Methane dehydrogenation on Cu and Ni surfaces with low and moderate oxygen coverage

First-principles density functional theory calculations are carried out to evaluate energy barriers and mechanisms for the dehydrogenation reactions of CH₄ on clean and oxygen-covered surfaces of Cu (111) and Ni (111) with low and moderate oxygen coverage. In the presence of oxygen, two possible pathways have been evaluated. The more likely pathway, which is further analyzed, is that CH₄ loses an H to the surface O. Results from this pathway agree with previous findings showing that oxygen promotes CH₄ dissociation on Cu (111) and hinders that on Ni (111). In addition, our results show lower energy barriers on Cu with higher oxygen coverages up to 0.38 monolayer. However, such an increase in oxygen coverage did not show any favorable effect for CH₄ dissociation on Ni (111). The findings are analyzed through electronic factors revealed by charge analysis and density of states.     

Fe3O4@ZrO2/SO42‐: A recyclable magnetic heterogeneous nanocatalyst for synthesis of β‐amino carbonyl derivatives and synthesis of benzylamino coumarin derivatives through Mannich reaction

In the present work, we developed an effective protocol for the synthesis of β‐amino carbonyl compounds and synthesis of benzylamino coumarin derivatives through Mannich type reaction in high yields. Fe₃O₄@ZrO₂/SO₄^2‐ was employed as an effective heterogeneous nanocatalyst for the Mannich reaction. This research consists of two sections. In first section, β‐amino carbonyl derivatives were synthesized under solvent‐free condition. In the other section, benzylamino coumarin compounds were synthesized at room temperature. The present approach offers several advantages such as short reaction times, low cost, easy work‐up, mild reaction conditions, high yields and ease of recovery and reusability of the catalyst without significant loss of activity.     

Cu(I)-anchored polyvinyl alcohol coated-magnetic nanoparticles as heterogeneous nanocatalyst in Ullmann-type C–N coupling reactions

In this paper, the preparation of a novel magnetic nanocatalyst (Fe₃O₄@PVA/CuCl) is described, which involves coating of polyvinyl alcohol (PVA) onto the surface of Fe₃O₄ nanoparticles and its subsequent coordination with CuCl catalyst. The nanocatalyst was characterized by various analytical methods, including Fourier-transform infrared, X-ray diffraction, inductively coupled plasma spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy, vibrating-sample magnetometry, and EDX elemental mapping. Moreover, the nanocatalyst was efficiently used in the N-arylation of amines via the formation of a carbon–nitrogen bond between the aryl halides and amines by Ullmann-type coupling reactions. The catalyst was sufficiently stable and can be reused for at least seven times in a model Ullmann reaction without remarkable alteration in its catalytic behavior. Heterogeneity of the catalyst was investigated by a hot filtration test.     

Green synthesis of palladium nanoparticles using Pistacia atlantica kurdica gum and their catalytic performance in Mizoroki–Heck and Suzuki–Miyaura coupling reactions in aqueous solutions

A one‐pot green method for the synthesis of palladium nanoparticles (Pd‐NPs) supported on Pistacia atlantica kurdica (P. a. kurdica) gum is described. This natural gum is used as a reducing and stabilising agent. The formation of the Pd‐NPs/P. a. kurdica gum catalyst was verified using several techniques, such as Fourier transform infrared spectroscopy, ultraviolet–visible spectrophotometry, scanning and transmission electron microscopies, X‐ray diffraction, energy‐dispersive X‐ray spectroscopy, dynamic light scattering and wavelength‐dispersive X‐ray spectroscopy. The Pd‐NPs stabilised by P. a. kurdica gum were employed as a heterogeneous catalyst in Mizoroki–Heck and Suzuki–Miyaura cross‐coupling reactions at low palladium loading (0.1 mol%) under aerobic, phosphine‐free and ligand‐free conditions in water. Product yields of up to 98%, a facile work‐up, no evidence of leached palladium from the catalyst surface and smooth recovery of the catalyst, which can be reused at least eight times, confirm the efficiency of the catalysts in the reactions investigated. Copyright © 2015 John Wiley & Sons, Ltd.     

Application of copper nanoparticles containing natural compounds in the treatment of bacterial and fungal diseases

The development of nanotechnology has generated different nanoscale-sized materials, with metal-based nanomaterials being some of the most interesting and promising. Thousands of articles in various specialized journals all over the world are dedicated to different metallic nanomaterials. Metallic nanomaterials are being widely researched, with gold-, silver-, iron-, and copper-based materials showing potential in medicine. Studies have demonstrated the effect of copper nanoparticles in medicinal herbs on the prevention, control, and treatment of microbial diseases. Experiments have examined the chemical characterization and assessment of the antioxidant, cytotoxicity, antibacterial, and antifungal activities of copper nanoparticles (Cu NPs) using the aqueous extract of Stachys lavandulifolia Vahl flower. These nanoparticles were characterized by UV–visible spectroscopy, field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy, transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), and X-ray diffraction analysis. TEM and FE-SEM images exhibited a uniform spherical morphology and diameters of 10–25 nm for the biosynthesized nanoparticles. FT-IR results suggested polysaccharides and protein in S. lavandulifolia acted as reducing agents, reducing copper ions to Cu NPs. In vitro biological experiments indicated that Cu NPs have excellent antioxidant potential against 2,2-diphenyl-1-picrylhydrazyl, antifungal effects against Candida krusei, Candida parapsilosis, Candida guilliermondii, Candida glabrata, and Candida albicans, and antibacterial activities against Staphylococcus aureus, Enterococcus faecalis, Staphylococcus saprophyticus, Bacillus subtilis, Streptococcus pneumonia, Escherichia coli O157:H7, Salmonella typhimurium, Listeria monocytogenes, Proteus mirabilis, and Pseudomonas aeruginosa. These nanoparticles did not have cytotoxicity properties against human umbilical vein endothelial cells. These results indicate that the inclusion of S. lavandulifolia extract ameliorates the solubility of Cu NPs, which leads to a remarkable enhancement in fungicidal and bactericidal effects under in vitro conditions.     

Silica Phenyl Sulfonic Acid as a Solid Acid Heterogeneous Catalyst for Chemoselective Thioacetalization of Carbonyl Compounds and Dethioacetalization under Mild Conditions

Silica phenyl sulfonic acid (SPSA) is an effective catalyst for chemoselective thioacetalization of aldehydes in the presence of ketones under neutral conditions. In addition, a simple and an efficient procedure for deprotection of 1,3‐dithianes and 1,3‐dithiolanes of aromatic, aliphatic, and α,β‐unsaturated aldehydes and ketones in the solvent‐free to the corresponding parent carbonyl compounds was successfully carried out with SPSA in excellent yields.     

SiO2-functionalized melamine-pyridine group–supported Cu(OAc)2 as an efficient heterogeneous and recyclable nanocatalyst for the N-arylation of amines through Ullmann coupling reactions

This study reports a convenient approach to prepare SiO₂/CCPy/Cu(OAc)₂ as a novel nanocatalyst, in which melamine-bearing pyridine groups have functionalized SiO₂ and can act as a capping agent to stabilize Cu(II) species. The catalyst is characterized through Fourier transform infrared, transmission electron microscopy, field emission scanning electron microscopy (FESEM), Brunauer–Emmett–Teller (BET), thermogravimetric analysis, inductivity coupled plasma (ICP), and energy dispersive X-ray (EDX) techniques. Furthermore, its catalytic behavior is evaluated in the N-arylation of indole, imidazole, and aniline during Ullmann-type C–N coupling reactions. Moreover, it has been proved that the heterogeneous nanocatalyst can be feasibly recovered by filtration and reused in five consecutive reaction cycles without any noticeable loss of its catalytic activity. The results clarified that the devised method is advantageous from several perspectives, that is, low catalyst loading, high product yield, experimental simplicity, broad substrate scope, and short reaction time.     

Luciferin‐Regenerating Enzyme Crystal Structure Is Solved but its Function Is Still Unclear

Contribution of luciferin‐regenerating enzyme (LRE) for in vitro recycling of D‐luciferin has been reported. According to crystal structure of LRE, it is a beta‐propeller protein which is a type of all β‐protein architecture. In this overview, reinvestigation of the luciferase‐based LRE assays and its function is reported. Until now, sequence of LRE genes from four different species of firefly has been reported. In spite of previous reports, T‐LRE (from Lampyris turkestanicus) was cloned and expressed in Escherichia coli as well as Pichia pastoris in a nonsoluble form as inclusion body. According to recent investigations, bioluminescent signal of soluble T‐LRE–luciferase‐coupled assay increased and then reached an equilibrium state in the presence of D‐cysteine. In addition, the results revealed that both D‐ and L‐cysteine in the absence of T‐LRE caused a significant increase in bioluminescence intensity of luciferase over a long time. Based on activity measurements and spectroscopic results, D‐cysteine increased the activity of luciferase due to its redox potential and induction of conformational changes in structure and kinetics properties. In conclusion, in spite of previous reports on the effect of LRE (at least T‐LRE) on luciferase activity, most of the increase in luciferase activity is caused by direct effect of D‐cysteine on structure and activity of firefly luciferase. Moreover, bioinformatics analysis cannot support the presence of LRE in peroxisome of photocytes in firefly lanterns.     

Entire solutions of first-order nonlinear partial differential equations

We show that any entire solution of an essentially nonlinear first-order partial differential equation in two variables must be linear.

     

Highly Efficient Method for Synthesis of Bis(Indolyl)Methanes Catalyzed by FeCl3−based Ionic Liquid

A simple and highly efficient green protocol for synthesis of bis(indolyl)methanes was carried out by the reaction of indole with aldehydes and ketones in the presence of FeCl_3?based ionic liquid. These liquids serve as efficient media as well as Lewis acid catalysts.