Assembly Disassembly Research Articles

A side-by-side capillaries-based microfluidic system for synthesizing size- and morphology-controlled magnetic anisotropy janus beads

With two segments having different chemical or physical properties, janus particles have gained widespread attention in recent years. A fast assembly–disassembly side-by-side capillaries-based microfluidic system was designed for rapid and easy generation of janus particles with magnetic anisotropic properties. Two immiscible organic phases, among which one contained magnetic particles, were emulsified by a stream of an aqueous phase into janus droplets formed at capillaries’ tips and transported after break-up by the continuous aqueous phase in an outlet tubing. Then upon downstream UV irradiation, droplets were hardened into solid janus microparticles containing magnetic particles in one of their two segments. By changing the flow rates of organic and aqueous phases, not only the overall size of janus particles but also the relative volume of the two hemispherical segments could be controlled. Generated janus particles were proved having magnetic anisotropy by their forced-driven rotation in an external magnetic field, which makes them potentially interesting materials in chemical and biomedical applications.

Synthesis of size-controlled Pt/C/PTFE hydrophobic catalyst pellets in a capillary-based microfluidic system

The size-controlled Pt/C/PTFE hydrophobic catalyst pellets employed in the hydrogen–water isotope exchange reaction were prepared using microfluidic technology. An assembly–disassembly capillary-based microfluidic system was demonstrated for easy fabrication of narrow size-distribution catalyst beads (CV ＜ 5%), and the size of the beads were precisely controlled in the range of 150–1500 μm by manipulating the flow rate of the disperse and continuous phase, as well as the continuous phase viscosity. Approximately 3 nm platinum nanoparticles with uniform dispersion in a porous PTFE/C support were synthesized by γ-ray-induced reduction without using any chemical reducing agents. Polyvinyl alcohol (PVA) was introduced as both a solidified agent and porogen in the fabrication process. The porosity of the as-prepared catalyst pellets were characterized using a scanning electron microscope (SEM) and a BET instrument, and the hydrophobicity of the catalyst was examined by observation of the contact angle between water and the surface of the catalyst beads.

The ADOR synthesis of new zeolites: In silico investigation

Recently, a new strategy for the zeolite synthesis was proposed and successfully applied for several systems. This strategy, called ADOR (assembly–disassembly–organization–reassembly), can lead to synthesis of many new materials with defined structure and porosity. Proposed hypothetical structures of the UTL, IWW, IWV, IWR, ITH and ITR families are investigated using empirical and DFT calculations with focus on the relationship between their structure and target synthesis feasibility.

Key Interactions for Clathrin Coat Stability

Clathrin-coated vesicles are major carriers of vesicular traffic in eukaryotic cells. This endocytic pathway relies on cycles of clathrin coat assembly and Hsc70-mediated disassembly. Here we identify histidine residues as major determinants of lattice assembly and stability. They are located at the invariant interface between the proximal and distal segments of clathrin heavy chains, in triskelions centered on two adjacent vertices of the coated-vesicle lattice. Mutation of these histidine residues to glutamine alters the pH dependence of coat stability. We then describe single-particle fluorescence imaging experiments in which we follow the effect of these histidine mutations on susceptibility to Hsc70-dependent uncoating. Coats destabilized by these mutations require fewer Hsc70 molecules to initiate disassembly, as predicted by a model in which Hsc70 traps conformational distortions during the auxilin- and Hsc70:ATP-mediated uncoating reaction.

Disassembly Modeling Method for Complex Products Based on Connector Structure Units

In the light of the limitation of traditional disassembly modeling methods for complex product, a novel disassembly modeling method for design for disassembly(DFD) based on connector structure units is presented. The parts combination connected by physical, chemical or mechanical method is defined as connection structure unit. Thus, the product is mapped into the organic combination of connection structure units. The disassembly precedence rules are extracted by analyzing the disassembly knowledge and experience of connection structure units. In addition, the extension matter-element model of connection structure unit is constructed to describe its disassembly knowledge. To describe the assembly constraints and disassembly precedence between components of product, the disassembly multi-constrained graph model(DMCGM) is defined. The DMCGM is deduced fast based on reuse of connection structure units, which could eliminate uncommon or unrealistic solutions for subsequent disassembly sequence planning. A mould clamping device of injection molding machine case study proves the validity and feasibility of the proposed method.

Voltage-responsive micelles based on the assembly of two biocompatible homopolymers

Voltage stimulus is considered as a clean and simple method in the field of stimuli-responsive polymer systems, in which the system based on β-cyclodextrin (β-CD) and ferrocene (Fc) has attracted considerable attention. Herein, we report voltage-responsive micelles based on the assembly of two biocompatible homopolymers, namely, the poly(ethylene glycol) homopolymer modified with β-CD (PEG–β-CD) and the poly(L-lactide) homopolymer modified with Fc (PLLA–Fc). Through host–guest interactions between β-CD and Fc, the two homopolymers connect together, forming a non-covalent supramolecular block copolymer PLLA–Fc/PEG–β-CD. PLLA–Fc/PEG–β-CD can further self-assemble to form stable micelles in aqueous solution. Through electrochemical control, a reversible assembly–disassembly transition of this micellar system was realized. Voltage-controlled drug release based on this system was also conducted successfully.

The Isolation of Single MMX Chains from Solution: Unravelling the Assembly–Disassembly Process

Herein, we provide a systematic theoretical and experimental study of the structural and optical properties of MMX (M=metal, X=halide) chains. The influence of solvent, temperature, and concentration has been analyzed to find suitable parameters for initial building-block associations in solution. By using density functional calculations, we have computed the dissociation energy of different MMX oligomers (up to the tetramer) in the gas phase. On the basis of these findings, we discuss the most likely disassembly scenario and propose a new interpretation of these compounds. We also calculated the charge redistribution that occurs upon MM+XMMX binding in vacuum. Time-dependent density functional theory (TDDFT) is used to calculate the UV/visible spectra of different MMX chains up to the tetramer in the gas phase. The implications of these theoretical findings in the analysis of our experiments are discussed in the text. The overall body of data presented suggests a new way of looking at such linear structures. By taking into account these new data, we have been able to isolate single/few MMX chains on mica.

Poly(d-glucose carbonate) Block Copolymers: A Platform for Natural Product-Based Nanomaterials with Solvothermatic Characteristics

A natural product-based polymer platform, having the characteristics of being derived from renewable materials and capable of breaking down, ultimately, into natural byproducts, has been prepared through the ring-opening polymerization (ROP) of a glucose-based bicyclic carbonate monomer. ROP was carried out via chain extension of a polyphosphoester (PPE) macroinitiator in the presence of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) organocatalyst to afford the PPE-b-poly(D-glucose carbonate) (PDGC) block copolymer. This new copolymer represents a functional architecture that can be rapidly transformed through thiol-yne reactions along the PPE segment into a diverse variety of amphiphilic polymers, which interestingly display stimuli-sensitive phase behavior in the form of a lower critical solution temperature (LCST). Below the LCST, they undergo self-assembly to form spherical core-shell nanostructures that display a poorly defined core-shell morphology. It is expected that hydrophobic patches are exposed within the micellar corona, reminiscent of the surface complexity of proteins, making these materials of interest for triggered and reversible assembly disassembly processes.

Identification of the lamin A/C phosphoepitope recognized by the antibody P-STM in mitotic HeLa S3 cells

BackgroundLamins A and C, two major structural components of the nuclear lamina that determine nuclear shape and size, are phosphoproteins. Phosphorylation of lamin A/C is cell cycle-dependent and is involved in regulating the assembly–disassembly of lamin filaments during mitosis. We previously reported that P-STM, a phosphoepitope-specific antibody raised against the autophosphorylation site of p21-activated kinase 2, recognizes a number of phosphoproteins, including lamins A and C, in mitotic HeLa cells.ResultsHere, using recombinant proteins and synthetic phosphopeptides containing potential lamin A/C phosphorylation sites in conjunction with in vitro phosphorylation assays, we determined the lamin A/C phosphoepitope(s) recognized by P-STM. We found that phosphorylation of Thr-19 is required for generating the P-STM phosphoepitope in lamin A/C and showed that it could be created in vitro by p34cdc2/cyclin B kinase (CDK1)-catalyzed phosphorylation of lamin A/C immunoprecipitated from unsynchronized HeLa S3 cells. To further explore changes in lamin A/C phosphorylation in living cells, we precisely quantified the phosphorylation levels of Thr-19 and other sites in lamin A/C isolated from HeLa S3 cells at interphase and mitosis using the SILAC method and liquid chromatography-tandem mass spectrometry. The results showed that the levels of phosphorylated Thr-19, Ser-22 and Ser-392 in both lamins A and C, and Ser-636 in lamin A only, increased ~2- to 6-fold in mitotic HeLa S3 cells.ConclusionsCollectively, our results demonstrate that P-STM is a useful tool for detecting Thr-19-phosphorylated lamin A/C in cells and reveal quantitative changes in the phosphorylation status of major lamin A/C phosphorylation sites during mitosis.

Activation loop phosphorylation of a protein kinase is a molecular marker of organelle size that dynamically reports flagellar length

Specification of organelle size is crucial for cell function, yet we know little about the molecular mechanisms that report and regulate organelle growth and steady-state dimensions. The biflagellated green alga Chlamydomonas requires continuous-length feedback to integrate the multiple events that support flagellar assembly and disassembly and at the same time maintain the sensory and motility functions of the organelle. Although several length mutants have been characterized, the requisite molecular reporter of length has not been identified. Previously, we showed that depletion of Chlamydomonas aurora-like protein kinase CALK inhibited flagellar disassembly and that a gel-shift-associated phosphorylation of CALK marked half-length flagella during flagellar assembly. Here, we show that phosphorylation of CALK on T193, a consensus phosphorylation site on the activation loop required for kinase activity, is distinct from the gel-shift-associated phosphorylation and is triggered when flagellar shortening is induced, thereby implicating CALK protein kinase activity in the shortening arm of length control. Moreover, CALK phosphorylation on T193 is dynamically related to flagellar length. It is reduced in cells with short flagella, elevated in the long flagella mutant, lf4, and dynamically tracks length during both flagellar assembly and flagellar disassembly in WT, but not in lf4. Thus, phosphorylation of CALK in its activation loop is implicated in the disassembly arm of a length feedback mechanism and is a continuous and dynamic molecular marker of flagellar length during both assembly and disassembly.

Virtual assembly modeling method of disassembly process based on matrix calculation

There are many defects in the existing assembly modeling method such as large information redundancy or complex modeling process when descripting the disassembly process of virtual maintenance training system.A modeling method for virtual maintenance's disassembly process was proposed in the paper based on researching the existing assembly modeling methods and analyzing the different between assembly process and disassembly process.In this method,the matrix was used to describe the assembly model and the matrix calculation was used to describe the parts'disassembly process,so the modeling process was simplified and the model's data was reduced.It is a new idea and method for constructing the virtual maintenance training system.

Building professionals’ attitudes towards the use of wood in building design and construction in Taiwan

This study aims to analyse the attitudes of building professionals towards the use of wood in building design and construction in Taiwan, and to investigate how professionals’ backgrounds affect their attitudes upon the wood usage using statistical analysis. 123 valid questionnaires were collected from various building professionals, including architecture students, architects, interior designers and building construction engineers. It has been shown that wood is regarded as the most environmentally-friendly material in building design and construction. ‘Beauty’ and ‘proprietor’ are the most two essential factors identified by professionals that may influence their decisions to use wood, whereas the deconstruction phase and post-use of demolished wood are considered less important. With respect to the wood utilisation in construction, building professionals prefer using wood in the substructure to main structure at present. On the other hand, the differences between professionals’ experience in designing wood houses or wood elements, and their attitudes towards the importance of reasons in using wood are generally insignificant, except for the easy assembly (p = 0.03) and easy disassembly (p = 0.02) of wood construction. Professionals in favour of wood substitution are more likely to choose wood in column, beam, window, outdoor wall and door. Moreover, there are significant differences between professionals’ occupations and their opinions upon the recyclability issues of materials (p = 0.02). In the future, more sufficient communications are required through the design process among various professional groups.

A novel method for purification of polymerizable tubulin with a high content of the acetylated isotype

Tubulin can be acetylated/deacetylated on Lys40 of the α-subunit. Studies of the post-translational acetylation/deacetylation of tubulin using biochemical techniques require tubulin preparations that are enriched in AcTubulin (acetylated tubulin) and (for comparison) preparations lacking AcTubulin. Assembly-disassembly cycling of microtubules gives tubulin preparations that contain little or no AcTubulin. In the present study we demonstrated that this result is owing to the presence of high deacetylating activity in the extracts. This deacetylating activity in rat brain homogenates was inhibited by TSA (Trichostatin A) and tubacin, but not by nicotinamide, indicating that HDAC6 (histone deacetylase 6) is involved. TSA showed no effect on microtubule polymerization or depolymerization. We utilized these properties of TSA to prevent deacetylation during the assembly-disassembly procedure. The effective inhibitory concentration of TSA was 3 μM in the homogenate and 1 μM in the subsequent cycling steps. By comparison with immunopurified AcTubulin, we estimated that ~64% of the tubulin molecules in the three cycled preparations were acetylated. The protein profiles of these tubulin preparations, as assessed by SDS/PAGE and Coomassie Blue staining, were identical to that of a preparation completely lacking AcTubulin obtained by assembly-disassembly cycles in the absence of TSA. The tyrosination state and in vitro assembly-disassembly kinetics were the same regardless of the degree of acetylation.

Novel dual-functional regulation of a chair-like antiparallel G-quadruplex inducing assembly–disassembly of a cyanine dye

Biomolecules are promising templates that play important roles in controlling the supramolecular assembly process more flexibly and precisely due to their unique characteristic structures. Here we first present a G-quadruplex with a chair-like antiparallel motif as a novel dual-functional regulation template in the aggregation of a cyanine dye.

Reversible luminescence switching accompanied by assembly–disassembly of metallosupramolecular amphiphiles based on a platinum(ii) complex

The electrostatic self-assembly of anionic surfactants with a cationic platinum(II) complex bearing triethylene glycol leads to the formation of metallosupramolecular amphiphiles with rod- and sheet-like aggregates in aqueous solutions. The resulting solutions show strong luminescence enhancement, which can decrease back to the original emissive intensity of the platinum(II) complex by disassembling the aggregates through host–guest recognition with α-cyclodextrin. Both the self-assembly and disassembly processes are monitored in real time by UV-vis absorption and emission spectra and dynamic light scattering. The critical aggregation concentrations are determined by concentration-dependent measurements of emission spectra and dynamic light scattering. The present study provides an efficient and convenient strategy to fabricate dynamic metallosupramolecular amphiphiles with controllable photophysical properties.

Assembly–disassembly driven “off–on” fluorescent perylene bisimide probes for detecting and tracking of proteins in living cells

We have developed an assembly–disassembly driven “off–on” fluorescent bioprobe based on amphiphilic perylene bisimide. In aqueous solutions, the amphiphilic probes can form self-assembled nanostructures with quenched fluorescence. These probes could then be disassembled by the binding of the probes to the targeted proteins, and the disassembly process leads to a 23-fold enhancement in fluorescence intensity. Amphiphilic perylene bisimides could be used as probes for the detection and tracking of targeted proteins under live cell conditions.

Synthesis of rhombic hierarchical YF3 nanocrystals and their use as upconversion photocatalysts after TiO2 coating

A facile method has been developed to synthesize uniform nanoscale YF3 architectures. Interestingly, the unique YF3 nanostructure exhibits a flat and rhombic appearance which is formulated through the hierarchical assembly of YF3 nanocrystals along a specific crystalline orientation. Investigations on the formation process suggest that an assembly disassembly process is responsible for the construction of this novel structure. Enabled by doping with different lanthanides ions, the products can exhibit various down- or up-conversion luminescences, showing their potentials in serving as versatile host matrixes. The tunable luminescent properties allow designing effective upconversion photocatalysts when the doped YF3 nanostructures are coated with a TiO2 shell on their surface. In particular, the YF3@TiO2 hybrid structures have the porous nature that is partially inherited from the YF3 architectures, whose high surface-to-volume ratio facilitates their use as photocatalysts. In this article, we have demonstrated that the YF3:Yb,Tm@TiO2 structures exhibit satisfactory photocatalytic activities under the irradiation of both UV and near IR light. As compared with the conventional TiO2 catalysts, the hybrid structures here offer better performance in photocatalysis in the full solar spectrum. It is anticipated that this work provides a new approach to designing photocatalysts with responses to a broader spectral range.

Structural Basis for dsRNA Recognition, Filament Formation, and Antiviral Signal Activation by MDA5

MDA5, a viral double-stranded RNA (dsRNA) receptor, shares sequence similarity and signaling pathways with RIG-I yet plays essential functions in antiviral immunity through distinct specificity for viral RNA. Revealing the molecular basis for the functional divergence, we report here the crystal structure ofMDA5 bound to dsRNA, which shows how, using the same domain architecture, MDA5 recognizes the internal duplex structure, whereas RIG-I recognizes the terminus of dsRNA. We further show that MDA5 uses direct protein-protein contacts to stack along dsRNA in a head-to-tail arrangement, and that the signaling domain (tandem CARD), which decorates the outside of the core MDA5 filament, also has an intrinsic propensity to oligomerize into an elongated structure that activates the signaling adaptor, MAVS. These data support a model in which MDA5 uses long dsRNA as a signaling platform to cooperatively assemble the core filament, which in turn promotes stochastic assembly of the tandem CARD oligomers for signaling.

Lysophosphatidylcholine inhibits membrane-associated SNARE complex disassembly.

In cells, N-ethylmaleimide-sensitive factor (NSF) attachment protein receptors called SNAREs are involved in membrane fusion. In neurons, for example, target membrane proteins SNAP-25 and syntaxin called t-SNAREs present at the pre-synaptic membrane, and a synaptic vesicle-associated membrane protein (VAMP) or v-SNARE, is part of the conserved protein complex involved in neurotransmission. Cholesterol and LPC (L-α-lysophosphatidylcholine) are known to contribute to the negative and positive curvature respectively of membranes. In this study, using purified recombinant neuronal membrane-associated SNAREs, we demonstrate for the first time that membrane-curvature-influencing lipids profoundly influence SNARE complex disassembly. Exposure of cholesterol-associated t-SNARE and v-SNARE liposome mixtures to NSF–ATP results in dissociated vesicles. In contrast, exposure of LPC-associated t-SNARE and v-SNARE liposome mixtures to NSF–ATP, results in inhibition of t-/v-SNARE disassembly and the consequent accumulation of clustered vesicles. Similarly, exposure of isolated rat brain slices and pancreas to cholesterol or LPC, also demonstrates LPC-induced inhibition of SNARE complex disassembly. Earlier studies demonstrate a strong correlation between altered plasma LPC levels and cancer. The altered plasma LPC levels observed in various cancers may in part contribute to defects in SNARE assembly–disassembly and membrane fusion, consequently affecting protein maturation and secretion in cancer cells.

Spatiotemporal regulation of Src and its substrates at invadosomes

In the past decade, substantial progress has been made in understanding how Src family kinases regulate the formation and function of invadosomes. Invadosomes are organized actin-rich structures that contain an F-actin core surrounded by an adhesive ring and mediate invasive migration. Src kinases orchestrate, either directly or indirectly, each phase of the invadosome life cycle including invadosome assembly, maturation and matrix degradation and disassembly. Complex arrays of Src effector proteins are involved at different stages of invadosome maturation and their spatiotemporal activity must be tightly regulated to achieve effective invasive migration. In this review, we highlight some recent progress and the challenges of understanding how Src is regulated temporally and spatially to orchestrate the dynamics of invadosomes and mediate cell invasion.