Optically Active Helical Polyacetylene Bearing Ferrocenyl Amino-Acid Derivative in Pendants. Preparation and Application as Chiral Organocatalyst for Asymmetric Aldol Reaction

The article reports a novel type of helical polymer-based chiral catalyst for catalyzing asymmetric aldol reactions. Chiral acetylenic monomers containing ferrocenyl amino-acid derivative substituent were synthesized for the first time and structurally identified. The investigated amino acids include alanine and threonine enantiomers. The obtained monomers separately underwent solution homopolymerization and copolymerization with an achirally substituted acetylene monomer in the presence of [Rh­(nbd)­Cl]₂ and Et₃N. Circular dichroism and UV–vis absorption spectra demonstrated that the copolymer chains adopted predominantly one-handed helices, endowing the copolymers with optical activity. The resulting (co)­polymers were further used to catalyze aldol reaction between cyclohexanone and <i>p</i>-nitrobenzaldehyde. Only threonine-derived copolymers efficiently catalyzed the aldol reaction. A remarkable yield (up to 90%) and enantiomeric excess (up to 93%) were obtained. A synergic effect between the helical structures in the copolymer main chains and the pendent catalytic moieties was found to play a crucial role in the asymmetric catalysis

Optically Active Helical Polyacetylene Self-Assembled into Chiral Micelles Used As Nanoreactor for Helix-Sense-Selective Polymerization

Chiral micelles have been drawing ever-increasing attention because of their potentials in mimicking the unique stereochemical effects of enzymes. This article reports on the first success in preparing chiral micelles through self-assembly of helical polyacetylene bearing cholic acid pendants. The micelles were further used as chiral nanoreactor, in which achiral acetylenic monomer smoothly underwent helix-sense-selective polymerization (HSSP). The HSSPs directly established optically active core/shell nanoparticles whose shell and core both were constructed by helical polymers. The shells (or micelles) provided a protective effect for the preferably induced one-handed helical polymer chains in the cores. The present work provides insights into the self-assembly of chiral helical polymers, and also provides a powerful strategy for constructing novel chiral polymer nanoarchitectures

Optically Active Porous Microspheres Consisting of Helical Substituted Polyacetylene Prepared by Precipitation Polymerization without Porogen and the Application in Enantioselective Crystallization

A novel chiral acetylenic monomer derived from cholic acid was synthesized and structurally characterized. The monomer underwent precipitation polymerization in tetrahydrofuran/<i>n</i>-heptane mixed solvent with [Rh­(nbd)­Cl]₂ as catalyst. Without adding porogen, porous microspheres were successfully prepared in a high yield (>80 wt %). The formation mechanism of the porous structure was proposed. Circular dichroism and UV–vis absorption spectra demonstrated that the porous microspheres possessed optical activity. The optical activity was originated in the chiral helical conformations of substituted polyacetylene forming the microspheres. The porous microspheres were further used as specific chiral additive to induce enantioselective crystallization of racemic BOC-alanine, in which BOC-l-alanine was preferentially induced forming rod-like crystals with e.e. of 69%. This strongly indicates the significant potential applications of the porous microspheres in chiral technologies. The present study also provides a new approach to prepare chiral porous polymer microspheres

Facile Synthesis of Novel Heterostructure Based on SnO₂ Nanorods Grown on Submicron Ni Walnut with Tunable Electromagnetic Wave Absorption Capabilities

In this work, the magnetic–dielectric core-shell heterostructure composites with the core of Ni submicron spheres and the shell of SnO₂ nanorods were prepared by a facile two-step route. The crystal structure and morphology were investigated by X-ray diffraction analysis, transmission electron microscopy (TEM), and field emission scanning electron microscopy (FESEM). FESEM and TEM measurements present that SnO₂ nanorods were perpendicularly grown on the surfaces of Ni spheres and the density of the SnO₂ nanorods could be tuned by simply varying the addition amount of Sn²⁺ in this process. The morphology of Ni/SnO₂ composites were also determined by the concentration of hydrochloric acid and a plausible formation mechanism of SnO₂ nanorods-coated Ni spheres was proposed based on hydrochloric acid concentration dependent experiments. Ni/SnO₂ composites exhibit better thermal stability than pristine Ni spheres based on thermalgravimetric analysis (TGA). The measurement on the electromagnetic (EM) parameters indicates that SnO₂ nanorods can improve the impedance matching condition, which is beneficial for the improvement of electromagnetic wave absorption. When the coverage density of SnO₂ nanorod is in an optimum state (diameter of 10 nm and length of about 40–50 nm), the optimal reflection loss (RL) of electromagnetic wave is −45.0 dB at 13.9 GHz and the effective bandwidth (RL below −10 dB) could reach to 3.8 GHz (12.3–16.1 GHz) with the absorber thickness of only 1.8 mm. By changing the loading density of SnO₂ nanorods, the best microwave absorption state could be tuned at 1–18 GHz band. These results pave an efficient way for designing new types of high-performance electromagnetic wave absorbing materials

Morphology-Control Synthesis of a Core–Shell Structured NiCu Alloy with Tunable Electromagnetic-Wave Absorption Capabilities

In this work, dendritelike and rodlike NiCu alloys were prepared by a one-pot hydrothermal process at various reaction temperatures (120, 140, and 160 °C). The structure and morphology were analyzed by scanning electron microscopy, energy-dispersive spectrometry, X-ray diffraction, and transmission electron microscopy, which that demonstrate NiCu alloys have core–shell heterostructures with Ni as the shell and Cu as the core. The formation mechanism of the core–shell structures was also discussed. The uniform and perfect dendritelike NiCu alloy obtained at 140 °C shows outstanding electromagnetic-wave absorption properties. The lowest reflection loss (RL) of −31.13 dB was observed at 14.3 GHz, and the effective absorption (below −10 dB, 90% attenuation) bandwidth can be adjusted between 4.4 and 18 GHz with a thin absorber thickness in the range of 1.2–4.0 mm. The outstanding electromagnetic-wave-absorbing properties are ascribed to space-charge polarization arising from the heterogeneous structure of the NiCu alloy, interfacial polarization between the alloy and paraffin, and continuous micronetworks and vibrating microcurrent dissipation originating from the uniform and perfect dendritelike shape of NiCu prepared at 140 °C

Intense Circularly Polarized Fluorescence and Room-Temperature Phosphorescence in Carbon Dots/Chiral Helical Polymer Composite Films

Chiral carbon dots (C-dots) with a circularly polarized fluorescence (CPF) property have attracted tremendous attention due to their significant applications in chiral optoelectronics and theranostics. However, constructing circularly polarized room-temperature phosphorescent (CPRTP) C-dots remains a great challenge. Herein, a strategy is established to achieve efficient CPF and CPRTP emissions in C-dots/chiral helical polymer bilayer composite film. Taking advantage of the chiral filter effect of chiral helical polymer, intense CPF and CPRTP emissions with large dissymmetric factors up to 1.4 × 10–1 and 1.2 × 10–2 are respectively obtained, even though there is only a simple interface contact between the C-dots layer and the chiral helical polymer layer. More importantly, white-color CPF emission and multiple information display and encryption are further realized based on the prepared chiral luminescent composite films

Preparation of Honeycomb SnO₂ Foams and Configuration-Dependent Microwave Absorption Features

Ordered honeycomb-like SnO₂ foams were successfully synthesized by means of a template method. The honeycomb SnO₂ foams were analyzed by X-ray diffraction (XRD), thermogravimetric and differential scanning calorimetry (TG-DSC), laser Raman spectra, scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR). It can be found that the SnO₂ foam configurations were determined by the size of polystyrene templates. The electromagnetic properties of ordered SnO₂ foams were also investigated by a network analyzer. The results reveal that the microwave absorption properties of SnO₂ foams were dependent on their configuration. The microwave absorption capabilities of SnO₂ foams were increased by increasing the size of pores in the foam configuration. Furthermore, the electromagnetic wave absorption was also correlated with the pore contents in SnO₂ foams. The large and high amounts pores can bring about more interfacial polarization and corresponding relaxation. Thus, the perfect ordered honeycomb-like SnO₂ foams obtained in the existence of large amounts of 322 nm polystyrene spheres showed the outstanding electromagnetic wave absorption properties. The minimal reflection loss (RL) is −37.6 dB at 17.1 GHz, and RL less than −10 dB reaches 5.6 GHz (12.4–18.0 GHz) with thin thickness of 2.0 mm. The bandwidth (<−10 dB, 90% microwave dissipation) can be monitored in the frequency regime of 4.0–18.0 GHz with absorber thickness of 2.0–5.0 mm. The results indicate that these ordered honeycomb SnO₂ foams show the superiorities of wide-band, high-efficiency absorption, multiple reflection and scatting, high antioxidation, lightweight, and thin thickness