SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Wheel and axle

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We developed novel size-complementary molecular and macromolecular rotaxanes using a 2,6-dimethylphenyl terminal as the axle-end-cap group in dibenzo-24-crown-8-ether (DB24C8)-based rotaxanes, where the 2,6-dimethylphenyl group was found to be less bulky than the 3,5-dimethylphenyl group. A series of molecular and macromolecular [2]rotaxanes that bear a 2,6-dimethylphenyl group as the axle-end-cap were synthesized using unsubstituted and fluorine-substituted DB24C8. Base-induced decomposition into their constituent components confirmed the occurrence of deslipping, which supports the size-complementarity of these rotaxanes. The deslipping rate was independent of the axle length but dependent on the DB24C8 substituents. A kinetic study indicated the rate-determining step to be the step that the wheel is getting over the end-cap group, and the deslipping proceeded via a hopping-over mechanism. Finally, the present deslipping behavior was applied to a stimulus-degradable polymer as an example for the versatile utility of this concept in the context of stimulus-responsive materials.

Concepts: Tire, Present, Wheel and axle, Time, Molecule, Axle, Wheel

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The threading of ‘U’ shaped bent axles having diverse functionalities (Axle1-Axle10) is investigated by using a heteroditopic amido-amine macrocyclic (MC) wheel via Ni(II) or Cu(II) metal ion templation. These bent shaped axles are the derivatives of 4,4'-substituted 2,2'-bipyridine, which are composed of various terminal groups like alkene, alkyne, bromide, hydroxyl and azide. Such metallo [2]pseudorotaxanes are well characterised by ESI-MS, EPR and FT-IR spectroscopic studies, UV-Vis absorption studies, elemental analysis and single-crystal X-ray diffraction studies wherever possible. Experimental evidence supports 1 : 1 : 1 ternary complexation between MC, the metal ion and axle. The single crystal X-ray structures of three Cu(II) templated ternary complexes (PR1', PR3' and PR7') show the penta-coordination arrangement around the templating metal ion. Interestingly, judicious selection of chemical functionalities in the complementary wheel and axle components enables to show the existence of various covalent and non-covalent interactions.

Concepts: Spectroscopy, Ionic bond, PageRank, Chemical element, Wheel and axle, Wheel, Axle, Solid

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Wheels are very important for the safety of a train. The diameter of the wheel is a significant parameter that needs regular inspection. Traditional methods only use the contact points of the wheel tread to fit the rolling round. However, the wheel tread is easily influenced by peeling or scraping. Meanwhile, the circle fitting algorithm is sensitive to noise when only three points are used. This paper proposes a dynamic measurement method based on structured-light vision. The axle of the wheelset and the tread are both employed. The center of the rolling round is determined by the axle rather than the tread only. Then, the diameter is calculated using the center and the contact points together. Simulations are performed to help design the layout of the sensors, and the influences of different noise sources are also analyzed. Static and field experiments are both performed, and the results show it to be quite stable and accurate.

Concepts: Wheels, Wheel and axle, Tire, Axle, Circle, Wheel

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Phenylacetylene-based [2]rotaxanes were synthesized by a covalent-template approach by aminolysis of the corresponding prerotaxanes. The wheel and the bulky stoppers are made of phenylene-ethynylene-butadiynylene macrocycles of the same size. The stoppers are large enough to enable the synthesis and purification of the rotaxane. However, the wheel unthreads from the axle at elevated temperatures. The deslipping kinetics and the activation parameters were determined. We described theoretically the unthreading by state-of-the-art DFT-based molecular-mechanics models and a string method for the simulation of rare events. This approach enabled us to characterize in detail the unthreading mechanism, which involves the folding of the stopper during its passage through the wheel opening, a process that defies intuitive geometrical considerations. The conformational and energetic features of the transition allowed us to infer the molecular residues controlling the disassembly timescale.

Concepts: Transition state, Catenane, Wheel and axle, Macrocycle, Axle, Rotaxane, Wheel, Supramolecular chemistry

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A strategy for threading an axle having a hydrogen bond acceptor unit in the cavity of a C3v symmetric amido-amine macrobicycle is investigated. The macrobicycle acts as a wheel in its neutral as well as triprotonated states to form threaded architectures with a pyridine N-oxide derivative. The negative oxygen dipole of the axle is capable of [2]pseudorotaxane formation in two different orientations with the wheel in its neutral and triprotonated states.

Concepts: Covalent bond, Rosanne Cash, Wheel and axle, Axle, Wheel, Hydrogen bond, Hydrogen, Oxygen

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Topology transformation of a star polymer to a linear polymer is demonstrated for the first time. A three-armed star polymer possessing a mechanical linking of two polymer chains was synthesized by the living ring-opening polymerization of δ-valerolactone initiated by a pseudo[2]rotaxane having three hydroxy groups as the initiator sites on the wheel component and at both axle termini. The polymerization was followed by the propagation end-capping reaction with a bulky isocyanate not only to prevent the wheel component deslippage but also to introduce the urethane moiety at the axle terminal. The resulting rotaxane-linked star polymer with a fixed rotaxane linkage based on the ammonium/crown ether interaction was subjected to N-acetylation of the ammonium moiety, which liberated the components from the interaction to move the wheel component to the urethane terminal as the interaction site, eventually affording the linear polymer. The physical property change caused by the present topology transformation was confirmed by the hydrodynamic volume and viscosity.

Concepts: Transport, Polymer physics, Wheel and axle, Polyurethane, Axle, Wheel, Functional group, Polymer

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The (15-oxo-3,7,11-triazadispiro[5.1.5.3]hexadec-7-yl)oxidanyl, a bis-spiropiperidinium nitroxide derived from TEMPONE, can be included in cucurbit[7]uril to form a strong (Ka ∼ 2 × 10(5) M(-1)) CB[7]@bPTO complex. EPR and MS spectra, DFT calculations, and unparalleled increased resistance (a factor of ∼10(3)) toward ascorbic acid reduction show evidence of deep inclusion of bPTO inside CB[7]. The unusual shape of the CB[7]@bPTO EPR spectrum can be explained by an anisotropic Brownian rotational diffusion, the global tumbling of the complex being slower than rotation of bPTO around its “long molecular axis” inside CB[7]. The CB[7] (stator) with the encapsulated bPTO (rotator) behaves as a supramolecular paramagnetic rotor with increased rotational speed of the rotator that has great potential for advanced nanoscale machines requiring wheels such as cucurbiturils with virtually no friction between the wheel and the axle for optimum wheel rotation (i.e. nanopulleys and nanocars).

Concepts: Wheel and axle, Nanotechnology, Wheels, Fundamental physics concepts, Acid, Axle, Classical mechanics, Wheel

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High yields syntheses of Cu (II) and Ni(II) templated [2]pseudorotaxane precursors, CuPRT and NiPRT are achieved by threading bis-azide-bis-amide-2,2´-bipyridine axle into bis-amide-tris-amine macrocycle. Single crystal X-ray structural analysis of CuPRT reveals complete threading of the axle fragment into the wheel cavity where strong aromatic pi-pi stacking interactions (ranges from 3.474 to 3.494 Angstrom) between two parallel arene moieties of the wheel and the pyridyl unit of axle are operative besides metal ion templation. These azide terminated [2]pseudorotaxane precursors are further explored towards synthesis of metal free [2]rotaxane upon attaching a newly developed bulky stopper molecule with alkyne terminal via Cu(I)-catalyzed azide-alkyne cycloaddition reaction. Attachment of the stopper to CuPRT precursor via click chemistry, fails due to de-threading of azide terminated axle in the reaction conditions. However, synthesis of metal free [2]rotaxane containing triazole with other functionalities in the axle is achieved upon coupling between azide terminated NiPRT and the alkyne terminated stopper with ~45% yield. The [2]rotaxane is characterized by mass spectrometry, 1D and 2D NMR (COSY, DOSY, ROESY) experiments. Comparative solution state NMR studies of [2]rotaxane and in its protonated state are carried out to locate the position of the wheel on the axle of metal free [2]rotaxane. Furthermore, variable temperature 1H- NMR study in DMSO-d6 of [2]rotaxane supports the kinetic-inertness of the interlocked structure, where newly developed stopper prevents dethreading of 30-membered wheel from the axle.

Concepts: Organic chemistry, Solid, Wheel and axle, Axle, Azide alkyne Huisgen cycloaddition, Wheel, Alkyne, Functional group

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A new templating motif for the formation of [2]pseudorotaxanes is described in which rigid, Y-shaped axles with an imidazolium core and aromatic substituents at the 2-, 4- and 5-positions interact with [24]crown-8 ether wheels ([24]crown-8 and dibenzo[24]crown-8). The Y-shape of the axle significantly enhances the association between axle and wheel when compared to simple imidazolium cations.

Concepts: Wheels, Live axle, The Association, Wheel and axle, Axle, Wheel

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Train loads and travel speeds have increased over time, requiring more efficient non-destructive inspection methods. Railway axles are critical elements; despite being designed to last more than 20 years several cases of premature failure have been recorded. Train axles are inspected regularly, but the limits associated to the traditional inspection technologies create a growing interest towards new solutions. Here a novel non-destructive inspection method of in-service axles based on non-contact data collection is presented. The propagation of surface waves, generated by a thermo-elastic laser source, is investigated using a finite element method based on dynamic explicit integration. Coupled thermo-mechanical simulations allow visualization of the ultrasonic field guiding the definition of the optimal NDT setup. The geometry of the axle and of the elements mounted on it is accurately reproduced; moreover the press fit effect caused by the wheel and the bearing rings is implemented. The current NDT techniques for railway axles require removing wheels and other components from the axle. The presented scheme uses non-contact ultrasonic generation and detection allowing non-contact in-service inspection of railway axles at trackside station. The numerical results are promising and encourage us to test the new approach experimentally.

Concepts: Numerical analysis, Wheel and axle, Element, The Elements, Finite element method, Axle, Nondestructive testing, Wheel