Ladder-like Architecture Research Articles

FOXP3 recognizes microsatellites and bridges DNA through multimerization

FOXP3 is a transcription factor that is essential for the development of regulatory T cells, a branch of T cells that suppress excessive inflammation and autoimmunity1–5. However, the molecular mechanisms of FOXP3 remain unclear. Here we here show that FOXP3 uses the forkhead domain—a DNA-binding domain that is commonly thought to function as a monomer or dimer—to form a higher-order multimer after binding to TnG repeat microsatellites. The cryo-electron microscopy structure of FOXP3 in a complex with T3G repeats reveals a ladder-like architecture, whereby two double-stranded DNA molecules form the two ‘side rails’ bridged by five pairs of FOXP3 molecules, with each pair forming a ‘rung’. Each FOXP3 subunit occupies TGTTTGT within the repeats in a manner that is indistinguishable from that of FOXP3 bound to the forkhead consensus motif (TGTTTAC). Mutations in the intra-rung interface impair TnG repeat recognition, DNA bridging and the cellular functions of FOXP3, all without affecting binding to the forkhead consensus motif. FOXP3 can tolerate variable inter-rung spacings, explaining its broad specificity for TnG-repeat-like sequences in vivo and in vitro. Both FOXP3 orthologues and paralogues show similar TnG repeat recognition and DNA bridging. These findings therefore reveal a mode of DNA recognition that involves transcription factor homomultimerization and DNA bridging, and further implicates microsatellites in transcriptional regulation and diseases.

Double-stranded surface-grafted polymer brushes with ladder-like architecture

This feature paper focuses on recently introduced double-stranded surface-grafted polymer brushes with ladder-like architecture, the method of their synthesis, self-templating surface-initiated polymerization (ST-SIP), as well as their unique properties. ST-SIP synthetic approach is based on a sequential polymerization of a bifunctional monomer leading to formation of multimonomer chains in the first step followed by a second polymerization producing ladder-like structures. This approach was developed primarily for conjugated polymer brushes, which synthesis using other methods is challenging. Such brushes enable anisotropic conductance at the nanometer scale that is highly demanded for e.g., photovoltaic and optoelectronic applications. ST-SIP was applied to form ladder-like brushes containing polyacetylene, polythiophene and polyethynylpyridine conjugated chains arranged normally to the grafting surface and exhibiting high electrical conductance as measured using conductive atomic force microscopy. The conjugated chains were shown to exhibit long term stability that is one of the crucial benefit of this novel brush topology. The nanomechanical characterization revealed enhanced stiffness and high elasticity of the ladder-like structures compared to the parent single-stranded brushes. The double-stranded brush topology due to anisotropic conductance, unique nanomechanical properties and versatility of ST-SIP approach, have a high potential for fabrication of robust nanocoating for tailoring (bio)interafaces.

Efficient Mechanical Stress Transfer in Multilayer Graphene with a Ladder-like Architecture.

We report that few graphene flakes embedded into polymer matrices can be mechanically stretched to relatively large deformation (>1%) in an efficient way by adopting a particular ladder-like morphology consisting of consecutive mono-, bi-, tri-, and four-layer graphene units. In this type of flake architecture, all of the layers adhere to the surrounding polymer inducing similar deformation on the individual graphene layers, preventing interlayer sliding and optimizing the strain transfer efficiency. We have exploited Raman spectroscopy to quantify this effect from a mechanical standpoint. The finite element method and molecular dynamics simulations have been used to interpret the above experimental findings. The results suggest that a step pyramid-like architecture of a flake can be ideal for efficient loading of layered materials embedded into a polymer and that there are two prevailing mechanisms that govern axial stress transfer, namely, interfacial shear transfer and axial transmission through the ends. This concept can be easily applied to other two-dimensional materials and related van der Waals heterostructures fabricated either by mechanical exfoliation or chemical vapor deposition by appropriate patterning. This work opens new perspectives in numerous applications, including high volume fraction composites, flexible electronics, and straintronic devices.

Unraveling the nanomechanical properties of surface-grafted conjugated polymer brushes with ladder-like architecture

Surface-grafted polymer brushes with ladder-like architecture enforce extended conformation of the chains affecting their mechanical and tribological properties.

Unveiling the hybrid interface in polymer nanocomposites enclosing silsesquioxanes with tunable molecular structure: Spectroscopic, thermal and mechanical properties

Organic–inorganic nanobuilding blocks (NBBs) based on silsesquioxanes (SSQs) have potential applications as nanofillers, thermal stabilizers, and rheological modifiers, which can improve thermomechanical properties of polymer hosts. The possibility to tune both siloxane structure and pendant groups can promote compatibilization and peculiar interactions with a plethora of polymers. However, the control on SSQs molecular architecture and functionalities is usually delicate and requires careful synthetic details. Moreover, investigating the influence of NBBs loading and structure on the hybrid interface and, in turn, on the polymer chains mobility and mechanical properties, may be challenging, especially for low-loaded materials.Herein, we describe the preparation and characterization of polybutadiene (PB) nanocomposites using as innovative fillers thiol-functionalized SSQs nanobuilding blocks (SH-NBBs), with both tailorable functionality and structure. Swelling experiments and, more clearly, solid-state NMR, enlightened a remarkable effect of SH-NBBs on the molecular structure and mobility of the polymeric chains, envisaging the occurrence of chemical interactions at the hybrid interface. Finally, thermal and DMTA analyses revealed that nanocomposites, even containing very low filler loadings (i.e. 1, 3 wt%), exhibited enhanced thermomechanical properties, which seem to be connected not only to the loading, but also to the peculiar cage or ladder-like architecture of SH-NBBs.

Photoactive Surface‐Grafted Polymer Brushes with Phthalocyanine Bridging Groups as an Advanced Architecture for Light‐Harvesting

Surface-grafted polymer brushes of novel ladder-like architecture were proposed for inducing ordering of chromophores embedded therein. The brushes with acetylene side groups were obtained by surface-initiated photoiniferter-mediated polymerization. The acetylene moieties reacted then through a "click" process with an axially azide-bifunctionalized silicon phthalocyanine bridging the neighboring chains that inherently adopt extended conformations in dense brushes. FTIR, quartz crystal microbalance, and atomic force microscopy were used to study formation and structure of the photoactive brushes varying in grafting densities. Importantly, photophysical properties of the chromophores were virtually unaffected upon embedding them into the brushes, as evidenced by UV/Vis absorption and emission spectroscopy. Owing to the unique ordering of the chromophores, the proposed method may open new opportunities for the fabrication of light-harvesting systems suitable for photovoltaic or sensing applications.

Ladder-like polyacetylene with excellent optoelectronic properties and regular architecture.

Novel double-stranded polyacetylene with a perylene bisimide bridge has been efficiently synthesized by metathesis cyclopolymerization of bis(1,6-heptadiyne) derivatives, and exhibited good solubility, highly thermal and oxidative stability, low LUMO energy levels, narrow bandgaps, and regular ladder-like architecture.

Numerical simulation of the remodelling process of trabecular architecture around dental implants

Dental implants may alter the mechanical environment in the jawbone, thereby causing remodelling and adaptation of the surrounding trabecular bone tissues. To improve the efficacy of dental implant systems, it is necessary to consider the effect of bone remodelling on the performance of the prosthetic systems. In this study, finite element simulations were implemented to predict the evolution of microarchitecture around four implant systems using a previously developed model that combines both adaptive and microdamage-based mechano-sensory mechanisms in bone remodelling process. Changes in the trabecular architecture around dental implants were mainly focused. The simulation results indicate that the orientational and ladder-like architecture around the implants predicted herein is in good agreement with those observed in animal experiments and clinical observations. The proposed algorithms were shown to be effective in simulating the remodelling process of trabecular architecture around dental implant systems. In addition, the architectural features around four typical dental implant systems in alveolar bone were evaluated comparatively.

Thermolysis of new hybrid silsesquioxane–carbosilane materials

Thermal decomposition of new silsesquioxane materials [(Me 3Si) 3CSiMe 2CH 2CH 2SiO 3/2] n (PT SiSS), substituted with sterically hindered carbosilane groups, was studied in an inert atmosphere (N 2) and air. It was found that a specific degradation of carbosilane moieties occurs at high temperatures. A ceramic residue was obtained > 900 K both in nitrogen (Si x O y C z ) and air (Si x O y ). Thermal rearrangements in the structure of polyhedral and ladder-like PT SiSS were studied, and related to those observed for a polymethylsilsesquioxane resin (PMSS) of regular ladder-like architecture. Thermally induced transformations were evaluated by TGA(DTA)-MS, FTIR, NMR, XRD and SEM.

Fabrication and characterization of porous poly(l-lactide) scaffolds using solid–liquid phase separation

Freeze-extraction, which involves phase separation principle, gave highly porous scaffolds without the time and energy consuming freeze-drying process. The presented method eliminates the problem of formation of surface skin observed in freeze-drying methods. The effects of different freezing temperature (-80 and -24 degrees C), medium (dry ice/ethanol bath and freezer) and polymer concentrations (1, 3, and 5 wt.%) on the scaffold properties were investigated in connection with the porous morphology and physicomechanical characteristics of the final scaffolds. The FESEM micrographs showed porous PLLA scaffolds with ladder-like architecture. The size of the longitudinal pores was in the range of 20-40 microm and the scaffolds had high porosity values ranging from 90% to 98%. Variation in porosity, mechanical resistance, and degree of regularity in the spatial organization of pores were observed when polymer concentration was changed. More open scaffold architecture with enhanced pore interconnectivity was achieved when a dry ice/ethanol bath of -80 degrees C was used. Polymer concentration played an important role in fabricating highly porous scaffolds, with ladder-like architecture only appearing at polymer concentrations of above 3 wt.%. With the freeze-extraction method used here, highly porous and interconnected poly(L-lactide) scaffolds were successfully fabricated, holding great potential for tissue engineering applications.

2,2′-Bipyridine,1,10-phenanthroline and 2,2′:6′,2″-terpyridine in gallium(III) chemistry: Complexes containing the [formula omitted] core

The reactions of Ga(NO 3) 3 · 9H 2O with 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen) and 2,2′:6′,2″-terpyridine (terpy) in alcohols afford the complexes [Ga 2(OH) 2(bpy) 4](NO 3) 4 ( 1), [Ga 2(OH) 2(phen) 4](NO 3) 4 ( 2) and [Ga 2(OH) 2(H 2O) 2(terpy) 2](NO 3) 4 ( 3), respectively, in good yields. The crystal structures of 1 · 1.3MeOH · 1.4H 2O, 2 · 4.5MeOH and 3 have been solved by single-crystal X-ray crystallography. The three complexes contain the { Ga III 2 ( μ -OH ) 2 } 4 + core. Four nitrogen atoms from two chelating bpy ( 1) or phen ( 2) complete distorted octahedral coordination at each metal centre. In 3 one tridentate chelating terpy and one aquo ligand complete six coordination at each Ga III atom. The crystal structure of 2 · 4.5MeOH is stabilized by hydrogen bonds and intermolecular π–π stacking interactions, while in 3 hydrogen bonds create a double-chain, ladder-like architecture. Characteristic IR data are discussed in terms of the nature of bonding and the structures of the three complexes. The 1H NMR spectra of complexes 2 and 3 suggest the presence of the free ligand and one solution species containing the coordinated ligand. The structure of the cation [Ca 2(OH) 2(bpy) 4] 4+ is retained in D 2O as deduced by the 2D homonuclear COSY map.

Hydrothermal synthesis and characterization of a new inorganic–organic hybrid cadmium phosphate Cd(phen)(H 2PO 4) 2⋅H 2O

A new inorganic–organic hybrid solid, Cd(phen)(H 2PO 4) 2⋅H 2O (phen = 1,10-phenanthroline), has been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction, FTIR, elemental analysis, ICP analysis, powder X-ray diffraction and fluorescent spectrum. The compound crystallizes in the triclinic system, space group P-1 (No. 2), a = 6.8027 ( 3 ) Å , b = 11.0806 ( 4 ) Å , c = 12.1725 ( 5 ) Å , α = 63.8120 ( 10 ) ° , β = 81.043 ( 2 ) ° , γ = 86.935 ( 2 ) ° , V = 813.19 ( 6 ) Å 3 , Z = 2 . The structure is built from strictly alternating CdO 4N 2 octahedra and H 2PO 4 tetrahedra through their vertices, forming an infinite ladder-like architecture. This compound shows intense photoluminescence upon photoexcitation at 358 nm.

H-bonding assisted template synthesis of a novel ladder-like organo-bridged polymethylsiloxane

A novel soluble aryl amide-bridged ladder-like polymethylsiloxane (ALPS) was synthesized via a stepwise coupling polymerization by means of H-bonding self-assembling template. The new monomer N, N′-di(4-methyldiethoxysiloxyl-phenyl)-terephthaloyl amide, prepared by dehydrocoupling reaction of N, N′-di(4-hydroxy-phenyl)-terephthaloyl amide with methyldiethoxysilane, was hydrolyzed in a dilute solution at low temperature to form a proposed ladder-like supramolecular intermediate through amido H-bonding interaction, which was further condensed to form polymer ALPS using dibuthyltindilaurate as catalyst. A combination of techniques including 1H NMR, 29Si NMR, FTIR, X-ray diffraction (XRD), DSC, and light scattering were used to characterize the titled polymer ALPS. The results indicate the polymer ALPS possesses an ordered ladder-like architecture.

Hydrogen‐bonding‐aided synthesis of novel ladderlike organobridged polysiloxane containing side‐chain naphthyl groups

AbstractWith a hydrogen‐bonding template, a novel soluble aryl amide‐bridged ladderlike polysiloxane, containing naphthyl as the side‐chain group, has been successfully synthesized via a stepwise coupling polymerization. It is proposed that the monomer, N,N′‐di(3‐naphthyldiethoxylsilyl‐propyl)‐[4,4′‐oxybis(benzyl amide)], prepared by Grignard and hydrosilylation reactions, undergoes self‐assembly first via amido hydrogen bonding and then via hydrolysis, followed by condensation under controlled reaction conditions to yield a high molecular weight, soluble, dark yellow polymer. The analytical results (Fourier transform infrared, 1H NMR, 29Si NMR, X‐ray diffraction, differential scanning calorimetry, and vapor pressure osmometry) show that the polymer possesses an ordered ladderlike architecture. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 636–644, 2003