The stepwise supramolecular organisation of guanosine derivatives

Several supramolecular architectures generated by guanosine derivatives are described. The research started from the fortuitous observation of a lyotropic behavior exhibited by a guanylic nucleotide in water. This observation stimulated extensive research on several natural and lipophilic guanosine derivatives which self-assemble in different architectures (discs, ribbons, helices...), according to their structure and environment. These ordered structures can be used as scaffolds for photo- or electro-active moieties and for the fabrication of molecular electronic devices.     

超分子化学发展简介

本文综述了超分子化学的定义 , 范围及内容. 着重介绍了分子识别, 分子自组装, 超分子催化, 超分子器件及超分子材料等概念. 对由此可能形成的新的前沿科学如分子电子学, 分子离子学, 分子光子学及超分子工艺学等作了扼要介绍 .     

CO2 in supramolecular chemistry: preparation of switchable supramolecular polymers

CO2 gas was used to construct novel types of supramolecular polymers. Self-assembling nanostructures 11 and 13 were prepared, which employ both hydrogen bonding and dynamic, thermally reversible carbamate bonds. As precursors, calixarene ureas 1 and 2 were synthesized, which strongly aggregate/dimerize (K(D)>/=10(6) M(-1) per capsule) in apolar solution with the formation of self-assembling capsules 7 and linear polymeric chains 8, respectively, and also possess "CO2-philic" primary amino groups on the periphery. CO2 effectively reacts with molecules 7 and 8 in apolar solvents and cross-links them with the formation of multiple carbamate salt bridges. Oligomeric aggregate 11 and three-dimensional polymeric network 13 were prepared and characterized by 1H and 13C NMR spectroscopy. The morphology of supramolecular gel 13 was studied by scanning electron microscopy. Addition of a competitive solvent destroyed the hydrogen bonding in assembling structures 11 and 13, but did not influence the carbamate linkers; carbamate salts 12 and 14, respectively, were obtained. On the other hand, thermal release of CO2 from 11 and 13 was easily accomplished (1 h, 100 degrees C) while retaining the hydrogen-bonding capsules. Thus, three-dimensional polymeric network 13 was transformed back to linear polymeric chain 8 without breaking up. Encapsulation and storage of solvent molecules by 11 and 13 was demonstrated. This opens the way for switchable materials, which reversibly trap, store, and then release guest molecules. A two-parameter switch and control over hydrogen bonding and CO2-amine adducts was established.     

Assembly of a self-complementary monomer: formation of supramolecular polymer networks and responsive gels

Self-complementary monomer 1, which combines a macrotricyclic polyether and two dibenzylammonium ions together, was synthesized, and its self-assembly into supramolecular polymer networks by host-guest interactions was studied. For the purpose of comparative study, two model molecules 2 and 3 were also prepared. It was found that model molecule 2 and dibenzylammonium ion 4 form a 1:2 complex in solution and in the solid state, which afforded a model system for the investigation of the assembly behavior of monomer 1. Consequently, the (1)H NMR spectrum of 1 in CD(3)CN showed characteristic proton signals similar to the model system, which suggested that 1 self-assembles into a supramolecular polymer network. Formation of the supramolecular polymer was further evidenced by the MALDI-TOF MS spectrum, viscometry, and dynamic light-scattering (DLS) experiments. Moreover, it was found that the decomposition and re-formation of the supramolecular polymer could be chemically controlled by the use of triethylamine and trifluoroacetic acid. Interestingly, the supramolecular polymer forms an organogel both in CD(3)CN and in 1:1 (v/v) CDCl(3)/CD(3)CN, and reversible thermo- and pH-induced gel-sol transitions were also found. The presented work will provide a new strategy for the construction of supramolecular polymers with specific structures and properties.     

A competitive molecular recognition study: syntheses and analysis of supramolecular assemblies of 3,5-dihydroxybenzoic acid and its bromo derivative with some N-donor compounds

A molecular recognition study of 3,5-dihydroxybenzoic acid (1) and its bromo derivative 4-bromo-3,5-dihydroxybenzoic acid (2) with the N-donor compounds 1,2-bis(4-pyridyl)ethene (bpyee), 1,2-bis(4-pyridyl)ethane (bpyea), and 4,4'-bipyridine (bpy) is reported. Thus, the syntheses and structural analysis of molecular adducts 1 a-1 c (1 with bpyee, bpyea, and bpy, respectively) and 2 a-2 c (2 with bpyee, bpyea, and bpy, respectively) are discussed. In all these adducts, recognition between the constituents is established through either O--H...N and/or O--H...N/C--H...O pairwise hydrogen bonds. In all the adducts both OH and COOH functional groups available on 1 and 2 interact with the N-donor compounds, except in 2 a, in which only COOH (COO-) is involved in the recognition process. The COOH moieties in 1 a, 1 b, and 2 b form only single O--H...N hydrogen bonds, whereas in 1 c and 2 c, they form pairwise O--H...N/C--H...O hydrogen bonds. In addition, subtle differences in the recognition patterns resulted in the formation of cyclic networks of different dimensions. In fact, only 1 c forms a four-molecule cyclic moiety, as was already documented in the literature for this kind of assemblies. All complexes have been characterized by single-crystal X-ray diffraction. The supramolecular architectures are quite elegant and simple, with stacking of sheets in all adducts, but a rather complex network with a threefold interpenetration pattern was found in 2 c.     

Using Diffusion NMR To Characterize Guanosine Self‐Association: Insights into Structure and Mechanism

This paper presents results from a series of pulsed field gradient (PFG) NMR studies on lipophilic guanosine nucleosides that undergo cation‐templated assembly in organic solvents. The use of PFG‐NMR to measure diffusion coefficients for the different aggregates allowed us to observe the influences of cation, solvent and anion on the self‐assembly process. Three case studies are presented. In the first study, diffusion NMR confirmed formation of a hexadecameric G‐quadruplex [G 1 ]₁₆ ? 4 K⁺ ? 4 pic^? in CD₃CN. Furthermore, hexadecamer formation from 5′‐TBDMS‐2′,3′‐isopropylidene G 1 and K⁺ picrate was shown to be a cooperative process in CD₃CN. In the second study, diffusion NMR studies on 5′‐(3,5‐bis(methoxy)benzoyl)‐2′,3′‐isopropylidene G 4 showed that hierarchical self‐association of G₈‐octamers is controlled by the K⁺ cation. Evidence for formation of both discrete G₈‐octamers and G₁₆‐hexadecamers in CD₂Cl₂ was obtained. The position of this octamer–hexadecamer equilibrium was shown to depend on the K⁺ concentration. In the third case, diffusion NMR was used to determine the size of a guanosine self‐assembly where NMR signal integration was ambiguous. Thus, both diffusion NMR and ESI‐MS show that 5′‐O‐acetyl‐2′,3′‐O‐isopropylidene G 7 and Na⁺ picrate form a doubly charged octamer [G 7 ]₈ ? 2 Na⁺ ? 2 pic^? 9 in CD₂Cl₂. The anion's role in stabilizing this particular complex is discussed. In all three cases the information gained from the diffusion NMR technique enabled us to better understand the self‐assembly processes, especially regarding the roles of cation, anion and solvent.     

Supramolecular chemistry in water

Supramolecular chemistry in water is a constantly growing research area because noncovalent interactions in aqueous media are important for obtaining a better understanding and control of the major processes in nature. This Review offers an overview of recent advances in the area of water-soluble synthetic receptors as well as self-assembly and molecular recognition in water, through consideration of the functionalities that are used to increase the water solubility, as well as the supramolecular interactions and approaches used for effective recognition of a guest and self-assembly in water. The special features and applications of supramolecular entities in aqueous media are also described.     

Hierarchical self-assembly of a bow-shaped molecule bearing self-complementary hydrogen bonding sites into extended supramolecular assemblies

The bow-shaped molecule 1 bearing a self-complementary DAAD-ADDA (D=donor A=acceptor) hydrogen-bonding array generates, in hydrocarbon solvents, highly ordered supramolecular sheet aggregates that subsequently give rise to gels by formation of an entangled network. The process of hierarchical self-assembly of compound 1 was investigated by the concentration and temperature dependence of UV-visible and (1)H NMR spectra, fluorescence spectra, and electron microscopy data. The temperature dependence of the UV-visible spectra indicates a highly cooperative process for the self-assembly of compound 1 in decaline. The electron micrograph of the decaline solution of compound 1 (1.0 mM) revealed supramolecular sheet aggregates forming an entangled network. The selected area electronic diffraction patterns of the supramolecular sheet aggregates were typical for single crystals, indicative of a highly ordered assembly. The results exemplify the generation, by hierarchical self-assembly, of highly organized supramolecular materials presenting novel collective properties at each level of organization.     

High-tech applications of self-assembling supramolecular nanostructured gel-phase materials: from regenerative medicine to electronic devices

It is likely that nanofabrication will underpin many technologies in the 21st century. Synthetic chemistry is a powerful approach to generate molecular structures that are capable of assembling into functional nanoscale architectures. There has been intense interest in self-assembling low-molecular-weight gelators, which has led to a general understanding of gelation based on the self-assembly of molecular-scale building blocks in terms of non-covalent interactions and packing parameters. The gelator molecules generate hierarchical, supramolecular structures that are macroscopically expressed in gel formation. Molecular modification can therefore control nanoscale assembly, a process that ultimately endows specific material function. The combination of supramolecular chemistry, materials science, and biomedicine allows application-based materials to be developed. Regenerative medicine and tissue engineering using molecular gels as nanostructured scaffolds for the regrowth of nerve cells has been demonstrated in vivo, and the prospect of using self-assembled fibers as one-dimensional conductors in gel materials has captured much interest in the field of nanoelectronics.     

Enzyme mimics based upon supramolecular coordination chemistry

Recent advances in supramolecular coordination chemistry have allowed chemists to synthesize macromolecular complexes that exhibit various properties intrinsic to enzymes. This Review focuses on structures inspired by properties and functions observed in enzymes rather than precise models of enzyme active sites. These structures are synthesized using convergent, modular, and high-yielding coordination-chemistry-based methods, which allow one to tailor the size, shape, and properties of the resulting complexes. Many of the structures discussed exhibit reactivity and specificity reminiscent of natural systems, and some of them have functions that exceed the natural systems which provided the inspiration for initially making them.     

Conformer-independent ureidoimidazole motifs--tools to probe conformational and tautomeric effects on the molecular recognition of triply hydrogen-bonded heterodimers

Linear arrays of hydrogen bonds are useful for the reversible assembly of “stimuli‐responsive” supramolecular materials. There is thus an ongoing requirement for easy‐to‐synthesise motifs that are capable of presenting hydrogen‐bonding functionality in a predictable manner, such that high‐affinity and high‐fidelity recognition occurs. The design of linear arrays is made challenging as a consequence of their ability to adopt multiple conformational and tautomeric configurations; with each additional hydrogen‐bonding heteroatom added to an array, the available tautomeric and conformational space increases and it can be difficult to anticipate where unproductive conformers/tautomers will arise. This paper describes a detailed study on the complementary ureidoimidazole donor–donor–acceptor (DDA) array ( 1 ) and amidoisocytosine donor–acceptor–acceptor (DAA) array ( 2 ). A specific feature of 1 is that two degenerate, intramolecular hydrogen‐bonded conformations are postulated, both of which present a DDA array that is complementary to appropriate DAA partners. 1D and 2D ¹H NMR spectroscopy, isothermal titration calorimetry, and ab initio structure calculations confirm 1 interacts with 2 (K_a≈33000 M ^?1 in CDCl₃) in a conformer‐independent fashion driven by enthalpy. Comparison of the binding behaviour of 1 with hexylamidocytosine ( 4 ) and amidonaphthyridine ( 5 ) provides insight on the role that intramolecular hydrogen‐bonding plays in mediating affinity towards DAA partners.     

Tetra- and octalactam macrocycles and catenanes with exocyclic metal coordination sites: versatile building blocks for supramolecular chemistry

The synthesis of a new tetralactam macrocycle and the simultaneous formation of catenanes and larger octalactam macrocycles is reported. These species bear 2,2'-biquinoline moieties suitably positioned to bind a metal center at the outer periphery of the macrocycles. (1)H NMR chemical shifts permit the unambiguous distinction of transoid and cisoid conformations of the biquinoline moiety, thereby allowing an unequivocal identification of the catenane and octalactam structures, despite the fact that both have the same elemental composition and bear identical structural subunits. With the aid of an anion template effect, rotaxanes can be prepared from the smaller tetralactam macrocycle. These reveal significantly altered requirements in terms of the stopper size as compared to previously reported tetralactam wheels. Several copper(I)-mediated dimers and a (bpy)(2)Ru(II) complex (bpy=2,2'-bipyridine) have been synthesized from the tetralactam macrocycle and the rotaxanes. The anion binding abilities of the tetralactam macrocycle and its (bpy)(2)Ru(II) complex in DMSO have been compared by (1)H NMR titration experiments, which revealed significantly enhanced binding by the metal complex. Mass spectrometry has been used to study the potential formation of larger assemblies of copper(I) and the catenane built-up from two tetralactam macrocycles. Indeed, a 2:2 complex was identified. In contrast, the octalactam macrocycle of the same elemental composition yields only 1:1 complexes, with the Cu(I) ion connecting its two biquinoline moieties in the center of a figure-eight-shaped molecule. Molecular modeling studies support the structural assignments made.     

Approaching supramolecular functionality

Functional molecules require a high degree of complexity which is difficult to achieve by covalent synthesis. This article discusses supramolecular approaches to the creation of larger architectures through noncovalent bonds, self-assembly, and template strategies. It highlights selected examples for the structural and conformational control of function and attempts to identify difficulties and challenges which may arise in future.     

Size-determining dependencies in supramolecular organometallic host-guest chemistry

Treatment of the pentaphosphaferrocene [Cp*Fe(η⁵‐P₅)] with Cu^I halides in the presence of different templates leads to novel fullerene‐like spherical molecules that serve as hosts for the templates. If ferrocene is used as the template the 80‐vertex ball [Cp₂Fe]@[{Cp*Fe(η⁵‐P₅)}₁₂{CuCl}₂₀] ( 4 ), with an overall icosahedral C₈₀ topological symmetry, is obtained. This result shows the ability of ferrocene to compete successfully with the internal template of the reaction system [Cp*Fe(η⁵‐P₅)], although the 90‐vertex ball [{Cp*Fe(η⁵:η¹:η¹:η¹:η¹:η¹‐P₅)}₁₂(CuCl)₁₀(Cu₂Cl₃)₅{Cu(CH₃CN)₂}₅] ( 2 a ) containing pentaphosphaferrocene as a guest is also formed as a byproduct. With use of the triple‐decker sandwich complex [(CpCr)₂(μ,η⁵‐As₅)] as a template the reaction between [Cp*Fe(η⁵‐P₅)] and CuBr leads to the 90‐vertex ball [(CpCr)₂(μ,η⁵‐As₅)]@[{Cp*Fe(η⁵‐P₅)}₁₂{CuBr}₁₀{Cu₂Br₃}₅{Cu(CH₃CN)₂}₅] ( 6 ), in which the complete molecule acts as a template. However, if the corresponding reaction is instead carried out with CuCl, cleavage of the triple‐decker complex is found and the 80‐vertex ball [CpCr(η⁵‐As₅)]@[{Cp*Fe(η⁵‐P₅)}₁₂{CuCl}₂₀] ( 5 ) is obtained. This accommodates as its guest [CpCr(η⁵‐As₅)], which has only 16 valence electrons in a triplet ground state and is not known as a free molecule. The triple‐decker sandwich complex [(CpCr)₂(μ,η⁵‐As₅)] requires 53.1 kcal mol^?1 to undergo cleavage (as calculated by DFT methods) and therefore this reaction is clearly endothermic. All new products have been characterized by single‐crystal X‐ray crystallography. A favoured orientation of the guest molecules inside the host cages has been identified, which shows π???π stacking of the five‐membered rings (Cp and cyclo‐As₅) of the guests and the cyclo‐P₅ rings of the nanoballs of the hosts.