the diameter of a symmetric, energy-minimized model structure, (2) the conformational envelope has limits of 3 A positional dispersion and full rotational freedom for all six porphyrin groups, and (3) insertion of the tripyridyl guest molecule expands the diameter of the host conformer by 0.6 A and decreases the configurational dispersion by approximately 2-fold. These results validate the molecular design, provide a new measure of conformational ensembles in solution that cannot be obtained by other techniques, and establish a structural basis for understanding the photophysical and guest-hosting functions of the hexameric porphyrin architectures in liquids.     

Conjugated radical cation dimerization-driven generation of supramolecular architectures

The application of the homodimerization of the tetrathiafulvalene and 4,4‘-dipyridinium radical cation as a non-covalent driving force in supramolecular self-assembly has beensummarized.