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Abstract: Operating molecular machines are based on switchable systems whose components can be set in motion in a controllable fashion. The presence of nonsymmetrical elements is a mandatory requirement to obtain and demonstrate the unidirectionality of motion. Calixarene‐based macrocycles have proved to be very efficient hosts in the design of oriented rotaxanes and of pseudorotaxanes with strict control over the direction of complexation. A series of two‐station rotaxanes based on bipyridinium–ammonium axles was synthesized and characterized. A recently reported supramolecularly assisted strategy for the synthesis of different orientational isomers was exploited, and the ammonium unit was identified as a proper secondary station for the calixarene. Displacement of the macrocycle was triggered by electrochemical reduction of the bipyridinium primary station, and it was shown that the shuttling is influenced both by the length of the chain of the axle component and by the position of the secondary station with respect to the calixarene rims. [ABSTRACT FROM AUTHOR]

Understanding the role played by the nature, number, and arrangement of binding sites anchored to a macrocycle remains a topic of current interest for the synthesis of new interwoven species. We report the synthesis and detailed structural characterization of a new calix[6]arene derivative decorated with two phenylureido groups anchored at the diametrical position of the calix upper rim that adopts a 1,2,3‐alternate conformation in solution and in the solid state. Preliminary data on the ability of this host to form redox‐active pseudorotaxanes and rotaxanes are reported. [ABSTRACT FROM AUTHOR]

The article discusses in pseudorotaxanes and rotaxanes. Topics include synthesis of rotaxanes based on various macrocycles such as cyclodextrins and calixarenes; molecular mobility of pseudorotaxanes based on stimuli response; and their applications such as protection of dyes and unstable species and use in metal-organic framework.

Since the dawn of supramolecular chemistry, calixarenes have been employed as platforms onto which functional groups and binding sites can be loaded in a regio‐ and stereocontrolled manner for the recognition of charged and neutral species. Despite their wider annulus, potentially suitable to bind larger guests, the larger members of the calixarene series have been relatively less employed, mainly because of the synthetic difficulties to control their conformational flexibility and their regioselective functionalization. In this account, we will present the achievements gained during the last two decades on the use of the calix[6]arene as a platform to build‐up structures in which the macrocycle acts as a wheel for the synthesis of oriented (pseudo)rotaxanes. We also account on how these calix[6]arene hosts affect the reactivity or spectroscopic properties of their bound guests. [ABSTRACT FROM AUTHOR]

We describe the active template effect of a calix[6]arene host towards the alkylation of a complexed pyridylpyridinium guest. The acceleration of the reaction within the cavity is significant and rim-selective, enabling the efficient preparation of rotaxanes with full control of the mutual orientation of their nonsymmetric components. [ABSTRACT FROM AUTHOR]

Abstract: We have synthesized a series of three rotaxanes constituted of a calix[6]arene wheel and a 4,4′-bipyridinium unit on the axle, which differ in the length of the two aliphatic chains that connect the central bipyridinium unit with the two terminal stoppers. We have investigated the photophysical and electrochemical properties of these systems and of suitable model compounds in two prototypical solvents, namely, acetonitrile and methylene chloride. Our results show that these rotaxanes are characterized by a complex pattern of intercomponent interactions whose strength can be influenced by the length of the axle as well as the nature of the solvent. [Copyright &y& Elsevier]

Two calix[6]arene directional wheels can be ordered in the right stereosequence by their through-the-annulusthreading with a rationally designed bis(benzylalkylammonium) axle. These stereoisomeric pseudo[3]rotaxanes can be considered as a minimal “informational system” because the “written information” on the thread is transferred to a specific sequence stereoisomer. [ABSTRACT FROM AUTHOR]

A topological-chemical reactivity studies (using electronegativity, chemical hardness, chemical power, electrophilicity indices and topological indices like Wiener indice) has been applied on calixare-based rotaxane complexes containing tris(N-phenylureido)- calix[6]arene as wheel and a 4,4'-bipyridinium dication's units as axle. The results indicate that the formation of this type of rotaxanic complex needs a preorganisational modifications undertaken by the calixarene to match with its molecular surface the shape of the guest molecule (axle of rotaxane). The obtained chemical binding scenario suggests that we are dealing with a system that remains open until the delayed maximization of the HOMO-LUMO interval, fact that allows the continuous transfer of charge between the components of the rotaxane. [ABSTRACT FROM AUTHOR]

Review: [73 refs. [ABSTRACT FROM AUTHOR]

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

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

The development of functional materials and smart surfaces has received tremendous attention in recent years. The anchoring of molecular machines and the transfer of their properties on to solid substrates may facilitate the design of new smart devices. Herein, we report an approach to the covalent modification of glassy carbon electrodes with electrochemically responsive tris( N- phenylureido)calix[6]arene-based pseudorotaxanes. The main focus of this study has been the electrochemically driven threading/de-threading process of the redox active dialkylviologen axial component of the supramolecular assemble. After the creation of an amine monolayer on the electrode, pseudorotaxane systems were generated at the surface using different approaches. It was revealed, through electrochemical investigations, that the reversibility of the threading/de-threading process of the axle depended on the nature of the alkyl substituents on the axle. [ABSTRACT FROM AUTHOR]

The article presents information about calix arenes substituted by urea groups at the wide rim. It is now well established, that calix arenes of type 1 substituted by urea groups at the wide rim form hydrogen-bonded dimeric capsules in apolar solvents. If these functional groups are preorganized in heterodimers, which are exclusively formed with tetratosyl ureas as template, multimacrocyclic compounds are available in excellent yield from which the newly formed macrocycles can be detached in a final step. The structure of the tetra rotaxanes was unambiguously confirmed not only by the nuclear magnetic resonance-spectroscopic changes, but also by ESI-MS or MALDI-TOF-MS showing the expected molecular peaks.

The first example of an oriented handcuff rotaxane has been obtained by through-the-annulusthreading of a double-calix[6]arene system with a bis-ammonium axle. The relative orientation of the two calix-wheels can be predefined by exploiting the “endo-alkyl rule” which controls the directionality of the threading of alkylbenzylammonium axles with calixarene macrocycles. [ABSTRACT FROM AUTHOR]

Partner preferences in pseudorotaxane formation were exploited to establish an integrative self‐sorting system able to discriminate simultaneously at the sequence and stereochemical level (see picture). It was found that calix[6]arenes were threaded selectively with a preferred orientation onto bisammonium axles, even when the structural differences between the possible building blocks were small and located remote from the binding sites. [ABSTRACT FROM AUTHOR]

Inherent chirality represents a distinct category of molecular chirality that does not fall within the traditional classification of four chiral elements: central, axial, planar, and helical chirality. While extensive research has been conducted on the catalytic enantioselective construction of these conventional chiralities, the corresponding synthesis of inherently chiral molecules has remained largely unexplored. This minireview provides a comprehensive summary of recent advancements in this field, focusing on the catalytic asymmetric synthesis of inherently chiral calixarenes, saddle‐shaped tetraphenylenes and their heterocycle derivatives, mechanically planar chiral rotaxanes and chiral multilayer 3D frameworks, as well as our perspective in this field. [ABSTRACT FROM AUTHOR]

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Review: [synthesis and properties of pillar[n]arene based supramolecular complexes]. [ABSTRACT FROM AUTHOR]

This article reports that the rotaxanes are considered to be a typical prototype of molecular machines bearing a rotor and an axle in the molecule. Crown ethers, cyclodextrins (CDs), calixarenes, and cucurbituril have been used as ring components of rotaxanes. CD has a rigid, well-defined "nonsymmetric" ring structure. Although there are a few reports on the isolation of unidirectional pseudo-rotaxane composed CDs and axle molecules, there are no reports on the kinetic control of the face-direction of CDs in the complex formation step. Researchers report here, for the first time, the face-direction control of CD in the construction of a pseudo-rotaxane with an alkyl chain bearing pyridyl end caps without any purification procedure.

The title compound consists of a 1-hexyl-4,4′-bipyridinium guest and cucurbit[8]uril (CB[8]) and α-cyclodextrin. [ABSTRACT FROM AUTHOR]

Review: 107 refs. [ABSTRACT FROM AUTHOR]

A complete study of the through-the-annulus threading of the larger calix[8]arene macrocycle with di-n-alkylammonium cations has been performed in the presence of the "superweak" TFPB counterion. Thus, it was found that such threading occurs only upon partial preorganization of the calix[8]arene macroring by intramolecular bridging. In particular, 1,5-bridged calix[8]arenes with a meta- or para-xylylene bridge (2 and 3) gave pseudo[2]rotaxanes in which one dialkylammonium axle (4a-4e+) was threaded into one of the two subcavities of the calix[8]-wheel. Conformational studies by using chemical shift surface maps and DFT calculations evidenced a 3/4-cone geometry for these subcavities. Higher pseudorotaxane Kass values were obtained for calix[8]-wheels 2 and 3, with respect to calix[6]-host 1a, due to the cooperative effect of their two subcavities. Dynamic NMR studies on calix[8]-pseudorotaxanes evidenced a direct correlation between Kass (and ΔGass) values and energy barriers for calix inversion due to the effectiveness of thread templation. In accordance with DFT calculations, an endo-alkyl preference, over the endo-benzyl one, was observed by threading calix[8]-wheel 3 with the directional n-butylbenzylammonium axle 4d+. [ABSTRACT FROM AUTHOR]

Novel type III-B dendrimers are synthesized via a modified copper-catalyzed alkyne-azide cycloaddition, a Glaser-Hay′s acetylenic oxidative homocoupling, and an amide formation. [ABSTRACT FROM AUTHOR]

Review: [121 refs. [ABSTRACT FROM AUTHOR]

The article presents chemical equations related to the article "Design and Efficient Synthesis of a Pillar[5]arene-Based [1]Rotaxane" by B. Xia and others, published in the 2013 issue of the journal "Chemical Communications."

Review: 120 refs. [ABSTRACT FROM AUTHOR]

Non-covalent molecular interactions are crucial for the formation of supramolecular systems whose applications in the transport and release of drugs, the development of nanoreactors or the design of molecular sensors, among others, make them very hot topic of investigation. The use of mass spectrometry (MS) and soft ionization methods as electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) has allowed the characterization of supramolecular systems. This comprises the characterization of non-covalent complexes formed by synthetic molecules and biomolecules and the study of these host-guest systems with different molecular interactions and thermodynamic aspects. Mass spectrometry is capable of answering many questions regarding analytical characterization of these systems including composition, stoichiometry, and structural aspects as e.g., connectivities and building blocks in the supramolecular complex. These soft ionization techniques together with MS have become the technique of choice for characterizing molecular interactions allowing the design of new molecules capable of self-assembly in supramolecular systems. In this review, the synthetic macromolecules cucurbiturils, calixarenes, crown ethers, catenanes, rotaxanes and cyclodextrins are reviewed due to the wide range of non-covalent interactions that they are able to form in their supramolecular assemblies. Both the non-covalent interactions and the supramolecular structures of these synthetic molecules have been studied by mass spectrometry to characterize their structures, thus showing the power of the technique as a tool for supramolecular analysis. Image 1 • Soft ionization methods for characterizing non-covalent complexes are reviewed. • Update information on complexes composition, stoichiometry and structural aspects obtained by MS is provided. • MALDI and ESI-MS are powerful tools to investigate supramolecular systems. • Cucubiturils, calixarenes, crown ethers, catenanes, rotaxanes and cyclodextrins are used for the study of interactions and assemblies. [ABSTRACT FROM AUTHOR]

Review: chemistry of gold catenanes; 76 refs. [ABSTRACT FROM AUTHOR]

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Review: recent attempts of building monolayers of rotaxanes/pseudorotaxanes on surface; 54 refs. [ABSTRACT FROM AUTHOR]

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The development of a pseudorotaxane motif capable of performing unidirectional threading and dethreading processes under control of external stimuli is particularly important for the construction of processive linear motors based on rotaxanes and, at least in principle, it discloses the possibility to access to rotary motors based on catenanes. Here, we report a strategy to obtain the solvent-controlled unidirectional transit of a molecular axle through a molecular wheel. It is based on the use of appropriately designed molecular components, the essential feature of which is their non-symmetric structure. Specifically they are an axle containing a central electron-acceptor 4,4′-bipyridinium core functionalized with a hexanol chain at one side, and a stilbene unit connected through a C6 chain at the other side, and a heteroditopic tris(phenylureido)-calix[6]arene wheel. In apolar solvents the axle threads into the wheel from its upper rim and with the end carrying the OH group, giving an oriented pseudorotaxane structure. After a stoppering reaction, which replaces the small hydroxy group with a bulky diphenylacetyl moiety, and replacement of the apolar solvent with a polar one, dethreading occurs through the slippage of the stilbene unit from the lower rim of the wheel, that is, in the same direction of the threading process. The essential role played by the stilbene unit to achieve the unidirectional transit of the axle through the wheel, and to tune the dethreading rate by light is also demonstrated. [ABSTRACT FROM AUTHOR]

Review: 'classic' and recent results concerning their chemistry, applications and crysal structure; 128 refs. [ABSTRACT FROM AUTHOR]

Review: 127 refs. [ABSTRACT FROM AUTHOR]

An abstract of the article "Host-Guest Properties of Pillar(n)arenes" by T. Ogoshi and T.-A. Yamagishi is presented.

A reference of an article "Assembled Structures of Pillar[n]arenes" by T. Ogoshi and T.A. Yamagishi which was published in the 2016 issue of periodical "Monographs in Supramolecular Chemistry" is presented.

The article presents chemical equations related to the article "Functionalization of Pillararenes" by T. Ogoshi and others, published in the "Monographs in Supramolecular Chemistry" in 2016.

The article presents chemical equations related to the article "Synthesis of Pillar[n]arenes" by T. Ogoshi and others, published in the "Monographs in Supramolecular Chemistry" in 2016.

The article presents chemical equations related to the article "Conformation and Planar Chirality of Pillar[n]arenes" by T. Ogoshi and others published in the "Monographs in Supramolecular Chemistry" in 2016.