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    Öğe
    All-solid-state PVC membrane Ag+-selective electrodes based on diaza-18-crown-6 compounds
    (Springer Wien, 2004) Isildak, I; Yolcu, M; Isildak, O; Demirel, N; Topal, G; Hosgoren, H
    Two diaza-crown ether compounds were synthesized and evaluated as Ag+-selective carriers in polyvinylchloride (PVC) membrane electrodes of solid-state type. The all-solid-state PVC membrane electrode based on N,N-Dibenzyl-dibenzo-diaza-18-crown-6 exhibited a super-Nernstian response (75+/-10 mV per decade) over the concentration range of 1x10(-1) to 7x10(-6) M of Ag+ ion and a detection limit of 3x10(-6) M, at a wide range of pH (pH 4-7). The response time of the electrode was fast (less than similar to10s), and it can be used for three months without any significant deviation in potential. The proposed all-solid-state PVC membrane electrodes revealed high selectivity toward Ag+ ion with respect to alkali, alkaline earth, heavy and transition metal ions. A flow-through cell of all-solid-state PVC membrane Ag+-selective electrode based on N,N-Dibenzyl-dibenzo-diaza-18-crown-6 has also been prepared and applied for flow-injection analysis of Ag+ ion in solution.
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    Öğe
    The effects of organic pesticides on inner membrane permeability in Escherichia coli ML35
    (Springer, 2005) Guven, K; Yolcu, M; Gul-Guven, R; Erdogan, S; De Pomerai, D
    We have tested whether some pesticides might cause inner membrane leakage in ML35 Escherichia coli cells, which express beta-galactosidase (lacZ; EC 3.2.1.23) constitutively but lack the permease (lacY) required for substrate entry. The activity of beta-galactosidase (indicative of substrate leakage through the inner membrane) was increased by various concentrations of pesticides, including the organometallic fungicides maneb and mancozeb, the insecticide Thiodan, and the herbicide Ally, as well as by antibiotics such as ampicillin, gramicidin D, and the calcium ionophore A23187. The enzyme activity was increased by up to similar to 30% when the E. coli ML35 strain was exposed to various concentrations (between 50 and 250 ppm) of both fungicides. Thiodan had only a slight effect on beta-galactosidase activity (increase of 12.8%), whereas, among the antibiotics, the calcium ionophore at 20 mu g/ml caused a significant increase in enzyme activity by up to 61.8%. This effect is similar to that of sodium dodecyl sulfate, used as positive control (similar to 70% increase). Accumulation of maneb and mancozeb by bacterial cells was also studied taking advantage of their metal content and using atomic absorption spectrophotometry. In parallel with the increase in enzyme activity, both fungicides accumulated in the cells as a function of their concentration. Time course experiments (3, 6, and 9 h) of fungicide accumulation and of bacterial growth at various pesticide concentrations were also carried out. Maneb seems to inhibit the bacterial growth better than mancozeb. In addition, maneb uptake increases with time up to 9 h at all tested concentrations, whereas the accumulation of mancozeb is similar at all the exposure times tested. This indicates a different uptake and/or metabolizing strategy by E. coli cells for the two fungicides.