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Understanding the fundamental reactivity of polymetallic complexes is challenging due to the complexity of their structures with many possible bond breaking and forming processes. Here, we apply ion mobility mass spectrometry coupled with density functional theory to investigate the disassembly mechanisms and energetics of a family of heterometallic rings and rotaxanes with the general formula [NH 2 RR'][Cr 7 MF 8 (O 2 C t Bu) 16 ] with M = Mn II , Fe II , Co II , Ni II , Cu II , Zn II , Cd II . Our results show that their stability can be tuned both by altering the d-metal composition in the macrocycle and by the end groups of the secondary ammonium cation [NH 2 RR'] + . Ion mobility probes the conformational landscape of the disassembly process from intact complex to structurally distinct isobaric fragments, providing unique insights to how a given divalent metal tunes the structural dynamics.

Mechanochemical syntheses of rotaxanes have attracted considerable attention of late because of the superior reaction rates and higher yields associated with their production compared with analogous reactions carried out in solution. Previous investigators, however, have focused on the demonstration of the mechanochemical syntheses of rotaxanes per se, rather than on studying the solid-phase host-guest molecular interplay related to their rapid formation and high yields. In this investigation, we attribute the lower yields of rotaxanes prepared in solution to the limited concentration and a desolvation energy penalty that must be compensated for by host-guest interactions during complexation that precedes the templation leading to rotaxane formation. It follows that, if the desolvation energy can be removed and higher concentrations can be attained, even weak host-guest interactions can drive the complexation of host and guest molecules efficiently. In order to test this hypothesis, we chose two host-guest pairs of permethylated pillar[5]arene/1,6-diaminohexane and permethylated pillar[5]arene/2,2'-(ethylenedioxy)bis(ethylamine) for the simple reason that they exhibit extremely low binding constants (2.7 ± 0.4 M -1 when 1,6-diaminohexane is the guest and <0.1 M -1 when 2,2'-(ethylenedioxy)bis(ethylamine) is the guest in CDCl 3 ; i.e., ostensibly no pseudorotaxane formation is observed). We argue that the amount of pseudorotaxanes formed in the solid state is responsive to mechanical treatments or otherwise and changes in temperature during stoppering reactions. Compared to the amount of pseudorotaxanes that can be obtained in solution, large quantities of pseudorotaxanes are formed in the solid state because of concentration and desolvation effects. This mechanochemical enhancement of pseudorotaxane formation is referred to as a self-correction in the current investigation. Rotaxanes based on permethylated pillar[5]arene/1,6-diaminohexane and permethylated pillar[5]arene/2,2'-(ethylenedioxy)bis(ethylamine) have been synthesized in much higher yields compared to those obtained in solution, aided and abetted by self-correction effects during mechanical treatments and heating at a mild temperature of 50 °C.

The synthesis of new triphenylphosphonium-capped cucurbit[7]uril (CB[7])- and cucurbit[8]uril (CB[8])-based [2]rotaxanes was achieved by a simultaneous threading-capping strategy. While the use of CB[7] produced the designed [2]rotaxane, attempts to obtain the CB[8] analogue were unsuccessful due to the unexpected strong interaction found between the host and the phosphonium caps leading to pseudo-heteroternary host-guest complexes. This unusual binding motif has been extensively studied experimentally, with results in good agreement with those obtained by dispersion-corrected DFT methods.

Stereoisomerism, stemming from the spatial orientation of components in molecular structures, plays a decisive role in nature. While the unconventional bonding found in mechanically interlocked molecules gives rise to unique expressions of stereochemistry, the exploration of their stereoisomers is still in its infancy. Sequence isomerism, characterized by variations in the ordering of mechanically interlocked components in catenanes and rotaxanes, mirrors the sequence variations found in biological macromolecules. Herein, we report the use of artificial molecular pumps for the precise and simple production of sequentially isomeric hetero[3]rotaxanes. Utilizing redox-driven pumping cassettes with different rings, we have synthesized two hetero[3]rotaxane isomers in high isolated yields from two [2]rotaxanes. This research represents a significant advance in sequential molecular assembly, paving the way for the development of sophisticated, functionalized, mechanically interlocked materials.

Slide-ring hydrogels containing polyrotaxane structures have been widely developed, but current methods are more complex, in which modified cyclodextrins, capped polyrotaxanes, and multistep reactions are often needed. Here, a simple one-pot method dissolving the pseudopolyrotaxane (pPRX) in a mixture of acrylamide and boric acid to form a slide-ring hydrogel by UV light is used to construct a tough, puncture-resistant antibacterial polyrotaxane hydrogel. As a new dynamic ring cross-linking agent, boric acid effectively improves the mechanical properties of the hydrogel and involves the hydrogel with fracture toughness. The polyrotaxane hydrogel can withstand 1 MPa compression stress and maintain the morphology integrity, showing 197.5 mJ puncture energy under a sharp steel needle puncture. Meanwhile, its significant antibacterial properties endow the hydrogel with potential applications in the biomedical field.

Rotaxane cross-linkers enhance the toughness of the resulting rotaxane cross-linked polymers through a stress dispersion effect, which is attributed to the mobility of the interlocked structure. To date, the compositional diversity of rotaxane cross-linkers has been limited, and the poor compatibility of these cross-linkers with peptides and proteins has made their use in such materials challenging. The synthesis of a rotaxane composed of peptides may result in a biodegradable cross-linker that is compatible with peptides and proteins, allowing the fortification of polypeptides and proteins and ultimately leading to the development of innovative materials that possess excellent mechanical properties and biodegradability. However, the chemical synthesis of all-peptide-based rotaxanes has remained elusive because of the absence of strong binding motifs in peptides, which prevents an axial peptide from penetrating a cyclic peptide. Here, we synthesized all-peptide-based rotaxanes using an active template method for proline-containing cyclic peptides. The results of molecular dynamics simulations suggested that cyclic peptides with an expansive inner cavity and carbonyl oxygens oriented toward the center are favorable for rotaxane synthesis. This rotaxane synthesis method is expected to accelerate the synthesis of peptides and proteins with mechanically interlocked structures, potentially leading to the development of peptide- and protein-based materials with unprecedented functionalities.

Advances in supramolecular chemistry are often underpinned by the development of fundamental building blocks and methods enabling their interconversion. In this work, we report the use of an underexplored dynamic covalent reaction for the synthesis of stimuli-responsive [2]rotaxanes. The formamidinium moiety lies at the heart of these mechanically interlocked architectures, because it enables both dynamic covalent exchange and the binding of simple crown ethers. We demonstrated that the rotaxane self-assembly follows a unique reaction pathway and that the complex interplay between crown ether and thread can be controlled in a transient fashion by addition of base and fuel acid. Dynamic combinatorial libraries, when exposed to diverse nucleophiles, revealed a profound stabilizing effect of the mechanical bond as well as intriguing reactivity differences between seemingly similar [2]rotaxanes.

Encapsulation of active pharmaceutical ingredients (APIs) in confined spaces has been extensively explored as it dramatically alters the molecular dynamics and physical properties of the API. Herein, we explored the effect of encapsulation on the molecular dynamics and physical stability of a guest drug, salicylic acid (SA), confined in the intermolecular spaces of γ-cyclodextrin (γ-CD) and poly(ethylene glycol) (PEG)-based polypseudorotaxane (PPRX) structure. The sublimation tendency of SA encapsulated in three polymorphic forms of the γ-CD/PEG-based PPRX complex, monoclinic columnar (MC), hexagonal columnar (HC), and tetragonal columnar (TC), was investigated. The SA sublimation rate was decreased by 3.0-6.6-fold and varied in the order of MC form > HC form > TC form complex. The 13 C and 1 H magic-angle spinning (MAS) solid-state nuclear magnetic resonance (NMR) spectra and 13 C spin-lattice relaxation time ( T 1 ) indicated that the encapsulated SA molecules existed as the monomeric form, and its molecular mobility increased in the order of MC form > HC form > TC form complex. In the complexes, a rapid chemical exchange between two dynamic states of SA (free and bound) was suggested, with varying adsorption/desorption rates accounting for its distinct molecular mobility. This adsorption/desorption process was influenced by proton exchange at the interaction site and interaction strength of SA in the complexes, as evidenced by 1 H MAS spectra and temperature dependency of the 13 C carbonyl chemical shift. A positive correlation between the molecular mobility of SA and its sublimation rate was established. Moreover, the molecular mobility of γ-CD and PEG in the complexes coincided with that of SA, which can be explained by fast guest-driven dynamics. This is the first report on the stability improvement of an API through complexation in polymorphic supramolecular host structures. The relationship between the molecular dynamics and physical properties of encapsulated API will aid in the rational design of drug delivery systems.

Hyaline cartilage, a soft tissue enriched with a dynamic extracellular matrix, manifests as a supramolecular system within load-bearing joints. At the same time, the challenge of cartilage repair through tissue engineering lies in replicating intricate cellular-matrix interactions. This study attempts to investigate chondrocyte responses within double-network supramolecular hybrid hydrogels tailored to mimic the dynamic molecular nature of hyaline cartilage. To this end, we infused noncovalent host-guest polyrotaxanes, by blending α-cyclodextrins as host molecules and polyethylene glycol as guests, into a gelatin-based covalent matrix, thereby enhancing its dynamic characteristics. Subsequently, chondrocytes were seeded into these hydrogels to systematically probe the effects of two concentrations of the introduced polyrotaxanes (instilling different levels of supramolecular dynamism in the hydrogel systems) on the cellular responsiveness. Our findings unveiled an augmented level of cellular mechanosensitivity for supramolecular hydrogels compared to pure covalent-based systems. This is demonstrated by an increased mRNA expression of ion channels (TREK1, TRPV4, and PIEZO1), signaling molecules (SOX9) and matrix-remodeling enzymes (LOXL2). Such outcomes were further elevated upon external application of biomimetic thermomechanical loading, which brought a stark increase in the accumulation of sulfated glycosaminoglycans and collagen. Overall, we found that matrix adaptability plays a pivotal role in modulating chondrocyte responses within double-network supramolecular hydrogels. These findings hold the potential for advancing cartilage engineering within load-bearing joints.

Pseudomonas aeruginosa (P.A.) is a human pathogen belonging to the top priorities for the discovery of new therapeutic solutions. Its propensity to generate biofilms strongly complicates the treatments required to cure P.A. infections. Herein, we describe the synthesis of a series of novel rotaxanes composed of a central galactosylated pillar[5]arene, a tetrafucosylated dendron, and a tetraguanidinium subunit. Besides the high affinity of the final glycorotaxanes for the two P.A. lectins LecA and LecB, potent inhibition levels of biofilm growth were evidenced, showing that their three subunits work synergistically. An antibiofilm assay using a double Δ lecA Δ lecB mutant compared to the wild type demonstrated that the antibiofilm activity of the best glycorotaxane is lectin-mediated. Such antibiofilm potency had rarely been reached in the literature. Importantly, none of the final rotaxanes was bactericidal, showing that their antibiofilm activity does not depend on bacteria killing, which is a rare feature for antibiofilm agents.

Integrating an NIR fluorescent probe with a magnetic resonance imaging (MRI) agent to harvest complementary imaging information is challenging. Here, we have designed water-soluble, biocompatible, noncytotoxic, bright-NIR-emitting, sugar-functionalized, mechanically interlocked molecules (MIMs)-capped superparamagnetic ultrasmall Fe 3 O 4 NPs for targeted multimodal imaging. Dual-functional stoppers containing an unsymmetrical NIR squaraine dye interlocked within a macrocycle to construct multifunctional MIMs are developed with enhanced NIR fluorescence efficiency and durability. One of the stoppers of the axle is composed of a lipophilic cationic TPP + functionality to target mitochondria, and the other stopper comprises a dopamine-containing catechol group to anchor at the surface of the synthesized Fe 3 O 4 NPs. Fe 3 O 4 NPs surface-coated with targeted NIR rotaxanes help to deliver ultrasmall magnetic NPs specifically inside the mitochondria. Two carbohydrate moieties are conjugated with the macrocycle of the rotaxane via click chemistry to improve the water solubility of MitoSQRot-(Carb-OH) 2 -DOPA-Fe 3 O 4 NPs. Water-soluble, rotaxane-capped Fe 3 O 4 NPs are used for live-cell mitochondria-targeted NIR fluorescence confocal imaging, 3D and multicolor imaging in combination with T 2 -weighted MRI on a 9.4 T MR scanner with a high relaxation rate ( r 2 ) of 180.7 mM -1 s -1 . Biocompatible, noncytotoxic, ultrabright NIR rotaxane-capped superparamagnetic ultrasmall monodisperse Fe 3 O 4 NPs could be a promising agent for targeted multimodal imaging applications.

Acid-degradable polyrotaxanes (PRXs) containing threading β-cyclodextrins (β-CDs) are promising candidates for therapeutic applications of β-CDs in metabolic diseases with cholesterol overload or imbalance. To improve cellular uptake specificity and efficiency of PRXs in hepatocytes, N -acetyl-d-galactosamine (GalNAc)-modified PRXs were developed to facilitate asialoglycoprotein receptor (ASGR)-mediated endocytosis. Binding affinity studies revealed that the dissociation constant ( K D ) values between recombinant ASGR and GalNAc-PRXs decreased with an increase in the number of modified GalNAc units. Additionally, the K D values for GalNAc-PRXs were smaller than those for GalNAc-modified β-CD and amylose, suggesting that the PRX backbone structure improves the binding affinity with ASGR. However, the intracellular uptake levels of GalNAc-PRXs in HepG2 cells increased with a decrease in the number of modified GalNAc units, which was opposite to the trend observed in the binding affinity study. We found that GalNAc-PRXs had a large number of GalNAc units localized in recycling endosomes, resulting in the low intracellular uptake. The cholesterol-reducing abilities of GalNAc-PRXs were assessed using cholesterol-overloaded HepG2 cells. GalNAc-PRXs with a small number of GalNAc units were demonstrated to show superior cholesterol-reducing effects compared to previously designed acid-degradable PRX and clinically tested β-CD derivatives. Thus, we conclude that GalNAc modification is a promising molecular design for the therapeutic application of β-CD-threaded PRXs in various metabolic diseases with cholesterol overload or imbalance in the liver.

In spite of widespread interest in rotaxane-based molecular machines and materials, rotaxanes have not been attached covalently to proteins. We describe the near-quantitative aqueous synthesis of [2]rotaxanes based on neutral and charged aqueous hosts-cucurbit[7]uril (CB7) and cyclobis(paraquat-p-phenylene) (CBPQT 4+ ), respectively-using the thiol-ene addition of cysteine and maleimide as a stoppering protocol. After verifying the high efficiency of the reaction using glutathione (GSH) as an oligopeptide stopper, we have employed cytochrome C (CytC) as a protein stopper to produce the first well-characterized protein-rotaxane bioconjugates. We anticipate that this methodology will enable the preparation of novel materials that combine the unique properties of proteins and mechanical bonds.

Dual-emissive tetraphenylethene (TPE) and pyrene-containing amphiphilic molecules are of great interest because they can be integrated to form stimuli responsive materials with various biological applications. Herein, we report the study of mechanically interlocked molecules (MIMs) with aggregation-induced static excimer emission (AISEE) property through a series of TPE and pyrene-based amphiphilic [2]rotaxanes, where t -butylcalix[4]arene with hydrophobic nature was used as the macrocycle. Evidently, by adorning TPE and pyrene units in [2]rotaxanes P1 , P2 , P1-b , and P2-b , they display remarkable emission bands in 70% of water fraction ( f w ) in tetrahydrofuran (THF)/water mixture, which could be attributed to the restricted intramolecular rotation of phenyl groups, whereas prominent blue-shifted excimer emission of pyrene started to appear as f w reached 80% for P1 and 90% for P1-b , which was ascribed to the favorable π-π stacking and hydrophobic interactions of the pyrene rings that enabled their static excimer formation. The well-defined distinct amphiphilic nanostructures of [2]rotaxanes including hollowspheres, mesoporous nanostructures, spheres, and network linkages can be driven smoothly depending on the molecular structures and their aggregated states in THF/water mixture. These fascinating diversiform nanostructures were mainly controlled by the skillful manner of reversible molecular shuttling of P2 -butylcalix[4]arene macrocycle and also the interplay of multinoncovalent interactions. To further understand the aggregation capabilities of [2]rotaxanes, the human lung fibroblasts (MRC-5) living cell incubated with either P2-b , which was ascribed to the favorable π-π stacking and hydrophobic interactions of the pyrene rings that enabled their static excimer formation. The well-defined distinct amphiphilic nanostructures of [2]rotaxanes including hollowspheres, mesoporous nanostructures, spheres, and network linkages can be driven smoothly depending on the molecular structures and their aggregated states in THF/water mixture. These fascinating diversiform nanostructures were mainly controlled by the skillful manner of reversible molecular shuttling of t -butylcalix[4]arene macrocycle and also the interplay of multinoncovalent interactions. To further understand the aggregation capabilities of [2]rotaxanes, the human lung fibroblasts (MRC-5) living cell incubated with either P1 , P2 was studied and monitored by confocal laser scanning microscopy. The AISEE property was achieved at an astonishing level by integrating TPE and pyrene to MIM-based reversible molecular switching [2]rotaxanes; furthermore, distinct nanostructures, especially hollowspheres and mesoporous nanostructures, were observed, which are rarely reported in the literature but are highly desirable for future applications.P1-b , or P2-b was studied and monitored by confocal laser scanning microscopy. The AISEE property was achieved at an astonishing level by integrating TPE and pyrene to MIM-based reversible molecular switching [2]rotaxanes; furthermore, distinct nanostructures, especially hollowspheres and mesoporous nanostructures, were observed, which are rarely reported in the literature but are highly desirable for future applications.

Bulky photolabile masked alkyne equivalents (MAEs) are needed for the synthesis of polyyne polyrotaxanes, as insulated molecular wires and as stabilized forms of the linear polymeric allotrope of carbon, carbyne. We have synthesized a novel MAE based on phenanthrene and compared it with an indane-based MAE. Photochemical unmasking of model compounds was studied at different wavelengths (250 and 350 nm), and key products were identified by NMR spectroscopy and X-ray crystallography. UV irradiation at 250 nm leads to unmasking of both MAEs. Irradiation of the phenanthrene system at 350 nm results in quantitative dimerization via [2 + 2] cycloaddition to form a [3]-ladderane; irradiation of this ladderane at 250 nm generates a dihydrotriphenylene, which can be oxidized easily to a triphenylene. Irradiation of the indane-based MAE at 350 nm in the presence of traces of oxygen forms an endoperoxide and a bisepoxide. Both MAEs have been incorporated into rotaxanes via copper-mediated active metal template Glaser or Cadiot-Chodkiewicz coupling. The identity of the rotaxanes was confirmed by NMR spectroscopy and mass spectrometry. The phenanthrene rotaxane decomposes during attempted photochemical unmasking, whereas photolysis of the indane rotaxane results in unmasking of the polyyne thread to form a rotaxane with a chain of 16 sp -hybridized carbon atoms. This approach opens avenues toward the synthesis of encapsulated carbon allotropes.

The relation between the chemical structure and the mechanical behavior of molecular machines is of paramount importance for a rational design of superior nanomachines. Here, we report on a mechanistic study of a nanometer scale translational movement in two bistable rotaxanes. Both rotaxanes consist of a tetra-amide macrocycle interlocked onto a polyether axle. The macrocycle can shuttle between an initial succinamide station and a 3,6-dihydroxy- or 3,6-di- tert -butyl-1,8-naphthalimide end stations. Translocation of the macrocycle is controlled by a hydrogen-bonding equilibrium between the stations. The equilibrium can be perturbed photochemically by either intermolecular proton or electron transfer depending on the system. To the best of our knowledge, utilization of proton transfer from a conventional photoacid for the operation of a molecular machine is demonstrated for the first time. The shuttling dynamics are monitored by means of UV-vis and IR transient absorption spectroscopies. The polyether axle accelerates the shuttling by ∼70% compared to a structurally similar rotaxane with an all-alkane thread of the same length. The acceleration is attributed to a decrease in activation energy due to an early transition state where the macrocycle partially hydrogen bonds to the ether group of the axle. The dihydroxyrotaxane exhibits the fastest shuttling speed over a nanometer distance (τ shuttling ≈ 30 ns) reported to date. The shuttling in this case is proposed to take place via a so-called harpooning mechanism where the transition state involves a folded conformation due to the hydrogen-bonding interactions with the hydroxyl groups of the end station.

Malonate diesters can thread into the cavity of a di(ethylene glycol)-containing macrocycle under the templating effect of a Na + ion; the corresponding rotaxanes can be synthesized with good efficiency by applying several stoppering reactions. A molecular switch, in which the interlocked macrocycle was moved between two rarely used stations (i.e., malonate and TAA) through the addition of acid/base and the presence/absence of Na + ions, was constructed using this new recognition system.

Bistable [ c 2] daisy chain rotaxanes with respective extended and contracted forms of [ c 2 ]A and [ c 2 ]B containing a blue-emissive anthracene ( AN 2] daisy chain rotaxanes with fluorescence changes from blue to orange, including bright-white-light emissions, could be modulated by the aggregation-induced emission (AIE) characteristics and Förster resonance energy transfer (FRET) processes through altering water fractions and shuttling processes (i.e., acid/base controls). Accordingly, as a result of excellent fine-tuning AIE (at 60% water content of H IC ) acceptor were successfully synthesized via click reaction. Tunable-emission bistable [ c 2] daisy chain rotaxanes with fluorescence changes from blue to orange, including bright-white-light emissions, could be modulated by the aggregation-induced emission (AIE) characteristics and Förster resonance energy transfer (FRET) processes through altering water fractions and shuttling processes (i.e., acid/base controls). Accordingly, as a result of excellent fine-tuning AIE (at 60% water content of H 2 O/THF) and FRET (with a compatible energy transfer of E FRET = 33.2%) behaviors after the shuttling process (by adding base), the brightest white-light emission at CIE (0.31, 0.37) with a quantum yield of Φ = 15.64% was obtained in contracted [ c 2 ]B 2] daisy chain rotaxanes. Especially, both bistable [ AN 2] daisy chain rotaxanes IC acceptors with a proper water content of 60% H 2 O. Furthermore, dynamic light-scattering (DLS) and time-resolved photoluminescence (TRPL) measurements, along with theoretical calculations, were utilized to investigate and confirm AIE and FRET phenomena of bistable [ c 2] daisy chain rotaxanes. Especially, both bistable [ c 2] daisy chain rotaxanes [ c 2 ]A and [ c 2 ]B and noninterlocked monomer M could be exploited for the applications of ratiometric fluorescence temperature sensing due to the temperature effects on the AIE and FRET features. Based on these desirable bistable [ c 2] daisy chain rotaxane structures, this work provides a potential strategy for the future applications of tunable multicolor emission and ratiometric fluorescence temperature-sensing materials.

The molecular shuttling function of rotaxanes can be exploited to design mechanoresponsive reporter molecules. Here, we report a new approach to such rotaxane-based mechanophores, in which the fluorescence resonance energy transfer (FRET) between a donor-acceptor pair is mechanically controlled. A cyclic molecule containing a green-light-emitting FRET donor connected to a red-light-emitting FRET acceptor was threaded onto an axle equipped with a quencher at its center and two stoppers in the peripheral positions. In the force-free state, the green emitter is located near the quencher so that charge transfer interactions or photo-induced electron transfer between the two moieties suppress green emission and prevent the FRET from the green to the red emitter. The mechanophore was covalently incorporated into a linear polyurethane-urea (PUU), and stretchable hydrogels were prepared by swelling this polymer with water. Upon deformation of the PUU hydrogels and under an excitation light that selectively excites the donor, the intensity of the red fluorescence increases, as a result of a force-induced separation of the green emitter from the quencher, which enables the FRET. The switching contrast is much more pronounced in the gels than in dry films, which is due to increased molecular mobility and hydrophobic effects in the hydrogel, which both promote the formation of inclusion complexes between the ring containing the green emitter and the quencher.

Interlocked DNA nanostructures perform programmable movements in nanoscales such as sliding, contraction, and expansion. However, utilizing nanoscaled interlocked movements to regulate the functions of larger length scaled matrix and developing their applications has not yet been reported. Herein we describe the assembly of DNA-based daisy chain rotaxane nanostructure (DNA-DCR) composed of two hollow DNA nanostructures as macrocycles, two interlocked axles and two triangular prism-shaped DNA structures as stoppers, in which three mechanical states─fixed extended state (FES), sliding state (SS), and fixed contracted state (FCS)─are characterized by using toehold-mediated strand displacement reaction (SDR). The DNA-DCRs are further used as nanocomposites and introduced into hydrogel matrix to produce interlocked hydrogels, which shows modulable stiffness by elongating the interlocked axles to regulate the hydrogel swelling with hybridization chain reaction (HCR) treatment. Then the DCR-hydrogels are employed as dynamic biointerfaces for human mesenchymal stem cells (hMSCs) adhesion studies. First, hMSCs showed lower cell density on bare DCR-hydrogel treated with HCR-initiated swelling for stiffness decreasing. Second, the cell adhesion ligand (RGD) modified DNA-DCRs are constructed for hydrogel functionalization. DCR (RGD) hydrogel endows the mobility of RGDs by switching the mechanical states of DNA-DCR. HMSCs showed increased cell density on DCR SS(RGD) hydrogel than on DCR FCS(RGD) hydrogel. Therefore, our DNA-DCR nanocomposite hydrogel exhibit dual-programmable performances including swelling adjustment and offering sliding for incorporated ligands, which can be both utilized as dynamic scaffolds for regulating the stem cell adhesion. The dual-programmable cross-scale regulation from interlocked DNA nanostructures to hydrogel matrix was achieved, demonstrating a new pathway of DNA-based materials.

Mono- and (bis)benzimidazoliums were evaluated both experimentally and computationally for their potential as pseudopolyrotaxane axle building blocks. Their aggregation and photophysical behavior, along with their potential to form a [2]pseudorotaxane with dibenzyl-24-crown-8, was studied through the synergistic application of 1D/2D and diffusion-ordered NMR spectroscopy, mass spectrometry, ultraviolet-visible and fluorescence spectroscopy, and time-dependent density functional theory. Their photophysical behavior was measured and modeled as a function of protonation state, solvent, and concentration. The axles show strong solvochromaticism and a very pronounced concentration-dependent optical profile, including self-quenching when a pseudorotaxane is formed. This axle with multiple recognition sites has the potential to form pseudorotaxanes with tunable optical behavior.

To achieve a systemic targeted delivery of siRNA using polymeric carriers, there is a dilemma between ligand modification and stabilization of the polyplex. Namely, ligand modification often leads to destabilization of the polyplex in the blood circulation. In fact, we previously developed cyclodextrin (CD)/polyamidoamine dendrimer conjugates (CDE) as siRNA carriers, and the interaction of CDE/siRNA was decreased by the conjugation with folate-polyethylene glycol, leading to the destabilization. To overcome this dilemma, in this study, folate-appended polyrotaxanes (Fol-PRX) were developed. Fol-PRX stabilized CDE/siRNA polyplex by intermolecularly connecting CDE molecules through a host-guest interaction between adamantane at the terminals of Fol-PRX and β-CD in the polyplex. Moreover, the intermolecular connection of the polyplex with Fol-PRX provided movable folate moieties on the surface. As a result, Fol-PRXs enhanced the in vivo antitumor activity of the polyplex after intravenous administration, suggesting their utility as the dual-functional materials for systemic delivery of siRNA polyplexes.

Polyrotaxanes (PRXs) containing acetylated α-cyclodextrins exhibit a temperature-dependent phase transition in aqueous solutions across their lower critical solution temperature (LCST) of approximately 26.6 °C. To gain insights into the interactions of acetylated PRXs (Ac-PRXs) with biological components, thermoresponsive supramolecular surfaces were prepared by coating tissue culture polystyrene (TCPS) surfaces with Ac-PRX triblock copolymers, and their surface properties across the LCST were evaluated. The wettability and protein adsorption of Ac-PRX-coated surfaces changed significantly between 10 and 37 °C, whereas the uncoated TCPS and unmodified PRX-coated surfaces did not alter the wettability and protein adsorption at 10 and 37 °C. The adhesion, proliferation, morphology, and adhesion strength of NIH/3T3 cells on Ac-PRX-coated surfaces were found to be similar to those of the uncoated and unmodified PRX-coated surfaces. However, the adhesion strength of NIH/3T3 cells on Ac-PRX-coated surfaces decreased drastically at 10 °C. Consequently, the cells spontaneously detached from the Ac-PRX-coated surfaces without enzymatic treatment. Additionally, when incubating confluent cells at 10 °C, the cells detached from Ac-PRX-coated surfaces as cell sheets while retaining extracellular matrix proteins. The findings of this study provide new directions for the design of thermoresponsive supramolecular biointerfaces for applications in bioseparation and cell manipulation.

β-Cyclodextrins (β-CDs) and β-CD-containing polymers have attracted considerable attention as potential candidates for the treatment of cholesterol-related metabolic and intractable diseases. We have advocated the use of β-CD-threaded acid-degradable polyrotaxanes (PRXs) as intracellular delivery carriers for β-CDs. As unmodified PRXs are insoluble in aqueous solutions, chemical modification of PRXs is an essential process to improve their solubility and impart novel functionalities. In this study, we investigated the effect of the modification of zwitterionic sulfobetaines on PRXs due to their excellent solubility, biocompatibility, and bioinert properties. Sulfobetaine-modified PRXs were synthesized by converting the tertiary amino groups of precursor 2-( N , N -dimethylamino)ethyl carbamate-modified PRXs (DMAE-PRXs) using 1,3-propanesultone. The resulting sulfobetaine-modified PRXs showed high solubility in aqueous solutions and no cytotoxicity, while their intracellular uptake levels were low. To further improve this system, we designed PRXs cografted with zwitterionic sulfobetaine and cationic DMAE groups via partial betainization of the DMAE groups. Consequently, the interaction with proteins, intracellular uptake levels, and liver accumulation of partly betainized PRXs were found to be higher than those of completely betainized PRXs. Additionally, partly betainized PRXs showed no toxicity in vitro or in vivo despite the presence of residual cationic DMAE groups. Furthermore, partly betainized PRXs ameliorated the abnormal free cholesterol accumulation in Niemann-Pick type C disease patient-derived cells at lower concentrations than β-CD derivatives and previously designed PRXs. Overall, the cografting of sulfobetaines and amines on PRXs is a promising chemical modification for therapeutic applications due to the high cholesterol-reducing ability and biocompatibility of such modified PRXs. In addition, modification with both zwitterionic and cationic groups can be used for the design of various polymeric materials exhibiting both bioinert and bioactive characteristics.

Autonomous chemically fueled molecular machines that function through information ratchet mechanisms underpin the nonequilibrium processes that sustain life. These biomolecular motors have evolved to be well-suited to the tasks they perform. Synthetic systems that function through similar mechanisms have recently been developed, and their minimalist structures enable the influence of structural changes on machine performance to be assessed. Here, we probe the effect of changes in the fuel and barrier-forming species on the nonequilibrium operation of a carbodiimide-fueled rotaxane-based information ratchet. We examine the machine's ability to catalyze the fuel-to-waste reaction and harness energy from it to drive directional displacement of the macrocycle. These characteristics are intrinsically linked to the speed, force, power, and efficiency of the ratchet output. We find that, just as for biomolecular motors and macroscopic machinery, optimization of one feature (such as speed) can compromise other features (such as the force that can be generated by the ratchet). Balancing speed, power, efficiency, and directionality will likely prove important when developing artificial molecular motors for particular applications.

Traditionally, the synthesis of polyrotaxanes has been limited by synthetic methods that rely on an innate affinity between the rings and the polymer chains. The use of rotaxane-forming molecular pumps allows this limitation to be circumvented in the production of non-equilibrium polyrotaxanes in which rings are trapped on polymer chains for which they have little or no affinity. Pumping cassettes, each composed of a bipyridinium unit linked (i) by a bismethylene bridge to a terminal 2,6-dimethylpyridinium cationic unit and (ii) by a methylene group to an isopropylphenylene steric barrier, were attached using copper-catalyzed azide-alkyne cycloadditions to the ends of a polypropylene glycol (PPG) chain of number-average molecular weight M n ≈ 2200. Using a one-pot electrosynthetic protocol, a series of PPG-based polyrotaxanes with cyclobis(paraquat- p -phenylene) as the rings were synthesized. Despite the steric bulk of the PPG backbone, it was found to be a suitable collecting chain for threading up to 10 rings. The pumping of two rings is sufficient to render these hydrophobic polymers soluble in aqueous solution. Their hydrodynamic diameters and diffusion constants vary according to the number of pumped rings. The non-equilibrium nature of these polyrotaxanes is manifested in their gradual degradation and dethreading at elevated temperatures.

A dynamic silver(I)-loaded [2]rotaxane shuttle ( k 298 = 135 kHz) was converted allosterically into a conformationally restricted [2]rotaxane due to the creation of a bulky imine in the center of the axle component. Only the dynamic silver(I)-loaded [2]rotaxane was able to catalyze a 6- endo -cyclization reaction, whereas the static one was catalytically quiet. The mechanism of catalyst deactivation was elucidated.

We report a new class of synthetic molecular pumps that use a stepwise information ratchet mechanism to achieve the kinetic gating required to sequester their macrocyclic substrates from bulk solution. Threading occurs as a result of active template reactions between the pump terminus amine and an acyl electrophile, whereby the bond-forming reaction is accelerated through the cavity of a crown ether. Carboxylation of the resulting amide results in displacement of the ring to the collection region of the thread. Conversion of the carbamate to a phenolic ester provides an intermediate rotaxane suitable for further pumping cycles. In this way rings can be ratcheted onto a thread from one or both ends of appropriately designed molecular pumps. Each pumping cycle results in one additional ring being added to the thread per terminus acyl group. The absence of pseudorotaxane states ensures that no dethreading of intermediates occurs during the pump operation. This facilitates the loading of different macrocycles in any chosen sequence, illustrated by the pump-mediated synthesis of a [4]rotaxane containing three different macrocycles as a single sequence isomer. A [5]rotaxane synthesized using a dual-opening transamidation pump was structurally characterized by single-crystal X-ray diffraction, revealing a series of stabilizing CH···O interactions between the crown ethers and the polyethylene glycol catchment region of the thread.

Threading of di-, tri-, and tetra(ethylene glycol) through the macrocycle BPX26C6 in the presence of templating Na(+) ions was proven by the synthesis of the corresponding [2]rotaxanes under solvent-free conditions. Among them, a [2]rotaxane featuring both tetra(ethylene glycol) and carbamate stations behaves as a molecular switch that can be controlled reversibly through the application of the KTFPB/[2.2.2]cryptand reagent pair.

We report the synthesis of crown ether-ammonium, amide and amine [2]rotaxanes via transition state stabilization of axle-forming reactions. In contrast to the two-step "clipping" and "capping" strategies generally used for rotaxane synthesis, here the components assemble into the interlocked molecule in a single, reagent-less, step under kinetic control. The crown ether accelerates the reaction of the axle-forming components through the cavity to give the threaded product in a form of metal-free active template synthesis. Rotaxane formation can proceed through the stabilization of different transition states featuring 5-coordinate (e.g., SN2) or 4-coordinate (e.g., acylation, Michael addition) carbon. Examples prepared using the approach include crown-ether-peptide rotaxanes and switchable molecular shuttles. [ABSTRACT FROM AUTHOR]

The first Quantum Theory of Atoms in Molecules (QTAIM) analysis of [2]rotaxanes was used in combination with quantum mechanical calculations and variable temperature NMR experiments. The study shows all the intramolecular interactions of tetraalkylsuccinamide[2]rotaxanes with different templates. The threads have different stoppers [R¹R²NC(O)-CH2CH2-C(O)NR²R¹, in which R²/R¹ = CH2cy-Hex/CH2Ph, i-Bu, Bu, and Pr]. The different threads used allowed us verify that the contact area between the submolecular components (CMcy•••Thr) is closely correlated with the interaction energy (GMcy•••Thr) in the [2]rotaxanes studied. Furthermore, the QTAIM data and quantum mechanical calculations confirmed that, in all of the compounds, the hydrogen bonds are responsible for most of the energy from the intramolecular interactions that follow the C-H•••p and H•••H interactions, independent of the thread used. In the liquid state, using NMR ¹H some intramolecular interactions were observed, which is in agreement with the data obtained in the solid state, thus making possible a comparison between the energy data obtained via the quantum mechanical calculations and the molecular movements of the [2]rotaxanes in solution. Consequently, a new way of understanding the intramolecular interactions in [2]rotaxanes and the influence they have on the movement of molecular machines is presented. [ABSTRACT FROM AUTHOR]

To improve the mechanical properties of collagen hydrogels, which are widely utilized as biomaterials, post-cross-linking of collagen hydrogels was performed using polyrotaxane (PRX) as a cross-linker. Herein, carboxymethyl group-modified PRXs (CMPRs) composed of carboxymethylated α-cyclodextrins (α-CDs) threaded along poly(ethylene glycol) (PEG) capped with bulky stoppers were used to cross-link via reaction with the amino groups in the collagen. Four series of CMPRs with different α-CD threading ratios and axle PEG molecular weights were used for the post-cross-linking of the collagen hydrogels to verify the optimal CMPR chemical compositions. The post-cross-linking of the collagen hydrogels with CMPRs improved the swelling ratios and mechanical properties, such as viscoelasticity and tensile strength. Among the tested CMPRs, CMPRs with an axle PEG molecular weight of 35,000 (PEG35k) resulted in better mechanical properties than CMPRs with a PEG10k axis. Additionally, the cell adhesion and proliferation were greatly improved on the surface of the collagen hydrogels post-cross-linked with CMPRs with the PEG35k axle. These findings suggest that the molecular weight of an axle polymer in CMPRs is a more important parameter than the α-CD threading ratios. Accordingly, the post-cross-linking of hydrogels with PRXs is promising for improving the mechanical properties and biomaterial functions of collagen hydrogels.

Simple cyclophanes containing four distant amino N atoms or ether O atoms behave as hosts for the threading of guest diarylguanidinium ions. The recognition system exhibits high synthetic flexibility, allowing unique O-free [2]rotaxanes to be synthesized efficiently (yields of up to 80%) through both "threading-followed-by-stoppering" and "clipping" approaches. [ABSTRACT FROM AUTHOR]

The integration of mechanophores, motifs that transduce mechanical forces into chemical reactions, allows creating materials with stress-dependent properties. Typical mechanophores are activated by cleaving weak covalent bonds, but these reactions can also be triggered by other stimuli, and this renders the behavior unspecific. Here we show that this problem can be overcome by extending the molecular-shuttle function of rotaxanes to mechanical activation. A mechanically interlocked mechanophore composed of a fluorophore-carrying macrocycle and a dumbbell-shaped molecule containing a matching quencher was integrated into a polyurethane elastomer. Deformation of this polymer causes a fluorescence turn-on, due to the spatial separation of fluorophore and quencher. This process is specific, efficient, instantly reversible, and elicits an easily detectable optical signal that correlates with the applied force. [ABSTRACT FROM AUTHOR]

An efficient synthesis of a doubly stranded [3]rotaxane has been developed through bridging of a pseudo[3]rotaxane featuring two axle components. Reversible azine formation was effective as the bridging reaction. Kinetic and thermodynamic conditions provided the [2]- and [3]rotaxanes, respectively. [ABSTRACT FROM AUTHOR]

A multicomponent pseudorotaxane quadrilateral was reversibly toggled between three distinct switching states. Switching in the forward conversion was achieved by addition of H + and K + ions, and switching in the reverse direction was performed by addition of 18-crown-6 and 1-aza-18-crown-6. In both the forward and backward ways, the inputs operated an AND gate with distinct catalytic outputs. While in the forward direction the logic AND operation starting from a heteroleptic five-component assembly turned "ON" an imine hydrolysis as output (AND-1), in the inverse direction a Michael addition was ignited as the output starting from a seven-component aggregate following the AND gate logic (AND-2).

We describe a [2]rotaxane whose recognition sites for the ring are a dibenzylammonium moiety, endowed with acidic and H-bonding donor properties, and an imidazolium center bearing a photoactive phenylazo substituent. Light irradiation of this compound triggers a network of E / Z isomerization and proton transfer reactions that enable autonomous and reversible ring shuttling away from equilibrium.

A series of [2]rotaxanes with various functional groups in the axle component was synthesized by the oxidative dimerization of alkynes, which is mediated by a macrocyclic phenanthroline-Cu complex. The rotaxanes were fully characterized by spectroscopic methods, and the structure of a rotaxane was determined by X-ray crystallographic analysis. The interaction between the ring component and the axle component was studied in detail to understand the conformation of the rotaxanes. The presence of the hydrogen bond between the phenanthroline moiety in the macrocyclic component and the acidic proton in the axle component influenced the conformation of rotaxane.