Variation in the regioselectivity of levulinic acid bromination in ionic liquids

The reaction of levulinic acid and its esters with bromine in ionic liquids results in the formation of 3-bromo derivatives as the major products and not the 5-bromo substituted isomers, which are typically formed in organic solvents. The bromination of levulinic acid in ionic liquids in the presence of urea leads to the formation of 5-bromolevulinic acid.     

Novel Ionophores for Barium‐Selective Electrodes: Synthesis and Analytical Characterization

A novel way of synthesis is developed for the Ba²⁺ selective neutral Ionophore 2a : 2,2′‐[1,2‐phenylenebis(oxyethane‐2,1‐diyloxy)]bis(N‐benzyl‐N‐phenylacetamide) and its methyl ( 2b ), buthyl ( 2c ), and hexyl ( 2d ) derivatives. Ba²⁺ selective electrodes based on Ionophores 2a – d are compared with those with commonly used Ionophore 1 : N,N,N′,N′‐tetracyclohexyl‐oxybis(o‐phenyleneoxy) diacetamide. It is shown that Ionophores 2a – d , particularly 2b , are superior for measurements of Ba²⁺ in the presence of Ca²⁺, and in acidic solutions. Segmented sandwich membrane studies suggest formation of complexes IL₂²⁺ for Ba²⁺, Ca²⁺ and Mg²⁺ ions with Ionophore 2b , while H⁺ ions apparently form complexes H₂L²⁺. The values of the complex formation constants are consistent with the selectivity coefficients.     

Simultaneous determination of fluoroquinolones,sulfonamides and tetracyclines in sewage sludge by pressurized liquid extraction and liquid chromatography electrospray ionization-mass spectrometry

A new scheme for the quantitative determination of traces of fluoroquinolones (FQs), tetracyclines (TCs) and sulfonamides (SAs) in sewage sludge was developed. The compounds were simultaneously extracted from sewage sludge by pressurized liquid extraction (PLE). A novel and effective method for PLE was developed. Solid-phase extraction was used for cleaning up the extracts. Identification and quantification of the compounds was done using high-performance liquid chromatography with electrospray ionization mass spectrometry in selected reaction monitoring mode. The best recovery of FQs and TCs was obtained by using hydrophilic–lipophilic balance cartridges, recoveries ranged 59% for norfloxacin to 82% for ofloxacin and 95% for doxycycline; for SAs strong cation-exchange cartridges were more efficient, recoveries were 96% for sulfamethoxazole and 43% for sulfadimethoxine. Limit of quantification ranged from 0.1 ng/g for SAs to 160 ng/g for tetracycline. Method precision for TCs was 5.06% and 1.12%, and for SAs 0.43% and 2.01%. FQs precision ranged from 0.77% to 1.89%.     

Copper(II), palladium(II) and platinum(II) chloride complexes with 5-amino-2-tert-butyltetrazole: Synthesis, characterization and cytotoxicity

Complexes CuL₃Cl₂, PdL₂Cl₂ and PtL₂Cl₂, where L is a novel ligand from the series of 2-substituted 5-aminotetrazoles, namely 5-amino-2-tert-butyltetrazole (1), have been synthesized by the reaction of metal(II) chlorides with 1 and characterized by IR spectroscopy, thermal and X-ray analyses. The crystallographic structural analysis of these complexes revealed that 1 acts as a monodentate ligand coordinated to the metal via endocyclic N4 atom. Platinum complex demonstrates promising cytotoxicity against human cervical carcinoma cells with IC₅₀ value average between those of cisplatin and carboplatin.     

The influence of the conditions of the anodic formation and the thickness of Ag(I) oxide nanofilm on its semiconductor properties

The anodic formation of Ag(I) oxide nanofilms on polycrystalline silver and Ag–Au alloys as well as on low-index single crystals of silver in 0.1?М KOH was examined. By the methods of photocurrent i _ph and photopotential E _ph measurements, the n-type conductivity of Ag₂O film was established. Since the film (6–120 nm) is thinner than the space charge region, the dependence of photocurrent and photopotential appears on the film thickness L: i _ph ~L and E _ph ~L ². The transition from polycrystalline silver to single crystals as well as the addition of a small amount of gold (X _Au?≤?4 at.%) into the silver lattice decreases the degree of deviation from the stoichiometric composition Ag₂O. The parameters of Ag₂O film (optical absorption coefficient α, donor defects concentration N _D, space charge region W, and Debye’s length of screening L _D) depend on the index of a crystal face of silver, volume concentration of gold X _Au in the alloy, and film-formation potential E. At Е?=?0.52 V, the sequences of variation of these parameters correlate with the reticular density sequence. The growth of the potential disturbs these sequences. The band gap in Ag₂O formed on Ag_poly, Ag_hkl, and Ag–Au is 2.32, 2.23, and 2.19 eV. Flat band potential in Ag(I) oxide, formed on Ag_poly in 0.5 M KOH is 0.37 V. The appearance of the clear dependence between the state of the oxide/metal interface and the structure-sensitive parameters of semiconductor Ag(I) oxide phase allows considering the anodic formation of Ag₂O on Ag as a result of the primary direct electrochemical reaction, not of the precipitation from the near-electrode layer.     

Spherical polymer brushes under good solvent conditions: molecular dynamics results compared to density functional theory

A coarse grained model for flexible polymers end-grafted to repulsive spherical nanoparticles is studied for various chain lengths and grafting densities under good solvent conditions by molecular dynamics methods and density functional theory. With increasing chain length, the monomer density profile exhibits a crossover to the star polymer limit. The distribution of polymer ends and the linear dimensions of individual polymer chains are obtained, while the inhomogeneous stretching of the chains is characterized by the local persistence lengths. The results on the structure factor of both single chain and full spherical brush as well as the range of applicability of the different theoretical tools are presented. Finally, a brief discussion of the experiment is given.     

Nondestructive three-dimensional analysis of layered polymer structures with chemical imaging

Three-dimensional (3D) chemical information was obtained by means of a combination of two-dimensional attenuated total reflection Fourier transform infrared (ATR-FT-IR) imaging with a focal plane array detector and variable angle depth profiling. Since the penetration depth of the evanescent wave in ATR spectroscopy is not limited by diffraction, it was possible to resolve thin sandwiched polymer layers nondestructively within a stack of polymer layers. Chemical images were obtained from layers of different thickness of the laminate by moving a custom-made aperture to specific positions on the condenser lens of the ATR accessory. Sequences of absorption images detect the successive appearance of thin, buried layers of polybutylmethacrylate (d(PBMA) = 400 nm) and polycarbonate (d(TMPC) = 300 nm) in different depths of the stack of polymer layers. The depth resolution of variable-angle ATR-FT-IR imaging is sufficiently high to detect surface roughness at the interface between different polymer layers. Two different stacks of polymers with reordered sandwich-layers were imaged simultaneously, demonstrating the potential of variable angle ATR-FT-IR for 3D-imaging of a sample with xyz-heterogeneity, which can be a powerful analytical technique for materials science and biomedical research.     

A Conductometric Sensor Specific for Cationic Surfactants

In this work, a fast, sensitive and miniaturised conductometric sensor based on interdigitated electrodes, working in differential mode, was developed for the determination of cationic surfactants. The membrane was composed of a polymer (PVC), a plasticizer (dinonylphtalate (DNP)) and a carrier (sodium tetraphenylborate (NaBΦ₄)). The sensor response was linear from at least 10^?9 M to 10^?2 M for dodecyltrimethylammonium (DTA⁺). No significant loss of sensor response was observed after 8 weeks. The sensor exhibited a lower sensitivity and a narrower dynamic range for tetrabutylammonium, decyltrimethylammonium and cetyltrimethylammonium cationic surfactants. A ten times lower sensitivity was observed for laurylsulfate anionic surfactant, (LS^?).     

Application of ICP-MS for Multielement Analysis in Small Sample Amoun ts of Pathological Thyroid Tissue

 As a result of the Chernobyl nuclear power plant accident in 1986, thyroid pathologies occurred among children in some regions of Belarus. Besides the irradiation of children’s thyroids by radioactive iodine and caesium nuclides, toxic elements from fallout are a direct risk to health. Inductively coupled plasma quadrupole-based mass spectrometry was used for multielement determination in small amounts (1–10 mg) of thyroid tissue samples obtained during thyroid operations in Minsk hospitals. The accuracy of the applied analytical technique for small biological sample amounts was checked using NIST Standard Reference Material oyster tissue (SRM 1566b) and by comparison with independent analytical methods, such as neutron activation analysis. Almost all essential elements as well as a number of toxic elements such as Cd, Pb, Hg, U etc. were determined in a multitude of human and animal thyroid tissues (up to 1 mg sample material) by quadrupole-based ICP-MS using micronebulization. In general, the thyroid tissue affected by pathology is characterized by higher calcium content. Some other elements, among them Fe, Mn, V, As, Cr, Ni, Pb, U, Ba, Sb, were also accumulated in such tissue. The results obtained will be used as initial material for further specific studies of the role of particular elements in thyroid pathology development. Received November 15, 1999. Revision March 15, 2000.