Palladium-catalysed [3+2] cycloaddition of alk-5-ynylidenecyclopropanes to alkynes: a mechanistic DFT study

The mechanism of the palladium-catalysed [3+2] intramolecular cycloaddition of alkylidenecyclopropanes to alkynes has been computationally explored at DFT level. The energies of the reaction intermediates and transition states for different possible pathways have been calculated in a model system that involves the use of PH3 as a ligand. The results obtained suggest that the most favourable reaction pathway involves the initial C--C oxidative addition of the cyclopropane to a Pd0 complex to give an alkylidenepalladacyclobutane, which isomerises to a methylenepalladacyclobutane intermediate. Subsequent cyclisation by alkyne carbometallation, followed by reductive elimination affords the final product. An alternative mechanism consisting of a palladaene-type rearrangement is less probable in terms of Gibbs energy, but cannot be fully discarded because it is competitive if one considers electronic energies. For substrates that present an ester group at the terminal position of the triple bond we have found an alternative, more favourable mechanistic route that explains why the [3+2] cycloaddition of these types of systems does not lead to the expected cycloadducts.     

Fluid Simulation of Capacitively Coupled HBr/Ar Plasma for Etching Applications

In this work, a fluid model has been applied to study HBr/Ar capacitively coupled plasma discharges that are being used for anisotropic etching process. Based on time average reaction rates, the model identify the most dominant species in HBr/Ar plasma. Our simulation results show that the neutral species like H and Br, which are the key precursors in chemical etching, have bell shape distribution while ions like HBr⁺, Br⁺ and Ar⁺ which plays a dominant role in the physical etching, have double humped distribution and shows peaks near electrodes. The effect of HBr/Ar mixing ratios on densities of dominant species are analyzed. The addition of Ar to HBr plasma decreases H, Br and HBr⁺ densities slightly while increases Br⁺ and Ar⁺ densities. It was found that the dilution of HBr by Ar results in an increase in electron density and electron temperature, which results in more ionization and dissociation. The densities and hence the fluxes of the neutrals and positive ions for etching and subsequently chemical etching versus physical etching in HBr/Ar plasmas discharge can be controlled by tuning Ar concentration in the discharge and the desire etching can be achieved.     

Numerical Study of HBr/He Discharges in Capacitive Coupled Plasma Reactor

Br-based plasmas potentially provide selective etching of Si. The characteristics of homogenous discharge in mixed gases of HBr and He are investigated numerically based on a self-consistent 2D fluid model. The model takes into account the primary processes like excitation and ionization. The reactions of radicals with radicals, neutrals with neutrals and radicals and neutrals are taken into account in HBr/He discharge and therefore can adequately represent discharge plasma. Based on simulation results of the self-consistent 2D fluid model, the dominant species for Si etching in HBr/He plasma discharge are Br, Br⁺, H and HBr⁺. The impact of frequency, voltage, electrode gap, and gas mixture ratio on the densities of these important species in HBr/He has been explored. Simulation results indicate that elevating high frequency electrode’s frequency and voltage, enhances etching species densities. Increasing the electrode gap, the densities of all plasma species decrease and vice versa. The addition of He to HBr plasma decreases Br and HBr⁺ densities while increases Br⁺ density. Densities of active species for Si etching and subsequently chemical etching versus physical sputtering in HBr/He plasma can be controlled by tuning input parameters and the desired etching can be achieved.     

Electrochemical degradation of tetracycline in artificial urine medium

The electrochemical degradation of tetracycline hydrochloride (TeC) was comparatively investigated in artificial urine and chloride-containing media using a one-compartment filter-press flow cell composed of a Ti/Ru_0.3Ti_0.7O₂ dimensionally stable anode. The effect of the current density (10–40 mA cm^?2) on the removal levels attained for TeC and total organic carbon (TOC) (in both media), as well as for urea and creatinine in artificial urine medium, was assessed. The TeC removal rate in the artificial urine medium was much lower than in chloride-containing medium, probably due to the higher consumption of the electrogenerated active chlorine species by the urea and creatinine in the artificial urine medium. Moreover, the obtained removal levels for the urea and creatinine were negligible at current densities lower than 30 mA cm^?2. As TOC abatement was also very small, it is possible that TeC oxidation leads to intermediate compounds. Thus, if current densities less than 20 mA cm^?2 are applied, TeC can be selectively removed.     

Manufacturing Man‐Made Magnetosomes: High‐Throughput In Situ Synthesis of Biomimetic Magnetite Loaded Nanovesicles

A new synthetic method for the production of artificial magnetosomes, i.e., lipid‐coated vesicles containing magnetic nanoparticles, is demonstrated. Magnetosomes have considerable potential in biomedical and other nanotechnological applications but current production methods rely upon magnetotactic bacteria which limits the range of sizes and shapes that can be generated as well as the obtainable yield. Here, electrohydrodynamic atomization is utilized to form nanoscale liposomes of tunable size followed by electroporation to transport iron into the nanoliposome core resulting in magnetite crystallization. Using a combination of electron and fluorescence microscopy, dynamic light scattering, Raman spectroscopy, and magnetic susceptibility measurements, it is shown that single crystals of single‐phase magnetite can be precipitated within each liposome, forming a near‐monodisperse population of magnetic nanoparticles. For the specific conditions used in this study the mean particle size is 58 nm (±8 nm) but the system offers a high degree of flexibility in terms of both the size and composition of the final product.

     

Application of fractional factorial design and Doehlert matrix in the optimization of experimental variables associated with the ultrasonic-assisted acid digestion of chocolate samples for aluminum determination by atomic absorption spectrometry

A simple and rapid method based on ultrasound energy is described for the determination of aluminum (AI) in complex matrixes of chocolate and candy samples by electrothermal atomic absorption spectrometry. The optimization strategy was carried out using multivariate methodologies. Five variables (temperature of the ultrasonic bath; exposure time to ultrasound energy; volumes of 2 acid mixtures, HNO3-H2SO4-H2O2 (1 + 1 + 1) and HNO3-H2O2 (1 + 1); and sample mass) were considered as factors in the optimization process. Interactions between analytical factors and their optimal levels were investigated using fractional factorial and Doehlert matrix designs. Validation of the ultrasonic-assisted acid digestion procedure was performed against standard reference materials, milk powder (SRM 8435) and wheat flour (SRM 1567a). The proposed procedure allowed Al determination with a detection limit of 2.3 microg/L (signal-to-noise = 3) and a precision, calculated as relative standard deviation, of 2.2% for a set of 10 measurements of certified samples. The recovery of Al by the proposed procedure was close to 100%, and no significant difference at the 95% confidence level was found between determined and certified values of Al. The proposed procedure was applied to the determination of Al in chocolate and candy samples. The results indicated that cocoa-based chocolates have higher contents of Al than milk- and sugar-based chocolates and candies.     

Determination of the anthraquinones aloe-emodin and aloin-A by liquid chromatography with mass spectrometric and diode array detection

Methods using liquid chromatography/mass spectrometry (LC/MS) and LC with diode array detection (DAD) in the UV range (LC/UV) were developed for the determination of low levels of the anthraquinones aloe-emodin and aloin-A (barbaloin) in aloe-based products. The methods were used to analyze several commercial products (liquids, semisolids, and solids) for the 2 anthraquinones. The wavelengths used for quantification of aloin-A, aloe-emodin, and emodin (internal standard) by DAD were 357, 257, and 289 nm, respectively. The on-column sensitivities were 0.25 and 0.05 ng by LC/UV and 0.01 and 0.025 ng by LC/MS for aloin-A and aloe-emodin, respectively. The methods are simple and sensitive and provide reproducible results; therefore, they are suitable for the determination of these anthraquinones in various aloe-based products.     

Cannabinoids,Phenolics, Terpenes and Alkaloids of Cannabis

Cannabis sativa is one of the oldest medicinal plants in the world. It was introduced into western medicine during the early 19th century. It contains a complex mixture of secondary metabolites, including cannabinoids and non-cannabinoid-type constituents. More than 500 compounds have been reported from C. sativa, of which 125 cannabinoids have been isolated and/or identified as cannabinoids. Cannabinoids are C₂₁ terpeno-phenolic compounds specific to Cannabis. The non-cannabinoid constituents include: non-cannabinoid phenols, flavonoids, terpenes, alkaloids and others. This review discusses the chemistry of the cannabinoids and major non-cannabinoid constituents (terpenes, non-cannabinoid phenolics, and alkaloids) with special emphasis on their chemical structures, methods of isolation, and identification.     

Phenothiazine-based chalcones as potential dual-target inhibitors toward cholinesterases (AChE,BuChE) and monoamine oxidases (MAO-A,MAO-B)

Chalcones targeting neurodegenerative diseases have been known as attractive structures in drug design and discovery. In this study, phenothiazine-based chalcones as ChEs and MAOs inhibitors were designed and synthesized via base-catalyzed Claisen-Schmidt condensation, and chemical structures of the compounds were elucidated by NMRs and HRMS. Compounds 3 and 9 showed promising inhibition potency against AChE enzyme with IC₅₀ values of 0.221 μM and 0.053 μM while compound 9 displayed remarkable inhibition potency toward MAO-B enzyme with IC₅₀ value of 0.048 μM. Compound 9 , as a dual-target inhibitor, selectively inhibited AChE and MAO-B enzymes. This promising behavior is an advantage for the compound since MAO-B and AChE inhibition have a role in Alzheimer's disease. Fused tricyclic ring systems such as phenothiazine incorporated with chalcone moiety being multitargeting ligands may help scientists for the rational design of novel lead compounds targeting neurodegenerative illnesses.