High Calorific Values Boron Powder: Ignition and Combustion Mechanism, Surface Modification Strategies and Properties.

Boron powder is a kind of metal fuel with high gravimetric and volumetric calorific values, which has been widely used in military fields such as solid propellants, high-energy explosives, and pyrotechnics. However, the easily formed liquid oxide layer can adhere to the surface of boron powder and react with the hydroxyl (-OH) group of hydroxyl-terminated polybutadiene (HTPB) binder to form a gel layer that is detrimental to propellant processing and restricts the complete oxidation of boron powder. Therefore, to improve the combustion efficiency of boron powder, the ignition and combustion mechanisms of boron powder have been studied, and surface coating modification strategies have been developed by researchers worldwide, aiming to optimize the surface properties, improve the reaction activity, and promote the energy release of boron powder. In this review, recent studies on the ignition and combustion mechanisms of boron powder are discussed. Moreover, the reported boron powder coating materials are classified according to the chemical structure and reaction mechanism. Additionally, the mechanisms and characteristics of different coating materials are summarized, and the mechanism diagrams of fluoride and metal oxide are provided. Furthermore, promising directions for modification methods and the potential application prospects of boron powder are also proposed.

Preparation and Properties of (Sc2O3-MgO)/Pcl/Pvp Electrospun Nanofiber Membranes for the Inhibition of Escherichia coli Infections.

Due to their high porosity, large specific surface area, and structural similarity with the extracellular matrix (ECM), electrospun nanofiber membranes are often endowed with the antibacterial properties for biomedical applications. The purpose of this study was to synthesize nano-structured Sc2O3-MgO by doping Sc3+, calcining at 600 °C, and then loading it onto the PCL/PVP substrates with electrospinning technology with the aim of developing new efficient antibacterial nanofiber membranes for tissue engineering. A scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDS) were used to study the morphology of all formulations and analyze the types and contents of the elements, and an X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Fourier transform attenuated total reflection infrared spectroscopy (ATR-FTIR) were used for further analysis. The experimental results showed that the PCL/PVP (SMCV-2.0) nanofibers loaded with 2.0 wt% Sc2O3-MgO were smooth and homogeneous with an average diameter of 252.6 nm; the antibacterial test indicated that a low load concentration of 2.0 wt% Sc2O3-MgO in PCL/PVP (SMCV-2.0) showed a 100% antibacterial rate against Escherichia coli (E. coli).

Investigation of the Biosafety of Antibacterial Mg(OH)2 Nanoparticles to a Normal Biological System.

The toxicity of Mg(OH)2 nanoparticles (NPs) as antibacterial agents to a normal biological system is unclear, so it is necessary to evaluate their potential toxic effect for safe use. In this work, the administration of these antibacterial agents did not induce pulmonary interstitial fibrosis as no significant effect on the proliferation of HELF cells was observed in vitro. Additionally, Mg(OH)2 NPs caused no inhibition of the proliferation of PC-12 cells, indicating that the brain's nervous system was not affected by Mg(OH)2 NPs. The acute oral toxicity test showed that the Mg(OH)2 NPs at 10,000 mg/kg induced no mortality during the administration period, and there was little toxicity in vital organs according to a histological analysis. In addition, the in vivo acute eye irritation test results showed little acute irritation of the eye caused by Mg(OH)2 NPs. Thus, Mg(OH)2 NPs exhibited great biosafety to a normal biological system, which was critical for human health and environmental protection.

Research on synthesis and property of nano-textured Sc2O3-MgO efficient antibacterial agents.

In order to obtain the inorganic efficient antibacterial agents, the means of ion doping and morphology construction in this research are used to enhance the antibacterial property of nano-MgO, which is according to the "oxidative damage mechanism" and "contact mechanism". In this work, the nano-textured Sc2O3-MgO are synthesized by doping Sc3+ in nano-MgO lattice through calcining at 600 °C. When the Sc3+ content reaches 10%, the nanotextures on the powders surface are pretty clearly visible and uniform, and the specific surface area and the oxygen vacancy are ideal, so that the 10% Sc3+-doped powders (SM-10) has the excellent antibacterial property against E. coli and S. aureus (MBC = 0.03 mg/mL). The efficient antibacterial agents in this research have a better antibacterial effect than the 0% Sc3+-doped powders (SM-0, MBC = 0.20 mg/mL) and the commercial nano-MgO (CM, MBC = 0.40 mg/mL), which have application prospects in the field of antibacterial.

Fluorinated leaning pillar[6]arene: synthesis, structure and selective iodide anion binding by anion-π interactions.

Anion recognition has continuously attracted significant attention due to its important role in environmental and biological sciences. Here, we have designed and synthesized an electron-deficient fluorinated leaning pillar[6]arene 1 that contains two tetrafluoro-benzene units. The electron-deficient fluorinated leaning pillar[6]arene 1 is capable of selectively recognizing iodide anions to form a host-guest complex with 1 : 1 stoichiometry driven by anion-π interactions. Our work ascribes this selective recognition to the preorganization of macrocycles, suitable cavity size, and the effect of anion-π interactions. The innovative application of this macrocycle offers us a new avenue for the design of selective receptors for anions and electron-deficient macrocyclic arenes.

Preparation of Nano-Mg(OH)2 and Its Flame Retardant and Antibacterial Modification on Polyethylene Terephthalate Fabrics.

The multifunctional polyethylene terephthalate (PET) fabrics were successfully prepared through a dip-coating technology to endow the flame retardant and antibacterial properties of PET fabrics, which are extensively used in many fields. The flame retardant and antibacterial agent was synthesized by a double drop-reverse precipitation method and surface-modified by the mixtures of titanate coupling agents and stearic acid to result in a good compatibility of the hydrophilic nano-Mg(OH)2 and the hydrophobic PET fabrics. The results indicated that the suitable synthesis conditions of nano-Mg(OH)2 are: Mg2+ concentration 1.5 mg/mL, reaction temperature 50 °C and reaction time 50 min, and the optimal modification conditions of nano-Mg(OH)2 are: modifier ratio 5/5, modification temperature 70 °C and modification time 40 min. The flame retardant test and the antibacterial test showed that the multifunctional PET fabrics had excellent flame retardant and antibacterial properties.

Selective Separation of Phenanthrene from Aromatic Isomer Mixtures by a Water-Soluble Azobenzene-Based Macrocycle.

Selective separation of phenanthrene (PHE) from aromatic isomer mixtures is a big challenge in industry. In this work, a light-responsive water-soluble azobenzene-based macrocycle 1 is synthesized and an aqueous solution of E,E-1 is employed to separate PHE from anthracene via a solid-liquid extraction method under ambient conditions. After five extraction cycles, the average purity for PHE is about 91.1% and macrocycle 1 can be reused at least five times without obvious reduction of separation performance for PHE. This work not only comprises a new and clean way to separate PHE by taking advantage of a macrocyclic host but also promotes the application of host-guest chemistry.

Azobenzene-Based Macrocyclic Arenes: Synthesis, Crystal Structures, and Light-Controlled Molecular Encapsulation and Release.

Azobenzene (azo)-based macrocycles are highly fascinating in supramolecular chemistry because of their light-responsiveness. In this work, a series of azo-based macrocyclic arenes 1, 2, 3, and 4, distinguished by the substituted positions of azo groups, is rationally designed and synthesized via a fragment-cyclization method. From the crystal and computed structures of 1, 2, and 3, we observe that the cavity size of these azo-macrocycles decreases gradually upon E→Z photoisomerization. Moreover, light-controlled host-guest complexations between azo-macrocycle 1 and guest molecules (7,7,8,8-tetracyanoquinodimethane, terephthalonitrile) are successfully achieved. This work provides a simple and effective method to prepare azo-macrocycles, and the light-responsive molecular-encapsulation systems in this work may further advance the design and applications of novel photo-responsive host-guest systems.

Rationally Designed Self-Immolative Rotaxane Sensor Based on Pillar[5]arene for Fluoride Sensing.

We develop a self-immolative rotaxane sensor for fluoride sensing based on host-guest interactions between pillar[5]arene and fluoride-promoted cleavage of Si-O bond. Because of the selective and fast reaction between silane and fluoride, the rotaxane sensor shows anion selectivity and rapid response. The self-immolative nature of the rotaxane improve its sensitivity. Moreover, a fluoride sensing test paper based on the rotaxane sensor is made, which shows the practicable application of the rotaxane sensor.

Dual-Emissive Platinum(II) Metallacage with a Sensitive Oxygen Response for Imaging of Hypoxia and Imaging-Guided Chemotherapy.

Imaging of hypoxia in vivo helps with accurate cancer diagnosis and evaluation of therapeutic outcomes. A PtII metallacage with oxygen-responsive red phosphorescence and steady fluorescence for in vivo hypoxia imaging and chemotherapy is reported. The therapeutic agent and diagnostic probe were integrated into the metallacage through heteroligation-directed self-assembly. Nanoformulation by encapsulating the metallacage into nanoparticles greatly enhanced its stability the in physiological environment, rendering biomedical applications feasible. Apart from enhanced red phosphorescence upon hypoxia, the ratio between red and blue emissions, which only varies with intracellular oxygen level, provides a more precise standard for hypoxia imaging and detection. Moreover, in vivo explorations demonstrate the promising potential applications of the metallacage-loaded nanoparticles as theranostic agents for tumor hypoxia imaging and chemotherapy.

Spontaneous Formation of a Cross-Linked Supramolecular Polymer Both in the Solid State and in Solution, Driven by Platinum(II) Metallacycle-Based Host-Guest Interactions.

The recent progress in platinum(II) coordination-driven supramolecular polymers has had a substantial effect on the design of functional soft materials. However, the prospect of realizing polymerization induced by platinum(II) metallacycle-based host-guest interactions has received little attention until recently. Here we report the realization of supramolecular polymerization driven by platinum(II) metallacycle-based host-guest interactions both in the solid state and in solution. On the basis of the disclosed polymerization mechanism, we present a new strategy for the preparation of platinum(II) metallacycle-based supramolecular polymers.

A multi-responsive cross-linked supramolecular polymer network constructed by mussel yield coordination interaction and pillar[5]arene-based host-guest complexation.

Here a novel cross-linked supramolecular polymer network with thermal, pH, and H2S responsiveness was prepared inspired by mussel yield catechol-Fe3+ coordination and pillar[5]arene-based host-guest interactions.

Construction of Metallacage-Cored Supramolecular Gel by Hierarchical Self-Assembly of Metal Coordination and Pillar[5]arene-Based Host-Guest Recognition.

In this work, a Pd2 L4 metallacage 2•([BF4 ]- )4 with four pillar[5]arene units is first prepared and characterized by 1D multinuclear NMR (1 H, 11 B, and 19 F NMR), 2D 1 H-1 H correlation spectra, 1 H-13 C heteronuclear single quantum coherence, and diffusion-ordered NMR spectroscopy, and electrospray ionization time-of-flight mass spectrometry. By the introduction of a ditopic guest molecule 3 into a chloroform solution of 2•([BF4 ]- )4 , a supramolecular polymer network gel is successfully constructed based on the metal coordination interactions and host-guest recognition between the pillar[5]arene units of 2•([BF4 ]- )4 and neutral ditopic guest molecule 3. The temperature and pH responsivenesses of the supramolecular gel are studied, which are further employed for the controlled release of different cargos. As a demonstration, emodin and methylene blue are trapped in the cavities of the metallacage and in the pores of the supramolecular gel, respectively. Methylene blue is first released along with the gel-sol transition while emodin is then released by the further addition of acid to destroy the metallacage. This study explores the use of metallacage-cored supramolecular network gels for sequential controlled release and contributes to the development of smart and adaptive materials.