The first total synthesis of the (±)-17-methyl-trans-4,5-methyleneoctadecanoic acid and related analogs with antileishmanial activity

The first total synthesis of the marine cyclopropane fatty acid (±)-17-methyl-trans-4,5-methyleneoctadecanoic acid was accomplished in eight steps and in 9.1% overall yield starting from 1-bromo-12-methyltridecane. The cis analog (±)-17-methyl-cis-4,5-methyleneoctadecanoic acid was also synthesized but in seven steps and in 16.4% overall yield. With the two isomeric cyclopropane fatty acids at hand it was possible to unequivocally corroborate the trans relative configuration of the naturally occurring fatty acid by gas chromatographic co-elution of the corresponding methyl esters. The cis isomer was cytotoxic to Leishmania donovani promastigotes with an IC₅₀ of 300.2 ± 4.2 μM.     

An Efficient N‐Arylation of Heterocycles with Aryl‐, Heteroaryl‐, and Vinylboronic Acids Catalyzed by Copper Fluorapatite

N‐Arylation of N‐containing heterocycles, such as pyrazoles, imidazoles, and benzimidazoles with aryl‐, heteroaryl‐, and vinylboronic acids was efficiently carried out by copper fluorapatite (CuFAP) catalyst in MeOH at room temperature under base‐free conditions. The N‐arylated heterocycles were isolated in good‐to‐excellent yields.     

Structure of Three Related Diphosphorus Ligands: Highlighting the Significance of the Backbone

Abstract  

The three compounds contained in this report—4,6-bis(diphenylphosphino)-10,10-dimethylphenoxasilin (sixantphos), 1; 4,5-bis(diphenylphosphino)-9-isopropylidenexanthene, (isopropxantphos) 2 and bis-(2-diphenylphosphino)-p-tolyl) ether (PTEphos) 3, all contain a common ether-linked diphenylphosphino backbone. These structures are of interest with respect to the intra-molecular P···P distance which is 3.884(2), 4.104(2) and 5.151(2) ? for 1, 2 and 3 respectively. The differences in the P···P distances are as a result of the variations in the backbones. Structure 1 shows a significant roof-like bending of the backbone along the axis of planarity involving the oxygen and Si donor atoms. Compound 2 is also folded with a larger dihedral angle of 35.85(2)° as compared to 24.14(2)° found in 1. The backbone in structure 3 is significantly bent and twisted with a dihedral angle of 67.34(2)°. These data show the effect on the intra-molecular P···P distance of varying the backbone of three xantphos-type ligands, with respect to the nature of the heterocycle donor 1, the substituent on the donor 2 and total loss of xanthene character 3.     

Synthesis,structural and electrical properties of Ti modified Bi2Sn2O7 pyrochlore

Polycrystalline ceramic samples of Bi₂Sn_2−xTi_xO₇ (x=0.00, 0.2, 0.4, 0.6 and 0.8) have been synthesized by standard high temperature solid state reaction method. The effect of homovalent cation (titanium) substitution on the Sn-site on the structural and electrical properties of the pure Bi₂Sn₂O₇ ceramic have been studied by X-ray diffraction followed by SEM, dielectric and dc conductivity studies. The structural analysis indicates that the increase of titanium contents do not lead to any secondary phase. The frequency and temperature dependent dielectric studies have been carried out. It is found that the Ti doping reduces the material particle size. The size of the particles are strongly influenced by the addition of titanium to the system. The substitution of Ti for Sn ions affected the degree of disorder and modified the dielectric properties leading to more resistive ceramic compounds. The activation energies of all the compounds were calculated using the relation σ=σ₀exp(−Ea/kT).     

The effect of dendritic pendants on the folding of amphiphilic copolymers via supramolecular interactions

The supramolecular folding of amphiphilic heterograft copolymers equipped with dendritic pendants is investigated using a combination of proton nuclear magnetic resonance (¹H NMR) spectroscopy, small‐angle X‐ray scattering, and circular dichroism spectroscopy. Hereto, the linear poly(ethylene glycol) pendants normally used to convey water compatibility are partially substituted with branched analogues. For one set of copolymers, second‐generation polyglycerol dendrons are directly attached to the polymer backbone, while for the other a hydrophilic linker is placed in between. The results show that the branching of the hydrophilic pendants affects the local structure of the folded copolymer but does not influence the overall conformation and single‐chain character of the folded copolymers in solution. All copolymers fold into 4–5 nm single‐chain polymeric nanoparticles with a very compact spherical morphology, independent of the dendritic content of the copolymer. Intriguingly, the incorporation of the dendritic pendants affects the formation of a structured interior even at low incorporation ratios. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 411–421     

Copper(I) Derivative of Pyridine-3-carbaldehyde-N-ethylthiosemicarbazone and Triphenylphosphine—First Case of Crystal Structure Study

The synthesis and crystal structure of pyridine-3-carbaldehyde-N-ethylthiosemicarbazone (3-pytscH-NHEt) 1, and its Cu^I complex of stoichiometry, [CuCl(3-pytscH-NHEt)(PPh₃)₂] 2, studied using single crystal X-ray crystallography, are reported in this paper. Crystal data: 1, monoclinic, P2₁/n, a?=?6.6322(3), b?=?21.1200(8), c?=?7.2989(3) Å; β?=?91.883(4), T?=?173(2), R factor?=?0.0457; 2: triclinic, P-1, a?=?19.3600(5), b?=?20.6241(6), c?=?23.8015(6) Å,α?=?92.647(2), β?=?104.388(2), γ?=?114.377(3), R factor?=?0.0662. The thio-ligand, as a neutral entity, is coordinating to Cu through its S donor atom in complex 2. It has exhibited an unusual feature of forming four independent molecules (A, B, C, D) in the unit cell, with minor differences in the bond angles / distances / torsion angles. The geometry of each molecule of 2 is distorted tetrahedral. Crystal packing, as well as Infrared, electronic absorption and proton NMR spectroscopic studies, are also reported. Copper compound 2 represents the first example of a structurally studied copper coordination compound of 3-pyridyl based thiosemicarbazones.

Graphical Abstract

Copper(I) chloride with pyridine-3-carbaldehyde-N-ethylthiosemicarbazone and PPh₃ in CH₃CN yielded a copper compound, 2 (Green-Cl, blue-N; aqua-Cu, orange-S, magneta-P).

     

Hydrogen diffusivity,kinetics of H2O/H2 charge transfer and corrosion properties of LaNi5-powder,composite electrodes in 6 M KOH solution

Meticulous analysis of galvanostatic charge/discharge dependencies of the LaNi₅-based, powder composite electrode, in terms of determination of characteristic kinetic parameters of hydrogen storage electrode materials working in concentrated alkaline solution has been carried out. A special attention has been paid to the precise determination of charge and discharge times. The cathodic curves reveal their stepwise nature which allows to receive information of hydride material corrosion phenomena and determine the real time of atomic hydrogen absorption. The graphical way of determining of reduction times, based on differential cathodic curves is proposed. The knowledge of hydrogen absorption and desorption times allows to determine hydrogen diffusivity within the tested material with acceptable accuracy. The effect of external pressure (0.5–4 bar) on hydrogen absorption ability of LaNi₅-based material is also discussed. The exchange current density of H₂O/H₂ system distinctly increases with external pressure, at the same time, kind of gas atmosphere (Ar or H₂) scarcely affects the exchange current on the LaNi₅ electrode. The hydrogen capacity increases when the charge/discharge rate decreases. The reduction times of oxide phases formed during electrode discharge can be a measure of material corrosion rate. It is shown that the rate of LaNi₅ corrosion process strongly increases with the electrode cycling.     

Hydrogen diffusivity in the massive LaNi5 electrode using voltammetry technique

The Randles–Sev?ik relationship has been applied to evaluate atomic hydrogen diffusivity in massive LaNi₅ intermetallic compound. The electrode was cathodically hydrogenated in 6 M KOH solution (22 °C), and then voltammetry measurements were carried out at various, very slow potential scan rates (υ?=?0.01–0.1 mV?·?s^?1). At potentials more noble than the equilibrium potential of the H₂O/H₂ system, the anodic peaks were registered as a consequence of oxidation of hydrogen absorbed in cathodic range. The peak potentials linearly increase with the logarithm of the scan rate with a slope of 0.059 V. The slope testifies to a symmetric charge transfer process with symmetry factor α?=?½. The peak currents linearly increase with the square root of the potential scan rate, and the straight line runs through the origin of the coordinate system. The slope of the I _a ^(peak) ?=?f(υ ^1/2) straight line is a measure of the atomic hydrogen diffusion coefficient. Assuming the hydrogen concentration in the LaNi₅ material after cathodic exposure to be C _0,H?=?0.071 mol?·?cm^?3 (63 % of theoretical value), the hydrogen diffusion coefficient equals D _H?=?2.0?·?10^?9 cm²s^?1. Extrapolation of rectilinear segments of potentiodynamic polarization curves with Tafel slopes of 0.12 V and linear polarization dependencies from voltammetry tests allowed the exchange current densities of the H₂O/H₂ system on the tested material to be determined. The exchange current densities on initially hydrogenated LaNi₅ alloy are close to 1 mA?·?cm^?2, irrespective of the electrode potential scan rate.     

Stress analysis by combination of holographic interferometry and boundary-integral method

The paper describes a hybrid experimental and numerical method analysis of bodies. It consists of the experimental method of double-aperture speckle interferometry and the boundary-integral method. The interference patterns allowing evaluation of the displacement vector are obtained by the speckle interferometry. The boundary displacements obtained experimentally are conveniently used for the calculation of stresses in the body by the boundary-integral method. Some examples bear witness of the effectiveness and accuracy of the hybrid technique.     

Second‐sphere coordination in anion binding: cis‐diazido­bis(ethyl­ene­diamine‐κ2N,N′)cobalt(III) picrate

In the title compound, [Co(N₃)₂(C₂H₈N₂)₂](C₆H₂N₃O₇), the cations share NH₂⋯NH₂ edges with picrate anions via second‐sphere N—H⋯O hydrogen bonds.