Kinetic Controlled Chirality Transfer and Induction in 2D Hydrogen-Bonding Assemblies of Glycylglycine on Au(111).

Chirality transfer is of vital importance that dominates the structure and functionality of biological systems and living matters. External physical stimulations, e.g. polarized light and mechanical forces, can trigger the chirality symmetry breaking, leading to the appearance of the enantiomeric entities created from a chiral self-assembly of achiral molecule. Here, several 2D assemblies with different chirality, synthesized on Au(111) surface by using achiral building blocks - glycylglycine (digly), the simplest polypeptide are reported. By delicately tuning the kinetic factors, i.e., one-step slow/rapid deposition, or stepwise slow deposition with mild annealing, achiral square hydrogen-bond organic frameworks (HOF), homochiral rhombic HOF and racemic rectangular assembly are achieved, respectively. Chirality induction and related symmetry broken in assemblies are introduced by the handedness (H-bond configurations in principle) of the assembled motifs and then amplified to the entire assemblies via the interaction between motifs. The results show that the chirality transfer and induction of biological assemblies can be tuned by altering the kinetic factors instead of applying external forces, which may offer an in-depth understanding and practical approach to peptide chiral assembly on the surfaces and can further facilitate the design of desired complex biomolecular superstructures.

Synthesis and Characterization of Fluorescence Active G4-Quartet and Direct Evaluation of Self-Assembly Impact on Emission.

Fluorescence (FL) active 8-aryl guanosine derivatives were prepared and applied for cation mediated self-assembly to form the H-bonded G8-quadruplexes. The p-cyano (p-CN) and 8-anthracene (8-An) substituted guanosines were identified to give the strongest fluorescence with the formation of G8-octamers (G8) both in solution (NMR) and solid state (X-ray). This well-defined G8-octamer system has provided the first direct evidence on the self-assembled G-quadruplex fluorescence emission with aggregation-induced emission (AIE), which could be applied as the foundation for FL molecular probe design toward G-quadruplex recognition.

Chain-Extending Polymerization for Significant Improvement in Organic Thin-Film Transistor Performance.

To achieve high-performance polymer semiconductors, it is crucially important to explore novel and effective synthesis strategies. Here, chain-extending polymerization as a synthesis strategy to design polymer semiconductors is introduced. Furthermore, we demonstrate its superiority over a conventional synthesis strategy─one-pot polymerization. Diketopyrrolopyrrole-thieno[3,2-b]thiophene-containing polymers (PDPPTT and PDPPTT-vinylene) are used in this study. PDPPTT and PDPPTT-vinylene are synthesized through one-pot polymerization and chain-extending polymerization, respectively. The utilization of this novel strategy enhances the hole/electron mobilities of PDPPTT-vinylene to up to 3.70/2.96 cm2 V-1 s-1 (compared to 2.71/0.63 cm2 V-1 s-1 for PDPPTT), thereby achieving the required performance for organic circuits like inverters and ring oscillators. The significant improvement in the transistor performance of PDPPTT-vinylene is attributed to the introduced vinylene linking units during the polymerization process, which can fine-tune the electronic structure, expand π-conjugation, and induce stronger intermolecular π-π interactions with more significant crystallization. These results demonstrate that chain-extending polymerization is an effective synthesis strategy for developing high-performance polymer semiconductors.

Excellent Microwave Absorption Properties Derived from the Synthesis of Hollow Fe3o4@Reduced Graphite Oxide (RGO) Nanocomposites.

Magnetic nanoparticles, such as Fe3O4 and Co3O4, play a vital role in the research on advanced microwave absorbing materials, even if problems such as high density and narrow band impedance matching are still unsolved. Herein, the study of lightweight hollow Fe3O4@reduced graphite oxide (RGO) nanocomposites synthesized via the solvothermal method is presented. The microstructure and crystal morphology of the materials were characterized by X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses. Single crystalline hollow Fe3O4 spheres were grown onto RGO flakes, leading to the formation of heterojunction, which further influenced the microwave absorption properties. The latter were evaluated by standard microwave characterization in the frequency range of 2⁻18 GHz. It was found that, for a specific Fe3O4@0.125 g RGO composite, the minimum reflection loss can reach -41.89 dB at 6.7 GHz, while the reflection loss was less than -10 dB from 3.4 GHz to 13.6 GHz for a nanocomposite sample thickness in the range of 1⁻4 mm. The combination of these two materials thus proved to give remarkable microwave absorption properties, owing to enhanced magnetic losses and favorable impedance matching conditions.

A facile method to fabricate ZnO hollow spheres and their photocatalytic property.

This paper presents a novel and facile method for the fabrication of ZnO hollow spheres. In this approach, zinc ions were first adsorbed onto the surfaces of sulfonated polystyrene core-shell template spheres, and then reacted with NaOH to form a ZnO crystal nucleus, which was followed by a growth step to form ZnO nanoshells. During the formation of ZnO nanoshells or later on, the template spheres were "dissolved" in the same media to obtain ZnO hollow spheres directly. Neither additional dissolution nor calcination process was needed in this method to remove the templates, and the reaction conditions were very mild: neither high temperature nor long time was needed. Transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Brunauer-Emmett-Teller analysis were used to investigate the morphology, surface composition, crystalline structure, specific surface area, and porosity of the ZnO hollow spheres, respectively. UV-visible spectra show that these ZnO hollow spheres had very good photocatalytic activity.

Fe3O4 nanoparticles decorated on a CuS platelet-based sphere: a popcorn chicken-like heterostructure as an ideal material against electromagnetic pollution.

Electromagnetic irradiation has caused environmental pollution and harmful effects on human health. The use of effective materials to attenuate electromagnetic energy is urgently required. In this study, Fe3O4 nanoparticles (NPs) decorated on a CuS platelet-based sphere (CuS/Fe3O4) with popcorn chicken-like micromorphology were synthesized through a solvothermal deposition method. The effects of reaction temperature and quantity of Fe3O4 NPs on the heterostructures, morphologies and electromagnetic absorption (EA) properties of the heterostructures were investigated. CuS/Fe3O4 heterostructures exhibited remarkable enhancement in comparison with pure Fe3O4 NPs and the CuS platelet-based sphere. With the contribution from dielectric and magnetic losses, a CuS/Fe3O4 heterostructure-loaded composite could achieve a minimum reflection loss (RL) of -61.32 dB at 14.00 GHz and an effective EA bandwidth (≤-10 dB) of 4.15 GHz at a thickness of only 1.5 mm simultaneously. The current study indicates that the CuS/Fe3O4 heterostructures can potentially be applied as advanced electromagnetic absorbers.

PHEA-g-PMMA Well-Defined Graft Copolymer: ATRP Synthesis, Self-Assembly, and Synchronous Encapsulation of Both Hydrophobic and Hydrophilic Guest Molecules.

A series of well-defined amphiphilic graft copolymer bearing a hydrophilic poly(2-hydroxyethyl acrylate) (PHEA) backbone and hydrophobic poly(methyl methacrylate) (PMMA) side chains was synthesized by successive reversible addition-fragmentation chain transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP) through the grafting-from strategy. A well-defined PHEA-based backbone with Cl-containing ATRP initiating group in every repeated unit (M w/M n = 1.08), poly(2-hydroxyethyl 2-((2-chloropropanoyloxy)methyl)acrylate) (PHECPMA), was first prepared by RAFT homopolymerization of 2-hydroxyethyl 2-((2-chloropropanoyloxy)methyl)acrylate (HECPMA), a Cl-containing trifunctional acrylate. ATRP of methyl methacrylate was subsequently initiated by PHECPMA homopolymer to afford the target well-defined poly(2-hydroxyethyl acrylate)-graft-poly(methyl methacrylate) (PHEA-g-PMMA) graft copolymers (M w/M n ≤ 1.36) with 34 PMMA side chains and 34 pendant hydroxyls in PHEA backbone using CuCl/dHbpy as catalytic system. The critical micelle concentration (cmc) of the obtained graft copolymer was determined by fluorescence spectroscopy using N-phenyl-1-naphthylamine as probe while micellar morphologies in aqueous media were visualized by transmission electron microscopy. Interestingly, PHEA-g-PMMA graft copolymer could self-assemble into large compound micelles rather than common spherical micelles, which can encapsulate hydrophilic rhodamine 6 G and hydrophobic pyrene separately or simultaneously.

Spin-Casting Polymer Brush Films for Stimuli-Responsive and Anti-Fouling Surfaces.

Surfaces modified with amphiphilic polymers can dynamically alter their physicochemical properties in response to changes of their environmental conditions; meanwhile, amphiphilic polymer coatings with molecular hydrophilic and hydrophobic patches, which can mitigate biofouling effectively, are being actively explored as advanced coatings for antifouling materials. Herein, a series of well-defined amphiphilic asymmetric polymer brushes containing hetero side chains, hydrophobic polystyrene (PS) and hydrophilic poly(ethylene glycol) (PEG), was employed to prepare uniform thin films by spin-casting. The properties of these films were investigated by water contact angle, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and quartz crystal microbalance (QCM). AFM showed smooth surfaces for all films with the roughness less than 2 nm. The changes in water contact angle and C/O ratio (XPS) evidenced the enrichment of PEG or PS chains at film surface after exposed to selective solvents, indicative of stimuli- responsiveness. The adsorption of proteins on PEG functionalized surface was quantified by QCM and the results verified that amphiphilic polymer brush films bearing PEG chains could lower or eliminate protein-material interactions and resist to protein adsorption. Cell adhesion experiments were performed by using HaCaT cells and it was found that polymer brush films possess good antifouling ability.

Effects of surface properties of colloidal silica particles on redispersibility and properties of acrylic-based polyurethane/silica composites.

Nanosilica particles with different surface properties were designed and prepared using colloidal silica particles and four different qualitative silane coupling agents (SCA), namely methyltriethoxysilane (MTES), octyltriethoxysilane (OTES), vinyltriethoxysilane (VTES) and methacryloxypropyltrimethoxysilane (MATMS), and further applied in acrylic resins and corresponding polyurethane coats by in situ polymerization. It was found that different qualitative SCA molecules had very different impacts on the redispersibility of nanosilica particles, the adsorbed acrylic polyol molecules, the viscosities of acrylic polyol/silica hybrid resins, and the properties of acrylic-based polyurethane/silica composites.

Preparation and characterization of nanocomposite polyurethane.

Polyurethane/nanosilica composites were prepared using polyester polyol/nanosilica composite resins obtained from in situ polymerization or blending methods and investigated by Fourier transform infrared spectra (FTIR), dynamical mechanical analysis (DMA), transmittance electron microscopy (TEM), contact angle measurement, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM), respectively. It was found that more polyester segments had chemically bonded with silica particles during in situ polymerization than during blending, introducing nanosilica increased the Tgs of polyurethanes, and different preparation methods and different particle sizes caused various impact on Tg. Contact angle measurement and XPS analyses indicated that nanosilica tended to move towards the surfaces and interfaces of polyurethane coats, decreasing the free energies of the surfaces and interfaces, but the nanosilica particles were just observed at interfaces not surfaces by AFM.

Wettability switching of SDS-doped polyaniline from hydrophobic to hydrophilic induced by alkaline/reduction reactions.

In this paper, sodium dodecyl sulfate (SDS) is used as dopant to manipulate both morphology and wettability of polyaniline (PANI). When SDS amount is controlled within a certain range, micro/nano double-rough PANI with hydrophobic surface can be obtained, while insufficient or excess SDS can only lead to hydrophilic PANI. The double-rough PANI shows stimuli-responsive change in wettability to either alkaline reaction or reduction reaction from hydrophobicity to hydrophilicity. This quick response can be applied to quantitatively estimate NaOH concentrations within the range of 10(-3)-10(-1)M and to detect various reducing liquids.

Synthesis and antibacterial property of hollow SiO2/Ag nanocomposite spheres.

This paper presents a novel and facile method to fabricate hollow silica/sliver (SiO(2)/Ag) nanocomposite spheres. In this approach, the monodisperse hollow SiO(2) colloids bearing quantenary ammonium groups were prepared by dispersion polymerization combined sol-gel process and used as templates. The Ag(+) ions were first adsorbed onto the surfaces of the hollow SiO(2) beads via electrostatic interaction and then in situ reduced by the deprotonated silanol groups of the hollow SiO(2) beads, no extra reducing agents or catalysts were added during the reduction process. TEM, SEM and EDX analyses indicated that Ag nanoparticles were successfully deposited onto the surfaces of hollow SiO(2) beads. Some influencing parameters, such as the amount of quantenary ammonium groups in the inner wall of hollow SiO(2) colloids, Ag(+) ions concentration and reaction temperature, on the deposition of Ag nanoparticles onto SiO(2) colloids were investigated. Preliminary antibacterial tests indicated that these hollow nanocomposite spheres showed excellent antibacterial ability.

Dispersion and functionalization of nonaqueous synthesized zirconia nanocrystals via attachment of silane coupling agents.

Zirconia (ZrO 2) nanocrystals, synthesized from zirconium(IV) isopropoxide isopropanol complex and benzyl alcohol, were dispersed and functionalized in organic solvents using three kinds of bifunctional silane coupling agents (SCAs), 3-glycidoxypropyltrimethoxysilane (GPTMS), 3-aminopropyltriethoxysilane (APTES), and 3-isocyanatopropyltriethoxysilane (IPTES). Completely transparent ZrO 2 dispersions were achieved in tetrahydrofuran (THF) with all three SCAs, in pyridine and toluene with APTES and IPTES, and in N, N-dimethylformamide with IPTES. Dynamic laser scattering (DLS) measurements and high-resolution transmission electron microscopical (HRTEM) observation indicated that the ZrO 2 nanocrystals are dispersed on a primary particle size level. Fourier transform infrared spectroscopy, solid-state (13)C- and (29)Si NMR spectroscopy, and thermogravimetric analysis demonstrated that all three SCAs are chemically attached to the surface of the ZrO 2 nanoparticles, however, in different bonding modes. Except for GPTMS/ZrO 2/THF dispersion and IPTES/ZrO 2/pyridine dispersion, all other transparent dispersions have poor long-term stability. The increasing polarity, due to high amount of APTES attached and high hydrolysis and condensation degree of the bonded APTES, and the aggregation, due to interparticle coupling via the bonded triethoxysilyl group, are the causes of the poor long-term stability for the ZrO 2 dispersions with APTES and IPTES, respectively. Nevertheless, the APTES-functionalized ZrO 2 precipitates can be deagglomerated in water to get a stable and transparent aqueous ZrO 2 dispersion via addition of a little hydrochloric acid.

Novel and facile method for the preparation of monodispersed titania hollow spheres.

The fabrication of monodispersed hollow spheres in varying sizes and shapes is very interesting and has a lot of potential applications. This paper provides a very simple route to preparing hollow titania spheres using polystyrene (PS) as a template. In this approach, the titania shells were first formed and the PS cores were dissolved subsequently, even synchronously, in the same medium; neither an additional dissolution nor a calcination process was needed to remove the PS cores. Transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and Barret-Emmet-Teller measurements were used to characterize the monodispersed hollow titania spheres. A possible formation mechanism of the hollow spheres was proposed.