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Abstract: Review: 100 refs. [ABSTRACT FROM AUTHOR]

Abstract: Review: synthesis, properties and possible applications; 140 refs. [ABSTRACT FROM AUTHOR]

Review: properties and possible applications; 121 refs. [ABSTRACT FROM AUTHOR]

Abstract: A CuI bis‐phenanthroline rotaxane was prepared by using the [2+2] cycloaddition‐retroelectrocyclization (CA‐RE) reaction to graft a bulky dicyanoquinodimethane (DCNQ) stopper. The electronic properties were investigated with electrochemical and photophysical techniques, in parallel with three reference compounds, namely, the DCNQ derivative alone, the DCNQ‐based phenanthroline ligand, and an analogue CuI complex lacking the DCNQ moiety. In all the systems containing the DCNQ unit, the lowest electronic excited states are centered thereon, with the singlet level (S1) located at about 1.0 eV, as suggested by TDDFT calculations. Accordingly, in the DCNQ‐equipped rotaxane, the typical metal‐to‐ligand charge‐transfer luminescence of the CuI center is totally quenched. Ultrafast transient absorption and emission studies show that, in the rotaxane, the final sink of photoinduced processes is the lowest singlet state of the DCNQ moiety (S1), which exhibits strong charge‐transfer character and a lifetime of 0.4 ps. Its deactivation leads to population of another excited state with a lifetime of 1.3 ps, which can be the related triplet state (T1) or a vibrationally hot level (hot‐S0). Notably, S1 also shows stimulated fluorescence in the near‐infrared (NIR) region between 1100 and 1500 nm, corroborating the TDDFT prediction. This unusual finding opens up the study of ultrashort‐lived NIR luminescence in organic donor–acceptor systems. [ABSTRACT FROM AUTHOR]

Transformation of a methylene group of the pillar[5]arene scaffold into a ketone has been achieved by treatment with N‐bromosuccinimide followed by hydrolysis of the bromide intermediate and oxidation of the resulting secondary benzylic alcohol with BaMnO4. Condensation of the resulting macrocycle including a ketone function with p‐toluenesulfonyl hydrazide followed by reaction of the corresponding tosylhydrazone with C60 under modified Bamford–Stevens conditions gave a fulleropillar[5]arene derivative. This building block has been used to prepare a rotaxane. The resulting molecule combining the fullerene‐functionalized macrocycle with an axle bearing a porphyrin stopper is a photoactive molecular device in which the porphyrin emission is efficiently quenched by the fullerene moiety. [ABSTRACT FROM AUTHOR]

Abstract: We report a rotaxane based on a simple urea motif that binds Cl− selectively as a separated ion pair with H+ and reports the anion binding event through a fluorescence switch‐on response. The host selectively binds Cl− over more basic anions, which deprotonate the framework, and less basic anions, which bind more weakly. The mechanical bond also imparts size selectivity to the ditopic host. [ABSTRACT FROM AUTHOR]

We present the first [2]rotaxane featuring a functional organometallic host. In contrast to the known organic scaffolds, this assembly shows a high post-synthetic modifiability. The reactivity of the Ag8 pillarplex host is fully retained, as is exemplified by the first transmetalation in a rotaxane framework to provide the respective Au8 analogue. Additionally, a transformation under acidic conditions to give a purely organic [3]rotaxane is demonstrated which is reversible upon addition of a suitable base, rendering the assembly a pH-dependent switch. Hereby, it is shown that the mechanically interlocked nature of the system enhances the kinetic stability of the NHC host complex by a factor of >1000 and corresponds to the first observation of a stabilizing 'rotaxand effect'. [ABSTRACT FROM AUTHOR]

Crosslinking Structure, Mechanical Properties, Polymers, Rotaxanes, Supramolecular Chemistry Keywords: Crosslinking Structure; Mechanical Properties; Polymers; Rotaxanes; Supramolecular Chemistry EN Crosslinking Structure Mechanical Properties Polymers Rotaxanes Supramolecular Chemistry 1 1 1 08/09/23 20230814 NES 230814 B Rotaxanes b . In their Research Article (e202303341), Toshikazu Takata et al. investigate the effect of the axle end structure and number of through-space bonds on the properties of rotaxane crosslinked polymers. [Extracted from the article]

The article presents information on the synthesis and molecular shuttling of rotaxanes.

Molecular interlocked systems with mechanically trapped components can serve as versatile building blocks for dynamic nanostructures. Here we report the synthesis of unprecedented double-stranded (ds) DNA [2]- and [3]rotaxanes with two distinct stations for the hybridization of the macrocycles on the axle. In the [3]rotaxane, the release and migration of the "shuttle ring" mobilizes a second macrocycle in a highly controlled fashion. Different oligodeoxynucleotides (ODNs) employed as inputs induce structural changes in the system that can be detected as diverse logically gated output signals. We also designed nonsymmetrical [2]rotaxanes which allow unambiguous localization of the position of the macrocycle by use of atomic force microscopy (AFM). Either light irradiation or the use of fuel ODNs can drive the threaded macrocycle to the desired station in these shuttle systems. The DNA nanostructures introduced here constitute promising prototypes for logically gated cargo delivery and release shuttles. [ABSTRACT FROM AUTHOR]

ABSTRACT Rotaxane-type hyperbranched polymers are synthesized for the first time from A2B type semi-rotaxane monomers formed in situ via complexation of bis( m-phenylene)-32-crown-10 dimethanol ( 1) and two paraquat ω- n-alkylenecarboxylic acid derivatives with tris( p-t-butylphenyl)methylphenylalkylene stoppers ( 8 and 9). Rotaxane and taco complexes exist in solutions of the hyperbranched polyesters in CD3CN/CDCl3 as confirmed by NMR spectroscopy, but the taco complexes, which derive from non-rotaxanated paraquat units, disappear in DMSO- d6. NMR spectroscopy indicates the portion of rotaxanes strongly interlocked by the environment (inner rotaxanes) is larger in HP1•9, which has longer alkylene spacers, perhaps indicating a higher degree of polymerization. The molecular size increases upon formation of the hyperbranched polymers are confirmed by dynamic light scattering and by viscometry. As with covalent hyperbranched polymers a number of potential applications exist; the unique mechanically linked character and the presence of uncomplexed host and guest moieties foreshadow the use of such systems for their responses to external stimuli with the added benefit of providing molecular recognition sites useful as delivery vehicles. Use of other host-guest motifs to form the semirotaxane A2B monomers is possible and complementary systems with higher binding constants will enable efficient syntheses of high molecular weight, mechanically linked hyperbranched polymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1647-1658 [ABSTRACT FROM AUTHOR]

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Whilst the exploitation of interlocked host frameworks for anion recognition is widely established, examples incorporating halogen bond donor groups are still relatively rare. Through the integration of a novel tetra(iodotriazole)‐pyridinium motif into macrocycle and axle components, a family of halogen bonding catenane and rotaxanes are constructed for anion recognition studies in a competitive aqueous‐organic solvent mixture. Importantly, the degree of anion selectivity displayed is dictated by the topological nature and charged state of the respective interlocked host cavity. All the interlocked hosts exhibit iodide anion selectivity over other halides and sulfate, with the level of discrimination being the greatest with the mono‐cationic rotaxane. Arising from greater electrostatic interactions working in tandem with halogen bonding and hydrogen bonding, the di‐cationic rotaxane displays stronger anion association at the expense of a relatively lower degree of iodide selectivity. Fishing for iodide: Through the integration of a novel tetra‐iodotriazole halogen bonding motif into a family of interlocked host structures, strong halide binding and a high degree of iodide anion selectivity is achieved in aqueous‐organic solvent media. [ABSTRACT FROM AUTHOR]

Abstract: Ein BODIPY‐basierter Bis(3‐pyridyl)‐Ligand bildet in einem Selbstorganisationsprozess bei der Koordination an tetravalente Palladium(II)‐Ionen ein metallosupramolekulares Pd6L12‐Aggregat mit einem neuartigen Strukturmotiv, das als ein rotaxanartiges Käfig‐im‐Ring‐Arrangement beschrieben werden kann. In diesem Assemblat nimmt der Ligand zwei unterschiedliche Konformationen ein – eine C‐förmige, um einen Pd2L4‐Käfig aufzubauen, der sich im Zentrum eines Pd4L8‐Rings befindet, welcher aus Liganden in einer W‐förmigen Konformation zusammengesetzt ist. Dieses Aggregat ist nicht im Sinne einer Katenierung mechanisch ineinander verschlungen, sondern es wird lediglich durch attraktive π‐Stapelwechselwirkungen zwischen den BODIPY‐Chromophoren in der Peripherie und den Rückgraten der Liganden sowie den Van‐der‐Waals‐Wechselwirkungen zwischen den langen Alkoxyketten stabilisiert. Durch dieses Arrangement beider Komponenten kommt es zu einem sehr effektiven Ausfüllen des Raumes. Die gesamte Struktur kann daher als ein rotaxanartiges Assemblat beschrieben werden, in dem ein metallosupramolekularer Käfig die Achse in einem metallosupramolekularen Ring bildet. Dieses einzigartige Strukturmotiv konnte mittels ESI‐Massenspektrometrie, NMR‐Spektroskopie und Einkristall‐Röntgenbeugungsexperimenten charakterisiert werden. [ABSTRACT FROM AUTHOR]

Abstract: The structural complexity of mechanically interlocked molecules are very attractive to chemists owing to the challenges they present. In this article, novel mechanically interlocked molecules with a daisy‐chain‐containing hetero[4]rotaxane motif were efficiently synthesized. In addition, a novel integrative self‐sorting strategy is demonstrated, involving an ABB‐type (A for host, dibenzo‐24‐crown‐8 (DB24C8), and B for guest, ammonium salt sites) monomer and a macrocycle host, benzo‐21‐crown‐7 (B21C7), in which the assembled species in hydrogen‐bonding‐supported solvent only includes a novel daisy‐chain‐containing hetero[4]pseudorotaxane. The found self‐sorting process involves the integrative recognition between B21C7 macrocycles and carefully designed components simultaneously containing two types of secondary ammonium ions and a host molecule, DB24C8 crown ether. The self‐sorting strategy is integrative to undertake self‐recognition behavior to form one single species of pseudorotaxane compared with the previous report. This self‐sorting system can be used for the efficient one‐pot synthesis of a daisy‐chain‐containing hetero[4]rotaxane in a good yield. The structure of hetero[4]rotaxane was confirmed by 1H NMR spectroscopy and high‐resolution electrospray ionization (HR‐ESI) mass spectrometry. [ABSTRACT FROM AUTHOR]

A novel [2]rotaxane ligand has been prepared that contains a bidentate N,N′-chelate as part of a rigid, H-shaped axle and a 24-membered crown ether macrocycle containing six ether O-atoms and a trans olefinic group as the wheel. This unique interlocked connectivity allows access to a number of different donor sets, which are shown to be capable of binding AgI metal ions. [ABSTRACT FROM AUTHOR]

A series of six [2]rotaxane molecular shuttles was designed which contain an axle with a benzo-bis(imidazole) core (in either a neutral or dicationic form) and a single 24-membered, crown ether wheel ( 24C6, B24C6, or DMB24C6), and the shuttling rates of the ring along the axle were determined. The charged versions showed much slower shuttling rates as a result of the increase in noncovalent interactions between the axle and wheel. The [2]rotaxane with a B24C6 wheel shows a difference in fluorescence between the charged and neutral species, while the [2]rotaxane with a DMB24C6 wheel exhibits a difference in color between the charged and neutral compounds. These changes in optical properties can be attributed to the structural differences in the co-conformations of the [2]rotaxane as they adapt to the changes in acid/base chemistry. This allowed the relative rate of the translational motion of a molecular shuttle to be determined by observation of a simple optical probe. [ABSTRACT FROM AUTHOR]

Amplification of molecular motions into the macroscopic world has great potential in the development of smart materials. Demonstrated here is an approach that integrates mechanically interlocked molecules into complex three-dimensional (3D) architectures by direct-write 3D printing. The design and synthesis of polypseudorotaxane hydrogels, which are composed of α-cyclodextrins and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers, and their subsequent fabrication into polyrotaxane-based lattice cubes by 3D printing followed by post-printing polymerization are reported. By switching the motion of the α-cyclodextrin rings between random shuttling and stationary states through solvent exchange, the polyrotaxane monolith not only exhibits macroscopic shape-memory properties but is also capable of converting the chemical energy input into mechanical work by lifting objects against gravity. [ABSTRACT FROM AUTHOR]

Use of molecular electron spins as qubits for quantum computing will depend on the ability to produce molecules with weak but measurable interactions between the qubits. Here we demonstrate use of pulsed EPR spectroscopy to measure the interaction between two inequivalent spins in a hybrid rotaxane molecule. [ABSTRACT FROM AUTHOR]

A CuI-catalyzed azide-alkyne cycloaddition reaction between an azide-terminated NiII-templated [2]pseudorotaxane with an oxy-ether tris(amino) macrocycle (MC) and an alkyneterminated triphenylene stopper unit produces a new [2]rotaxane (ROT) with multiple functional groups. A detailed mass spectrometry study and various 1D and 2D NMR spectroscopy studies confirm the interpenetration of the axle in the macrocycle of ROT. The tri-acetylation of the tris(amine) moiety of ROT produces AcROT with three tertiary amide functionalities. Prior to this selection, a detailed study of the dynamic properties was undertaken with the tertiary amide functionalized macrocycle MC1 and the tri-methylated derivative of MC, MC2. A 1H NMR study of AcROT at room temp. reveals multiple signals for most of the protons owing to the existence of multiple conformers and co-conformers in solution through tertiary amide bond rotations. Furthermore, the ethereal pocket of the heteroditopic macrocycle was explored to demonstrate the reversible locking and unlocking of the dynamic behaviour of AcROT through the addition and removal, respectively, of alkalimetal ions. [ABSTRACT FROM AUTHOR]

Donor-acceptor materials with small HOMO-LUMO gaps are important in molecular electronics, but are often difficult to synthesise. A simple and efficient way to position tetrathiafulvalene (TTF) as the donor and naphthalene diamide (NDI) as the acceptor in close proximity to each other in a divalent crown/ammonium pseudo[2]rotaxane is presented. The divalent design provides high chelate cooperativity and much stronger binding compared with a monovalent analogue. The pseudo[2]rotaxane was then doubly interlocked by stoppering it in a catalyst-free 1,3-dipolar cycloaddition. UV/Vis and cyclic voltammetry experiments with the resulting [2]rotaxane revealed the optoelectronic properties of an intramolecular charge transfer with a small HOMO-LUMO energy gap. Redox-switching experiments showed the rotaxane to be pentastable. DFT calculations provided insights into the electronic structures of the five redox states. [ABSTRACT FROM AUTHOR]

The helical structures of m-ethynylpyridine (2,6-pyridyleneethynylene) oligomers have been stabilized by mechanical crosslinking. A heptameric oligomer, in which the two terminal pyridine rings bear two carbaldehyde groups, has been designed. When this heptamer was treated with octyl β- d-glucopyranoside, a circular dichroism (CD) band was induced at around 330 nm, which corresponds to the formation of a chiral ethynylpyridine helix. The CD band was enhanced by the addition of a diamine and a diammonium dumbbell as a result of the formation of a [3]rotaxane structure linked to the terminal pyridines of the helical structure. A decameric oligomer containing four diformylarene units showed stronger CD enhancement in similar experiments owing to two crosslinking events. [ABSTRACT FROM AUTHOR]

Rotaxane and pseudorotaxane are two types of mechanically interlocked molecular architectures, and there is a clear topological difference and boundary between them. In this work, a 'suggested [2]rotaxane 1⊂α-CD' was constructed based on axle molecule 1 bearing two terminal ferrocene groups and a wheel component α-cyclodextrin (α-CD), but the result obtained indicated that the ferrocene group cannot prevent α-CD dethreading under UV irradiation. That is, 1⊂α-CD is just a pseudo[2]rotaxane. Furthermore, the two ferrocene groups in 1⊂α-CD were encapsulated by two cucurbit[7]uril (CB[7]) units to obtain a heteropseudo[4]rotaxane 1⊂α-CD⋅2CB[7]. This heteropseudo[4]rotaxane displayed high stability towards harsh temperatures and the isomerization of azobenzene in 1, so it can be regarded as a [2]rotaxane. In this [2]rotaxane, the stoppers are not the bulky groups covalently bonded to the axle, but the cyclic CB[7] units connected through noncovalent interactions. [ABSTRACT FROM AUTHOR]

In einem Ruck können Polyrotaxane bestehend aus bis zu 64 Ringen durch 1,3 ‐ dipolare Azid ‐ Alkin ‐ Cycloadditionen mit Cucurbit[6]uril als Templat in Gegenwart von Cyclodextrinen synthetisiert werden. Der Schlüssel zu diesem Prozess ist die Bildung von Wasserstoffbrücken, die Selbstsortierung und positive Kooperativität bewirken. Einfaches Mischen von sechs Komponenten (siehe Bild) liefert ein Hetero[4]rotaxan binnen einer Minute in quantitativer Ausbeute. [ABSTRACT FROM AUTHOR]

An electrostatic potential (ESP)-based image segmentation method has been used to estimate the ability of proton donation and acceptance involved in ring-rod recognition. The relative binding strength of [2]rotaxane has also been further estimated from the difference of the characteristic image-segmentation derived ESP between proton donor and proton acceptor. The size and electrostatic compatibility criteria are introduced to guide the design of interlocked [2]rotaxane. A library of 75 thermodynamically stable [2]rotaxane candidates has been generated, including 16 experimentally known systems. The theoretical results for 16 experimentally known [2]rotaxanes are in good agreement with both the experimental association constants and density functional theory-calculated binding energies. Our ESP-based image segmentation model is also applicable to the tristable [2]rotaxane molecular shuttle as well as [1]rotaxane with self-inclusion function, indicating this simple method is generic in the field of constructing other supramolecular architectures formed with donor/acceptor molecular recognition. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The synthesis of the first halogen bonding [3]rotaxane host system containing a bis-iodo triazolium-bis-naphthalene diimide four station axle component is reported. Proton NMR anion binding titration experiments revealed the halogen bonding rotaxane is selective for nitrate over the more basic acetate, hydrogen carbonate and dihydrogen phosphate oxoanions and chloride, and exhibits enhanced recognition of anions relative to a hydrogen bonding analogue. This elaborate interlocked anion receptor functions via a novel dynamic pincer mechanism where upon nitrate anion binding, both macrocycles shuttle from the naphthalene diimide stations at the periphery of the axle to the central halogen bonding iodo-triazolium station anion recognition sites to form a unique 1:1 stoichiometric nitrate anion-rotaxane sandwich complex. Molecular dynamics simulations carried out on the nitrate and chloride halogen bonding [3]rotaxane complexes corroborate the 1H NMR anion binding results. [ABSTRACT FROM AUTHOR]

A stacked assembly composed of a porphyrin and two phthalocyanines was prepared through fourfold rotaxane formation. Two phthalocyanine molecules, bearing four 24-crown-8 units, were assembled onto a porphyrin template incorporating four sidechains with two dialkylammonium ions each through pseudorotaxane formation between crown ether units and ammonium ions. The Staudinger phosphite reaction, as the stoppering reaction, resulted in the formation of the stacked heterotrimer composed of a porphyrin and two phthalocyanines connected through a fourfold rotaxane structure. UV/Vis spectroscopic and electrochemical studies of the heterotrimer indicated that there is a significant electronic interaction between the two phthalocyanine units due to the close stacking. The electrochemical oxidation process of the stacked heterotrimer was studied by cyclic voltammetry and spectroelectrochemistry. Electron paramagnetic resonance (EPR) spectroscopy of a dinuclear CuII complex, in which two CuII phthalocyanines were assembled on a metal-free porphyrin template, revealed that two CuII phthalocyanines were located within the stacking distance, which resulted in an antiferromagnetic interaction between the two S= [ABSTRACT FROM AUTHOR]

The hierarchical assembly of well-organized submoieties could lead to more complicated superstructures with intriguing properties. We describe herein an unprecedented polyrotaxane polythreading framework containing a two-fold nested super-polyrotaxane substructure, which was synthesized through a uranyl-directed hierarchical polythreading assembly of one-dimensional polyrotaxane chains and two-dimensional polyrotaxane networks. This special assembly mode actually affords a new way of supramolecular chemistry instead of covalently linked bulky stoppers to construct stable interlocked rotaxane moieties. An investigation of the synthesis condition shows that sulfate can assume a vital role in mediating the formation of different uranyl species, especially the unique trinuclear uranyl moiety [(UO2)3O(OH)2]2+, involving a notable bent [O=U=O] bond with a bond angle of 172.0(9)°. Detailed analysis of the coordination features, the thermal stability as well as a fluorescence, and electrochemical characterization demonstrate that the uniqueness of this super-polyrotaxane structure is mainly closely related to the trinuclear uranyl moiety, which is confirmed by quantum chemical calculations. [ABSTRACT FROM AUTHOR]

High-yielding synthesis of cyclic block copolymer (CBC) using the rotaxane protocol by linear-cyclic polymer topology transformation was first demonstrated. Initial complexation of OH-terminated sec-ammonium salt and a crown ether was followed by the successive living ring-opening polymerizations of two lactones to a linear block copolymer having a rotaxane structure by the final capping of the propagation end. CBC was obtained in a high yield by an exploitation of the mechanical linkage through the translational movement of the rotaxane component to transform polymer structure from linear to cyclic. Furthermore, the change of the polymer topology was translated into a macroscopic change in crystallinity of the block copolymer. [ABSTRACT FROM AUTHOR]

A synthetic approach combining recent concepts for the preparation of multifunctional nanomolecules (click chemistry on multifunctional scaffolds) with supramolecular chemistry (self-assembly to prepare rotaxanes) gave easy access to a large variety of sophisticated [2]rotaxane heteroglycoclusters. Specifically, compounds combining galactose and fucose have been prepared to target the two bacterial lectins (LecA and LecB) from the opportunistic pathogen Pseudomonas aeruginosa. [ABSTRACT FROM AUTHOR]

The synthesis of an all-halogen-bonding rotaxane for anion recognition is achieved by using active-metal templation. A flexible bis-iodotriazole-containing macrocycle is exploited for the metal-directed rotaxane synthesis. Endotopic binding of a CuI template facilitates an active-metal CuAAC iodotriazole axle formation reaction that captures the interlocked rotaxane product. Following copper-template removal, exotopic coordination of a more sterically demanding rhenium(I) complex induces an inversion in the conformation of the macrocycle component, directing the iodotriazole halogen-bond donors into the rotaxane's interlocked binding cavity to facilitate anion recognition. [ABSTRACT FROM AUTHOR]

A sophisticated photoactive molecular device has been prepared by combining recent concepts for the preparation of multifunctional nanomolecules (click chemistry on multifunctional scaffolds) with supramolecular chemistry (self-assembly to prepare rotaxanes). Specifically, a clickable [2]rotaxane scaffold incorporating a free-base porphyrin stopper has been prepared and functionalized with ten peripheral Zn(II)-porphyrin moieties. Electrochemical investigations of the final compound revealed a peculiar behavior resulting from the intramolecular coordination of the Zn(II) porphyrin moieties to 1,2,3-triazole units. Finally, steady state investigations of the compound combining Zn(II) and free-base porphyrin moieties have shown that this compound is a light-harvesting device capable of channeling the light energy from the peripheral Zn(II)-porphyrin subunits to the core by singlet-singlet energy transfer. [ABSTRACT FROM AUTHOR]

Although motor proteins are essential cellular components that carry out biological processes by converting chemical energy into mechanical motion, their functions have been difficult to mimic in artificial synthetic systems. Daisy chains are a class of rotaxanes which have been targeted to serve as artificial molecular machines because their mechanically interlocked architectures enable them to contract and expand linearly, in a manner that is reminiscent of the sarcomeres of muscle tissue. The scope of external stimuli that can be used to control the musclelike motions of daisy chains remains limited, however, because of the narrow range of supramolecular motifs that have been utilized in their templated synthesis. Reported herein is a cyclic daisy chain dimer based on π-associated donor-acceptor interactions, which can be actuated with either thermal or electrochemical stimuli. Molecular dynamics simulations have shown the daisy chain's mechanism of extension/contraction in the ground state in atomistic detail. [ABSTRACT FROM AUTHOR]

Rotaxane cross-linked (RC) microgels that exhibit a decoupled thermo- and pH-responsive volume transition were developed. The pH-induced changes of the aggregation/disaggregation states of cyclodextrin in the RC networks were used to control the swelling capacity of the entire microgels. Different from conventional thermo- and pH-responsive microgels, which are usually obtained from copolymerizations involving charged monomers, the RC microgels respond to temperature as intended, even in the presence of charged functional molecules such as dyes in the microgel dispersion. The results of this study should lead to new applications, including drug delivery systems that require a retention of their smart functions even in environments that may contain foreign ions, for example, in in vivo experiments. [ABSTRACT FROM AUTHOR]

To a large extent, the field of 'molecular machines' started after several groups were able to prepare, reasonably easily, interlocking ring compounds (named catenanes for compounds consisting of interlocking rings and rotaxanes for rings threaded by molecular filaments or axes). Important families of molecular machines not belonging to the interlocking world were also designed, prepared, and studied but, for most of them, their elaboration was more recent than that of catenanes or rotaxanes. Since the creation of interlocking ring molecules is so important in relation to the molecular machinery area, we will start with this aspect of our work. The second part will naturally be devoted to the dynamic properties of such systems and to the compounds for which motions can be directed in a controlled manner from the outside, that is, molecular machines. We will restrict our discussion to a very limited number of examples which we consider as particularly representative of the field. [ABSTRACT FROM AUTHOR]

The [2]rotaxane cross-linkers (RCs) comprising vinyl group-terminated axle component having different axle lengths and vinyl group-containing crown ether were synthesized, and applied to prepare the corresponding rotaxane cross-linked polymers (RCPs). The preparations of RCP were performed by the radical polymerizations of n-butyl acrylate in the presence of 0.5 mol% of RCs. Properties of the RCPs were evaluated by swelling ratio, clearly demonstrating that axle length of RC affects swelling ratio of RCPs. [ABSTRACT FROM AUTHOR]

Bistable [2]rotaxanes in which the affinities of the two stations can be reversed form the basis of molecular shuttles. Gaining quantitative information on such rotaxanes in which the ring distribution between the two stations is largely nonsymmetric has proven to be very challenging. Herein, we report on two independent experimental methodologies, based on luminescence lifetime measurements and acid-base titrations, to determine the relative populations of the two co-conformations of a [2]rotaxane. The assays yield convergent results and are sensitive enough to measure an equilibrium constant ( K≈4000) out of reach for NMR spectroscopy. We also estimate the ring distribution constant in the switched (deprotonated) state ( K′<10−4), and report the highest positional efficiency for stimuli-induced shuttling to date (>99.92 %). Finally, our results show that the p Ka of the pH-responsive station depends on the ring affinity of the pH-insensitive station, an observation that paves the way for the design of new artificial allosteric systems. [ABSTRACT FROM AUTHOR]

For the purpose of developing higher level mechanically interlocked molecules (MIMs), such as molecular switches and machines, a new rotaxane system was designed in which both the 1,2-bis(pyridinium)ethane and benzimidazolium recognition templating motifs were combined. These two very different recognition sites were successfully incorporated into [2]rotaxane and [3]rotaxane molecular shuttles which were fully characterized by 1H NMR, 2D EXSY, single-crystal X-ray diffraction and VT NMR analysis. By utilizing benzimidazolium as both a recognition site and stoppering group it was possible to create not only an acid/base switchable [2]rotaxane molecular shuttle (energy barrier 20.9 kcal⋅mol−1) but also a [3]rotaxane molecular shuttle that displays unique dynamic behavior involving the simultaneous motion of two macrocyclic wheels on a single dumbbell. This study provides new insights into the design of switchable molecular shuttles. Due to the unique properties of benzimidazoles, such as fluorescence and metal coordination, this new type of molecular shuttle may find further applications in developing functional molecular machines and materials. [ABSTRACT FROM AUTHOR]

Since the advent of mechanically interlocked molecules (MIMs), many approaches to templating their formation using various different noncovalent bonding interactions have been introduced and explored. In particular, employing radical-pairing interactions between BIPY.+ units, the radical cationic state of 4,4′-bipyridinium (BIPY2+) units, in syntheses is not only a convenient but also an attractive source of templation because of the unique properties residing in the resulting catenanes and rotaxanes. Herein, we report a copper-mediated procedure that enables the generation, in the MIM-precursors, of BIPY.+ radical cations, while the metal itself, which is oxidized to CuI, catalyzes the azide-alkyne cycloaddition reactions that result in the efficient syntheses of two catenanes and one rotaxane, assisted by radical-pairing interactions between the BIPY.+ radical cations. This procedure not only provides a fillip for making and investigating the properties of Coulombically challenged catenanes and rotaxanes, but it also opens up the possibility of synthesizing artificial molecular machines which operate away from equilibrium. [ABSTRACT FROM AUTHOR]

A new mechanically interlocked molecular linker was prepared by using ring-closing metathesis (Grubbs I) to clip a [24]crown-6 ether wheel around an axle containing both Y-shaped diphenylimidazole and isophthalic acid groups. A metal-organic framework (MOF) material was prepared using this linker and ZnII ions. Single-crystal X-ray diffraction experiments showed that the MOF contains an imidazolium-based rotaxane linked by dimeric [Zn2(NO3)(DEF)] secondary building units (SBUs). Variable-temperature (VT), 2H solid-state NMR spectroscopy was used to characterize the motion of the 'soft' wheel component around the rigid 'hard' lattice of the framework. At higher temperatures (above 150 °C), it was demonstrated that the 24-membered, macrocyclic ring of the MOF undergoes rapid, thermally driven rotation about the axle inside the voids of the lattice. [ABSTRACT FROM AUTHOR]

The [c2]daisy chain rotaxane is an attractive interlocked molecule for the development of functional materials because of its unique mechanical properties that respond to various external stimuli, resulting in extension and contraction motions along the molecular axis. The synthesis of several ‘impossible’ [2]rotaxanes that do not exhibit obvious binding motifs between their axle and wheel moieties has been achieved through further chemical modification of their axle moieties within pre‐prepared [2]rotaxanes. However, no ‘impossible’ [c2]daisy chain rotaxane has been synthesized using similar strategies until now. In this study, we investigated the hydrogenation of diarylacetylene moieties within a permethylated α‐cyclodextrin (PM α‐CD)‐based [c2]daisy chain rotaxane using Pd/C or Pd/CaCO3 under hydrogen. A new [c2]daisy chain rotaxane featuring two diarylethane moieties was successfully synthesized through the simultaneous full hydrogenation of the insulated diarylacetylene moieties under optimized conditions. The new rotaxane is classified as an ‘impossible’ [c2]daisy chain rotaxane due to the lack of obvious binding motifs between diarylethane and the PM α‐CD. This work demonstrates for the first time that the insulated axle moieties of [c2]daisy chain rotaxanes can undergo novel chemical modifications using a synthetic strategy employing transition metal‐catalyzed hydrogenation, which can potentially advance the development of nanoarchitectures with functional interlocked molecules. [ABSTRACT FROM AUTHOR]

The article features a selection of work that has recently been published in other journals. One study describes the preparation of anion-templated rotaxanes incorporating an optical- and electroactive osmium(II) bipyridyl reporter group. Another study examines how ethanol electro-oxidation catalysis depends on differences in the particle size distribution of supported platinum-nanoparticle catalysts.