Carbon Ceramic Electrodes Modified with Laccase from Trametes hirsuta: Fabrication,Characterization and Their Use for Phenolic Compounds Detection

Fungal laccase (Lc) from the basidiomycete Trametes hirsuta was immobilized on top of a carbon ceramic electrode using physical absorption. Direct, unmediated heterogeneous electron transfer between Lc and the carbon ceramic electrode (CCE) under aerobic conditions was shown. The bioelectrocatalytic reduction of oxygen on Lc‐CCE started at about 430 mV vs. Ag|AgCl|KCl_sat at pH 3.5 and moved with about 57 mV in the cathodic region per pH unit. The Lc‐modified CCE was then used as a biosensing detection element in a single line flow injection system for the amperometric determination of a variety of phenolic substrates of the enzyme. The experimental conditions were studied and optimized for catechol serving as a model compound. Statistical aspects were applied and the sensor characteristics and Michaelis‐Menten constants of the investigated phenolic compounds were calculated and compared with those obtained for solid graphite electrodes modified with Trametes hirsuta laccase. The results showed that the CCE based biosensor in comparison with the solid graphite based biosensor offers a lower detection limit, a wider linear dynamic range, and excellent operational stability with no sensor passivation, indicating that the sol–gel lattice improves the electrochemical behavior of the biosensor.     

Enantioselective synthesis of cyclic secondary amines through Mo-catalyzed asymmetric ring-closing metathesis (ARCM)

Carbocyclic amines are synthesized efficiently in up to 93% ee by asymmetric ring-closing metathesis (ARCM) with 2-5 mol % chiral Mo complexes. An example is provided where the catalyst is prepared in situ (catalyst isolation not needed) to afford secondary amines that cannot be prepared by alternative methods. [reaction: see text]     

Ru complexes bearing bidentate carbenes: from innocent curiosity to uniquely effective catalysts for olefin metathesis

The discovery and development of a new class of Ru-based catalysts for olefin metathesis is described. These catalysts, particularly those that do not bear a phosphine ligand, have been demonstrated to promote unique levels of reactivity in a variety of olefin metathesis reactions. The design and development of supported and chiral optically pure variants of this class of Ru catalysts for use in enantioselective metathesis are discussed as well. All catalysts are air stable, reusable, and can be employed with unpurified solvents.     

Study of complexation reactions between alkali and alkaline-earth metal cations with dibenzo-18-crown-6(DB18C6) in mixed nonaqueous solvents using the conductometry method

The complexation reactions between alkali and alkaline-earth metal cations with DB18C6 were studied in acetonitrile-methanol (AN-MeOH) and tetrahydrofuran-threechloromethane (THF-CHCl₃) binary mixtures at different temperatures using the conductometric method. The obtained results show that in most cases, the DB18C6 forms 1:1 complexes with these metal cations and the stability of the complexes is affected by the nature and composition of the mixed solvents. The stability order of complexes in AN-MeOH binary systems was found to be Na⁺ > Li⁺, and in the case of THF-CHCl₃ binary mixtures was Na⁺ > Ba²⁺ > Li⁺. An anomalous and interesting behavior was observed for the case of complexation of a K+ ion with DB18C6 in the AN-MeOH binary mixture and also for complexation of Mg²⁺ and Ca²⁺ cations with this ligand in pure THF and also in THF-CHCl₃ binary systems. The values of the thermodynamic parameters (ΔH _c ^o and ΔS _c ^o ) for complexation reactions obtained from the temperature dependence of the stability constants and the results show that the complexes are both enthalpy-and entropy-stabilized. The text was submitted by the authors in English.     

Monitoring liposome-mediated delivery and fate of an antisense drug in cell extracts and in single cells by capillary electrophoresis with laser-induced fluorescence

Capillary electrophoresis with laser-induced fluorescence (CE-LIF) detection was used for evaluation of the effectiveness of delivery and fate of a model 25-mer DNA-based phosphorothiate antisense drug in cells. The antisense molecule was delivered to the cells through a simple incubation and by using a cationic liposome (Cytofectin GS 3815). The cationic lipid interacted with the negatively charged antisense to form a more positively charged complex. It was observed that uptake of the liposome-antisense complex by the cell was dependent on concentration of lipid, duration of transfection, and the cell type. The antisense drug interacted with intracellular components such as proteins and additional steps were needed to quantify the free antisense. Proteinase-K was able to release antisense from proteins. However, the addition of sodium dodecyl sulfate (SDS) to the sample or running buffer was more effective than Proteinase-K to release both naked and liposome-bound antisense from the cellular materials. Analysis of single HeLa cells for uptake of the unbound and liposome-complexed antisense revealed averages of 8.9x10(-19) moles and 4.9x10(-18) moles, respectively. The amount of uptake, however, varied greatly among individual cells and depended on the delivery method. With liposome-mediated delivery, the relative standard deviation (RSD) for the amount of antisense in individual cells was 130%, while the variation was much smaller (RSD = 45%) when the cells were incubated with the unbound antisense. These uptake variations agreed with those obtained from flow cytometry analysis.     

NLO properties of metallabenzene-based chromophores: a time-dependent density functional study

The static and dynamic first hyperpolarizabilities for a series of substituted metallabenzene-based nonlinear optical (NLO) chromophores were determined by time-dependent density functional theory (TDDFT). The electronic excitation contributions to the first hyperpolarizability are rationalized in terms of the two-level model. The effects on the hyperpolarizabilities of (a) the metal center (Os, Ir, Pt); (b) the ligand environment (PH3, CO, Cl); (c) various donor and acceptor substituents (NH2, OH, Me, H, Cl, Br, I, COOMe, COOH, CN, NO2); and (d) the length of pi-conjugation were studied. Our calculations predict that metallabenzenes have significant second-order NLO susceptibilities, ranging from = 1.0 x 10(-29) to 5.6 x 10(-28) esu and from mu = 3.0 x 10(-47) to 1.1 x 10(-44) esu, that can be tuned by changing the metal center and/or ligand environment.     

Kinetic studies and mechanism on the permanganic oxidation of L‐Glutamine in strong acid medium in the presence and absence of Silver (I)

The kinetic study and mechanism of the permanganic oxidation of L‐glutamine in sulfuric acid has been carried out both in the absence and presence of silver (I) using a spectrophotometric technique. Activation parameters have been evaluated using the Arrhenius and Eyring plots. Mechanisms consistent with the observed kinetic data have been proposed and discussed. The overall rate expression for the oxidation may be written as In the presence of silver (I) the rate law is The reaction appears to involve an acid catalyzed and data showed role of water molecules in the rate‐determining step is proton transfer which satisfies Bunnett's theory. A mechanism satisfying the various kinetic parameters has been proposed. ©1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 95–102, 1999     

The multiplicity of solutions in non-homogeneous boundary value problems

We use a method recently devised by Bolle to establish the existence of an infinite number of solutions for various non-homogeneous boundary value problems. In particular, we consider second order systems, Hamiltonian systems as well as semi-linear partial differential equations. The non-homogeneity can originate in the equation but also from the boundary conditions. The results are more satisfactory than those obtained by the standard “Perturbation from Symmetry” method that was developed – in various forms – in the early eighties by Bahri–Berestycki, Struwe and Rabinowitz. Received: 13 August 1998 / Revised version: 6 July 1999     

Preparation and characterization of polyaniline blends with polyvinyl acetate,polystyrene and polyvinyl chloride for toxic gas sensors

The conditions of processing and gas sensing of ­polyaniline (PANi) blends with polyvinyl acetate (PVAc), polystyrene (PS) and polyvinyl chloride (PVC) were investigated. Flexible, free‐standing and stretchable films of various blends compositions were obtained by casting. The mechanisms of the conducting blends response to a selection of gases and vapours were investigated using two techniques: measurement of conductance and mass changes using a four‐point probe method and X‐ray fluorescence (XRF) device, respectively. These responses to toxic gases and vapours are better explained by polymer blends than homopolymers. Prepared films were exposed to hydrogen halides, hydrogen cyanide, halogens, monochloroacetic acid (MCAA), 1‐3‐5 trichloromethyl benzene (TCMB), methylbenzyl bromide (MBB), bromoacetone (BA) and cyanogen bromide (CB). The changes in conductivity of various polymer frequently observed are partly due to one stage in the two‐stage sorption perhaps involving the swelling of the polymer and then diffusion of gases into polymer chains. The swelling of polymers is a slow process, therefore, we have pre‐swelled polymer films which tend to decrease the response times of blends in respect to gases. The structures of the blends are examined by STA (TGA & DSC) and SEM studies. Copyright © 2001 John Wiley & Sons, Ltd.