An X-ray diffraction, magnetic susceptibility and spectroscopic studies of Yb2−xCrxO3

Polycrystalline samples with general formula Yb_2−xCr_xO₃ (0<x<0.03), obtained by sol-gel method and analyzed by X-ray diffraction, formed solid solutions over all the mentioned range. Cr showed a maximum solubility of 2.8 mol% in Yb₂O₃ sesquioxide at 1000 °C. A preferential substitution of Cr³⁺ ions over two cationic sites, 8b and 24d in the space group Ia-3 was found. The lattice parameters a are found to vary linearly (10.4402(4) Å <a<10.4372(1) Å) with the composition x. The two independent atoms Yb/Cr have octahedral coordination; however, the degrees of distortion of their coordination polyhedron are different. Replacing Yb³⁺ by Cr³⁺ introduces slight changes in the atomic coordinates leading to an increase of the mean cation-anion distances. The ability of Raman spectroscopy to detect changes in local coordination is utilized. A pseudo-tetrahedral coordination for the Cr³⁺ in the 24d site was found. Magnetic susceptibility measurements of all samples were done in a temperature range of 2-50 K. For T<37 K, the inverse paramagnetic susceptibilities depend linearly on temperature. However, in the high-temperature region, for T>37 K, the inverse paramagnetic susceptibilities are non-linear versus temperature. This deviation from the Curie-Weiss behaviour was discussed.     

Highly Acidic Conjugate‐Base‐Stabilized Carboxylic Acids Catalyze Enantioselective oxa‐Pictet–Spengler Reactions with Ketals

Acyclic ketone‐derived oxocarbenium ions are involved as intermediates in numerous reactions that provide valuable products, however, they have thus far eluded efforts aimed at asymmetric catalysis. We report that a readily accessible chiral carboxylic acid catalyst exerts control over asymmetric cyclizations of acyclic ketone‐derived trisubstituted oxocarbenium ions, thereby providing access to highly enantioenriched dihydropyran products containing a tetrasubstituted stereogenic center. The high acidity of the carboxylic acid catalyst, which exceeds that of the well‐known chiral phosphoric acid catalyst TRIP, is largely derived from stabilization of the carboxylate conjugate base through intramolecular anion‐binding to a thiourea site.     

Synthesis, characterization and electro-spectroelectrochemical studies of four macrocyclic Schiff-base Co(II) complexes having N2O2 set of donor atoms

Four macrocyclic Schiff-base cobalt complexes, [CoL¹][NO₃]₂ · 3H₂O, [CoL²][NO₃]₂ · 4H₂O, [CoL³][NO₃]₂ · 4H₂O and [CoL⁴][NO₃]₂ · 2H₂O, were synthesized by reaction of salicylaldehyde derivatives with 1,4-bis(3-aminopropoxy)butane or (±)-trans-1,2-diaminocyclohexane and Co(NO₃)₂ · 6H₂O by template effect in methanol. The metals to ligand ratio of the complexes were found to be 1:1. The Co(II) complexes are proposed to be tetrahedral geometry. The macrocyclic Co(II) complexes are 1:2 electrolytes as shown by their molar conductivities (Λ_M) in DMF (dimethyl formamide) at 10^?3 M. The structure of Co(II) complexes is proposed from elemental analysis, Ft-IR, UV–visible spectra, magnetic susceptibility, molar conductivity measurements and mass spectra. Electrochemical and thin-layer spectroelectrochemical studies of the complexes were comparatively studied in the same experimental conditions. The electrochemical results revealed that all complexes displayed irreversible one reduction processes and their cathodic peak potential values (E _pc) were observed in around of ?1.14 to 0.95 V. It was also seen that [CoL¹][NO₃]₂ · 3H₂O and [CoL²][NO₃]₂ · 4H₂O exhibited one cathodic wave without corresponding anodic wave but, [CoL³][NO₃]₂ · 4H₂O and [CoL⁴][NO₃]₂ · 2H₂O showed one cathodic wave with corresponding anodic wave, probably due to the presence of different ligand nature even if the complexes have the same N₂O₂ donor set. In view of spectroelectrochemical studies [CoL³][NO₃]₂ · 4H₂O showed distinctive spectral changes in which the intensity of the band (λ = at 316 nm, assigned to n → π* transitions) decreased and a new broad band in a low intensity about 391 nm appeared as a result of the reduction process based on the cobalt center in the complex.     

Synthesis and spectroscopic studies of novel transition metal complexes with schiff base synthesized from 1,4-bis-(<Emphasis Type="Italic">o</Emphasis>-aminophenoxy)butane and salicyldehyde

The new Co(II), Cu(II), Ni(II) and Zn(II) complexes of potentially N₂O₂ Schiff base ligand [N,N’-bis(salicyldehydene)-1,4-bis-(o-aminophenoxy)butane] (H₂L) prepared from 1,4-bis-(o-aminophenoxy)butane and salicyldehyde in DMF. Microanalytical data, elemental analysis, magnetic measurements, ^lH NMR, ¹³C NMR, UV-visible and IR spectra as well as conductance measurements were used to confirm the structures. In all complexes, H₂L behaves as a tetradentate. The article is published in the original.     

Spectroscopic studies of inclusion complex of β-cyclodextrin and benzidine diammonium dipicrate

Formation of inclusion complex between benzidine diammonium dipicrate and β-cyclodextrin with stoichiometry 1:2 (guest–host) has been established by UV, ¹H NMR, ¹³C NMR, IR spectra and powder X-ray diffractometry. ¹H NMR studies are used to confirm the inclusion and to provide information on the geometry of dipicrate inside the cavity of β-cyclodextrin.     

Synthesis,Spectroscopic and Electrochemical Studies of Novel Transition Metal Complexes with Quadridentate Schiff Base

A novel quadridentate, N₂O₂ type Schiff base, synthesized from 1,4‐bis‐(o‐aminophenoxy)butane and 2‐hydroxynaphthalin‐1‐carbaldehyde, forms stable complexes with transition metal ions such as Co(II), Cu(II) and Ni(II) in DMF. Microanalytical data, elemental analysis, magnetic measurements, UV‐visible and IR‐spectra as well as conductance measurements were used to confirm the structures. Electrochemical measurements show that metal complexes undergo quasi‐reversible one‐electron redox processes. The voltammetric results also revealed that the CuL complex has the highest electron transfer rate indicating that both the Cu(II) and Cu(I) forms appear in a similar planar configuration, so the electron transfer does not require larger reorganization of the complex.     

Phytochemicals,antioxidant, anti-acetyl-cholinesterase,and antimicrobial activities of decoction and infusion of Pelargonium graveolens

Abstract

In Tunisia, Pelargonium graveolens is widely consumed as a food aromatizing hydrosol. Recent studies have shown the potential of plant solvent-free extracts as food and pharmaceutical natural additives. Accordingly, in this study, we investigate the phenolic content, the volatile fractions of green P. graveolens extracts such as infusion and decoction, and we evaluate their biological activities. The total phenolic content of the infusion (27.05?mg GAE/gDM) is significantly different from that of decoction (31.2?mg GAE/gDM). The GC-MS analysis identified about twenty volatile components in both extracts. The DPPH inhibition and the β-carotene bleaching tests of the infusion and the decoction had considerable results. Besides, infusion and decoction exhibited a relatively high anti-acetyl-cholinesterase activity and a considerable antimicrobial activity against S. aureus, among three tested pathogenic bacteria.     

Three-component,one-pot synthesis of pyrano[3,2-c]chromene derivatives catalyzed by ammonium acetate: Synthesis,characterization, cation binding,and biological determination

Three-component reaction of arylaldehydes with malononitrile and 4-hydroxycoumarine using CH₃COONH₄ as a catalyst at reflux was used for the synthesis of novel substituted pyrano[3,2-c]chromene derivatives. The structure of these compounds was assigned by spectroscopic data such as (IR, ¹HNMR, ¹³CNMR, and mass spectral data). The cation binding properties of chromene derivatives 4a-c towards Cu²⁺, Ni²⁺, and Zn²⁺ were studied in methanol. The results showed that Zn²⁺ is the most complexed in this series of cations, and 4c is best complexed with either Ni²⁺ and Zn²⁺. Antimicrobial properties of new pyrano[3,2-c]chromene derivatives are investigated, the compound 4c presents against Micrococcus luteus LB 14110 an MIC value of 0.0185 mg/mL quite better to that of ampicillin (0.0195 mg/mL) used as standard. Concerning acetylcholinesterase inhibition activity (AChEI), compound 4c presents an interesting AChEI activity with an inhibition of 52%.     

Synthesis,reactions, and antimicrobial activity of some novel pyrazolo[3,4-d]pyrimidine,pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine,and pyrazolo[4,3-e][1,2,4]triazolo[3,4-c]pyrimidine derivatives

Treatment of N-phenyl-substituted benzenecarbo-hydrazonoyl chlorides 1a - d with malononitrile in sodium ethoxide solution gave 5-amino-4-cyanopyrazole derivatives 2 - 5 . Compounds 2 - 5 were converted to formidate derivatives 6 - 9 upon treatment with TEOF in acetic anhydride. The reaction of the latter products 6 - 9 with hydrazine hydrate gave imino-amino derivatives 10 - 13 , which was converted to hydrazino derivatives 14 - 17 by refluxing with hydrazine hydrate. Hydrazino as well as imino-amino derivatives undergo condensation, cyclization, and cycloaddition reactions to give pyrazolo[3,4-d]pyrimidine 18 - 21 , pyrazolo[4,3-e][1,2,4]triazolo-[3,4-c]pyrimidine 22 - 27 , and pyrazolo[3′,4′:4,5]pyrimido[1,6-b][1,2,4]triazine 42 - 44 derivatives. Antimicrobial studies are performed using two Gram-positive bacteria and two Gram-negative bacteria. Data indicated that compounds 5 , 28D , 29B , and 31D are exploring elevated antibacterial effects against all strains tested. Compound 28D is the most promising antibacterial agent against the delicate bacterial strain Bacillus subtilis and Pseudomonas aeruginosa with high effectiveness (low minimum inhibitory concentration [MIC] value) 40 and 60 μg/mL, respectively.     

Optical,thermal, and magnetic properties of a microporous fluorinated iron phosphate: (H3O)2[Fe4(H2O)2F4(PO4)2(HPO4)2](H2O)

The non-centrosymmetric microporous fluorinated iron phosphate, (H₃O)₂[Fe₄(H₂O)₂F₄(PO₄)₂(HPO₄)₂](H₂O), is endowed with properties. In fact, the thermogravimetric analysis study shows a mass loss evolution as a temperature function. The optical study was also examined by UV–vis absorption. The magnetic results reveal the appearance of a ferromagnetic behavior at low temperature (Tc = 11.64 K).