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1.
    
Urea, which has both hydrogen bond acceptor and donor moieties, is an ideal structure for a supramolecular synthon. Various supramolecules having ureido group(s) have been widely developed. This article summarizes recent developments of urea derivatives that exhibit various functions: i) supramolecular capsules that form discrete urea–urea intermolecular hydrogen bonds, ii) supramolecular polymers that form continuous urea–urea intermolecular hydrogen bonds, iii) supramolecular gels that form continuous urea–urea intermolecular hydrogen bonds, iv) artificial host molecules based on the molecular recognition ability of the ureido group, and v) catalytic reactions developed by utilizing the molecular recognition ability of the ureido group.  相似文献   

2.
    
A new supramolecular paradigm is presented for reliable capture and co-precipitation of haloauric acids (HAuX4) from organic solvents or water. Two classes of acyclic organic compounds act as complementary receptors (tectons) by forming two sets of directional non-covalent interactions, (a) hydrogen bonding between amide (or amidinium) NH residues and the electronegative X ligands on the AuX4−, and (b) electrostatic stacking of the electron deficient Au center against the face of an aromatic surface. X-ray diffraction analysis of four co-crystal structures reveals the additional common feature of proton bridged carbonyls as a new and predictable supramolecular design element that creates one-dimensional polymers linked by very short hydrogen bonds (CO⋅⋅⋅OC distance <2.5 Å). Two other co-crystal structures show that the amidinium-π⋅⋅⋅XAu interaction will reliably engage AuX4− with high directionality. These acyclic compounds are very attractive as co-precipitation agents within new “green” gold recovery processes. They also have high potential as tectons for controlled self-assembly or co-crystal engineering of haloaurate composites. More generally, the supramolecular paradigm will facilitate the design of next-generation receptors or tectons with high affinity for precious metal square planar coordination complexes for use in advanced materials, nanotechnology, or medicine.  相似文献   

3.
    
The use of the electrostatic stoppers concept in the field of mechanically interlocked molecules is reported; these stoppers are chemically sensitive end groups on a linear guest molecule that allows for the conversion of a pseudo-rotaxane species into a rotaxane complex by a change in the medium acidity. The chemical stimulus causes the appearance of negative charges on both ends of the linear component, passing from cationic to anionic, and causing a significant ring-to-axle electrostatic repulsion. This phenomenon has two different and simultaneous effects: 1) destabilizes the complex as a consequence of confining an anionic ring into an anionic axle, and 2) increases the dissociation energy barrier, thus impeding ring extrusion. This newly formed metastable rotaxane species is resistant to solvent and temperature effects and performs as a two-state degenerated molecular shuttle in solution.  相似文献   

4.
    
Titanium oxide clusters (TOCs) have been emerging as a new type of inorganic molecular entities of supramolecular chemistry. Herein, a perspective on the structures and functionalities of TOCs over the past three decades is given and the paramount roles of TOCs in serving supramolecular chemistry are demonstrated. Four types of supramolecular assemblies based on TOCs are reviewed, namely, TOC hosts for ion inclusion, mechanically interlocked molecular systems built from cyclic TOCs, reactivities of surface sites toward ligand exchange, and hierarchical structures of TOCs. The principles and advantages of TOCs toward each application are fully discussed, along with structural analyses. Following this path, more functional TOC-based supramolecular systems may be designed and synthesized in the future, which, in turn, will certainly enhance research into both supramolecular and coordination chemistry of titanium.  相似文献   

5.
New star polypseudorotaxanes that include 4,4′-dipyridyl-terminated 4-arm-poly(ethylene glycol) (PC1) and cucurbit[7]uril (CB[7]) were easily synthesised. The 1H NMR, UV–vis and resonance light scattering (RLS) data show that the viologen units of the star polypseudorotaxanes could fall off from the hydrophobic cavity of CB[7] with the addition of 1-adamantylamine (ADA). The cyclic voltammograms results indicate that the star polypseudorotaxanes have the redox property with the addition of ADA compared with the non-redox property of the pure star polypseudorotaxanes. The biological toxicity experiment shows that the bactericidal activity of the star polypseudorotaxanes in Escherichia coli was aroused by adjusting CB[7] dethreading from the star polypseudorotaxanes with the addition of another competitive guest ADA, which has a very high affinity for CB[7].  相似文献   

6.
    
A photocontrolled, interconvertible supramolecular 2D-nanosheet/1D-nanotube system was constructed through the supramolecular assembly of adamantanyl-modified diphenylalanine with azobenzene-bridged bis(β-cyclodextrin). The nanosheet exhibited a greater fluorescence enhancement effect than the nanotube. Significantly, these nanosheets and nanotubes could interconvert via the photocontrolled trans/cis isomerization of azobenzene linkers in bis(β-cyclodextrin), and this photo-switchable one-dimensional/two-dimensional morphological interconversion was reversible and recyclable. This enables convenient routes to highly ordered nanostructures with various morphologies and dimensions that can be controlled by external stimuli.  相似文献   

7.
    
The sizes of available self-assembled hydrogen-bond-based supramolecular capsules and cages are rather limited. The largest systems have volumes of approximately 1400–2300 Å3. Herein, we report a large, hexameric cage based on intermolecular amide–amide dimerization. The unusual structure with openings, reminiscent of covalently linked cages, is held together by 24 hydrogen bonds. With a diameter of 2.3 nm and a cavity volume of ∼2800 Å3, the assembly is larger than any previously known capsule/cage structure relying exclusively on hydrogen bonds. The self-assembly process in chlorinated, organic solvents was found to be strongly concentration dependent, with the monomeric form prevailing at low concentrations. Additionally, the formation of host–guest complexes with fullerenes (C60 and C70) was observed.  相似文献   

8.
    
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9.
    
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10.
    
A wide variety of 2-methyl-resorcinol-based deepened cavitands were synthesised from readily available reagents in a four-step procedure with overall yields of up to 62%. A systematic variation of the rim was carried out by building up a flexible upper aromatic wall on the rigid cavitand platform through CH2, CH2O and CH2OCH2 spacers. These aromatic walls were further extended by a Suzuki cross-coupling reaction. Full characterisation of the synthesised cavitands was carried out. The solid-state structure of tetrakis(phenoxymethyl)cavitand was determined by X-ray crystallography. Gas-phase theoretical calculations for this molecule predict the presence of weak T-shaped interactions between the upper phenyl rings. The host–guest complex formation ability of two deepened cavitand hosts towards 4-chloro-benzotrifluoride was proved by photoluminescence method.  相似文献   

11.
The regulation of the concentration of a wide range of small molecules is ubiquitous in biological systems because it enables them to adapt to the continuous changes in the environmental conditions. Herein, we report an aqueous synthetic system that provides an orchestrated, temperature and pH controlled regulation of the complexation between the cyclobis(paraquat-p-phenylene) host ( BBox ) and a 1,5-dialkyloxynaphthalene ( DNP ) guest attached to a well-defined dual responsive copolymer composed of N-isopropylacrylamide as thermoresponsive monomer and acrylic acid as pH-responsive monomer. Controlled, partial release of the BBox , enabling control over its concentration, is based on the tunable partial collapse of the copolymer. This colored supramolecular assembly is one of the first synthetic systems providing control over the concentration of a small molecule, providing great potential as both T and pH chromic materials and as a basis to develop more complex systems with molecular communication.  相似文献   

12.
    
A novel macrocyclic host molecule was synthesized that forms in a single step from commercially available starting materials. The core of the macrocycle backbone possesses two quinone rings and, thus, it is redox-active. Host–guest binding involving the clip-shaped cavity indicates selective binding of pyridine N-oxides based on the electron density of and steric bulk around the anionic oxygen.  相似文献   

13.
    
A pseudo-rotaxane is a host−guest complex composed of a linear molecule encircled by a macrocyclic ring. These complexes can be assembled by sliding the host over the guest terminal groups. If there is a close match between the molecular volume of the flanking groups on the guest and the cavity size of the macrocycle, the slipping might occur slowly or even become completely hindered. We have previously shown that it is possible to overcome the restraints imposed by steric effects on the sliding process by integrating electrostatic attractive interactions during the slipping step. In this work, we extend our electrostatically assisted slipping approach (EASA) to a new host−guest system featuring a flexible macrocyclic ring and a series of asymmetric guests containing a cyclic tertiary ammonium group. Compelling evidence for pseudo-rotaxane formation is presented, along with thermodynamic and kinetic data. Experimental results suggests that the higher conformational flexibility of 24-crown-8 significantly increases the sliding rate, compared with the more rigid dibenzo-24-crown-8, without affecting complex stability. Furthermore, by combining the EASA and macrocycle flexibility, we were capable to slip a large eight-membered cyclic group across the 24-crown-8 annulus, setting a new limit on the ring molecular size that can pass through a 24-membered crown ether.  相似文献   

14.
    
Supramolecular vesicles (SMVs) self-assembled from the supra-amphiphiles, consisting of two scaffolds linked together through noncovalent interactions, can realize stimuli-responsive controlled release of encapsulated drugs for enhanced therapeutic efficacy and minimized side effect of drugs. Pillararenes (PAs), an emerging kind of macrocyclic hosts in 2008, are easy to modify with a variety of functionalities. SMVs from PAs and specific guests mainly based on the host–guest interactions have attracted increasing attention because of their drug delivery and controlled drug release. A great progress in the construction and stimuli-responsive drug delivery of the PA-based SMVs has been made since the first work was reported in 2012. This review summarizes the major achievements of the PA-based SMVs for stimuli-responsive drug delivery over the past 5 years, including the microstructures of SMVs, multiple stimuli-responsive SMVs, prodrug SMVs from prodrug PAs and guests, bola-type SMVs, multifunctional SMVs, glucose-responsive SMVs for insulin delivery, novel SMVs from responsive PAs, thermo-responsive SMVs, and ternary SMVs, for chemotherapy, photothermal therapy, photodynamic therapy, and other biological applications. The future challenges and research directions of PA-based SMVs are also outlined from the points of views of the fundamental research, biological applications, and clinical applications of PA-based SMVs.  相似文献   

15.
    
Some biological receptors change their shapes and rigidity by metalation to recognize substrates precisely via adaptive guest binding process. Herein we present a semi-flexible tricyclic host molecule whose conformation is rigidified by dimetalation to uptake organic guests selectively. Considering two metal binding sites and an empty space between them, pillar[5]-bis-thiacrown (L) was synthesized. The tricyclic host L forms a disilver(I) complex [Ag2L(NO3)2], with an Ag⋅⋅⋅Ag separation of 9.976 Å. Binding studies based on 1H NMR including 2D NOESY and DOSY experiments towards α,ω-dicyanoalkanes [CN(CH2)nCN, n=2–6, shortly C2–C6] demonstrated that the dimetalated L, Ag2L preferentially recognizes C2 over other guests than that of free L. Furthermore, the dimetalated the host only uptakes C2 in the presence of other guests. Crystal structures support the idea that the space between two silver(I) centers plays a decisive role on the selective guest binding forming an Ag-C2-Ag@L arrangement via the length-selective recognition. This work demonstrates the chemical example of the adaptive guest binding and presents a new perspective on the metallosupramolecules of pillararenes.  相似文献   

16.
    
Enzyme-mediated dynamic combinatorial chemistry combines the concept of thermodynamically controlled covalent self-assembly with the inherent biological relevance of enzymatic transformations. A system of interconverting cyclodextrins has been explored, in which the glycosidic linkage is rendered dynamic by the action of cyclodextrin glucanotransferase (CGTase). External factors, such as pH, temperature, solvent, and salinity are reported to modulate the composition of the dynamic cyclodextrin library. Dynamic libraries of cyclodextrins (CDs) could be obtained in wide ranges of pH (5.0–9.0), temperature (5–37 °C), and salinity (up to 7.5 m NaNO3), and with high organic solvent content (50 % by volume of ethanol), showing that enzyme-mediated dynamic systems can be robust and not limited to physiological conditions. Furthermore, it is demonstrated how strategic choice of reaction conditions can enhance template effects, in this case, to achieve highly selective production of α-CD, an otherwise challenging target due to competition from the structurally similar β-CD.  相似文献   

17.
    
Synthetic carbohydrate receptors (SCRs) that selectively recognize cell-surface glycans could be used for detection, drug delivery, or as therapeutics. Here we report the synthesis of seven new C2h symmetric tetrapodal SCRs. The structures of these SCRs possess a conserved biaryl core, and they vary in the four heterocyclic binding groups that are linked to the biaryl core via secondary amines. Supramolecular association between these SCRs and five biologically relevant C1-O-octyloxy glycans, α/β-glucoside ( α/β-Glc ), α/β-mannoside ( α/β-Man ), and β-galactoside ( β-Gal ), was studied by mass spectrometry, 1H NMR titrations, and molecular modeling. These studies revealed that selectivity can be achieved in these tetrapodal SCRs by varying the heterocyclic binding group. We found that SCR017 (3-pyrrole), SCR021 (3-pyridine), and SCR022 (2-phenol) bind only to β-Glc. SCR019 (3-indole) binds only to β-Man. SCR020 (2-pyridine) binds β-Man and α-Man with a preference to the latter. SCR018 (2-indole) binds α-Man and β-Gal with a preference to the former. The glycan guests bound within their SCR hosts in one of three supramolecular geometries: center-parallel, center-perpendicular, and off-center. Many host–guest combinations formed higher stoichiometry complexes, 2:1 glycan⋅SCR or 1:2 glycan⋅SCR , where the former are driven by positive allosteric cooperativity induced by glycan–glycan contacts.  相似文献   

18.
    
Smart supramolecular vesicles constructed by host–guest interactions between “acid-degradable” acyclic cucurbit[n]uril (CB[n]) and a doxorubicin prodrug are reported. “Acid-degradable” acyclic CB[n] is a high-affinity host for several common antitumor drugs, and its degradation leads to a more dramatic decrease in binding affinity than that observed for “acid-sensitive” hosts. Supramolecular complexation between acid-degradable acyclic CB[n] and a doxorubicin prodrug resulted in the formation of negatively charged supramolecular vesicles. The prodrug strategy allowed doxorubicin to be conjugated to vesicles in a stable manner with a high drug-loading ratio of 20 %. The resulting supramolecular vesicles were responsive to tumor acidity (pH 6.5). Induced by mildly acidic conditions (pH 6.5–5.5), acid-degradable acyclic CB[n] could be degraded, and this led to a vesicle-to-micelle transition to form positively charged micelles. This transition resulted in a pH-dependent change in size and surface charge, which improved tumoral-cell uptake for doxorubicin.  相似文献   

19.
    
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20.
    
Guest‐induced M18L6–M24L8 capsule–capsule conversion is reported. Both capsules are composed of PdII ethylenediamine units (M) and 1,3,5‐tris(3,5‐pyrimidyl)pyrimidine (L), and form trigonal bipyramidal (M18L6) and octahedral (M24L8) closed‐shell structures with huge hydrophobic inner spaces. The M18L6 trigonal bipyramid is converted to the M24L8 octahedron through encapsulation of large aromatic guests, with the latter capsule possessing a cavity volume three times larger than the former. Despite the dynamic properties of the capsule host, the encapsulated guests are difficult to extract and are thus isolated from the external environment.  相似文献   

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