Metal-ion oxidations in solution. Part XIX. Redox pathways in the oxidation of penicillamine and glutathione by chromium(VI)

1977 ◽  
Vol 55 (18) ◽  
pp. 3335-3340 ◽  
Author(s):  
Alexander McAuley ◽  
M. Adegboyega Olatunji
Keyword(s):  
Ion Exchange ◽  
Redox Reaction ◽  
Metal Ion ◽  
Hydrogen Ion ◽  
Stopped Flow ◽  
Ion Concentrations ◽  
Flow Method ◽  
Chromium Vi ◽  
Reaction Proceeds ◽  
Transient Intermediate

Three moles of penicillamine or glutathione are required to reduce chromium(VI) to chromium(III). The kinetics and mechanism of the redox reaction have been studied using the stopped-flow method. The reaction proceeds via the formation of a transient intermediate (K1) which decomposes either in a proton-catalyzed pathway or by reaction with a second mole of thiol. The rate law[Formula: see text]where n = 1 for penicillamine and 2 for glutathione has been shown to hold over a range of thiol and hydrogen-ion concentrations. At 25 °C k2 = 14.3 ± 1.0 M−1 s−1 for penicillamine (ΔH≠ = 9 ± 2 kcal mol−1, ΔS≠ = −33 ± 6 cal K−1 mol−1) and 12.1 ± 0.4 M−1 s−1 for glutathione (ΔH≠ = 7 ± 2 kcal mol−1, ΔS≠ = −40 ± 5 cal K−1 mol−1). Several chromium(III) products have been identified by ion-exchange methods. The significance of the second-order pathways in these reactions is discussed.

Kinetic behavior of alkali metal ion on zeolite 4A surface using the stopped-flow method

1984 ◽  
Vol 97 (1) ◽  
pp. 278-283 ◽  
Author(s):  
Tetsuya Ikeda ◽  
Junji Nakahara ◽  
Minoru Sasaki ◽  
Tatsuya Yasunaga
Keyword(s):  
Alkali Metal ◽  
Metal Ion ◽  
Stopped Flow ◽  
Kinetic Behavior ◽  
Alkali Metal Ion ◽  
Flow Method ◽  
Zeolite 4A

scholarly journals Effects of Mg2+, Ca2+ and Mn2+ on sheep liver cytoplasmic aldehyde dehydrogenase

1982 ◽  
Vol 205 (2) ◽  
pp. 443-448 ◽  
Author(s):  
F M Dickinson ◽  
G J Hart
Keyword(s):  
Aldehyde Dehydrogenase ◽  
Esterase Activity ◽  
Metal Ion ◽  
Stopped Flow ◽  
Maximal Effect ◽  
Ion Concentrations ◽  
Sheep Liver ◽  
High Concentrations ◽  
Flow Experiments ◽  
Active Centres

Sheep liver cytoplasmic aldehyde dehydrogenase is strongly inhibited by Mg2+, Ca2+ and Mn2+. The inhibition is only partial, however, with 8-15% of activity remaining at high concentrations of these agents. In 50 mM-Tris/Hcl, pH 7.5, the concentrations giving half-maximal effect were: Mg2+, 6.5 micrometers; Ca2+, 15.2 micrometers; Mn2+, 1.5 micrometer. The esterase activity of the enzyme is not affected by such low metal ion concentrations, but appears to be activated by high concentrations. Fluorescence-titration and stopped-flow experiments provide evidence for interaction of Mg2+ with NADH complexes of the enzyme. As no evidence for the presence of increased concentrations of functioning active centres was obtained in the presence of Mg2+, it is concluded that effects of Mg2+ (and presumably Ca2+ and Mn2+ also) are brought about by trapping increased concentrations of NADH in a Mg2+-containing complex. This complex must liberate products more slowly than any of the complexes involved in the non-inhibited mechanism.

scholarly journals Experiments on the removal of chromium (VI) from its aqueous solution in batch reactors

2018 ◽  
Vol 1 (1) ◽  
pp. 12-18
Author(s):  
P Mullai Mullai ◽  
◽  
S. Kothai Nayaki ◽  
R. Nirmala Nirmala ◽  
◽  
...  
Keyword(s):  
Activated Carbon ◽  
Kinetic Data ◽  
Metal Ion ◽  
Batch Reactor ◽  
Ion Concentration ◽  
Batch Reactors ◽  
Adsorption Models ◽  
Ion Concentrations ◽  
First Order ◽  
Chromium Vi

The adsorption of chromium (VI) onto activated carbon experimented in a batch reactor under two different conditions, namely, initial metal ion concentration and adsorbent dosages. For the five different initial metal ion concentrations such as 500, 600, 800, 900, 1000 mg/L, the steady-state values of chromium removal efficiency were 64, 92, 83, 71 and 66 %, respectively, using 5 grams of activated carbon under shaking at the end of 8th hour. The equilibrium of the process was found to fit into the two well-known adsorption models, Freundlich and Langmuir. It was also observed that the experimental kinetic data followed the first order rate expression.

scholarly journals Stopped-Flow Spectrophotometric Studies of the Kinetics of Interaction of Dihydroxyfumaric Acid with the DPPH Free Radical

2010 ◽  
Vol 5 (2) ◽  
pp. 83-87
Author(s):  
Natalia Secara
Keyword(s):  
Free Radical ◽  
Reaction Kinetics ◽  
Rate Constant ◽  
Stopped Flow ◽  
Flow Method ◽  
Reaction Proceeds ◽  
Reaction Orders ◽  
Stoichiometric Reaction ◽  
Two Stages ◽  
Kinetics Of

The reaction of dihydroxyfumaric acid with the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) was studied using the stopped-flow method, in order to describe the reaction kinetics. Dihydroxyfumaric acid reacts very rapidly with DPPH, the reaction being completed in several minutes. This 2-stoichiometric reaction proceeds in two stages, with reaction orders of 1 and 0.76 with respect to DPPH, and 0.5 and 0.3 with respect to DHF, respectively. The rate constant of the two stages of the reaction were found to be 39.1 (L/mol•s) and 0.0012 (s-1) at 20º C and pH 4.0.

Metal-ion oxidations in solution. Part XVIII. Characterization, rates, and mechanism of formation of the intermediates in the oxidation of thiols by chromium(VI)

1977 ◽  
Vol 55 (18) ◽  
pp. 3328-3334 ◽  
Author(s):  
Alexander McAuley ◽  
M. Adegboyega Olatunji
Keyword(s):  
Complex Formation ◽  
Thermodynamic Parameters ◽  
Rate Constants ◽  
Metal Ion ◽  
Formation Mechanisms ◽  
Stopped Flow ◽  
Mechanism Of Formation ◽  
Chromium Vi ◽  
Kinetics Of ◽  
Absorbance Data

The stopped-flow technique has been used to study the reactions of [HCrO4−] and penicillamine, glutathione and β-mercaptoethylamine (RSH) in perchlorate media, [H+] = 0.02−0.100 M, I = 1.00 M over the temperature range 10–30 °C. The transient orange species formed as intermediates are 1:1 chromate esters,[Formula: see text]with λmax ∼ 420–430 nm and K1 ∼ 700 (DL-penicillamine) to 1440 M−1 (glutathione) at T = 25 °C. Thermodynamic parameters for complex formation have been derived from initial absorbance data and the evidence for sulphur bonding is discussed. Kinetics of the reactions conform to the rate law[Formula: see text]Activation enthalpies lie in the range 6–10 kcal/mol but ΔS≠ values vary considerably possibly reflecting solvation effects. The rate constants kfH+ are several orders of magnitude lower than those found for this parameter in other reactions of this type. The complex formation mechanisms are discussed and the possibility of some associative character in the present reactions is considered.

Metal-ion oxidations in solution. Part XXI. Kinetics and mechanism of the reaction of ascorbic acid, hydroquinone, and catechol with 12-tungstocobaltoate(III)

1977 ◽  
Vol 55 (20) ◽  
pp. 3581-3586 ◽  
Author(s):  
Zahid Amjad ◽  
Jean-Claude Brodovitch ◽  
Alexander McAuley
Keyword(s):  
Ascorbic Acid ◽  
Ionic Strength ◽  
Dissociation Constant ◽  
Metal Ion ◽  
Outer Sphere ◽  
Hydrogen Ion ◽  
Stopped Flow ◽  
Acid Media ◽  
Temperature Range ◽  
Mechanism Of The Reaction

The mechanisms of oxidation of the three di-hydroxy substrates in the title reactions have been investigated in acid media [HClO4] = 0.04–1.00 M, at an ionic strength of 1.0 M [LiClO4] over the temperature range 5–35 °C using the stopped-flow method. In contrast to the reactions of hydroquinone (k2(25 °C) = 1.43 × 104 M−1 s−1, ΔH≠ = 3.6 ± 0.4 kcal mol−1, ΔS≠ = −34 ± 8 cal deg−1 mol−1) and catechol (k2(25 °C) = 9.5 × 102 M−1 s−1, ΔH≠ = 5.9 ± 0.9 kcal mol−1, ΔS≠ = 27 ± 8 cal deg−1 mol−1) where no hydrogen ion dependence is observed over the range studied, the rate variations of oxidation of ascorbic acid (H2A) are consistent with two reactions involving H2A (k5 = 77.4 M−1 s−1, ΔH≠ = 4.5 ± 0.6 kcal mol−1, ΔS≠ = −35 ± 5 cal deg−1 mol−1) and HA− (k6 = 2.41 × 105M−1 s−1, ΔH≠ = 2.0 ± 1 kcal mol−1, ΔS≠ = −17 ± 6 cal deg−1 mol−1). The dissociation constant of ascorbic acid has been re-determined over the temperature range studied. Solvation effects are considered important in these outer-sphere systems, which may be discussed in terms of the Marcus relationship. Comparisons with related reactions are discussed.

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