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Oxidation of Hexacyanoferrate(II) by Peroxynitrite. A Mechanistic and Kinetic Study

Martinez E., Mucientes A., Poblete F., Rodriguez A.

Polish Journal of Chemistry

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2004

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Vol. 78 / nr 2

261-271

EN

Akinetic study of the oxidation of hexacyanoferrate(II) by peroxynitrite has been carried out, using a stopped-flow technique. The variation of the experimental rate constant over a wide concentration range of Fe(CN)6 4 has been investigated under different experimental conditions in terms of pH, ionic strength and temperature. Acorrelation between kexp and the substrate concentration has been obtained and this shows first-order behavior in substrate at high concentrations of Fe(CN)6 4 .Areaction mechanism is proposed, in which the hexacyanoferrate(II) reacts in competitive pathways with the peroxynitrous acid (direct oxidation) and with HOź and źNO2 radicals formed in the homolysis of the peroxide bond ofHOONO(indirect oxidation). Moreover, two individual constants, kc (the formation constant of the germinated radical pair [HOź źNO2]) and k7 (direct oxidation constant), have been evaluated together with the thermodynamic parameters of these elementary steps.

2

Kinetics and Mechanism of Complex Formation between Pentamminesuccinatocobalt(III) and Gallium(III)

Gouri S., Mohanty P.

Polish Journal of Chemistry

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2003

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Vol. 77 / nr 10

1221-1228

3

The stopped-flow determination of 2-, 6-, and 8-mercaptopurines by the induced iodine-azide reaction. Part II

Kurzawa J., Janowicz K.

Chemia Analityczna

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2003

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Vol. 48, No. 4

741-748

EN

A stopped-flow method for the determination of 2-, 6-, and 8-mercaptopurines by the io-dine-azide reaction has been elaborated. Spectrophotometric detection was applied and the decrease of the absorbance of the iodine-starch complex was monitored at 595 nm within several seconds. The rate of the absorbance decrease is related to the concentration of the sulfur compounds provided that the experimental conditions allow one to maintain a pseudo-first reaction order in respect of mercaptopurine. The linear calibration range depends on the concentration of iodine and sodium azide in the solution and on the analytical signals considered. Under the optimum conditions mercaptopurines can be determined at the concentration ranging between 0.01 and 0.5 ppm (6.6 * 10(-5)-3.3 x 10(-3) umol mL'1) with accuracy better than 5%.

PL

Opracowano metodę zatrzymanego przepływu do oznaczania 2-, 6-, i 8-merkaptopuryny z wykorzystaniem indukowanej reakcji jodo-azydkowej. Przy długości fali A = 595 nm rejestrowano spadek absorbancji kompleksu jodo-skrobiowego w ciągu kilkudziesięciu sekund. Dla reakcji pseudo-pierwszorzędowej względem merkaptopuryny szybkość spadku absorbancji zależy od stężenia induktora. Zakres liniowej zależności A od stężenia badanych merkaptopuryn zależy od stężenia jodu i azydku sodu w roztworze jodo-azydkowym oraz od rodzaju sygnałów analitycznych uwzględnianych podczas przygotowywania krzywych kalibracji. W optymalnych warunkach eksperymentalnych merkaptopuryny można oznaczać w zakresie od 0.01 do0.5ppm(6.6x 10(-5)-3.3x 10(-3) umol ml(-1)) z dokładnością poniżej 5%.

4

Application of stopped-flow technique to investigation of 2-, 6-, and 8-mercaptopurines as inductors of iodine-azide reaction. Part I

Kurzawa J., Janowicz K.

Chemia Analityczna

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2002

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Vol. 47, No. 6

883-893

EN

A stopped-flow technique is applied to investigate the behaviour of 2-, 6-, and 8-mercapto-purine in the induced iodine-azide reaction. This technique enables one to follow two stages of the reaction pathway and confirm the suggested mechanism. The influence of various parameters, on which the rate of the reaction depends, such as pH, sodium azide and iodine concentration, was investigated. The course of the reaction was registered by monitoring the decrease in the absorbance of the iodine-starch complex at 595 nm.

PL

Technikę zatrzymanego przepływu zastosowano do badania przebiegu reakcji jodo-azyd-kowej indukowanej 2-, 6-, i 8-merkaptopuryną. Metoda ta umożliwia śledzenie dwóch etapów reakcji co stanowi eksperymentalne potwierdzenie proponowanego mechanizmu. Badano wpływ pH, stężenia jonów azydkowych i jodu na szybkość reakcji tworzenia katalizatora oraz szybkość reakcji katalizowanej. Przebieg reakcji śledzono poprzez rejestrację spadku absorbancji kompleksu jodo-skrobiowego przy długości fali 595 nm.

5

Mechanism of Ring Opening Reaction of 4-Benzylidene-2-methyl-5-oxazolone. Part I. Reaction with n-Butylamine

Betłakowska B., Banecki B., Łankiewicz L., Wiczk W.

Polish Journal of Chemistry

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2001

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Vol. 75, nr 3

401-410

EN

The reaction between 4-benzylidene-2-methyl-5-oxazolone (Ox, c = 5.25 _ 10-5 M) with n-butylamine (nBuA, c = 0.026 to 1.66 M) in acetonitrile was studied by UV-Vis spectroscopy using steady-state and stopped-flow apparatus. The amine to Ox molar ratio higher than 500 allows to apply pseudo-first order approximation, whose rate constants depend on amine concentration according to a parabolic equation: kobs = 4.63 _ 0.02 _ CnBuA 2 , indicating a complex reaction mechanism. On the other hand, singular value decomposition (SVD) analysis, as well as global analysis of the data obtained from stopped-flow measurements support a simple A B reaction model. Nonlinear dependence of the pseudo- first order rate constant on amine concentration can be explained, assuming that the oxazolone ring opening reaction by n-butylamine in acetonitrile proceeds as parallel reactions: A + B C and A+2B C. Based on our experimental results and theoretical calculations of the oxazolone ring opening reaction, a mechanism of the reaction between 4-benzylidene-2-methyl-5-oxazolone and n-butylamine is proposed.