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A series of unprecedented supramolecular complexes of covalently modified Anderson‐type polyoxometalates (POMs) and α‐cyclodextrins (α‐CDs) have been obtained and characterized in solid state by single‐crystal X‐ray diffraction, and in aqueous solution using various techniques including 1H DOSY NMR, 2D NOESY 1H NMR, isothermal titration calorimetry (ITC), and electrospray ionization time‐of‐flight mass spectroscopy (ESI‐TOF‐MS). It has been demonstrated that the supramolecular assembly process could be modulated by different covalent modification modes of the Anderson POMs, giving rise to a new type of POM/α‐CD complexes featuring organic‐inorganic pseudo‐rotaxane structures, which are in good contrast to those of POM/γ‐CD complexes of poly‐rotaxane structures. Moreover, it is delighted to find that these pseudo‐rotaxanes of POM/α‐CD complexes exhibit stable chirality in aqueous solution, which has not been accomplished in previously reported POM/CD assemblies. [ABSTRACT FROM AUTHOR]

Chemical systems displaying directional motions are relevant to the operation of artificial molecular machines. Herein we present the functioning of a molecule capable of transporting a cyclic species in a preferential direction. Our system is based on a linear, non‐symmetric, positively charged molecule. This cation integrates into its structure two different reactive regions. On one side features a bulky ester group that can be exchanged by a smaller substituent; the other extreme contains an acid/base responsive moiety that plays a dual role, as part of the recognition motif and as a terminal group. In the acidic state, a dibenzo‐24‐crown‐8 ether slides into the linear component attracted by the positively charged recognition site. It does this selectively through the extreme that contains the azepanium group, since the other side is sterically hindered. After base addition, intermolecular interactions are lost; however, the macrocycle is unable to escape from the linear component since the energy barrier to slide over the neutral azepane is too large. Therefore, a metastable mechanically interlocked molecule is formed. A second reaction, now on the ester functionality, exchanges the bulky mesityl for a methyl group, small enough to allow macrocycle dissociation, completing the directional transit of the ring along the track. [ABSTRACT FROM AUTHOR]

Rotaxanic type molecular machines are very intensively investigated because of their potential for the development of nanotechnology. We have applied the consecrated HSAB principle ("hard likes hard and soft likes soft") to a small rotaxanes molecular series pH-switchable for determining which resulted interlocked system is more favorable to be further consider and functionalized as a molecular machine and also we have found the quantum structural models in inter-conversion dynamics in terms of frontier molecular orbitals and chemical reactivity. The obtained results strengthen the results obtained in previous studies. [ABSTRACT FROM AUTHOR]

The first examples of bis‐squaramide axle containing [2]rotaxanes linked via rigid aryl and flexible alkyl spacers synthesised using copper(I) catalysed active metal template methodology are reported. The halide and oxoanion binding properties of the [2]rotaxanes in aqueous‐organic solvent media are examined through extensive 1H‐NMR titration experiments to investigate the impact of integrating multiple squaramide motifs on the anion binding capabilities of the interlocked receptors. These studies reveal that the bis‐squaramide rotaxane host systems exhibit enhanced halide anion binding capabilities relative to a mono‐squaramide axle functionalised rotaxane, demonstrating a rare anti‐Hofmeister bias halide anion selectivity trend in aqueous‐organic mixtures and highlighting the efficacy of the potent solvent shielded hydrophobic interlocked binding pocket created upon mechanical bond formation. Notably, employing a rigid aryl linker between the two squaramide motifs in the axle component enables the rotaxane host to exhibit strong and selective binding of tetrahedral oxoanions. Conversely, a flexible alkyl spacer facilitates trigonal oxoanion selective recognition by the bis‐squaramide [2]rotaxane. [ABSTRACT FROM AUTHOR]

Biomolecular machines autonomously convert energy into functions, driving systems away from thermodynamic equilibrium. This energy conversion is achieved by leveraging complex, kinetically asymmetric chemical reaction networks that are challenging to characterize precisely. In contrast, all known synthetic molecular systems in which kinetic asymmetry has been quantified are well described by simple single‐cycle networks. Here, we report on a unique light‐driven [2]rotaxane that enables the autonomous operation of a synthetic molecular machine with a multi‐cycle chemical reaction network. Unlike all prior systems, the present one exploits a photoactive macrocycle, which features a different photoreactivity depending on the binding sites at which it resides. Furthermore, E to Z isomerization reverses the relative affinity of the macrocycle for two binding sites on the axle, resulting in a multi‐cycle network. Building on the most recent theoretical advancements, this work quantifies kinetic asymmetry in a multi‐cycle network for the first time. Our findings represent the simplest rotaxane capable of autonomous shuttling developed so far and offer a general strategy to generate and quantify kinetic asymmetry beyond single‐cycle systems. [ABSTRACT FROM AUTHOR]

Physical manipulation can be carried out on molecules and cells through the utilization of nanomachines which are machines with nano dimensions. There are different types of nanomachines. Among them, rotaxanes stand out as the most well-known. The term of rotaxane originates from the combination of the Latin words wheel and axis. The application of nanomachines is identifying and measuring the concentration of toxic substances in the environment, targeted drug delivery and cancer diagnosis. The objective of this study is to synthesize and identify several new nanomachines in the form of rotaxanes (internally locked molecules) with nanopharmaceutical properties from the corresponding crown compounds. In the first step, 2,2-dimethylphenol was converted into bisphenol compound (1) in reaction with thionyl chloride. Bisphenol compound (1) was converted into methyl diester compound (2) in reaction with methyl chloroacetate. The methyl diester compound (2) reacts with the appropriate diamine to form the diamide macrocycle compound (3). Rod (4) is prepared from the reaction of diethylene glycol ditosylate, 4,4-bipyridine and a bulk phenol such as 4-tert-butylphenol in DMF. Each of the rings in the presence of the prepared rod leads to the corresponding rotaxane compound (5). Chemical structure of the obtained compounds were established by 1HNMR, 13CNMR, FT-IR and SEM spectroscopic methods. [ABSTRACT FROM AUTHOR]

To address key concerns on solid‐state pyrene‐based luminescent materials, we propose a novel and efficient mechanical bond strategy. This strategy results in a transformation from ACQ to AIE effect and a remarkable enhancement of pyrene emission in the solid state. Moreover, an unusual purification of emission is also achieved. Through computational calculation and experimental characterisation, finally determined by X‐ray diffraction analysis, we prove that the excellent emissions result from mechanical bond induced refinement of molecular arrangements, including reduced π‐π stacking, well‐ordered packing and enhanced structural stability. This work demonstrates the potential of mechanical bond in the field of organic luminescent molecules, providing a new avenue for developing high‐performance organic luminescent materials. [ABSTRACT FROM AUTHOR]

In the design of dynamic supramolecular systems used in molecular machines, it is important to understand the binding preferences between the macrocycle and stations along the thread. Here, we apply 1H NMR spectroscopy to investigate the relative stabilities of a series of linear alkylammonium templated pseudorotaxanes with the general formula [H2NRR'][Cr7CoF8(O2CCH2tBu)16] by exchanging the cation in solution. Our results show that the pseudorotaxanes are able to exchange threads via a dissociative mechanism. The position of equilibrium is dependent upon the ammonium cation and solvent used. Short chain primary ammonium cations are shown to be far less favourable macrocycle stations than secondary ammonium cations. Collision‐induced dissociation mass spectrometry (CID‐MS) has been used to look at disassembly of the pseudorotaxanes in a solvent‐free environment and stability trends compared to those in acetone‐d6. The energy needed to induce 50 % of the precursor ion loss (E50) is used and shows a similar trend to the equilibria measured by NMR. The relative stabilities of these hybrid inorganic‐organic pseudo‐rotaxanes are different to those of host‐guest compounds involving crown ethers and this may be valuable for the design of molecular machines. [ABSTRACT FROM AUTHOR]

The interactions between ether naphthotube and a series of dication guests in organic solution were investigated. It was found that ether naphthotube formed stable host‐guest complexes selectively with these guests in a 1 : 1 stoichiometric ratio with association constants ranging from 102 to 106 M−1, which were confirmed by 1H‐NMR spectra and ITC experiments. The host‐guest interactions are driven by enthalpy change as the entropic factors are unfavorable. Positive correlations between ΔH and ΔS have been observed in the host‐guest complexes. Furthermore, the para‐substitution of the guests can significantly affect the binding affinities through a combination of field/inductive and resonance effects by following a linear free energy relationship. Based on the host‐guest complexes composed of ether naphthotube and organic cations, two interlocked [2]rotaxanes were prepared by cationization reaction and Huisgen cycloaddition between the cations and the stopper components. The ether naphthotube‐based host‐guest complexes are useful for creating sophisticated interlocked molecules. [ABSTRACT FROM AUTHOR]

Two BODIPYs and two boron β‐diketonates were threaded through a macrocycle bearing a 2,2'‐biphenol unit, showing thus the ability of boron to act as a gathering atom. The new threaded species were characterized by 1D and 2D NMR spectroscopy as well as by X‐ray crystallography for one of them and their properties rationalized with quantum chemistry to unravel the vibronic contributions. The BODIPYs exhibited interesting fluorescence features with quantum yields up to 91 % and enhanced photostability compared to their non‐threaded homologues. A rotaxane was synthesized using this threading strategy after stoppering and removing the boron with potassium hydroxide. [ABSTRACT FROM AUTHOR]

Diamine reagents have been used to functionalize a [2]rotaxane building block bearing an activated pentafluorophenyl ester stopper. Upon a first acylation, an intermediate host‐guest complex with a terminal amine function is obtained. Dissociation of the intermediate occurs in solution and acylation of the released axle generates a [2]rotaxane with an elongated axle subunit. In contrast, the corresponding [3]rotaxane can be obtained if the reaction conditions are appropriate to stabilize the inclusion complex of the mono‐amine intermediate and the pillar[5]arene. This is the case when the stopper exchange is performed under mechanochemical solvent‐free conditions. Alternatively, if the newly introduced terminal amide group is large enough to prevent the dissociation, the second acylation provides exclusively a [3]rotaxane. On the other hand, detailed conformational analysis has been also carried out by variable temperature NMR investigations. A complete understanding of the shuttling motions of the pillar[5]arene subunit along the axles of the rotaxanes reported therein has been achieved with the help of density functional theory calculations. [ABSTRACT FROM AUTHOR]

Switchable rotaxanes are good candidates for molecular machines because of their ability to undergo reversible and repeatable co-conformational isomerism in response to an external stimulus. An acid-base switchable [2](2)rotaxane reported by Li et al. [J Org Chem. 79(15): [6996–7004] has been reported to exhibit a 48% change in length upon a stimulus-induced change in protonation state, suggesting that it could serve as the fundamental element of a 'molecular muscle'. In the present work, the mechanical behaviour of this topologically complex system is explored with calculations based on semiempirical electronic structure theory. Our calculations predict that the original system will not work as envisioned. Although the calculations confirm a 48% change in length, they also reveal an energy barrier to ring shuttling upon deprotonation, preventing the immediate delivery of force. Therefore, a modification to the system is proposed. Similar semiempirical calculations were carried out on the modified system and the force calculated. The average force generated from the modified system is predicted to be approximately −86 pN. The results demonstrate that the proposed modification reduces the force generated by ring shuttling by 11% but largely eliminates the energy barrier to ring shuttling so that the force is immediately available. [ABSTRACT FROM AUTHOR]

To construct a supramolecular mechanophore library, expanding the variety of emitters that can be used is significant. In this study, we demonstrate that 9-(phenylethynyl)-10-((2-pyridyl)ethynyl)anthracene can be incorporated into a rotaxane-based supramolecular mechanophore as the luminophore. The polyurethane films in which the mechanophore was covalently incorporated exhibit instantly reversible on/off switches of green fluorescence upon cycle stretching. [ABSTRACT FROM AUTHOR]

Here is reported the synthesis and characterization of an interlocked figure‐of‐eight rotaxane molecular shuttle from a dibenzo‐24‐crown‐8 (DB24C8) derivative. This latter bears two molecular chains, whose extremities are able to react together by click chemistry. One of the two substituting chain holds an ammonium function aimed at driving the self‐entanglement through the complexation of the DB24C8 moiety. In the targeted figure‐of‐eight rotaxane, shuttling of the DB24C8 along the threaded axle from the best ammonium station to the weaker binding site triazolium was performed through deprotonation or deprotonation‐then‐carbamoylation of the ammonium. This way, two discrete co‐conformational states were obtained, in which the folding and size of the two loops could be changed. [ABSTRACT FROM AUTHOR]

Advanced Organic Chemical Materials Co‐constructed Mechanically bonded amphiphiles (MBAs), also known as mechanically interlocked molecules (MIMs), have emerged as an important kind of functional building block for the construction of artificial molecular machines and soft materials. Herein, a novel MBA, i. e., bistable [2]rotaxane H2 was designed and synthesized. In the solution state, H2 demonstrated pH and metal ion‐responsive emissions due to the presence of a distance‐dependent photoinduced electron transfer (PET) process and the fluorescence resonance energy transfer (FRET) process, respectively. Importantly, the amphiphilic feature of H2 has endowed it with unique self‐assembly capability, and nanospheres were obtained in a mixed H2O/CH3CN solvent. Moreover, the morphology of H2 aggregates can be tuned from nanospheres to vesicles due to the pH‐controlled shuttling motion‐induced alternation of H2 amphiphilicity. Interestingly, larger spheres with novel pearl‐chain‐like structures from H2 were observed after adding stoichiometric Zn2+. In particular, H2 shows pH‐responsive emissions in its aggregation state, allowing the visualization of the shuttling movement by just naked eyes. It is assumed that the well‐designed [2]rotaxane, and particularly the proposed concept of MBA shown here, will further enrich the families of MIMs, offering prospects for synthesizing more MIMs with novel assembly capabilities and bottom‐up building dynamic smart materials with unprecedented functions. [ABSTRACT FROM AUTHOR]

New nitroxides based on aza‐crown ethers were prepared and employed as selective sensors for the detection of inorganic and organic cations by EPR analysis of the corresponding host–guest complexes. The nitroxide unit behaves as a sensitive probe for a number of alkali and alkaline earth metal cations affording EPR spectra differing in the value of nitrogen hyperfine constants and in the appearance of splitted signals due to the non‐zero nuclear spin of some metal cation upon complexation. Owing to the remarkable EPR spectral differences between the host and the corresponding cation complex the new macrocycles are likely to act as multitasking tools to recognize several cationic species. EPR behaviour of the larger nitroxide azacrown 1⋅ when acting as a wheel in a radical synthetic bistable [2]rotaxane containing both secondary dialkylammonium and 1,2‐bis(pyridinium) molecular stations, was also investigated. Reversible movements of the macrocycle between the two recognition sites in the rotaxane were promptly revealed by EPR, which shows significant changes either in nitrogen coupling constant values (aN) or in the spectral shape in the two rotaxane co‐conformations. [ABSTRACT FROM AUTHOR]

A series of squaramide‐based heteroditopic [2]rotaxanes consisting of isophthalamide macrocycle and squaramide axle components are synthesized using an alkali metal cation template‐directed stoppering methodology. This work highlights the unprecedented sodium cation template coordination of the Lewis basic squaramide carbonyls for interlocked structure synthesis. Extensive quantitative 1H NMR spectroscopic anion and ion‐pair recognition studies reveal the [2]rotaxane hosts are capable of cooperative sodium halide ion‐pair mechanical bond axle‐macrocycle component recognition, eliciting up to 20‐fold enhancements in binding strengths for bromide and iodide, wherein the Lewis basic carbonyls and Lewis acidic NH hydrogen bond donors of the squaramide axle motif operate as cation and anion receptive sites simultaneously in an ambidentate fashion. Notably, varying the length and nature of the polyether cation binding unit of the macrocycle component dramatically influences the ion‐pair binding affinities of the [2]rotaxanes, even overcoming direct contact NaCl ion‐pair binding modes in polar organic solvents. Furthermore, the cooperative ion‐pair binding properties of the squaramide‐based heteroditopic [2]rotaxanes are exploited to successfully extract solid sodium halide salts into organic media. [ABSTRACT FROM AUTHOR]

The chemistry of mechanically interlocked molecules (MIMs) such as catenane and rotaxane is full of new opportunities for the presence of a mechanical bond, and the efficient synthesis of these molecules is therefore of fundamental importance in realizing their unique properties and functions. While many different types of preorganizing interactions and covalent bond formation strategies have been exploited in MIMs synthesis, the use of cucurbit[6]uril (CB[6]) in simultaneously templating macrocycle interlocking and catalyzing the covalent formation of the interlocked components is particularly advantageous in accessing high‐order catenanes and rotaxanes. In this review, catenane and rotaxane obtained from CB[6]‐catalyzed azide‐alkyne cycloaddition will be discussed, with special emphasis on the synthetic strategies employed for obtaining complex [n]rotaxanes and [n]catenanes, as well as their properties and functions. [ABSTRACT FROM AUTHOR]

Macrocyclic molecule‐based host–guest systems, which provide contributions for the design and construction of functional supramolecular structures, have gained increasing attention in recent years. In particular, platinum(II) metallacycle‐based host–guest systems provide opportunities for chemical scientists to prepare novel materials with various functions and structures due to the well‐defined shapes and cavity sizes of platinum(II) metallacycles. However, the research on platinum(II) metallacycle‐based host–guest systems has been given little attention. In this article, we demonstrate the host–guest complexation between a platinum(II) metallacycle and a polycyclic aromatic hydrocarbon molecule, naphthalene. Taking advantage of metallacycle‐based host–guest interactions and the dynamic property of reversible Pt coordination bonds, a [2]rotaxane is efficiently prepared by employing a template‐directed clipping procedure. The [2]rotaxane is further applied to the fabrication of an efficient light‐harvesting system with multi‐step energy transfer process. This work comprises an important supplement to macrocycle‐based host–guest systems and demonstrates a strategy for efficient production of well‐defined mechanically interlocked molecules with practical values. [ABSTRACT FROM AUTHOR]

A review of heteroditopic interlocked molecules and their application as receptors for simple inorganic ion pair species. The review details the design and ion recognition properties of the rotaxane and catenane receptors, as well as highlighting some of the experimental challenges; hence, it provides insight into possible future avenues of research in this youthful field.

A bistable [2]rotaxane based on dibenzylammonium (DBA+)/methyl triazolium (MTA+) stations and [23]crown ether (X23C7) wheel component has been obtained in excellent yield. The crown ether X23C7 predominantly occupies the DBA+ station, in the bistable [2]rotaxane. On addition of the base, the crown ether X23C7 shuttles across to the MTA+ station. Acid treatment led to the restoration of X23C7 back to the DBA+ station. Due to this reversibility, a pH‐responsive molecular switch has been obtained. This is the first example of a [23]crown ether, a smaller analogue of [24]crown ether, exhibiting shuttling motion in any crown ether‐based mechanically interlocked molecules. [ABSTRACT FROM AUTHOR]

Abstract Macrocyclic drugs are promising agents for treating a variety of diseases. However, these compounds usually present delivery limitations, such as low tissue selectivity and poor cellular uptake, which may impair efficacy and clinical translation. Here, we propose a molecular machine approach for delivering macrocyclic drugs based on their assembly into bioactive rotaxanes. To prove this concept, we use the extremely toxic macrocycle valinomycin (Val) as the host molecule, and identify dihydralazine (Dihyd) as a guest molecule after screening several guest compounds. The Val‐Dihyd complex is mechanically interlocked by capping one hydrazide group in Dihyd with fluorescein isothiocyanate (FITC) and the other with a Y‐shape branched poly(ethylene glycol) (PEG) via a pH‐sensitive hydrazone bond. Thus, the Val‐loaded rotaxanes (Vrot) are stable at physiological pH, but release Val at mild acidic conditions mimicking intratumoral and endosomal environments. In vitro studies revealed Vrot is less cytotoxic than free Val in pancreatic cancer cells, while modifying Vrot with cyclic arginine‐glycine‐aspartic acid (cRGD) peptides promotes the cytotoxicity by enhancing cellular uptake. These results indicate the potential of rotaxanes of macrocyclic drugs for generating cancer targeted prodrugs.

A review of heteroditopic interlocked molecules and their application as receptors for simple inorganic ion pair species. The review details the design and ion recognition properties of the rotaxane and catenane receptors, as well as highlighting some of the experimental challenges; hence, it provides insight into possible future avenues of research in this youthful field. [ABSTRACT FROM AUTHOR]

A [2]rotaxane‐based molecular shuttle with an acid‐responsive asymmetric macrocycle on a symmetric dumbbell axle is reported. Upon adding TFA, the macrocycle, namely the amine naphthotube, is protonated and translocates from the di(quaternary ammonium) station to the triazole stations because of electrostatic repulsion and weakened binding. The shuttling kinetics are slow due to the steric hindrance caused by the ethyl group on the quaternary ammonium center and can be followed by 1H NMR spectroscopy. Interestingly, it was found that the shuttling kinetics depends on the concentration of TFA. A kinetic intermediate was detected and can even be captured in the presence of a high concentration of TFA. Extensive control experiments revealed that the shuttling kinetics and the capture of the kinetic intermediate are related to the different protonation states of the rotaxanes. [ABSTRACT FROM AUTHOR]

Porphyrins have emerged as highly effective photosensitizers in the field of photodynamic therapy (PDT) because of their high singlet oxygen generation efficiency. However, most porphyrin derivatives do not have adequate water solubility and cell membrane permeability suitable for use in PDT. In addition, they frequently suffer from low durability under photoirradiation. Here, we propose rotaxane-type photosensitizers, in which a porphyrin axle is irreversibly encapsulated within cyclodextrins (CDs), to overcome the drawbacks of porphyrins for PDT. The rotaxane-type photosensitizers were synthesized in high yields by employing a cooperative capture strategy. The CD derivatives worked as a transparent shell to impart a porphyrin axle not only with water solubility but also with photostability. These rotaxanes showed higher cell membrane permeability and photoinduced cytotoxic abilities than talaporfin sodium, presently used as a clinical photosensitizer. The rotaxane-based photosensitizer could have potential for being ideal PDT drugs.

Dynamic mechanical chirality of [2]rotaxane consisting of a Cs symmetric wheel and a C2v symmetric axle is discussed via the synthesis, enantiomer separation, racemization, and chiral-prochiral interconversion. This [2]rotaxane is achiral and/or prochiral when its wheel locates at the center of the axle, but becomes chiral when the wheel moves from the center of the axle. These were proved by the experiments on the enantiomer separation and racemization. The racemization energy of the isolated single enantiomers was controlled by the bulkiness of the central substituents on the axle. Furthermore, the chiral-prochiral interconversion was achieved by relative positional control of the components. The present systematic studies will provide new insight into mechanically chiral interlocked compounds as well as the utility as dynamic chiral sources.

Macrocyclic drugs are promising agents for treating a variety of diseases. However, these compounds usually present delivery limitations, such as low tissue selectivity and poor cellular uptake, which may impair efficacy and clinical translation. Here, we propose a molecular machine approach for delivering macrocyclic drugs based on their assembly into bioactive rotaxanes. To prove this concept, we use the extremely toxic macrocycle valinomycin (Val) as the host molecule, and identify dihydralazine (Dihyd) as a guest molecule after screening several guest compounds. The Val‐Dihyd complex is mechanically interlocked by capping one hydrazide group in Dihyd with fluorescein isothiocyanate (FITC) and the other with a Y‐shape branched poly(ethylene glycol) (PEG) via a pH‐sensitive hydrazone bond. Thus, the Val‐loaded rotaxanes (Vrot) are stable at physiological pH, but release Val at mild acidic conditions mimicking intratumoral and endosomal environments. In vitro studies revealed Vrot is less cytotoxic than free Val in pancreatic cancer cells, while modifying Vrot with cyclic arginine‐glycine‐aspartic acid (cRGD) peptides promotes the cytotoxicity by enhancing cellular uptake. These results indicate the potential of rotaxanes of macrocyclic drugs for generating cancer targeted prodrugs. [ABSTRACT FROM AUTHOR]

Deciphering the molecular dynamics (MD) of rotaxanes is crucial for designing and refining their applications in molecular devices. This study employed fluorine-19 nuclear magnetic resonance (19F NMR) and magnetic resonance imaging (MRI) to unveil the interplay between mechanical bonds and steric hindrance in a series of fluorinated rotaxanes. 1H/19F NMR revealed stable "Z"-shaped wheel conformations minimizing steric clashes and favoring π-π interactions with the axle. Utilizing fluorines and axle protons as reporters, 1H/19F relaxation rates and solid-state 19F NMR studies demonstrated that mechanical bond primarily governs wheel motion, while steric hindrance dictates axle movement. Intriguingly, mechanical bond mainly affects local axle groups, leaving distant ones minimally impacted. MD simulations corroborated these findings. Temperature-dependent 19F NMR indicated that energy input enhances rotational motion and wheel conformational transitions. Furthermore, the drastic increase in 19F relaxation rates upon mechanical bond formation and steric hindrance enables sensitive and selective 19F MRI visualization of MD changes. This study, by elucidating the roles of internal and external factors on rotaxane molecular dynamics using 19F NMR/MRI, offers valuable insights that can advance the field of rotaxane-based molecular devices. Distinctive and complementary insights into the structural and dynamic characteristics of rotaxanes were obtained utilizing 19F NMR/MRI technologies through parameters such as 19F signal, relaxation rates, rotational correlation time, and imaging features, offering a new perspective for the understanding and rational design of molecular devices. [Display omitted] • Synthesized rotaxanes feature sensitive, selective, semi-quantitative 1H/19F NMR reporters for molecular dynamics analysis. • 19F NMR/MRI offers insights into rotaxanes' structure/dynamics using relaxation rates, rotational correlation time, and imaging features. • Reveals the interplay between mechanical bonds and steric hindrance in rotaxanes via comparative analysis. [ABSTRACT FROM AUTHOR]

Anion exchange membranes (AEMs) with high selective conductivity and low surface resistance are important for the development of electrodialysis desalination industry. In this work, we design and synthesize a rotaxane of β-cyclodextrin (CD)-alkyldiamine inclusion complex (CDIC) via a host-guest molecular recognition mechanism; the resulting CDIC rotaxane is employed for cross-linking chloromethylated, hydroxy quaternized polysulfone (HQPSf) to make AEMs. β-CD is inherently hydrophilic and its –OH on the outer surface can hydrogen-bond with HQPSf to promote ionic cluster aggregation, leading to enhanced microphase-separated morphology and improved conductivity; the rotaxane-cross-linked structure guarantees good ductility and ion selectivity of the membrane. Therefore, the optimized HQPSf-CDIC membrane gives the most excellent current efficiency discharge current efficiency (92.04 %), the lowest energy consumption (4.68 kWh kg−1), and the maximum Cl− mobility (75.38 mg m−2 s−1) in the electrodialysis tests, significantly better than the un-crosslinked HQPSf membrane (86.41 %, 5.17 kWh kg−1 and 71.29 mg m−2 s−1). Our work demonstrates that introducing CDIC rotaxane cross-linked structure can help to enhance microphase separation and improve the performance of AEMs for electrodialysis. The microphase separation mechanism of anion exchange membrane HQPSf-CDIC-x. [Display omitted] • Anion exchange membranes (AEMs) with high selective conductivity and low surface resistance are important for the development of electrodialysis desalination industry. In this work, we design and synthesize a rotaxane of β-cyclodextrin (CD) - alkyldiamine inclusion complex (CDIC) via a host-guest molecular recognition mechanism; the resulting CDIC rotaxane is employed for cross-linking chloromethylated, hydroxy quaternized polysulfone (HQPSf) to make AEMs. β-CD is inherently hydrophilic and its –OH on the outer surface can hydrogen-bond with HQPSf to promote ionic cluster aggregation, leading to enhanced microphase-separated morphology and improved conductivity; the rotaxane-cross-linked structure guarantees good ductility and ion selectivity of the membrane. Therefore, the optimized HQPSf-CDIC membrane gives the most excellent current efficiency discharge current efficiency (92.04 %), the lowest energy consumption (4.68 KWh kg 1), and the maximum Cl− mobility (75.38 mg m−2 s−1) in the electrodialysis tests, significantly better than the un-crosslinked HQPSf membrane (86.41 %, 5.17 kWh kg−1 and 71.29 mg m−2 s−1). Our work demonstrates that introducing CDIC rotaxane cross-linked structure can help to enhance microphase separation and improve the performance of AEMs for electrodialysis. [ABSTRACT FROM AUTHOR]

Ring-over-ring slippage and ring-through-ring penetration are important processes in the construction of ring-in-ring multiple interlocked architectures. We have successfully observed “ring-over-ring deslipping” on the rotaxane axle by exploiting the dynamic covalent nature of imine bonds in imine-bridged heterorotaxanes R1 and R2 with two macrocycles of different ring sizes on the axle. When the imine bridges of R1 were cleaved, a hydrolyzed hetero[4]rotaxane [4]R1′ was formed as an intermediate under dynamic equilibrium, and the larger 38-membered macrocycle M was deslipped over the 24-membered ring (24C8 or DB24C8) to dissociate into a [3]rotaxane [3]R3 and a macrocycle M. The time dependent NMR measurement and the determined thermodynamic parameters revealed that the rate-limiting step of the deslipping process was attributed to steric hindrance between two rings and reduced mobility of M due to proximity to the crown ether, which was bound to the anilinium on the axle molecule.

The lasso peptide benenodin‐1, a naturally occurring and bacterially produced [1]rotaxane, undergoes a reversible zip tie‐like motion under heat activation, in which a peptidic wheel stepwise translates along a molecular thread in a cascade of "tail/loop pulling" equilibria. Conformational and structural analyses of four translational isomers, in solution and in the gas phase, reveal that the equilibrium distribution is controlled by mechanical and non‐covalent forces within the lasso peptide. Furthermore, each dynamic pulling step is accompanied by a major restructuring of the intramolecular hydrogen bonding network between wheel and thread, which affects the peptide's physico‐chemical properties. [ABSTRACT FROM AUTHOR]

The templated clipping of a ferrocene-grafted isophthalic acid derivative to encircle a hydrogen-bonding axle through the reaction with 1,4-bis(aminomethyl)benzene is described. The constituent electroactive macrocycle of the resultant [2]rotaxane is a homologue of the versatile benchmark tetraamide variant developed by Leigh and co-workers. The relative templating effect of different hydrogen-bonding motifs in rotaxane and pseudorotaxane generation is compared, with yields varying from 0 to 41%. The electrochemical properties and single crystal X-ray structure of a doubly ferrocene-decorated [2]rotaxane are further reported.

In the design of dynamic supramolecular systems used in molecular machines, it is important to understand the binding preferences between the macrocycle and stations along the thread. Here, we apply 1 H NMR spectroscopy to investigate the relative stabilities of a series of linear alkylammonium templated pseudorotaxanes with the general formula [H 2 NRR'][Cr 7 CoF 8 (O 2 CCH 2 t Bu) 16 ] by exchanging the cation in solution. Our results show that the pseudorotaxanes are able to exchange threads via a dissociative mechanism. The position of equilibrium is dependent upon the ammonium cation and solvent used. Short chain primary ammonium cations are shown to be far less favourable macrocycle stations than secondary ammonium cations. Collision-induced dissociation mass spectrometry (CID-MS) has been used to look at disassembly of the pseudorotaxanes in a solvent-free environment and stability trends compared to those in acetone-d6. The energy needed to induce 50 % of the precursor ion loss (E 50 ) is used and shows a similar trend to the equilibria measured by NMR. The relative stabilities of these hybrid inorganic-organic pseudo-rotaxanes are different to those of host-guest compounds involving crown ethers and this may be valuable for the design of molecular machines., (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The experimental vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) spectra were measured for the enantiomers of [1]rotaxane 1. These experimental spectra have been analyzed using predicted VCD and ECD spectra for (S, Rmp) or (S, Smp) diastereomers using density functional theory. This comparison allowed for a definitive assignment of the absolute configuration of 1. [ABSTRACT FROM AUTHOR]

The electrochemical behavior of a giant rotaxane bearing 10 electroactive ferrocene centers has been analyzed by both fast scan cyclic voltammetry and impedance measurements. The measurements support the hypothesis that all redox centers are not equivalent and display different electron transfer rate constants, which would arise from several possible conformations of the adsorbed molecule. Effectively using such systems in molecular devices thus necessitates to minimize or at least control those dispersions. [ABSTRACT FROM AUTHOR]

Reversible switching between the closed cyclic dimeric assembly [Cu2(1)2]2+ (OFF state) and the extended dimeric homoleptic complex [FeCu2(1)2]4+ (ON State) by addition/removal of Fe2+ triggered catalysis of a double‐click reaction and high yield preparation of [2]rotaxanes. Mechanistic and computational studies provide valuable general insight for double‐click strategies by revealing cooperative effects in the second cycloaddition step due to a distance‐tolerant preorganization of the first‐click product by the two copper(I)‐loaded phenanthroline subunits of [FeCu2(1)2]4+. [ABSTRACT FROM AUTHOR]

Reversibles Umschalten zwischen der in sich geschlossenen cyclisch‐dimeren Anordnung [Cu2(1)2]2+ (AUS‐Zustand) und dem expandierten dimeren homoleptischen Komplex [FeCu2(1)2]4+ (AN‐Zustand) durch Zugabe/Entfernung von Fe2+ ermöglichte die Katalyse einer Doppel‐Clickreaktion und die Präparation von [2]‐Rotaxanen in hoher Ausbeute. Mechanistische und computergestützte Studien offenbaren kooperative Effekte im zweiten Cycloadditionsschritt aufgrund einer abstandstoleranten Präorganisation des ersten Clickprodukts an den beiden Kupfer(I)‐beladenen Phenanthrolin‐Untereinheiten von [FeCu2(1)2]4+, was wertvolle grundlegende Erkenntnisse für Doppel‐Click‐Strategien liefert. [ABSTRACT FROM AUTHOR]

The Hard-and-Soft-Acids-and-Bases (HSAB) principle has been challenged for the first time on molecular machines' precursors, while studying on calixarene-based rotaxane complexes containing tris(N-phenylureido)-calix[6]arene as wheel and a 4,4'-bipyridinium dication's units as axle; The results clearly indicate the invariance of genuine vs. hard and soft acidic - bonding complex with the interlocked molecular system is present in terms of maintaining the chemical reactivity combined pattern of charge exchange, charge tunneling, opening and stabilizing reactivity tendency as provided within the orthogonal chemical space of chemical global indicators – in first (electronegativity and chemical hardness) and second (chemical power and electrophilicity) generations and of their principles, respectively. Moreover, we asses for the first time the molecular machine precursor system with the 3D total charge density isosuface confinement within two ends of 3D electrostatic potentials branches of the optimized interlocked rotaxane system. Further investigations are thus called for best generalizing the present findings. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of a polyrotaxanated covalent organic network (CON) based on the association between the viologen and pillar[5]arene (P[5]OH) units are reported. The mechanical bond allows for the irreversible insertion of n‐type redox centers (P[5]OH macrocycles) within a pristine structure based on p‐type viologen redox centers. Both redox units are active on a narrow potential range and, in water, the presence of P[5]OH greatly increases the electroactivity of the material. [ABSTRACT FROM AUTHOR]