Complex Activity and Sensor Potential toward Metal Ions in Environmental Water Samples of N-Phthalimide Azo-Azomethine Dyes

Herein, the spectral and electrochemical characterizations of three different substituted N-phthalimide azo-azomethine (NAA) dyes (L) containing an o-hydroxy group and their NAA-M(II) chelates [M(II): Cu, Ni, Co, Pb] were reported by using UV–Vis and fluorescence spectroscopy and potentiometric and voltamperometric techniques. The pK value of the dyes as well as the stoichiometry and stability of the NAA-metal chelates were studied, and the stoichiometry was found to be mostly 1:2 (ML₂) with high complex stability constant values. The sensor activity of N-phthalimide azo-azomethine derivatives toward pH and metal ions has been also investigated and tested for indicator application in acid–base analysis and detection of Cu(II) ions in real samples of surface river water using voltamperometric detection. The results showed that one of the ligands possesses the highest electrochemical response upon binding to copper ions and could be successfully used in the analysis of copper in water at a concentration range of the analyte from 3.7 × 10⁻⁷ to 5.0 × 10⁻⁶ mol L⁻¹, with analytical characteristics of the method being Sr = 1.5%, LOD = 3.58 µg L⁻¹ and LOQ =11.9 µg L⁻¹     

A note on almost kähler manifolds

For anyn ≥ 2, we give examples of almost Kähler conformally flat manifoldsM ²ⁿ which are not Kähler. We discuss the meaning of these examples in the context of the Goldberg conjecture on almost Kahler manifolds.     

Crystal and molecular structure of diastereomeric 2-diphenylthiophosphinoyl-cis-(4,6-dimethyl)-1,3-dithianes

The crystal and molecular structures of a pair of diastereomeric 2-diphenylthiophosphinoyl-cis-(4,6-dimethyl)-1,3-dithianes 2 have been determined by the X-ray method. The differences in corresponding bond distances in cis-2 and trans-2 are discussed in context of the anomeric effect operating in this heterocyclic system. The comparison of selected structural parameters between diastereomeric cis- and trans-dithianes 2 and their 5-t-butyl analogs 1 is also discussed. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:537–541, 1998     

Charge carrier transport in heterogeneous conducting polymer materials

The similarities of conductivity mechanisms of composites and nanocomposites and doped conjugated polymers that are also characteristic of specific heterogeneity are discussed. It is shown that the formulae developed to account for internal heterogeneity of conductive polymers can be applied also for polymer composites in spite of low overall content of the conductive phase. For fully organic nanocomposites (reticulate doped polymers) showing metal-like conductivity and a crossover temperature effective contribution of metallic phase is estimated. Examples of different properties of nanoparticles forming conducting networks as compared with the bulk crystals are discussed.     

On some Closed Magnetic Curves on a 3-torus

We consider two magnetic fields on the 3-torus obtained from two different contact forms on the Euclidean 3-space and we study when their corresponding normal magnetic curves are closed. We obtain periodicity conditions analogues to those for the closed geodesics on the torus.     

Stereoselective Cyclopropanation of 2‐[(S)‐(4‐Methylphenyl)sulfinyl]cyclopent‐2‐en‐1‐one with Sulfur Ylides and α‐Halo Carbanions. Preliminary Communication

The cyclopropanation of the title compound (S)‐ 2 with various sulfur ylides has been examined. The reaction with methylenesulfonium ylides gave the corresponding cyclopropanes 4 with low diastereoselectivity. The formation of the second product 5 arising from the subsequent methylenation of the CO group was also observed. A clean cyclopropanation of (S)‐ 2 took place with ethyl (dimethylsulfanylidene)acetate affording the cyclopropanes 6 , with high π‐facial selectivity, but low endo/exo ratio. A high endo/exo selectivity, but low π‐facial selectivity was observed in the reaction of (S)‐ 2 with (2‐ethoxy‐2‐oxoethyl)(diphenyl)sulfonium tetrafluoroborate. The use of α‐bromoacetate carbanion as the cyclopropanation reagent resulted in the formation of 6 with very high facial and endo/exo‐selectivity. In a proposed explanation of the stereochemical outcome of the cyclopropanations investigated, the ground‐state conformation of the sulfoxide 2 and the transition‐state structure of the initial addition step were taken into account.     

Characterisation of multi-extruded poly(lactic acid)

The effect of multiple (up to 10 times) extrusion of polylactide on its mechanical properties (determined by a static tension test), Charpy impact strength, melt flow rate, phase transition temperatures, degradation temperature, and permeability of water vapour and oxygen is presented. It was found that, with raising the number of the extrusion cycles, the tensile strength at break slightly diminished and the impact strength clearly decreased, while the melt flow rate and water vapour and oxygen transmission rates steadily increased. Variation of the number of extrusion cycles did not affect the glass transition temperature, whereas it did cause a lowering of the cold crystallisation temperature and slight diminishing of the melting point. The presented results indicate that PLA technological waste is suitable to be reused as an additive to a neat polymer.     

Membrane-bound dehydrogenases from Gluconobacter sp.: Interfacial electrochemistry and direct bioelectrocatalysis

Although membrane-bound dehydrogenases isolated from Gluconobacter sp. (mainly PQQ-dependent alcohol and fructose dehydrogenase) have been used for preparing diverse forms of bioelectronic interfaces for almost 2 decades, it is not an easy task to interpret an electrochemical behaviour correctly. Recent discoveries regarding redox properties of membrane-bound dehydrogenases along with extensive investigations of direct electron transfer (DET) or direct bioelectrocatalysis with these enzymes are summarized in this review. The main aim of this review is to draw general conclusions about possible electronic coupling paths of these enzymes on various interfaces via direct electron transfer or direct bioelectrocatalysis. A short overview of the metabolism and respiration chain in Gluconobacter relevant to interfacial electrochemistry is given. Biosensor devices based on DET or direct bioelectrocatalysis using membrane-bound dehydrogenases from Gluconobacter sp. are described briefly with the emphasis given on practical applications of preparing enzymatic biofuel cells. Moreover, interfacial electrochemistry of Gluconobacter oxydans related to the construction of microbial biofuel cells is also discussed.