Interlocked Rings Research Articles

Exploring the Impact of Ring Mobility on the Macroscopic Properties of Doubly Threaded Slide-Ring Gel Networks.

The integration of mechanically interlocked molecules (MIMs) into polymeric materials has led to the development of mechanically interlocked polymers (MIPs). One class of MIPs that have gained attention in recent years are slide-ring gels (SRGs), which are generally accessed by crosslinking rings on a main-chain polyrotaxane. The mobility of the interlocked crosslinking moieties along the polymer backbone imparts enhanced properties onto these networks. An alternative synthetic approach to SRGs is to use a doubly threaded ring as the crosslinking moiety, yielding doubly threaded slide-ring gel networks (dt-SRGs). In this study, a photo-curable ligand-containing thread was used to assemble a series of metal-templated pseudo[3]rotaxane crosslinkers that allow access to polymer networks that contain doubly threaded interlocked rings. The physicochemical and mechanical properties of these dt-SRGs with varying size of the ring crosslinking moieties were investigated and compared to an entangled gel (EG) prepared by polymerizing the metal complex of the photo-curable ligand-containing thread, and a corresponding covalent gel (CG). Relative to the EG and CG, the dt-SRGs exhibit enhanced swelling behavior, viscoelastic properties, and stress relaxation characteristics. In addition, the macroscopic properties of dt-SRGs could be altered by "locking" ring mobility in the structure through remetalation, highlighting the impact of the mobility of the crosslinks.

Exploring the Impact of Ring Mobility on the Macroscopic Properties of Doubly Threaded Slide‐Ring Gel Networks

AbstractThe integration of mechanically interlocked molecules (MIMs) into polymeric materials has led to the development of mechanically interlocked polymers (MIPs). One class of MIPs that have gained attention in recent years are slide‐ring gels (SRGs), which are generally accessed by crosslinking rings on a main‐chain polyrotaxane. The mobility of the interlocked crosslinking moieties along the polymer backbone imparts enhanced properties onto these networks. An alternative synthetic approach to SRGs is to use a doubly threaded ring as the crosslinking moiety, yielding doubly threaded slide‐ring gel networks (dt‐SRGs). In this study, a photo‐curable ligand‐containing thread was used to assemble a series of metal‐templated pseudo[3]rotaxane crosslinkers that allow access to polymer networks that contain doubly threaded interlocked rings. The physicochemical and mechanical properties of these dt‐SRGs with varying size of the ring crosslinking moieties were investigated and compared to an entangled gel (EG) prepared by polymerizing the metal complex of the photo‐curable ligand‐containing thread, and a corresponding covalent gel (CG). Relative to the EG and CG, the dt‐SRGs exhibit enhanced swelling behavior, viscoelastic properties, and stress relaxation characteristics. In addition, the macroscopic properties of dt‐SRGs could be altered by “locking” ring mobility in the structure through remetalation, highlighting the impact of the mobility of the crosslinks.

Unraveling the Influence of Topology and Spatial Confinement on Equilibrium and Relaxation Properties of Interlocked Ring Polymers.

We use Langevin dynamics simulations to study linked ring polymers in channel confinement. We address the in- and out-of-equilibrium behavior of the systems for varying degrees of confinement and increasing topological and geometrical complexity of the interlocking. The main findings are three. First, metric observables of different link topologies collapse onto the same master curve when plotted against the crossing number, revealing a universal response to confinement. Second, the relaxation process from initially stretched states is faster for more complex links. We ascribe these properties to the interplay of several effects, including the dependence of topological friction on the link complexity. Finally, we show that transient forms of geometrical entanglement purposely added to the initial stressed state can leave distinctive signatures in force-spectroscopy curves. The insight provided by the findings could be leveraged in single-molecule nanochannel experiments to identify geometric entanglement within topologically linked rings.

Shape and size tunability of sheets of interlocked ring copolymers.

Mechanically bonded membranes of interlocked ring polymers are a significant generalization of conventional elastic sheets, where connectivity is provided by covalent bonding, and represent a promising class of topological meta-materials. In this context, two open questions regard the large-scale reverberations of the heterogeneous composition of the rings and the inequivalent modes of interlocking neighboring rings. We address these questions with Langevin dynamics simulations of chainmails with honeycomb-lattice connectivity, where the rings are block copolymers with two segments of different rigidity. We considered various combinations of the relative lengths of the two segments and the patterns of the over- and under-passes linking neighboring rings. We find that varying ring composition and linking patterns have independent and complementary effects. While the former sets the overall size of the chainmail, the latter defines the shape, enabling the selection of starkly different conformation types. Notably, one of the considered linking patterns favors saddle-shaped membranes, providing a first example of spontaneous negative Gaussian curvature in mechanically bonded sheets. The results help establish the extent to which mechanically bonded membranes can differ from conventional elastic ones, particularly for the achievable shape and size tunability.

Doubly Threaded Slide-Ring Polycatenane Networks.

Crosslinking in polymer networks leads to intrinsic structural inhomogeneities that result in brittle materials. Replacing fixed covalent crosslinks with mobile ones in mechanically interlocked polymers (MIPs), such as in slide-ring networks (SRNs) in which interlocked crosslinks are formed when polymer chains are threaded through crosslinked rings, can lead to tougher, more robust networks. An alternative class of MIPs is the polycatenane network (PCN), in which the covalent crosslinks are replaced with interlocked rings that introduce the unusual catenane's mobility elements (elongation, rotation, and twisting) as connections between polymer chains. A slide-ring polycatenane network (SR-PCN), with doubly threaded rings embedded as crosslinks in a covalent network, combines the mobility features of both the SRNs and PCNs, where the catenated ring crosslinks can slide along the polymer backbone between the two limits of network bonding (covalent and interlocked). This work explores using a metal ion-templated doubly threaded pseudo[3]rotaxane (P3R) crosslinker, combined with a covalent crosslinker and a chain extender, to access such networks. A catalyst-free nitrile-oxide/alkyne cycloaddition polymerization was used to vary the ratio of P3R and covalent crosslinker to yield a series of SR-PCNs that vary in the amount of interlocked crosslinking units. Studies on their mechanical properties show that metal ions fix the rings in the network, leading to similar behavior as the covalent PEG gels. Removal of the metal ion frees the rings resulting in a high-frequency transition attributed to the additional relaxation of polymer chains through the catenated rings while also increasing the rate of poroelastic draining at longer timescales.

Glass Formation in Mechanically Interlocked Ring Polymers: The Role of Induced Chain Stiffness

Polymer-related materials exhibit rich glassy behaviors at different length scales due to their various molecular structures and topological constraints. Recent studies have identified transient interpenetration of the long-chain rings contributing to dynamic arrest on the center-of-mass level. Interpenetration of rings is proposed as an approach to facilitate glass formation in polymer melts. In this work, inspired by recent advances in the synthesis of mechanically interlocked polymers, we investigate glass transition on the nanometer-scale segments influenced by permanent interpenetration of rings using molecular dynamics simulations. We find that decreasing chain length in the mechanically interlocked system is equivalent to inducing an effective chain stiffness on the subrings. The induced stiffness provides a unified explanation for these unique structural features and transient dynamic arrest in the system of interlocked rings with rather short chains. Further, a crossover is observed in the scaling relation between localization and glassy depth upon cooling. Our work reveals a dynamic transition from weak to strong caging at the crossover temperature. According to the localization model, we demonstrate that the chain stiffness increases the critical temperature and oscillation distance, which therefore leads to more fragile dynamics and a deeper glassy state. These findings are consistent with the predictions of molecular simulations and theories for polymers with real local stiffness. Our work deepens the understanding of the role of induced stiffness on glass transition, and it opens up a new direction to design rich glass materials by manipulating stiffness through mechanical bonds.

The effect of thread-like monomer structure on the synthesis of poly[n]catenanes from metallosupramolecular polymers.

The main-chain poly[n]catenane consists of a series of interlocked rings that resemble a macroscopic chain-link structure. Recently, the synthesis of such intriguing polymers was reported via a metallosupramolecular polymer (MSP) template that consists of alternating units of macrocyclic and linear thread-like monomers. Ring closure of the thread components has been shown to yield a mixture of cyclic, linear, and branched poly[n]catenanes. Reported herein are studies aimed at accessing new poly[n]catenanes via this approach and exploring the effect the thread-like monomer structure has on the poly[n]catenane synthesis. Specifically, the effect of the size of the aromatic linker and alkenyl chains of the thread-like monomer is investigated. Three new poly[n]catenanes (with different ring sizes) were prepared using the MSP approach and the results show that tailoring the structure of the thread-like monomer can allow the selective synthesis of branched poly[n]catenanes.

A multiplexed circulating tumor DNA detection platform engineered from 3D-coded interlocked DNA rings

Circulating tumor DNA (ctDNA) is a critical biomarker not only important for the early detection of tumors but also invaluable for personalized treatments. Currently ctDNA detection relies on sequencing. Here, a platform termed three-dimensional-coded interlocked DNA rings (3D-coded ID rings) was created for multiplexed ctDNA identification. The ID rings provide a ctDNA recognition ring that is physically interlocked with a reporter ring. The specific binding of ctDNA to the recognition ring initiates target-responsive cutting via a restriction endonuclease; the cutting then triggers rolling circle amplification on the reporter ring. The signals are further integrated with internal 3D codes for multiplexed readouts. ctDNAs from non-invasive clinical specimens including plasma, feces, and urine were detected and validated at a sensitivity much higher than those obtained through sequencing. This 3D-coded ID ring platform can detect any multiple DNA fragments simultaneously without sequencing. We envision that our platform will facilitate the implementation of future personalized/precision medicine.

Diastereoselective Amplification of a Mechanically Chiral [2]Catenane.

Achiral [2]catenanes composed of rings with inequivalent sides may adopt chiral co-conformations. Their stereochemistry depends on the relative orientation of the interlocked rings and can be controlled by sterics or an external stimulus (e.g., a chemical stimulus). Herein, we have exploited this stereodynamic property to amplify a mechanically chiral (P)-catenane upon binding to (R)-1,1′-binaphthyl 2,2′-disulfonate, with a diastereomeric excess of 85%. The chirality of the [2]catenane was ascertained in the solid state by single crystal X-ray diffraction and in solution by NMR and CD spectroscopies. This study establishes a robust basis for the development of a new synthetic approach to access enantioenriched mechanically chiral [2]catenanes.

Material properties and applications of mechanically interlocked polymers

Mechanically interlocked polymers (MIPs), such as polyrotaxanes and polycatenanes, are polymer architectures that incorporate a mechanical bond. In a polyrotaxane, the mechanical bond is the result of a linear dumbbell component threaded through a ring, while in a polycatenane, it is the consequence of interlocked ring components. The interlocked nature of these architectures can result in high degrees of conformational freedom and mobility of their components, which can give rise to unique property profiles. In recent years, the synthesis and studies of a range of MIPs has allowed researchers to build an initial understanding of how incorporating mechanical bonds within a polymer structure impacts its material properties. This Review focuses on the understanding of these structure–property relationships with an outlook towards their applications, specifically focusing on four main classes of MIPs: polyrotaxanes, slide-ring gels, daisy-chain polymers and polycatenanes.

Design and implementation of a snake-like robot with biomimetic 2-D gaits

ABSTRACT For the purposes of field explorations and rescues, this research designed and implemented a simple snake-like robot that can move in narrow space and various terrains. The frame of the robot was constructed by modular segments. Each segment consisted interlocked rings, connecting rods and servo-motors that enabled the robot to bend and oscillate the body and imitate the 2-D gaits of snakes. We used Motoduino module, Bluetooth, servo-motors and wireless micro-camera to activate the robot. In order to cut down the cost, the robot’s skeleton and mechanical components were designed by 3-D printing using PLA material. The weight of the robot is about 960g and the size is 79cm×14cm×9cm. The maximum speed and the radius of gyration are about 16cm/sec and 21cm, respectively.

Fluorescent aptasensors for parallel analysis of biomolecules based on interlocked DNA catenane nanomachines

Stimuli-responsive DNA catenane nanomachines have received considerable interest in the area of DNA nanotechnology. However, the sensing and bio-sensing applications of DNA catenane nanomachines are rarely explored. Herein, the biological small molecule and protein responsive DNA catenane nanomachines were designed by utilizing the specific aptamer/target interaction. In the presence of the target, the blocked catalytically inactive DNA catenane can be activated, while generating the metal ion-dependent DNAzyme as the signal output unit. The method allows the fluorescent detection of ATP and lysozyme with a detection limit of 20 nM and 200 pM, respectively. More importantly, through the use of different fluorophores as labels, the parallel analysis of ATP and lysozyme in the mixed solution was demonstrated based on two interlocked DNA catenanes. Compared with linear scaffold, the interlocked DNA rings showed enhanced stability against enzyme degradation and easily realized intramolecular reconfiguration. Due to its inherent advantages, the interlocked DNA catenane holds great promise in the field of DNA based sensors and nanodevices.

DNA Origami Catenanes Templated by Gold Nanoparticles.

Mechanically interlocked molecules have marked a breakthrough in the field of topological chemistry and boosted the vigorous development of molecular machinery. As an archetypal example of the interlocked molecules, catenanes comprise macrocycles that are threaded through one another like links in a chain. Inspired by the transition metal-templated approach of catenanes synthesis, the hierarchical assembly of DNA origami catenanes templated by gold nanoparticles is demonstrated in this work. DNA origami catenanes, which contain two, three or four interlocked rings are successfully created. In particular, the origami rings within the individual catenanes can be set free with respect to one another by releasing the interconnecting gold nanoparticles. This work will set the basis for rich progress toward DNA-based molecular architectures with unique structural programmability and well-defined topology.

Solvent‐Induced Cluster‐to‐Cluster Transformation of Homoleptic Gold(I) Thiolates between Catenane and Ring‐in‐Ring Structures

AbstractSupramolecular ensembles adopting ring‐in‐ring structures are less developed compared with catenanes featuring interlocked rings. While catenanes with inter‐ring closed‐shell metallophilic interactions, such as d10–d10 AuI–AuI interactions, have been well‐documented, the ring‐in‐ring complexes featuring such metallophilic interactions remain underdeveloped. Herein is described an unprecedented ring‐in‐ring structure of a AuI‐thiolate Au12 cluster formed by recrystallization of a AuI‐thiolate Au10 [2]catenane from alkane solvents such as hexane, with use of a bulky dibutylfluorene‐2‐thiolate ligand. The ring‐in‐ring AuI‐thiolate Au12 cluster features inter‐ring AuI–AuI interactions and underwent cluster core change to form the thermodynamically more stable Au10 [2]catenane structure upon dissolving in, or recrystallization from, other solvents such as CH2Cl2, CHCl3, and CH2Cl2/MeCN. The cluster‐to‐cluster transformation process was monitored by 1H NMR and ESI‐MS measurements. Density functional theory (DFT) calculations were performed to provide insight into the mechanism of the “ring‐in‐ring⇌ [2]catenane” interconversions.

Solvent-Induced Cluster-to-Cluster Transformation of Homoleptic Gold(I) Thiolates between Catenane and Ring-in-Ring Structures.

Supramolecular ensembles adopting ring-in-ring structures are less developed compared with catenanes featuring interlocked rings. While catenanes with inter-ring closed-shell metallophilic interactions, such as d10 -d10 AuI -AuI interactions, have been well-documented, the ring-in-ring complexes featuring such metallophilic interactions remain underdeveloped. Herein is described an unprecedented ring-in-ring structure of a AuI -thiolate Au12 cluster formed by recrystallization of a AuI -thiolate Au10 [2]catenane from alkane solvents such as hexane, with use of a bulky dibutylfluorene-2-thiolate ligand. The ring-in-ring AuI -thiolate Au12 cluster features inter-ring AuI -AuI interactions and underwent cluster core change to form the thermodynamically more stable Au10 [2]catenane structure upon dissolving in, or recrystallization from, other solvents such as CH2 Cl2 , CHCl3 , and CH2 Cl2 /MeCN. The cluster-to-cluster transformation process was monitored by 1 H NMR and ESI-MS measurements. Density functional theory (DFT) calculations were performed to provide insight into the mechanism of the "ring-in-ring⇌ [2]catenane" interconversions.

Knot your usual hydrocarbons

The nanocarbon family just got bigger and more complex. Chemists in Japan have created intertwined molecules, including a trefoil knot and interlocked rings known as catenanes, made up entirely of benzene rings (Science 2019, DOI: 10.1126/science.aav5021). This adds mechanically bonded molecules to the menagerie of carbon nanostructures, which includes fullerenes and nanotubes. Mechanical bonds are key to the movement of many types of molecular machines, the construction of which garnered their creators the 2016 Nobel Prize in Chemistry. “Occasionally a molecule is made that just looks impossible. This paper has three,” says David A. Leigh, an expert in topologically complex molecules at the University of Manchester who was not involved in the research. Nagoya University’s Kenichiro Itami and Yasutomo Segawa led the team that created the nanocarbon structures. Previous examples of catenanes and molecular knots typically contain heteroatoms like nitrogen. These heteroatoms are necessary for stitching toget...

How to make interlocked nanocarbons.

Interlocked nanocarbon rings have promising properties for molecular machines

Mechanical Properties of Interlocked-ring Polymers: A Molecular Dynamics Simulation Study

Interlocked-ring polymers, also known as polycatenanes, possess an interesting molecular architecture. These polymers are composed of many interlocked rings in a linear chain. The topological constrain between neighboring rings distinguishes the interlocked-ring polymer from its linear counterpart. Here we present extensive molecular dynamic simulations on the interlocked-ring polymers and analyze the static properties of the polymer. By applying external forces to the polymer, we also study the force-extension curves of the polymer, which provides rich information about the mechanical properties of the interlockedring polymers.

Selective Synthesis of Interlocked Molecules with Topological Chirality

Mechanically interlocked molecules can be chiral if each of the rings has no bilateral symmetry. Although chiral catenanes have been isolated from racemic mixtures via chromatographic techniques, these optically active molecules have not been directly synthesized until now. In this issue of Chem, Goldup and co-workers describe an auxiliary approach for the stereoselective synthesis of the topological enantiomers of chiral [2]catenanes. This methodology enables exploration of the potential applications of these chiral molecules in areas such as medicine and materials science.

Topological entanglement of interlocked knotted-unknotted polymer rings.

Topological entanglements in biopolymers could drive them to certain internal statics and dynamics with important implications for biological functions. In this study, by means of molecular dynamics simulations, we demonstrate that the minimal crossing pattern of a braid plays a major role in its structural and dynamical properties; the braid consists of a knotted ring and an interlocked entwined unknotted polymer ring. In particular, we show that depending on the bending rigidity of the chains, the conformational energy of the braid can be either lower or higher than the unlocked polymer rings. Additionally, we find that a non-identical crossing pattern in the braid could distinctly enforce concerted internal conformational fluctuations between the interlocked rings.