Stability Of Cages Research Articles

Interaction mechanisms between cage whirl motion, sliding of balls and vibration of bearing rings for angular contact ball bearings at various groove bottom circle diameters

An improved dynamic model of ball bearings with cage whirl motion and elastohydrodynamic lubrication was established for investigating the interaction mechanisms between cage whirl motion, slide of balls and vibration of bearing rings. Next, the combinations of outer and inner groove bottom circle diameters were varied to study their effects on the whirl characteristics of cage, interaction forces of bearing components, pressure and thickness of oil film characteristics, and vibration of inner ring. The results show that moderate combinations of inner and outer groove bottom circle diameters can reduce the intensities and fluctuations of interaction forces of bearing components to achieve the desired dynamic stability of cage and vibration of the bearing system.

A Discrete 3d–4f Metallacage as an Efficient Catalytic Nanoreactor for a Three-Component Aza-Darzens Reaction

The exploration and development of coordination nanocages can provide an approach to control chemical reactions beyond the bounds of the flask, which has aroused great interest due to their significant applications in the field of molecular recognition, supramolecular catalysis, and molecular self-assembly. Herein, we take the advantage of a semirigid and nonsymmetric bridging ligand (H5L) with rich metal-chelating sites to construct an unusual and discrete 3d-4f metallacage, [Zn2Er4(H2L)4(NO3)Cl2(H2O)]·NO3·xCH3OH·yH2O (Zn2Er4). The 3d-4f Zn2Er4 cage possesses a quadruple-stranded structure, and all of the ligands wrap around an open spherical cavity within the core. The self-assembly of the unique cage not only ensures the structural stability of the Zn2Er4 cage as a nanoreactor in solution but also makes the bimetallic lanthanide cluster units active sites that are exposed in the medium-sized cavity. It is important to note that the Zn2Er4 cage as a homogeneous catalyst has been successfully applied to catalyze three-component aza-Darzens reactions of formaldehyde, anilines, and α-diazo esters without another additive under mild conditions, displaying better catalytic activity, higher specificity, short reaction time, and low catalyst loadings. A possible mechanism for this three-component aza-Darzens reaction catalyzed by the Zn2Er4 cage has been proposed. These experimental results have demonstrated the great potential of the discrete 3d-4f metallacage as a host nanoreactor for the development of supramolecular or molecular catalysis.

Hydrazone- and imine-containing [PdPtL4]4+ cages: a comparative study of the stability and host-guest chemistry.

A new [PdPtL4]4+ heterobimetallic cage containing hydrazone linkages has been synthesised using the sub-component self-assembly approach. 1H and DOSY nuclear magnetic resonance (NMR) spectroscopy and electrospray ionisation mass spectrometry (ESIMS) data were consistent with the formation of the [PdPtL4]4+ architecture. The cage was stimulus-responsive and could be partially disassembled and reassembled by the addition of dimethylaminopyridine (DMAP) and p-tolenesulfonic acid (TsOH), respectively. Additionally, the stability of the hydrazone cage against hydrolysis in the presence of water and nucleophilic decomposition in the presence of guest molecules was compared to a previously synthesised imine-containing [PdPtL4]4+ cage. It was established that the hydrazone linkage was more resistant to hydrolysis. Furthermore, the host-guest (HG) chemistry with a series of drug and drug-like molecules was examined. The hydrazone cage was shown to interact with cisplatin while the smaller imine cage was shown to interact with 5-fluorouracil and oxaliplatin in CD3CN. No HG interactions were observed in the more polar d6-DMSO. In vitro antiproliferative activity studies demonstrated both cages were active against the cancer cell lines tested and displayed half-maximal inhibitory (IC50) values in the range of 25-35 μM. Most [PdPtL4]4+-drug mixtures tested had higher IC50 values than the hosts. However, the [PdPtL4]4+ cages, and [PdPtL4]4+:drug mixtures were less cytotoxic than the well established anticancer drugs cisplatin, oxaliplatin and 5-fluorouracil.

Experimental and theoretical approaches for determining cage motion dynamic characteristics of angular contact ball bearings considering whirling and overall skidding behaviors

Cage stability is an essential indicator of the guaranteed efficiency and reliability of the rolling element bearing. Moreover, cage instability can greatly shorten the bearing’s service life. The whirl characteristics of the cage caused by ball–cage collisions are closely related to the overall bearing skidding degree. To explore the stability and skidding characteristics of self-lubricated cages used in spacecraft angular contact bearings, a comprehensive bearing dynamic model focused on cage characteristics is proposed. The cage was divided into Nb (number of balls) segments owing to the low stiffness of the cage material (porous polyimide). The model comprised ball self-rotating and revolution motions with 4*Nb degrees of freedom (DOF) and cage motions with Nb + 3 DOF. In the latter, 3 represents the cage whirling motion in the translational and axial directions. The ball-pocket normal and tangential forces, ball-pocket axial collisions, the ball-raceway traction force and moment, imbalances, centrifugal force, and thin oil film lubrication are included in the model. A test bench for exploring the cage motion with a high-speed camera to capture cage images was developed. Three experimental case studies investigating the effects of operating speed and applied load validated the effectiveness and accuracy of the model. Several indicators describing cage stability and cage skidding degree were proposed based on the experimental and theoretical results. It was found that the rate of increase of the whirl radius reduced with a linear increase in the rotation speed. The whirling radius displayed an approximate hyperbolic downward trend with increasing axial force. The skidding results suggested that applying a large axial load to the bearing may have been counterproductive in preventing bearing skidding. In addition, the cage was prone to instability as the radial load increased owing to intensive cage-guide ring rubbing.

A Water Soluble Pd2 L4 Cage for Selective Binding of Neu5Ac.

The sialic acid N‐acetylneuraminic acid (Neu5Ac) and its derivatives are involved in many biological processes including cell‐cell recognition and infection by influenza. Molecules that can recognize Neu5Ac might thus be exploited to intervene in or monitor such events. A key obstacle in this development is the sparse availability of easily prepared molecules that bind to this carbohydrate in its natural solvent; water. Here, we report that the carbohydrate binding pocket of an organic soluble [Pd2L4]4+ cage could be equipped with guanidinium‐terminating dendrons to give the water soluble [Pd2L4][NO3]16 cage 7. It was shown by means of NMR spectroscopy that 7 binds selectively to anionic monosaccharides and strongest to Neu5Ac with K a=24 M−1. The cage had low to no affinity for the thirteen neutral saccharides studied. Aided by molecular modeling, the selectivity for anionic carbohydrates such as Neu5Ac could be rationalized by the presence of charge assisted hydrogen bonds and/or the presence of a salt bridge with a guanidinium solubilizing arm of 7. Establishing that a simple coordination cage such as 7 can already selectively bind to Neu5Ac in water paves the way to improve the stability, affinity and/or selectivity properties of M2L4 cages for carbohydrates and other small molecules.

Simulative Analysis of a Family of DNA Tetrahedrons Produced by Changing the Twisting Number of Each Double Helix

In this paper, three tetrahedral nanocages, composed of six DNA double helix edges with all having the twist number 1, 2 or 3, have been characterized using classical molecular dynamics simulation to measure the specific structural and conformational features produced by only changing the twisting number of each double helix. The simulation result indicates that three tetrahedral cages are relatively stable and are maintained along the entire trajectory. Each double helix is more inclined to behave as a whole in the 2TD and 3TD cages than in the 1TD cage according to the cross-correlation maps for three nanocages, and also their local motions are more easily induced by the conformational variability of the thymidine linkers due to the increased flexibility of each helix. Hence, the double helices become the important factors on the structural stability of total cages with the DNA twisting number, and also give the signification contributions to the sizes of these cages conferring the larger spaces of the 2TD and 3TD cages than the 1TD cage. Our result provides an insight into which roles the double helix edges play in assembling DNA polyhedron, and also contribute to improving the loading capacity of DNA tetrahedron in drug delivery.

Multistimuli-Responsive Fluorescent Organometallic Assemblies Based on Mesoionic Carbene-Decorated Tetraphenylethene Ligands and Their Applications in Cell Imaging

Multistimuli-Responsive Fluorescent Organometallic Assemblies Based on Mesoionic Carbene-Decorated Tetraphenylethene Ligands and Their Applications in Cell Imaging

Dynamic modeling and characteristics analysis of cylindrical roller bearing with the surface texture on raceways

The vibration responses of cylindrical roller bearings can be affected by the surface texture on raceways, which includes surface waviness and roughness. Thus, it is very important to develop a dynamic model which can describe the surface texture comprehensively and simulate vibration responses of bearings accurately at high rotating speed. In this paper, a complex dynamic model of cylindrical roller bearings with consideration of surface texture is developed. The developed model is verified by simulations and experiments about the relationship between wave numbers and vibration responses. Based on the developed model, several dynamic characteristics of roller bearings are discussed: a) the influence of radial clearance and rotation speed on the stability of cage; b) the contact between a roller and raceways; c) the variation of rotation angular speed of roller. Results show that with the radial clearance increase, the stability of cage rise first and decrease. The cage stability is also affected by the rotation speed of inner raceway. The constitution of contact force between a roller and raceway are different between loaded zone and unloaded zone. Changes of angular rotation velocity of roller also have some regulations.

Modeling Nucleation and Kinetics of Clathrin Assembly by Membrane Localization

The formation of clathrin lattices on the plasma membrane of cells is a multi-component assembly process in the time order of seconds to minutes, which plays an essential role in transport across the membrane. Recent in vitro fluorescence experiments have measured the kinetics of adaptor-mediated clathrin assembly on membranes. Here we develop a microscopic model that can quantitatively reproduce these in vitro kinetics, establishing how cooperativity due to both 2D membrane localization and adaptor protein interactions are necessary to drive the nucleation and growth of clathrin cages. This model is also consistent with the known biochemistry of interactions between clathrin and adaptor proteins, clathrin-clathrin interactions, and the effect of adaptor proteins in strengthening clathrin-clathrin interactions. It explicitly accounts for the multi-valency of the clathrin-clathrin contacts, and the necessary conversion factor between 3D binding rates and 2D rates. We simulated this model using the structure-resolved reaction-diffusion simulator NERDSS, collecting minutes-long time-dependent data and movies of the clathrin assembly on the membrane. We then show how changing the stickiness of the membrane controls the nucleation of clathrin-coated structures on the surface, with clathrin present now at physiologic concentrations. with this model, we can predict how tuning the stoichiometry of components and cargo will impact the nucleation and stability of clathrin cages on the membrane, resulting in productive or abortive assembly events. This quantitative model and corresponding space- and time-dependent simulations provide a critical quantitative framework for investigating how the selection of cargo at the membrane by associated adaptors controls the speed and success of vesicle formation.

Molecular Dynamics Simulation Study of N2/CO2 Displacement Process of Methane Hydrate

AbstractIn this paper, we construct three kinds of hydrate replacement models: N2, CO2 and N2‐CO2. The molecular dynamics (MD) method is used to study the dynamic process of N2‐CO2 replacement for natural gas hydrate. The replacement efficiency of N2/CO2 is simulated, and the influence of gas replacement on the stability of the water cage is assessed. The results show that CH4 molecules in the driving hydrate are all enriched in the gas‐liquid interface or gas region. Compared with the replacement of methane hydrate with CO2, when N2‐CO2 mixed gas is used to replace methane hydrate, the diffusion rate of CO2 is increased by 2 times, and the replacement efficiency of hydrate is significantly improved. The radial distribution function and free energy calculation results show that although the barrier of the water cage is significantly reduced after replacement, the water molecules in the cage still have difficulty jumping over the free energy barrier compared with the thermal motion energy, so the water cage structure remains highly stable.

Self-Assembly of Switchable Protein Nanocages via Allosteric Effect

Protein cages have promising applications in highly efficient gene transportation. Many methods of engineering protein–interface interactions have been developed to build such viral mimics. Missing...

A Study on the Minimization of Mooring Load in Fish-Cage Mooring Systems with a Damping Buoy

This study established the conditions in which mooring load is minimized in a fish cage that includes a damping buoy in specific wave conditions. To derive these conditions, numerical simulations of various mooring contexts were conducted on a fish cage (1/15 scale) using a simplified mass-spring model and fifth-order Stokes wave theory. The simulation conditions were as follows: (1) bridle-line length of 0.8–3.2 m; (2) buoyancy of 2.894–20.513 N for the damping buoy; and (3) mooring-rope thickness of 0.002–0.004 m. The wave conditions were 0.333 m in height and 1.291–2.324 s of arrival period. Consequently, the mooring tensions tended to decrease with decreasing mooring line thickness and increasing bridle-line length and buoyancy of the buoy. Accordingly, it was assumed to be advantageous to minimize the mooring tension by designing a thin mooring line and long bridle line and for the buoyancy of the buoy to be as large as possible. This approach shows a valuable technique because it can contribute to the improvement of the mooring stability of the fish cage by establishing a method that can be used to minimize the load on the mooring line.

Molecular mechanism of the clathrate cage formation in structure-II cyclopentane hydrate: An ab initio study

To understand the nucleation mechanism and formation process of CP hydrate cage, the structure and stability of CP hydrate cage, the effect of CP molecule on gas molecules adsorption were studied by the method of ab initio molecular dynamics simulation. The results show that CP molecule prefers to be parallel to the water ring. One hexagonal face is formed as the cage precursor, and gradually develop into a complete 51264 cage. The stabilization energy and interaction energy increase with the increasing water molecules, and the gas molecules have little influence on the stability of the clathrate cage.

Structure and redox tuning of gas adsorption properties in calixarene-supported Fe(ii)-based porous cages.

We describe the synthesis of Fe(ii)-based octahedral coordination cages supported by calixarene capping ligands. The most porous of these molecular cages has an argon accessible BET surface area of 898 m2 g−1 (1497 m2 g−1 Langmuir). The modular synthesis of molecular cages allows for straightforward substitution of both the bridging carboxylic acid ligands and the calixarene caps to tune material properties. In this context, the adsorption enthalpies of C2/C3 hydrocarbons ranged from −24 to −46 kJ mol−1 at low coverage, where facile structural modifications substantially influence hydrocarbon uptakes. These materials exhibit remarkable stability toward oxidation or decomposition in the presence of air and moisture, but application of a suitable chemical oxidant generates oxidized cages over a controlled range of redox states. This provides an additional handle for tuning the porosity and stability of the Fe cages.

Au42N20: A Stable Aromatic Deltoidal Hexecontahedron Molecule

A stable hollow cage, which contains 42 gold atoms and 20 nitrogen atoms, has been investigated using first-principles studies. This Au42N20 cage has an Ih group symmetry and a shape like Catalan deltoidal hexecontahedron. Molecular dynamics simulations demonstrate that the Au42N20 cage retains its geometric topology up to about 1317 K. Vibrational frequency analysis with no imaginary frequencies also emphasizes the stability of the Au42N20 molecule. The analysis for the bonding characteristic and electronic structure show that the p–d hybridization near the Fermi level is the key to the stability of the Au42N20 cage. The large negative nucleus-independent chemical shift value demonstrates its strong aromaticity. This stable cage-like Au42N20 structure with high surface area may have potential applications in catalysis.

Strain Release of Fused Pentagons in Fullerene Cages by Chemical Functionalization.

According to the isolated pentagon rule (IPR), for stable fullerenes, the 12 pentagons should be isolated from one another by hexagons, otherwise the fused pentagons will result in an increase in the local steric strain of the fullerene cage. However, the successful isolation of more than 100 endohedral and exohedral fullerenes containing fused pentagons over the past 20 years has shown that strain release of fused pentagons in fullerene cages is feasible. Herein, we present a general overview on fused-pentagon-containing (i.e. non-IPR) fullerenes through an exhaustive review of all the types of fused-pentagon-containing fullerenes reported to date. We clarify how the strain of fused pentagons can be released in different manners, and provide an in-depth understanding of the role of fused pentagons in the stability, electronic properties, and chemical reactivity of fullerene cages.

(Invited) New Advances in Magnetic Properties of Endohedral Metallofullerenes

An ongoing quest for lanthanide single molecule magnets (SMMs) operating at ever higher temperatures resulted in an impressive progress over the last two decades. On the next step from fundamental research to prospective applications, i.e. as components of spintronic devices, one has to consider stability and processability of SMM materials. Air-stability, thermal stability, ability to form thin molecular layers on different substrates are among the critical issues to be addressed. Encapsulation of magnetic species within robust molecular containers appears to be a natural route towards SMMs fulfilling required stability criteria. Chemical and thermal stability of carbon cages, fullerenes, makes them perfectly suitable for this goal. Fullerenes can encapsulate up to four metal atoms within their inner space, and a number of lanthanide EMFs was found to show SMM behavior. Besides, EMF-SMMs can form monolayers by sublimation or by self-assembly from solution, and such monolayers retain their SMM properties on metallic substrates. In this contribution we will highlight recent developments in the field of lanthanide-EMFs with peculiar magnetic properties.

(Invited) Electronic Structure and Properties of Boron-Doped Endohedral Metalloheterofullerenes

Since the discovery of buckminsterfullerene in 1985,1 intensive research has been devoted to this family of closed-cage carbon nanostructures. Endohedral metallofullerene La@C60 was already detected the same year and La@C82 was isolated few years later.2 In 1999, the synthesis, isolation and characterization of the first clusterfullerene Sc3N@C80 using the Krätschmer-Huffman method was a milestone in the field of endohedral metallofullerenes (EMF).3 The characteristic structural and electronic properties of EMFs, as well as their reactivity, have been extensively analyzed by experimental and theoretical groups.4 In particular, different rules to predict the relative stability of fullerene cages, based on the ionic model, were proposed.5 A different way to modify the properties of fullerenes is by replacing a carbon atom in the caged network with a heteroatom. The resulting heterofullerene shows distinct electronic structure and, therefore, properties from the all-carbon cage precursor. Nitrogen-doped heterofullerenes have received much more attention and investigation than boron-doped heterocages.6 Few years ago, Dunk et al. reported facile gas-phase formation of C59B by atom exchange resulting from exposure of C60 to boron vapor by means of a pulsed laser vaporization cluster source, which was the first report of borafullerene formation directly from pristine C60.7 Recent application of this technique to endohedral monometallofullerenes and clusterfullerenes at the National High Magnetic Field Laboratory in Florida lead to the formation of boron-doped EMFs with exciting electronic properties. We here analyze the characteristic electronic structure of observed B-doped metalloheterofullerenes, rationalize their stabilities and discuss about their properties. References Kroto, H. W.; Heath, J. R.; O’Brien, S. C.; Curl, R. F.; Smalley, R. E. Nature 1985, 318, 162-163.a) Heath, J. R.; O’Brien, S. C.; Zhang, Q.; Liu, Y.; Curl, R. F.; Kroto, H. W.;Tittel, F. K.; Smalley, R. E. J. Am. Chem. Soc. 1985, 107, 7779-7780; (b) Chai, Y.; Cuo, T.; Jin, C.; Haufler, R. E.; Felipe Chibante, L. P.; Fure, J.; Wang, L.; Alford, J. M.; Smalley, R. E. J. Phys. Chem. 1991, 95, 7564-7568.Stevenson, S.; Rice, G.; Glass, T.; Harich, K.; Cromer, F.; Jordan, M. R.; Craft, J.; Hadju, E.; Bible, R.; Olmstead, M. M.; Maitra, K.; Fisher, A. J.; Balch, A. L.; Dorn, H. C., Nature 1999, 401, 55.a) Rodríguez-Fortea, A.; Balch, A. L.; Poblet, J. M. Chem. Soc. Rev. 2011, 40, 3551-3563; b) Popov, A. A.; Yang, S.; Dunsch, L. Chem. Rev. 2013, 113, 5989-6113.a) Rodríguez-Fortea, A.; Alegret, N.; Balch, A. L.; Poblet, J. M., Nature Chem. 2010, 2, 955-961; b) Garcia-Borràs M., Osuna S., Swart M., Luis J.M., Solà M. Angew. Chem. Int.. Ed. 2013, 52, 9275-9278; c) Wang, Y.; Díaz-Tendero, S.; Martín, F. and Alcamí, M. J. Am. Chem. Soc., 2016, 138, 1551-1560.Lamparth, I.; Nuber, B.; Schick, G.; Skiebe, A.; Grosser, T.; Hirsch, A. Angew. Chem. Int. Ed. Engl. 1995, 34, 2257.Dunk, P. W.; Rodríguez-Fortea, A.; Kaiser, N. K.; Shinohara, H.; Poblet, J. M.; Kroto, H. W. Angew. Chem. Int. Ed. 2013, 52, 315-319.

New insights into methane hydrate dissociation: Utilization of molecular dynamics strategy

Hydrate reserves play a crucial role in energy storage and resources across the world. Gas hydrate formation may lead to various forms of blockages in oil/gas production and transportation processes, resulting in high capital and operating costs. Hence, it is important to determine the methane hydrate formation conditions and to understand the vital process and thermodynamic parameters. In this study, molecular dynamic (MD) simulations are conducted to investigate the microscopic mechanisms/phenomena and intermolecular forces involved in methane hydrate decomposition, where molecular interactions, structures, and behaviours need to be appropriately determined/selected. Through a systematic parametric sensitivity analysis, the impacts of temperature, pressure, and cage occupancy on hydrate dissociation are studied. Furthermore, the diffusion coefficient, density, and heat capacity of the methane hydrates are determined by employing MD strategy. The stability of water cages is examined at various decomposition times, temperatures, and pressures. According to the radial distribution function and mean square displacement of oxygen-oxygen and carbon-carbon atoms, the stability of hydrate cages decreases with increasing temperature, while it increases with increasing the cage occupancy and pressure. The addition of inhibitors (e.g., methanol) to small cavities in the hydrate structure creates new hydrogen bonds between the water and inhibitor molecules in the cages, accelerating the decomposition of hydrates. A good agreement is noticed between the outcomes of this research work and the results obtained in experimental and theoretical studies available in the literature. Analysing the outcome of the present and previous research works, the current study provides new reliable/logical information on the molecular level of the hydrate dissociation process. It is expected that such a research investigation offers effective tips/guidelines to deal with hydrate formation and dissociation in terms of utilization, prevention, and processing.

Stability, electronic and optical properties of the boron nitride cage (B47N53) from quantum mechanical calculations

The structural, electronic and optical properties of an isomer proposed for the boron nitride cage (BN; BxNy; x = 47, y = 53) in the gas phase were carried out by means of DFT calculations. The results of the quantum simulations indicate there is not magnetism associated to the stable structure with neutral charge. However, the system exhibits a high cohesion energy (−6.08 eV/atom), this feature is relating to its high chemical stability. The quantum descriptors indicate a moderate polarity, low chemical reactivity as well as low work function for this nano-cage. This system has electronic behavior like-conductor, opposite to others BN nanostructures. On the other hand, the electronic absorption spectrum was obtained using six density functionals under the formalism of the time-dependent DFT and show a good agreement with the experimental data, these calculations reveal a strong absorption band at ≈ 260 nm in the UV region. The natural transition orbitals suggest an intramolecular charge transfer inside of BN cage, and the laplacian of the electron density evaluated in the bond critical points confirms that the cage is stabilized by the presence of homo-nuclear bonds BB and NN.