Enantioselective Synthesis and Application to the Allylic Imidate Rearrangement of Amine‐Coordinated Palladacycle Catalysts of Cobalt Sandwich Complexes

The reaction of (η⁵‐(N,N‐dimethylaminomethyl)cyclopentadien‐yl)(η⁴‐tetraphenylcyclobutadiene)cobalt with sodium tetrachloropalladate and (R)‐N‐acetylphenylalanine gave planar chiral palladacycle di‐μ‐chloridebis[(η⁵‐(S_p)‐2‐(N,N‐dimethylaminomethyl)cyclopentadienyl,1‐C,3′‐N)(η⁴‐tetraphenylcyclobutadiene)cobalt]dipalladium [(S_p)‐Me₂‐CAP‐Cl] in 92 % ee and 64 % yield. Enantiopurity (>98 % ee) was achieved by purification of the monomeric (R)‐proline adducts and conversion back to the chloride dimer. Treatment with AgOAc gave (S_p)‐Me₂‐CAP‐OAc which was applied to asymmetric transcyclopalladation (up to 78 % ee). The (R)‐N‐acetylphenylalanine mediated palladation methodology was applicable also to the corresponding N,N‐diethyl (82 % ee, 39 % yield) and pyrrolidinyl (>98 % ee, 43 % yield) cobalt sandwich complexes. A combination of 5 mol % of the latter [(S_p)‐Pyrr‐CAP‐Cl] and AgNO₃ (3.8 equiv) is a catalyst for the allylic imidate rearrangement of an (E)‐N‐aryltrifluoroacetimidate (up to 83 % ee), and this catalyst system is also applicable to the rearrangement of a range of (E)‐trichloroacetimidates (up to 99 % ee). This asymmetric efficiency combined with the simplicity of catalyst synthesis provides accessible solutions to the generation of non‐racemic allylic amine derivatives.     

Graphene oxides as support for the synthesis of nickel sulfide–indium oxide nanocomposites for photocatalytic,antibacterial and antioxidant performances

NiS (nickel sulfide)–In₂O₃ (indium oxide) nanostructures and NiS–In₂O₃ decorated on graphene oxide (GO) were demonstrated by ultrasonic/hydrothermal method. The structural study demonstrates the preparation of bixbyite and hexagonal phase of In₂O₃ and NiS for all of the synthesized catalysts. The band gap of the synthesized catalyst was determined to be in the range of 2.30–3.00 eV. A morphological evaluation by field emission scanning electron microscopy of NiS–In₂O₃ decorated on graphene oxide shows support for the NiS–In₂O₃ on the graphene oxide layer. Different test parameters were performed to study the phase and morphology. The particle sizes of the In₂O₃, NiS–In₂O₃ and NiS–In₂O₃/GO nanocomposites were 56.0, 62.0 and 66.0 nm, respectively. The photocatalytic performance of NiS–In₂O₃/GO nanocomposites was examined for the degradation of methylene blue dye under a UV lamp. The prepared sample shows 98.25% photocatalytic degradation within 40 min and at pH 9. With the presence the NiS and GO, the photo-degradation capacities of In₂O₃ and NiS–In₂O₃ are improved owing to the low band gap being calculated in UV–vis DRS analysis. The high ratio of NiS causes the highest photocatalytic properties of NiS–In₂O₃ nanocomposites owing to the enhancement of charge separation efficiency and generation of hydroxyl radicals. This study presents a facile and low-cost method to prepare highly active NiS–In₂O₃/GO nanocomposites. The antibacterial data indicate the significant properties of NiS–In₂O₃/GO nanocomposites for this study.     

Efficient aerial oxidation of different types of alcohols using ZnO nanoparticle–MnCO3-graphene oxide composites

Graphene–metal nanocomposites have been found to remarkably enhance the catalytic performance of metal nanoparticle-based catalysts. In continuation of our previous report, in which highly reduced graphene oxide (HRG)-based nanocomposites were synthesized and evaluated, we present nanocomposites of graphene oxide (GRO) and ZnO nanoparticle-doped MnCO₃ ([ZnO–MnCO₃/(1%)GRO]) synthesized via a facile, straightforward co-precipitation technique. Interestingly, it was noticed that the incorporation of GRO in the catalytic system could noticeably improve the catalytic efficiency compared to a catalyst (ZnO–MnCO₃) without GRO, for aerial oxidation of benzyl alcohol (BzOH) employing O₂ as a nature-friendly oxidant under base-free conditions. The impacts of various reaction factors were thoroughly explored to optimize reaction conditions using oxidation of BzOH to benzaldehyde (BzH) as a model substrate. The catalysts were characterized using X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, Energy dispersive X-ray spectroscopy (EDX), Brunauer-Emmett-Teller (BET), and Raman spectroscopy. The (1%)ZnO–MnCO₃/(1%)GRO exhibited significant specific activity (67 mmol.g⁻¹.hr⁻¹) with full convversion of BzOH and >99% BzH selectivity within just 6 min. The catalytic efficiency of the (1%)ZnO–MnCO₃/(1%)GRO nanocomposite was significantly better than the (1%)ZnO–MnCO₃/(1%)HRG and (1%)ZnO–MnCO₃ catalysts, presumably due to the existence of oxygen-possessing groups on the GRO surface and as well as a very high surface area that could have been instrumental in uniformly dispersing the active sites of the catalyst, i.e., ZnO–MnCO₃. Under optimum circumstances, various kinds of alcohols were selectively transformed to respective carbonyls with full convertibility over the (1%)ZnO–MnCO₃/(1%)GRO catalyst. Furthermore, the highly effective (1%)ZnO–MnCO₃/(1%)GRO catalyst could be successfully reused and recycled over five consecutive runs with a marginal reduction in its performance and selectivity.     

High-yield synthesis of pure ZnO nanoparticles by one-step solid-state reaction approach for enhanced photocatalytic activity

Zinc oxide (ZnO) nanostructures were synthesized via a one-step solid-state reaction approach in ammonia (NH₃) gas environment with different temperature ramp rates. The so-formed nanostructures were characterized using X-ray diffraction (XRD) for phase identification, where the typical wurtzite hexagonal structure was observed. Scanning electron microscopy (SEM) confirmed the particle size to be in the range 45–50 nm, the same as calculated by the XRD pattern for the ramp rate of 10 °C/min. Energy dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the chemical purity of the samples. The photoluminescence (PL) spectrum indicated multiple near-band-edge emissions and energy-band emissions. Then, these ZnO nanomaterials were used for the degradation of crystal violet (CV) dye under UV light irradiation. The CV solution was completely degraded in 2 hr. The initial photocatalyst and dye amounts of 0.2 g/100 ml and 0.5 mg/L, respectively, were found to be the optimum values for maximum degradation efficiency. The ZnO-based photocatalyst was stable up to three cycles of reuse. These results indicate that the high surface area and porosity of the nanomaterials are responsible for the high efficiency, which was confirmed by specific surface area analysis.     

Synthesis of 3D IrRuMn Sphere as a Superior Oxygen Evolution Electrocatalyst in Acidic Environment

The design of a three-dimensional structure for an Ir-based catalyst offers a great opportunity to improve the electrocatalytic performance and maximize the use of the precious metal. Herein, a novel wet chemical strategy is reported for the synthesis of an IrRuMn catalyst with a sphere structure and porous features. In the synthetic process, the combined use of citric acid and formamide is requisite for the formation of the sphere structure. This method leads to a favorable 3D IrRuMn sphere structure with many fully exposed active sites. Furthermore, an alloying noble metal, such as Ir or Ru, with the transition metal leads to enhanced oxygen evolution reaction (OER) activity. The doping of a transition metal, such as Mn, is an interesting example, because it exhibits stability and activity in both acidic and alkaline media. For the OER, the IrRuMn sphere catalyst exhibits an overpotential of 260 mV at a current density of 10 mA cm⁻² in strongly acidic 0.1 m HClO₄, which is superior to that of a commercial IrO₂/C catalyst. This approach provides a novel way to synthesize an Ir-based multimetallic spherical electrocatalyst, which exhibits exceptional efficiency for the acidic OER. It will pave the way for new approaches to the practical utilization of PEM electrolyzers.     

Amphiphilic water soluble cationic ring opening metathesis copolymer as an antibacterial agent

Bacterial infection is a global problem, especially resistance acquired by bacteria against to antibiotics; there is urgent need for the development of antibiotics. Here, we proposed dendron-grafted polymers via ring opening metathesis polymerization (ROMP) featuring different with tailored hydrophobicity/hydrophilicity and cationic charges. Dendritic oxanorbornene derivatives were synthesized having two and six carbon linkers and their corresponding random and block copolymers were prepared having pendant pyridinium salt moieties via ROMP. In total, 12 different water-soluble dendronized cationic polymers featuring hexyl pyridinium moieties were prepared and investigated. Six carbon linker possessing triple charge density and hexyl pyridinium functionality each repeating unit copolymers exhibited high antibacterial activity against Gram-positive bacteria (S. aureus). However, all the polymers were inactive against Gram-negative bacteria (E. coli). Most of the copolymers are non-hemolytic (>HC ₅₀ = 1,000 μg/ml). It was also observed that, there is no significant effect between block copolymers and random copolymers keeping hydrophobicity and cationic charge density constant. Zeta potential was measured to investigate the mechanism in solution via the interaction of polymers with S. aureus, while scanning electron microscope (SEM) measurements image confirms damage of the bacterial cell wall after implementation of biocidal polymer.     

Darcy–Forchheimer three-dimensional flow of carbon nanotubes with nonlinear thermal radiation

The present study elaborates three-dimensional (3D) thermally radiative flow of carbon nanotubes dispersed in water with Darcy–Forchheimer porous space. A bidirectional linear stretchable sheet is used to generate the flow. Darcy–Forchheimer relation specifies porous space. Single-wall carbon nanotubes and multi-wall carbon nanotubes are accounted. Solutions development is due to optimal homotopy analysis technique. Optimal data of sundry variables are obtained. The optimal solution interpretations of velocities and temperature are interpreted via plots. Physical quantities are also elaborated. Our results reveal that thermal field against radiation and temperature ratio parameter is enhanced.

     

The role of biosensors in coronavirus disease-2019 outbreak

Herein, we have summarized and argued about biomarkers and indicators used for the detection of severe acute respiratory syndrome coronavirus 2. Antibody detection methods are not considered suitable to screen individuals at early stages and asymptomatic cases. The diagnosis of coronavirus disease 2019 using biomarkers and indicators at point-of-care level is much crucial. Therefore, it is urgently needed to develop rapid and sensitive detection methods which can target antigens. We have critically elaborated key role of biosensors to cope the outbreak situation. In this review, the importance of biosensors including electrochemical, surface enhanced Raman scattering, field-effect transistor, and surface plasmon resonance biosensors in the detection of severe acute respiratory syndrome coronavirus 2 has been underscored. Finally, we have outlined pros and cons of diagnostic approaches and future directions.     

Free-Standing CoO-POM Janus-like Ultrathin Nanosheets

A single-step solution-based strategy is used to obtain 2D Janus-like free-standing ultrathin nanosheets build from two structurally unrelated species, that is, polyoxomolybdate (POM) and CoO. A controlled 2D-to-1D morphological transition was achieved by judiciously adjusting the solvent choice. These POM-CoO heterostructures can behave as an ideal catalyst for the epoxidation of styrene. Benefiting from their amphiphilic nature, these 2D POM-CoO nanosheets have also been used as surfactant to emulsify immiscible solvents. It is anticipated that structurally diverse polyoxometalates will offer promise as design elements for variety of structurally and compositionally tunable van der Waals integrated heteromaterials having a broad range applications.     

The Effect of Grafting Zirconia and Ceria onto Alumina as a Support for Silicotungstic Acid for the Catalytic Dehydration of Glycerol to Acrolein

The effect of ceria and zirconia grafting onto alumina (α and θ–δ phases) as supports for silicotungstic acid for the dehydration of glycerol to acrolein was studied. 30 % Silicotungstic acid (STA) supported on 5 % zirconia/δ,θ‐alumina was the best catalyst, producing 85 % selectivity to acrolein at 100 % glycerol conversion, and it showed stable activity without using oxygen as a co‐feed. The catalyst produced a STA of 90 g_(acrolein) kg_(cat)^?1 h^?1, which was greater than the STA simply supported on δ,θ‐alumina, which only demonstrated 75 % selectivity towards acrolein. The effect of grafting on the support material was investigated by means of nitrogen adsorption, ammonia temperature‐programmed desorption, thermogravimetric analysis, Raman spectroscopy, and powder X‐ray diffraction. A pulsed‐field gradient (PFG) NMR technique was also used to study diffusion processes associated with the catalysts. Diffusion studies of the grafted catalysts showed that zirconia contributes to the formation of more tortuous pathways within the pore structure, leading to the diminution of acid strength and making the catalyst less susceptible to coke formation.