Copper-catalyzed oxidative C‒H,N‒H coupling of azoles and thiophenes

C?H, N?H coupling of azole and thiophene derivatives takes place in the presence of a catalytic amount of Cu(OAc)₂ and an additive. The reaction of azoles smoothly occurs with several amines and amides catalyzed by 20 mol % of Cu(OAc)₂–2PPh₃ and 4 equiv of NaOAc under O₂ or in the presence of Ag₂CO₃ under N₂. The coupling reaction leads to a facile synthesis of a N-substituted analogue of 2,5-diarylthiazole, which shows photoluminescent properties with extended π-conjugation. Spectroscopic characteristics of the obtained thiazole derivatives are discussed by measurements of UV–vis absorption and photoluminescent spectra. Under the reaction conditions using Ag₂CO₃ as an additive and Cu(OAc)₂–2PPh₃ as a catalyst, thiophene derivatives also react with 2-pyrrolidone to undergo C?H, N?H amidation.     

Isa‒NHC‒catalyzed intermolecular Stetter reaction of aromatic aldehydes with maleimides: An efficient access to 3‒aroylsuccinimides

An intermolecular Stetter reaction of aromatic aldehydes with maleimides has been developed using thiazolylidene salt derived Isa?NHC as an efficient organocatalyst. The synthesized Stetter products “3?aroylsuccinimides” are important building blocks for the synthesis of natural products and bioactive compounds. The reaction conditions are mild, and various substituents on aromatic aldehyde and maleimide nitrogen were tolerated.     

Synthesis of Organophosphorus Compounds with ‒P˭P≡ and ‒P˭S˭ Units

Abstract

The lithium phosphide tetrahydrofurane complexes 1 react with phosphinic acid chlorides (2) to yield diphosphenes (4), possessing a tri- and a quinquevalent phosphorus atom; the diphosphane oxides 3 are regarded to be intermediate steps of the transformation.     

Complexation of neurotransmitters ‒ dopamine,serotonin and melatonin ‒ with a DTPA-based cyclophane of high rigidity: 1H NMR shift and line-broadening

The ¹H NMR signals of the titled neurotransmitters undergo up-field shift accompanied by line-broadening in NMR titration with the DTPA-based cyclophane at pD 7.3; the cyclophane consists of a 4,4′-bis(1,1′-biphenyl-4,4′-dihydroxy)dianiline unit cyclised by a DTPA (diethylenetriaminepentaacetate) group through two amide linkages. Changes in chemical shifts of dopamine indicate the formation of a 1:1 complex with the formation constant K₁ 400 M^?1; the complex of serotonin is likely to form a 2:1 host?guest complex with β₂ ≈ 10⁵ M^?2; melatonin does not form a complex with definite stoichiometry. The primary binding forces in the dopamine and serotonin complexes are electrostatic interaction between cationic neurotransmitter and anionic cyclophane molecules, and the resulting ionic pairs are stabilised by encapsulation. The electrostatic interaction is weakened by electrolytes; in 0.1 M Trizma buffer, dopamine does not yield a definite complex, and serotonin forms a 1:1 complex with K₁ 80 M^?1. Extreme line-broadening of neurotransmitter signals suggests that the molecular motion of the guest molecule is slowed in the complex by interactions with the receptor molecule whose internal molecular motion is quenched partially. The high rigidity of the cyclophane enhances intermolecular interaction in the hydrophobic regions to prolong the lifetime of the complex.     

Alignment of liquid crystals using Langmuir‒Blodgett films of unsymmetrical bent-core liquid crystals

ABSTRACT

The properties of the thin films of liquid crystal (LC) molecules can be governed easily by external fields. The anisotropic structure of the LC molecules has a large impact on the electrical and optical properties of the film. The Langmuir monolayer (LM) of LC molecules at the air–water interface is known to exhibit a variety of surface phases which can be transferred onto a solid substrate using the Langmuir?Blodgett (LB) technique. Here, we have studied the LM and LB films of asymmetrically substituted bent-core LC molecules. The morphology of LB film of the molecules is found to be a controlling parameter for aligning bulk LC in the nematic phase. It was found that the LB films of the bent-core molecules possessing defects favour the planar orientation of nematic LC, whereas the LB films with fewer defects show homeotropic alignment. The defect in LB films may introduce splay or bend distortions in the nematic near the alignment layer which can govern the planar alignment of the bulk LC. The uniform layer of LB film facilitates the molecules of nematic to anchor vertically due to a strong van der Waals interaction between the aliphatic chains leading to a homeotropic alignment.     

Silver selective electrodes using ionophores functionalized with thioether‒amide‒amine

New poly(vinylchloride) (PVC) based liquid membrane sensors are reported containing neutral macrocyclic carrier as potential ionophores for sensing silver ions. Three macrocycles (L₁, L₂ and L₃) possessing two thioether, two amide and one secondary amine unit have been used in new PVC membrane-based sensor. At wide pH range of 4.5 to 8.0, these sensors exhibit linear responses in the concentration range of 1 × 10^–4 to 0.1 M and detection limit 6 × 10^–5 M for L₁ and 1 × 10^–4 M for L₂ and L₃ respectively with pseudo-Nernstian slopes between 43?46 mV/decade for all the three sensors. These sensors have short response time (<15 s) and long life time as these sensors do not show any considerable divergence in their performance over a period of four months. These sensors exhibit good selectivity for Ag⁺ over wide variety of interfering ions like alkali, alkaline earth, transition and some heavy metal ions. These proposed sensors could be used successfully as indicator electrodes in the potentiometric determination of Ag⁺ ions and also to determine anions like Cl^–, Br^–, I^–, S2^–, SCN^– and CN^–. Potentiometric titrations for halide ions in a mixture using these sensors and new titration method for the determination of detection limits are reported.     

Extraction of Metals in a Water‒Potassium Bis(Alkylpolyoxyethylene)Phosphate‒Ammonium Sulfate System with Various Photometric Reagents

The interfacial distribution of a number of organic photometric reagents in a water?potassium bis(alkylpolyoxyethylene)phosphate (oxyphos B)?ammonium sulphate splitting system is studied. It is found that alizarin complexone, 1-(2-pyridylazo)-2-naphthol-2 (PAN), bromothymol blue, rhodamine 6G, pyrogallol red, morin, fuchsine, malachite green, bromothymol blue, pyrocatechol violet (PCV), chromazurol S, and aluminon are extracted with partition coefficients higher than 100. A possibility of the extraction?photometric determination of gallium with PCV and cobalt with PAN is shown. The proposed procedures do not require the use of fire-hazardous, volatile, and toxic organic solvents.     

Magnetic properties of electrodeposited Ni‒P alloys with varying phosphorus content

The effect thermal treatment has on the magnetic properties (magnetization, saturation magnetization, and coercivity) of Ni?P alloys prepared via electrodeposition is studied. The process of amorphous Ni?P alloys devitrification is investigated by differential scanning calorimetry. The effects of chemical composition and thermal treatment on magnetic properties of the alloys are revealed.     

One-Pot Synthesis of 3,5-Disubstituted 1,2,4-Oxadiazoles Using Catalytic System NaOH‒DMSO

Russian Journal of Organic Chemistry - One-pot convenient process was developed for the production of 3,5-disubstituted 1,2,4-oxadiazoles by reaction of amidoximes with anhydrides or acyl chlorides...     

Analysis of diterpenoid compounds from the latex of two Euphorbiaceae by liquid chromatography‒electrospray ionisation mass spectrometry

The latex of Euphorbia papillosa A.St.-Hil. and Sapium glandulosum (L.) Morong was phytochemically investigated by liquid chromatography/mass spectrometry. The results reveal the presence of tigliane-type diterpenoid compounds, particularly 12-deoxyphorbol esters, in both species. In addition, ingenane-type diterpene esters were found in the latex of E. papillosa. The latex of S. glandulosum showed only tigliane-type diterpenes, confirming the literature data on this genus. According to mass data, we are proposing the presence of 10 compounds derived from 12-deoxyphorbol monoesters and diesters, from one 12-deoxyphorbaldehyde, from two ingenol derivatives and from one nitrogen-containing phorbol ester in the latex of the analysed species. Considering that 12-deoxy tigliane diterpenes are described as antitumour and antiviral agents, these results indicate a pharmacological potential for these two Euphorbiaceae species.     

Manipulation of the PdAu‒PdAuOx interface on Pd-Au bimetallic catalysts for the direct synthesis of hydrogen peroxide

Direct synthesis of H₂O₂ from H₂ and O₂ via heterogeneous catalysis is an environmentally friendly and atomically economic alternative to the traditional anthraquinone oxidation (AO) process. Optimizing the electronic and geometric structures of the active metals to break the current limitations of hydrogenation rate and H₂O₂ selectivity is a promising and challenging topic. In this study, a series of Pd-Au bimetallic catalysts supported on TiO₂ with a metal loading of 3.0 wt% and a constant Pd/Au molar ratio (Pd:Au = 2:1) were prepared. The catalysts were reduced in H₂ at different temperatures (473, 573 and 673 K), and their catalytic activity for the direct H₂O₂ synthesis were evaluated at 283 K and 0.1 MPa. H₂ reduced Pd-Au catalysts exhibited superior performance in direct H₂O₂ synthesis. The maximum H₂O₂ selectivity of 87.7% and H₂O₂ yield of 3116.4 mmol h⁻¹ g_Pd⁻¹ were achieved over the Pd_2.0Au_1.0-573 catalyst with a H₂ conversion of 12.8%. The tailored local chemical environment caused by H₂ reduction creates a balanced ratio of Pd⁰ and PdO_x sites, thus improving the selectivity towards H₂O₂. This work developed an effective strategy for fabrication of highly active and stable Pd-based H₂O₂ synthesis catalysts with high H₂O₂ yield.     

Ni(0)/NHC-catalyzed amination of N-heteroaryl methyl ethers through the cleavage of carbon‒oxygen bonds

Ni(0)/NHC-based catalyst system can promote the amination of N-heteroaryl methyl ethers via the cleavage of normally unreactive carbon–oxygen bonds. Electron-deficient N-heteroarenes including pyridine, quinoline, isoquinoline, and quinoxaline undergo amination to afford aminopyridine and related heteroarenes, which constitute an important class of compounds.     

Analysis of humic acid fouling during microfiltration using a pore blockage–cake filtration model

Fouling by natural organic matter, such as humic substances, is a major factor limiting the use of microfiltration for water purification. The objective of this study was to develop a fundamental understanding of the underlying mechanisms governing humic acid fouling during microfiltration using a combined pore blockage–cake filtration model. Data were obtained over a range of humic acid concentrations, transmembrane pressures, and stirring speeds. The initial flux decline was due to pore blockage caused by the deposition of large humic acid aggregates on the membrane surface, with a humic acid deposit developing over those regions of the membrane that have first been blocked by an aggregate. The rate of cake growth approaches zero at a finite filtrate flux, similar to the critical flux concept developed for colloidal filtration. The data were in good agreement with model calculations, with the parameter values providing important insights into the mechanisms governing humic acid fouling during microfiltration. In addition, the basic approach provides a framework that can be used to analyze humic acid fouling under different conditions.     

Constants of acid‒base equilibria in an aqueous amikacin aminoglycoside solution at 298 K

The acid dissociation constants of form pK₁ = 7.34 ± 0.01, pK₂ = 7.84 ± 0.01, pK₃ = 8.77 ± 0.01, pK₄ = 9.49 ± 0.01, and pK₅ = 10.70 ± 0.02 of cationic amikacin are determined by pH-metric titration at 25°C against the background of 0.1 mol/L KNO₃. K₁, K₂, K₃, and K₄ correspond to the dissociation of protons coordinated to amino groups, while K₅ characterizes the dissociation of the hydroxyl hydrogen atom, testifying to the amphoteric character of amikacin molecules. Applying density functional theory (DFT) with the B3LYP hybrid functional and the 6-311G**++ basis set, the partial charges on the atoms of an amikacin molecule are calculated. It is concluded that the dissociation of H(55)hydrogen atom occurs with a greatest partial charge of +0.53631.     

Effect of biochar on the mobility and photodegradation of metribuzin and metabolites in soil‒biochar thin-layer chromatography plates

Biochars obtained by biomass pyrolysis have been proposed as a soil amendment to improve soil properties and fertility as well as to retain pesticides and other environmental contaminants. The present study investigates the degradation of metribuzin herbicide and its metabolites deamino- (DA), deaminodiketo- (DADK) and diketo- (DK) metribuzin under simulated solar light and dark conditions as well as their mobility using TLC plates coated with soil and soil?biochar mixtures at 1% and 5% w/w ratio. Biochar was characterised by X-Ray diffraction, porosimetry, scanning electron microscopy and Fourier transform infrared spectroscopy. Degradation under light conditions followed biphasic kinetics, with bi-exponential model fitted better for the soil substrate, while the Gustafson–Holden model was found more appropriate to describe degradation kinetics in 1% soil/biochar mixture. In soil, DA presented the lowest degradation rate (DT₅₀:440.9 h), followed by metribuzin (DT₅₀:208.0 h), DADK (DT₅₀:110.8 h) and DK (DT₅₀:106.5 h). The addition of biochar reduced drastically the degradation or even inhibited the photolytic process for the studied reaction period. The mobility retention factor (Rf) in soil ranged from 0.49 for metribuzin to 0.63 for DADK. The addition of biochar practically immobilises the compounds in the surface layer as Rf ranged from 0.14 to 0.10 for metribuzin and from 0.23 to 0.16 for DADK in soil/biochar mixtures 1% and 5%, respectively. In conclusion, the addition of biochar reduced dramatically the photodegradation rates as well as the mobility of metribuzin and its metabolites due to increased adsorption.     

Kinetics and Mechanism of the Insertion Reaction of Arylisocyanates into C‒C Bond of Phosphabetaine Obtained ont the Basis of Triisopropylphosphine and 2-Cyanoethylacrylate

Abstract

On the basis of kinetic investigation o f previously discovered [I] insertion reaction of arylisocyanates into C-C bond of nvitter-ions, obtained on the basis of trialkylphoshines and Z-cyanoacrylates, the mechanism of this unusual reaction has been suggested. According to this mechanism the nucleophilic attack of nvitter-ion anionic center on the carbon atom of isocyanate group and nucleophilic attack of nitrogen atom on carbethoxylic group, leading to breakup of C-C bond, carry out relatively synchronously within one transition state on the concerted mechanism.     

Use of alternating electrical fields as anti-fouling strategy in ultrafiltration of biological suspensions – Introduction of a new experimental procedure for crossflow filtration

Results of a parameter study concerning the electro-ultrafiltration with alternating electric fields of aqueous solutions of bovine serum albumin are presented. The alternating electric field diminishes membrane fouling and hence yields a higher specific filtrate flux. The effect of the electric field depends on frequency (0.5–50 Hz), field strength (0–80 V cm⁻¹), conductivity (1–10 mS cm⁻¹), protein concentration (0.1–5 w%), and membrane material (values in brackets are the range of each parameter examined in this work). Low frequency and high field strength yield the best result for electro-ultrafiltration with alternating fields. The effectiveness of the electric field increases with rising conductivity up to the point where a limiting electrolytic current is reached. Increasing protein concentration diminishes the effect of the electric field. A new procedure to perform crossflow filtration experiments, the so-called step-change experiment, is proposed. The results of the new procedure are compared to results of conventional experiments. The step-change experiments yielded reproducible results in good agreement with conventional experiments.     

Syntheses of o-iodobenzyl alcohols‒BODIPY structures as potential precursors of bimodal tags for positron emission tomography and optical imaging

Aiming the faster development from bench to bedside of new potential tracers, multimodal tracers for positron emission tomography (PET) and optical imaging (OI) have emerged as a very promising tool. Indeed, they combine the simplicity of use of optical techniques for in vitro/in vivo pre-clinical studies with the various clinical possibilities offered by PET imaging using their radioactive versions. In this context, the preparation of new tags detectable by fluorescence imaging and potentially suitable for PET imaging after a last-step ¹¹C-labeling of the corresponding precursor has been investigated. Various designs and syntheses were explored by linking o-iodobenzyl alcohols and tetramethyl-BODIPY moieties together. Among them, the most promising structure was produced in 30% yield over five steps from a commercially available and inexpensive starting material.