Cyclodextrin-Based Catenanes and Rotaxanes

Supramolecular polymer assembly in aqueous solution arising from cyclodextrin host-guest complexation

The employment of cyclodextrin host–guest complexation to construct supramolecular assemblies with an emphasis on polymer networks is reviewed. The main driving force for this supramolecular assembly is host–guest complexation between cyclodextrin hosts and guest groups either of which may be discrete molecular species or substituents on a polymer backbone. The effects of such complexation on properties at the molecular and macroscopic levels are discussed. It is shown that cyclodextrin complexation may be used to design functional polymer materials with tailorable properties, especially for photo-, pH-, thermo- and redox-responsiveness and self-healing.

Enhanced User-Control of Small Molecule Drug Release from a Poly(ethylene glycol) Hydrogel via Azobenzene/Cyclodextrin Complex Tethers

We present a versatile and facile method to enhance user-control of small molecule drug release from a poly(ethylene glycol)-based hydrogel using the host/guest complex formed between an azobenzene derivative guest and a β-cyclodextrin host. A model drug is formed from a short peptide containing a fluorophore and an azobenzene functional group on one terminus. Upon irradiation with UV light, azobenzene isomerization leads to decreased complex formation and an on-demand acceleratation of the release rate of an entrapped model drug.

Light-triggered assembly–disassembly of an ordered donor–acceptor π-stack using a photoresponsive dimethyldihydropyrene π-switch

A dimethyldihydropyrene based photochromic π-switch in its closed state forms donor–acceptor stacks with 1,4,5,8-naphthalenetetracarboxylic dianhydride. The stacks collapse in the photoisomeric open form.

Polyoxometalate-based supramolecular architecture constructed from a purely inorganic 1D chain and a metal–organic layer with efficient catalytic activity

A new polyrotaxane structure constructed from a pure inorganic polyoxometalate-based 1D chain, exhibited efficient catalytic activity for desulfurization and electrocatalytic redox activity.

The synthesis and characterization of a processable polyrotaxane-based triblock copolymer via a “two steps” strategy

“Two steps ” strategy can prepare PR copolymer with controllable CD content as well as excellent processability and mechanical property.

Facile and efficient formation and dissociation of a pseudo[2]rotaxane by a slippage approach using pillar[5]arene-based cyclic host liquid and solvent

A pillar[5]arene-based [2]rotaxane was synthesized by heating an axle with valine ends in a cyclic host liquid.

Construction and Functions of Cyclodextrin-Based 1D Supramolecular Strands and their Secondary Assemblies

Cyclodextrins (CDs), a class of cyclic oligosaccharides, are water-soluble, nontoxic, and commercial available with a low price, and their well-defined hydrophobic cavity can bind various organic/biological substrates. Through their molecular assembly mediated by organic, inorganic, or polymeric molecules as templates, CDs and their functional derivatives can be assembled to 1D supramolecular strands, wherein the functional groups of the CDs are closely located in a highly ordered manner. This structural feature greatly favors the cooperative effect of numerous functional groups in the supramolecular strand, as well as the interactions of the supramolecular strands with the multiple binding sites of substrates, especially biological substrates. Therefore, CD-based 1D supramolecular strands exhibit many material, biological, and catalytic functions, and these properties can be further improved through their secondary assembly. An overview of recent advances in the development of the construction and functions of CD-based 1D supramolecular strands and their secondary assemblies is given here. It is expected that the representative contributions described can inspire future investigations and lead to discoveries that promote the research of CD-based functional materials.

Temperature sensitive supramolecular self assembly of per-6-PEO-β-cyclodextrin and α,ω-di-(adamantylethyl)poly(N-isopropylacrylamide) in water

The host/guest interactions in water of a star polymer consisting of a β-cyclodextrin (β-CD) core bearing six poly(ethylene oxide) arms linked to the C6 positions of β-CD (β-CD-PEO7, Mn 5000 g mol(-1)) and α,ω-di-(adamantylethyl)poly(N-isopropylacrylamide) (Ad-PNIPAM-12K, Mn 12,000 g mol(-1)) were studied by 1D and 2D (1)H and (13)C NMR spectroscopy, isothermal calorimetry (ITC), and light scattering (LS). In cold water (T < 26 °C) supramolecular "dumbbell" assemblies, consisting of PNIPAM chains with β-CD/Ad inclusion complexes at each end, formed viaβ-CD-insertion of the terminal Ads through the β-CD secondary face. Light scattering, microcalorimetry (DSC), and DOSY NMR studies indicated that mixed aqueous solutions of β-CD-PEO7 and Ad-PNIPAM-12K undergo a reversible heat-induced phase transition at ∼32 °C, accompanied by a release of a fraction of the Ad-bound β-CD-PEO7 into bulk solution and the formation of aggregated Ad-PNIPAM-12K stabilized by a β-CD-PEO7 shell.

Synthesis of [3]Rotaxanes by the Combination of Copper-Mediated Coupling Reaction and Metal-Template Approach

[3]Rotaxanes with two axle components and one ring component were synthesized by the combination of a coupling reaction using a transition-metal catalyst and a metal-template approach. Thus, [2]rotaxanes were prepared by the oxidative dimerization of alkyne promoted by macrocyclic phenanthroline-CuI complexes. The [2]rotaxane was reacted with a Cu(I) salt and an acyclic ligand to generate a tetrahedral Cu(I) complex. Metal-free [3]rotaxane was isolated by the end-capping reaction of the acyclic ligand, followed by the removal of Cu(I) ion. The stability of the tetrahedral Cu(I) complexes depended on the size of both the ring component and the acyclic ligand, which was correlated with the yield of the corresponding [3]rotaxane.

Selective Surface Acoustic Wave-Based Organophosphorus Sensor Employing a Host-Guest Self-Assembly Monolayer of β-Cyclodextrin Derivative

Self-assembly and molecular imprinting technologies are very attractive technologies for the development of artificial recognition systems and provide chemical recognition based on need and not happenstance. In this paper, we employed a β-cyclodextrin derivative surface acoustic wave (SAW) chemical sensor for detecting the chemical warfare agents (CWAs) sarin (O-Isoprophyl methylphosphonofluoridate, GB). Using sarin acid (isoprophyl hydrogen methylphosphonate) as an imprinting template, mono[6-deoxy-6-[(mercaptodecamethylene)thio]]-β-cyclodextrin was prepared by self-assembled method on one of the SAW oscillators. After templates’ removal, a sensitive and selective molecular imprinting (MIP) monolayer for GB was prepared. Electrochemical impedance spectroscopy and atomic force microscope (AFM) were used to characterize this film. Comparing the detection results to GB by MIP film and non-MIP film, the molecularly imprinting effect was also proved. The resulting SAW sensor could detect sarin as low as 0.10 mg/m³ at room temperature and the frequency shift was about 300 Hz. The response frequency increased linearly with increasing sarin concentration in the range of 0.7 mg/m³~3.0 mg/m³. When sarin was detected under different temperatures, the SAW sensor exhibited outstanding sensitivity and reliability.

One-pot synthesis of water-soluble, β-cyclodextrin-based polyrotaxanes in a homogeneous water system and its use in bio-applications

A small, nano-sized, water-soluble polyrotaxane (PR) was synthesized using a highly efficient one-pot synthesis strategy in a homogeneous water system, formed from β-cyclodextrin-(COOH)₂, poly(propylene glycol)bis(2-aminopropyl ether) (PPG, 2 kDa) and a mono-(6-azido-6-desoxy)-β-cyclodextrin stopper via room temperature click chemistry. β-cyclodextrin-(COOH)₂ and PR were characterized by one- and two-dimensional NMR as well as by high resolution transmission electron microscopy (HR-TEM). The number of carboxyl groups in one PR was determined by ¹H NMR. Two-dimensional diffusion-ordered NMR spectroscopy (2D DOSY) and nuclear Overhauser enhancement spectroscopy (2D NOESY) show that β-cyclodextrin-(COOH)₂ and PPG successfully formed an inclusion complex. HR-TEM revealed the morphology of water-soluble PR as a spherical nanoparticle with a size of approximately 3.5 nm ± 1.5 nm. PR was labeled with rhodamine to assess its biocompatibility and cell membrane penetrability in vitro. The in vivo real-time fluorescent imaging biodistribution experiments indicated that water-soluble PR can actively target tumor sites using an enhanced permeability and retention (EPR) effect, with a significantly prolonged blood circulation time in tumor-bearing mice.

[2]Pseudorotaxane composed of heteroditopic macrobicycle and pyridine N-oxide based axle: recognition site dependent axle orientation

A strategy for threading an axle having a hydrogen bond acceptor unit in the cavity of a C3v symmetric amido-amine macrobicycle is investigated. The macrobicycle acts as a wheel in its neutral as well as triprotonated states to form threaded architectures with a pyridine N-oxide derivative. The negative oxygen dipole of the axle is capable of [2]pseudorotaxane formation in two different orientations with the wheel in its neutral and triprotonated states.

Molecular binding behavior of bipyridium derivatives by water-soluble carboxylato-biphen[3]arene

Complexation of paraquat derivatives and bis(N-mono-substituted bipyridine) cations by a negatively charged carboxylato-biphen[3]arene in water is described.

Significant emission enhancement of a bola-amphiphile with salicylaldehyde azine moiety induced by the formation of [2]pseudorotaxane with γ-cyclodextrin

The emission of a bola-amphiphile with salicyladazine moiety was significantly enhanced by the formation of [2]pseudorotaxane with γ-cyclodextrin, which can specifically localize in mitochondria of living cells.

Protein recognition using synthetic small-molecular binders toward optical protein sensing in vitro and in live cells

This review describes the recognition and sensing techniques of proteins and their building blocks by use of small synthetic binders.

A supramolecular recyclable catalyst for aqueous Suzuki–Miyaura coupling

A Pd(ii) pyrazolyl complex is solubilized by host–guest inclusion to give an efficient, recyclable catalyst for Suzuki–Miyaura couplings in aqueous–organic solvents.

Sensitive fluorescence detection of lysozyme using a tris(bipyridine)ruthenium(ii) complex containing multiple cyclodextrins

A new series of metallocyclodextrins with increased fluorescence intensity upon binding with ssDNAs/aptamers has been demonstrated to sensitively detect lysozyme.

Synthesis of [3]rotaxanes that utilize the catalytic activity of a macrocyclic phenanthroline-Cu Complex: remarkable effect of the length of the axle precursor

[3]Rotaxanes, which consist of one macrocyclic phenanthroline compound and two axle components, were prepared by the oxidative dimerization of an alkyne compound with bulky tris[4'-cyclohexyl-(1,1'-biphenyl)-4-yl]methyl blocking group. The catalytic activity of a macrocyclic phenanthroline-Cu complex was utilized to thread the two axle components inside the ring. The alkyne compound with chain of 15 or 20 methylene groups gave [3]rotaxanes in high yields, whereas the axle with a chain of six methylene groups afforded a [3]rotaxane in very poor yield. We also examined the effect of the ring size on the synthesis of [3]rotaxanes. [3]Rotaxanes were not isolated when a macrocyclic phenanthroline compound with a smaller ring size was used.

Supramolecular polymers constructed from macrocycle-based host-guest molecular recognition motifs

CONSPECTUS: Supramolecular polymers, fabricated via the combination of supramolecular chemistry and polymer science, are polymeric arrays of repeating units held together by reversible, relatively weak noncovalent interactions. The introduction of noncovalent interactions, such as hydrogen bonding, aromatic stacking interactions, metal coordination, and host-guest interactions, endows supramolecular polymers with unique stimuli responsiveness and self-adjusting abilities. As a result, diverse monomer structures have been designed and synthesized to construct various types of supramolecular polymers. By changing the noncovalent interaction types, numbers, or chemical structures of functional groups in these monomers, supramolecular polymeric materials can be prepared with tailored chemical and physical properties. In recent years, the interest in supramolecular polymers has been extended from the preparation of intriguing topological structures to the discoveries of potential applications as functional materials. Compared with traditional polymers, supramolecular polymers show some advantages in the fabrication of reversible or responsive materials. The development of supramolecular polymers also offers a platform to construct complex and sophisticated materials with a bottom-up approach. Macrocylic hosts, including crown ethers, cyclodextrins, calixarenes, cucurbiturils, and pillararenes, are the most commonly used building blocks in the fabrication of host-guest interaction-based supramolecular polymers. With the introduction of complementary guest molecules, macrocylic hosts demonstrate selective and stimuli-responsive host-guest complexation behaviors. By elaborate molecular design, the resultant supramolecular polymers can exhibit diverse structures based on the self-selectivity of host-guest interactions. The introduction of reversible host-guest interactions can further endow these supramolecular polymers with interesting and fascinating chemical/physical properties, including stimuli responsiveness, self-healing, and environmental adaptation. It has been reported that macrocycle-based supramolecular polymers can respond to pH change, photoirradition, anions, cations, temperature, and solvent. Macrocycle-based supramolecular polymers have been prepared in solution, in gel, and in the solid state. Furthermore, the solvent has a very important influence on the formation of these supramolecular polymers. Crown ether- and pillararene-based supramolecular polymers have mainly formed in organic solvents, such as chloroform, acetone, and acetonitrile, while cyclodextrin- and cucurbituril-based supramolecular polymerizations have been usually observed in aqueous solutions. For calixarenes, both organic solvents and water have been used as suitable media for supramolecular polymerization. With the development of supramolecular chemistry and polymer science, various methods, such as nuclear magnetic resonance spectroscopy, X-ray techniques, electron microscopies, and theoretical calculation and computer simulation, have been applied for characterizing supramolecular polymers. The fabrication of macrocycle-based supramolecular polymers has become a currently hot research topic. In this Account, we summarize recent results in the investigation of supramolecular polymers constructed from macrocycle-based host-guest molecular recognition motifs. These supramolecular polymers are classified based on the different macrocycles used in them. Their monomer design, structure control, stimuli-responsiveness, and applications in various areas are discussed, and future research directions are proposed. It is expected that the development of supramolecular polymers will not only change the way we live and work but also exert significant influence on scientific research.

Three-step metal-promoted allene-based preparation of bis(heterocyclic) cyclophanes from carbonyl compounds

A straightforward metal-mediated method for the synthesis of bis(dihydrofuryl) cyclophane scaffolds from carbonyl compounds has been developed. The combination of the dihydrofuran moiety with different heterocycles such as β-lactams and sugars allows high levels of skeletal diversity. The process comprises indium-promoted one-pot carbonyl bis(allenylation) and gold- or palladium-catalyzed double cyclization in the resulting bis(allenols), followed by selective ruthenium-catalyzed macrocyclization. In some cases, the method has been successfully applied to the synthesis of the challenging Z-isomers. The E- versus Z-stereochemistry of the metathesis-formed double bonds could not be assigned taking into consideration the usual coupling constants criteria, but a diagnostic based on the chemical shifts of the two olefinic protons located at the macrocyclic double bond was established.

Cyclodextrin-templated porphyrin nanorings

α- and β-Cyclodextrins have been used as scaffolds for the synthesis of six- and seven-legged templates by functionalizing every primary CH₂OH with a 4-pyridyl moiety. Although these templates are flexible, they are very effective for directing the synthesis of macrocyclic porphyrin oligomers consisting of six or seven porphyrin units. The transfer of chirality from the cyclodextrin templates to their nanoring hosts is evident from NMR and circular dichroism spectroscopy. Surprisingly, the mean effective molarity for binding the flexible α-cyclodextrin-based template within the six-porphyrin nanoring (74 m) is almost as high as for the previously studied rigid hexadentate template (180 m). The discovery that flexible templates are effective in this system, and the availability of a template with a prime number of binding sites, open up many possibilities for the template-directed synthesis of larger macrocycles.

Supramolecular polymers based on cyclodextrins for drug and gene delivery

Supramolecular polymers based on cyclodextrins (CDs) have inspired interesting and rapid developments as novel biomaterials in a broad range of drug and gene delivery applications, due to their low cytotoxicity, controllable size, and unique architecture. This review will summarize the potential applications of polyrotaxanes in the field of drug delivery and gene delivery. Generally, cyclodextrin-based biodegradable polypseudorotaxane hydrogels could be used as a promising injectable drug delivery system for sustained and controlled drug release. Temperature-responsive, pH-sensitive, and controllable hydrolyzable polyrotaxane hydrogels have attracted much attention because of their controllable properties, and the self-assembly micelles formed by amphiphilic copolymer threaded with CDs could be used as a carrier for controlled and sustained drug release. Polyrotaxanes with drug or ligand conjugated CDs threaded on a polymer chain with a biodegradable end group could be useful for controlled and multivalent targeted delivery. In the field of gene delivery, cationic polyrotaxanes consisting of multiple OEI-grafted CDs threaded on a block copolymer chain are attractive non-viral gene carries due to the strong DNA-binding ability, low cytotoxicity, and high gene delivery capability. Furthermore, cytocleavable end-caps were introduced in the polyrotaxane systems in order to ensure efficient endosomal escape for intracellular trafficking of DNA. The development of the supramolecular approach using CD-containing polyrotaxanes is expected to provide a new paradigm for biomaterials.