Stereoconvergent Generation of a Contrasteric syn‐Bicyclopropylidene (=syn‐Cyclopropylidenecyclopropane) by Stille‐Like Coupling

Stereoisomerically pure endo‐ and exo‐7‐halo‐7‐(trimethylstannyl)benzonorcar‐3‐enes (=endo‐ and exo‐(1‐halo‐1a,2,7,7a‐tetrahydro‐1H‐cyclopropa[b]naphthalen‐1‐yl)trimethylstannane) 4 and 6 were selectively obtained by lithium? tin or magnesium? tin transmetalation in good yields (Scheme 2 and 3). The reaction of these compounds with copper(I) thiophene‐2‐carboxylate (CuTC) produced in both cases the corresponding C_S‐symmetric bicyclopropylidene (=cyclopropylidenecyclopropane) syn‐ 1 , a single diastereoisomer (Schemes 5 and 6). The structure of syn‐ 1 was undoubtedly elucidated by X‐ray single crystal diffraction. The coupling mechanism of the carbenoid cyclopropane is discussed (Scheme 7).     

Mesomorphic behaviour and TSDC measurements of ortho-metallated palladium(II) and platinum(II) complexes with S,O-donor co-ligands

A series of ortho-metallated Pd and Pt complexes containing an imine ligand carrying three alkoxy chains and N-benzoylthiourea derivatives as co-ligands were prepared and their liquid crystalline properties investigated. Their structures were assigned based on elemental analysis, IR and ¹H NMR spectroscopy, whereas thermal properties were investigated by differential scanning calotimetry and polarising optical microscopy. All the compounds exhibit monotropic transitions involving nematic and smectic A phases, with the mesomorphic behaviour strongly related to the type of N-benzoylthiourea as well as the metal centre used. The thermally stimulated depolarisation current technique was employed to determine the conduction mechanism, phase transition temperature and the activation energies for one of the ortho-metallated Pd complexes.     

Cloud point extraction of aluminum (III) in water samples and determination by electrothermal atomic absorption spectrometry,flame atomic absorption spectrometry and UV-visible spectrophotometry

Cloud point extraction was applied as a preconcentration step for the determination of trace level of Al(III) in water samples with electrothermal atomic absorption spectrometry (ETAAS), flame atomic absorption spectrometry (FAAS) and UV-visible spectrophotometry. The aluminum was extracted as aluminum-Eriochrome Cyanine R (ECR) complex, at pH 6 by micelles of the non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114). The investigations showed that the same CPE procedure can be used for different detection techniques. The results obtained from these techniques were evaluated. Under the optimal conditions, limit of detection obtained with ETAAS, FAAS and UV-visible spectrophotometry were 0.03 ng mL^?1, 0.06 µg mL^?1 and 0.01 µg mL^?1, respectively. The accuracy of the procedure was tested by analysing certified reference material. The method was successfully applied to determination of aluminum in water samples and dialysis fluid.     

Selective back-extraction and preconcentration of zinc(II) from metal-1,3,5-triketone extracts prior to its determination by flame atomic absorption spectrometry

A simple back-extraction method was developed for the separation and preconcentration of trace levels of zinc from different matrices. Ethyl-2-(4-methoxybenzoyl)-3-(4-methoxyphenyl)-3-oxopropanoylcarbamate (EMPC) was used as a new complexing agent for the extraction of zinc(II) from the aqueous sample phase to the methyl isobutyl ketone (MIBK) phase as Zn(EMPC)₂ complexes. The Zn(II) can be selectively stripped with 1?mL of 0.5?mol?L^?1 HCl from Mⁿ⁺(EMPC)_n complexes [Ag(I), Al(III), Cd(II), Cr(III), Cu(II), Fe(II), Fe(III), Mn(II), Ni(II), Pb(II) and Pd(II)] which dissolved in MIBK phase. Some experimental parameters, which are important for the whole extraction process, including pH, sample volume, shaking time, amount of the EMPC reagent, amount of MIBK, ionic strength, and type of back-extractant were investigated. The recovery for Zn(II) was greater than 95%. The detection limit of the method was found to be 0.2?µg?L ^{? 1} and the relative standard deviation as 6.4%. The concentrations of Zn(II) in the certified reference materials (LGC6019 river water and NIST-1547 peach leaves) by the presented method were in good agreement with the certified values. The proposed method was succesfully applied to the determination of zinc in some natural waters, rice, hair, soil, and tea samples.     

“Surface water” and “strong-bonded water” in cyclodextrins: a Karl Fischer titration approach

Cyclodextrins are some of the most used carriers for bioactive compounds (as host–guest complex) and many factors influence the association–dissociation of this complex, some of them being related to hydrophobicity. In the solid state, cyclodextrins contain two types of water molecules: “surface” water molecules (especially close to the crystal surface) and “strong-bonded” water molecules (especially from the cyclodextrin cavity), but the classification is hard to do, and the concentration of these water molecules are relatively difficult to estimate by simple methods. In the present study we used the volumetric Karl Fischer titration to estimate these types of water molecules in cyclodextrins by means of the rate of water reaction (related to diffusion from cyclodextrin crystals). “Surface” water molecules are titrated with rates between 1.8–2.8 mM/s for α-cyclodextrin, while for β-cyclodextrin these rates are little bit higher (2.9–3.4 mM/s). The rates corresponding to “strong-bonded” water molecules are approximately tens fold lower (0.05–0.3 mM/s for α-cyclodextrin and 0.15–0.33 mM/s for β-cyclodextrin). The approximate ratio between “surface” and “strong-bonded” water molecules could also be estimated by this simple and rapid method.     

The uranium recovery from aqueous solutions using amidoxime modified cellulose derivatives. IV. Recovery of uranium by amidoximated hydroxypropyl methylcellulose

Amidoxime modified hydroxypropyl methylcellulose (HPMC) films (HPMC-g-AO) were used for the recovery of uranium from aqueous solutions by a complexation process. The adsorption experiments were carried out by immersion of a certain amount of films in UO₂ ²⁺ solutions (resultant pH 4.1) ranging in concentration from 100 to 1,000 ppm. The effect of temperature (25–50 °C) on the adsorption capacity of HPMC-g-AO was investigated at the optimized time. The adsorption kinetics and the thermodynamics as well as the adsorption capacity of HPMC-g-AO films were investigated. The adsorption capacity was found as 765 mg UO₂ ²⁺/g dry film. The kinetic and the thermodynamic parameters (i.e. activation energy, enthalpy, entropy and Gibbs free energy) for the interaction of UO₂ ²⁺ with HPMC-g-AO were calculated based on known basic relations. The results showed that adsorption occurred through strong electrostatic interactions with an enthalpy of ?36.5 kJ/mol. The desorption of UO₂ ²⁺ were investigated using different desorption agents such as EDTA, HCl, NaHCO₃, and NaOH. After the 2 weeks treatment period, the highest desorption yield were found as 23 % with NaHCO₃.     

Synthesis of thio- and furan-fused heterocycles: furopyranone,furopyrrolone, and thienopyrrolone derivatives

We report herein the synthesis of a novel class of compounds, ethyl 4-oxo-4H-furo[3,2-c]pyran-6-yl carbonate, (7E)-7-[(dimethylamino)methylene]-4H-furo[3,2-c]pyran-4,6(7H)-dione, 5-oxo-N-phenyl-2,5-dihydro-4H-furo[3,2-b]pyrrole-4-carboxamide, and 5-oxo-N-phenyl-5,6-dihydro-4H-thieno[3,2-b]pyrrole-4-carboxamide starting from the corresponding acid derivatives. Intramolecular cyclization in the presence of thionyl chloride formed the target fused ring systems. Additional transformation was seen in the cyclization of furan-fused heterocycle. A mechanism was proposed based on experimental and computational findings.     

Synthesis and antibacterial properties of new phenothiazinyl- and phenyl-nitrones

The synthesis of new phenothiazinyl- and phenyl-nitrones under classical versus microwave heating conditions is described. Better yields were obtained under microwave irradiation in the condensation reactions of phenothiazyl-carbaldehyde with hydroxylamine derivatives. The structures of the new phenothiazinyl-nitrones were assigned on the basis of MS, FT–IR and NMR spectra. The new nitrones and some known phenyl-nitrones were screened for their antibacterial and antifungal activity against several Candida species, Gram negative bacteria, such as E. coli, Citrobacter spp, Morganella spp, Pseudomonas aeruginosa, Klebsiella pneumoniae (± ESBL), Proteus spp, Acinetobacter spp and the Gram positive bacterium Staphylococcus aureus, with moderate results.     

New fatty acid derivatives based on barbiturates and other cyclic β-dicarbonyl compounds and an acyl migration

The use of DCC, triethylamine and 4-dimethylaminopyridine in dichloromethane provides a general and standard one-pot procedure for the O-acylation of cyclic β-dicarbonyl compound derivatives (1) with palmitic and stearic acids which have long hydrocarbon tails, to synthesis of new type of fatty acid derivative in good to excellent yields. Structure elucidation was carried out by FT-IR, ¹H NMR and ¹³C NMR spectroscopy techniques. The acyl migration was also found in results and the corresponding structure was characterized by X-ray crystallography. A proposed mechanism was discussed for the formation of products.