Determination of atrazine, desethyl atrazine and desisopropyl atrazine in environmental water samples using hollow fiber-protected liquid-phase microextraction and high performance liquid chromatography

A new method based on hollow fiber-protected liquid-phase microextraction (LPME) was developed for the simultaneous determination of atrazine, desethyl atrazine and desisopropyl atrazine in environmental water samples. In LPME, analytes were extracted into 1-octanol immobilized in the micropores of a poly(vinylidene fluoride) porous hollow fiber membrane, and back extracted into the acceptor (4 M HCl) filled in the lumen of the hollow fiber. After LPME, the analytes trapped in the acceptor were analyzed with high-performance liquid chromatography after neutralization. The effect of extraction factors such as sample pH, acceptor pH, salinity, extraction time, stirring rate, and humic acid were studied. Under the optimized conditions, the limits of detection and relative standard deviations were respectively in the range of 0.5–1.0 μg L⁻¹ and 3.9–4.7% (n = 5). The proposed method was applied to determine atrazine, desethyl atrazine and desisopropyl atrazine in wastewater and groundwater samples. The three analytes were below the limits of detection, but good relative spiked recoveries over 90.1 ± 5.9% at 5 μg L⁻¹ spiked level were obtained.     

Chemical reaction studies in CH4/Ar and CH4/N2 gas mixtures of a dielectric barrier discharge

Chemical reactions in a dielectric barrier discharge at medium pressure of 250-300 mbar have been studied in CH(4)/Ar and CH(4)/N(2) gas mixtures by means of mass spectrometry. The main reaction scheme is production of H(2) by fragmentation of CH(4), but also production of higher order hydrocarbon molecules such as C(n)H(m) with n up to 9 including formation of different functional CN groups is observed. Formation of C(2)H(2), C(2)H(4), and C(2)H(6) molecules has been investigated in some detail. Significant differences are noted in comparison to a theoretical estimate.     

Voltammetric monitoring of laccase-catalysed mediated reactions

Six different compounds capable of mediating laccase-catalysed reactions have been tested by cyclic voltammetry. They exhibited quasi-reversible electrodic behaviour with formal redox potentials ranging from 150 to 800 mV (E(0)' vs. SCE). The immersion of a laccase-coated glassy carbon electrode (GCE) in mediator solutions generated large cathodic catalytic currents easily recorded by cyclic voltammetry at low-potential scan rates. This current showed two well-defined pH profiles, which correlated with the variation of the mediator redox potentials at the pH range tested. The relevant effect of temperature on the activity of laccase has been assessed here. Likewise, it was shown that the current record varied with the substrate concentration. This trend fitted Michaelis-Menten kinetics, which allowed us to give an estimation of the affinity of the fungal laccase for the different mediators.     

Isotachophoretic analysis of the dihydrofolate reductase reaction in the presence of methotrexate and ascorbic acid

The antifolate methotrexate (MTX) is widely used in cancer chemotherapy. In this study, we show that MTX (MTX-Glu1) and MTX-polyglutamates (MTX-Glu2-5) strongly inhibited the growth of the leukemic cell line MOLT-4. This effect, however, was mitigated by ascorbic acid. We investigated whether ascorbic acid is able to reduce dihydrofolic acid (DHF) to tetrahydrofolic acid (THF) directly or by circumventing the MTX inhibition of dihydrofolate reductase (DHFR). The inhibition of this NADPH-dependent reduction of DHF by MTX-Glun in the absence or presence of ascorbate, was determined by analytical isotachophoresis. Using 0.01 M HCl/histidine, pH 6.0, as a leading electrolyte (L) and 0.005 M 2-(N-morpholino)ethanesulfonic acid (MES)/histidine, pH 6.0, as a terminating electrolyte (T), MTX-Glun derivatives including MTX-Glu1 could be easily separated, whereas the quantitative estimation of THF was not possible. A quantitative characterization of the DHFR reaction by measuring NADPH, NADP+ and ascorbate was achieved with another system (L: 0.01 M HCI/beta-alanine, pH 3.73; T: 0.01 M caproic acid, pH 3.27). Nanomolar concentrations of MTX-Glu1-5 inhibited consumption of NADPH and production of NADP+. Ascorbic acid was not able to reduce DHF, neither directly nor after inhibition of DHFR by MTX. However, ascorbic acid seemed to diminish the oxidation of THF and this may account for its capacity to reduce the inhibitory effect of MTX on MOLT-4 cells.     

Metallacycloalkanes: I. Preparation and characterisation of α,α′-bipyridyl-5-nickela-3,3,7,7-tetramethyl-trans-tricyclo[4.1.0.02,4]heptane

Oxidative addition of 2 molecules of 3,3-dimethylcyclopropene (I) to α,α′-bipyridyl(1,5-cyclooctadiene)nickel(0) (III) gave the title compound (IV) in over 90% yield. Complex IV was characterized by mass, ¹H NMR and ¹³C NMR spectroscopy. Its structure was determined by X-ray diffraction (a 13.7081(2), b 14.638(2), c 9.5139(1) Å, β 110.82(1)°, C2/c, R = 0.05 for 1614 reflections).     

Synthesis and antiinflammatory activity of the sulfoxides of 4-[3-(dimethylamino)propyl] - 3,4- dihydro- 2-(1-hydroxyethyl)-3-phenyl-2H-1,4-benzothiazine

Oxidation of 4-[3-(dimethylamino)propyl]-3,4-dihydro-2-(1-hydroxyethyl)-3-phenyl-2H-1,4-benzothiazine, hydrochloride (I) with hydrogen peroxide yielded a mixture of two sulfoxides (II). Since this mixture exhibited antiinflammatory activity, the two components (Isomers A and B) were prepared in purified form by oxidation of I with N-chlorosuccinimide and hydrogen peroxide, respectively. Isomer A was more potent than Isomer B in the carrageenin-induced edema test.     

Influence of initial oxygen coverage and magnetic moment on the NO decomposition on rhodium (111)

In this study, density functional theory calculations were performed to investigate the influence of oxygen preoccupation on the nitrogen oxide decomposition on rhodium. Besides gauging the coverage dependence of the adsorption energy of NO on the (111) rhodium facet, the influence of the initial oxygen coverage on the kinetics and thermodynamics of the nitrogen oxide decomposition reaction was also studied. The results are discussed with respect to a novel NOx decomposition catalyst. Furthermore, the influence of spin effects on the adsorption geometry as well as the adsorption energy is examined. It will be addressed why spin effects only have a minor influence on the behavior of NO on a rhodium surface.     

Intramolecular hydroboration of unsaturated phosphine boranes

Homoallylic phosphine boranes undergo intramolecular hydroboration upon activation by triflic acid. The reaction occurs via an intermediate B-trifluorosulfonyloxyborane complex such as 15, followed by S(N)1-like or S(N)2-like displacement of the triflate leaving group, apparently leading to the formation of a four-center transition state. In the case of trisubstituted double bonds, as in the substrates 29 and 32, ionic hydrogenation of the alkene competes with internal hydroboration.     

EPR-untersuchungen an carbonsäureestern—III: Thiooxalsäureester-radikalanionen

Polarographic and cyclovoltammetric investigation of the thiooxalates 1–6 shows that they are reversibly reduced to the corresponding radical anions. Accordingly, EPR spectra are obtained after in-situ electroreduction. Taking also the electronic spectra into consideration, conclusions about the spin density distribution can be drawn. It is shown thatp^π is higher at the oxygen atoms of oxoesters than at the sulfur atoms of the corresponding thiono esters.     

Konzentrationsabhängigkeit der Dipolmomente in n-Hexan-Lösungen normaler α, ω-dichlorierter Kohlenwasserstoffe

Zusammenfassung Es wurden die Dipolmomente der, -dichlorierten Kohlenwasserstoffe in Lösung mit Hexan über den ganzen Konzentrationsbereich bei 25 °C bestimmt. Untersucht wurden die Verbindungen dieser Reihe vom 1,2-Dichloräthan bis zum 1,10-Dichlordekan.Die Dipolmomente dieser Verbindungen ließen sich gut deuten, wenn ein Gemisch starrer Rotationsisomerer angenommen wurde. Dabei zeigten sich auch noch die durch eine Kohlenstoffkette von 10 C-Atomen getrennten Partialmomente deutlich in ihrer Richtung gegenseitig abhängig.Die Konzentrationsabhängigkeit der Dipolmomente wurde an Hand der durch dieKirkwood-Fröhlichsche Theorie gegebeneng-Faktoren diskutiert. Es ergab sich, daß dieg-Faktoren des 1,2-Dichloräthans weitgehend auf eine DK-abhängige Konformationsänderung von der unpolaren trans- in die polare gauche-Konformation zurückzuführen sind. Dies scheint eine grundsätzliche Eigenschaft von Verbindungen zu sein, die Partialmomente in 1,2-Stellung haben. Dieg-Faktoren der Verbindungen, deren Partialmomente weiter voneinander entfernt sind, wie bei den höheren Gliedern der Reihe, wurden nahezu ausschließlich auf zwischenmolekulare Ausrichtung der Partialmomente zurückgeführt.Ein Vergleich mit deng-Faktoren des Hexylchlorids und des 2,2-Dichlorpropans zeigte, daß bis zu einer Konzentration von 1 Mol/l in erster Linie dimere bzw. kettenartige antiparallele bzw. parallele Assoziate der Partialmomente zu erwarten sind. Nach höheren Konzentrationen weichen dieg-Faktoren von diesem Verhalten nach größeren Werten hin ab. Daraus wurde auf parallele Ausrichtung in höherer Koordinationszahl geschlossen.Für die Unterstützung dieser Arbeit sprechen wir der Deutschen Forschungsgemeinschaft unseren verbindlichsten Dank aus.Der Firma Bayer, Leverkusen, danken wir für die Hilfe bei Beschaffung einiger der Substanzen.