scholarly journals The role of peroxide in haem degradation. A study of the oxidation of ferrihaems by hydrogen peroxide

1978 ◽  
Vol 174 (3) ◽  
pp. 901-907 ◽  
Author(s):  
S B Brown ◽  
H Hatzikonstantinou ◽  
D G Herries
Keyword(s):  
Hydrogen Peroxide ◽  
Catalytic Activity ◽  
Linear Dependence ◽  
Rate Constants ◽  
Experimental Error ◽  
Ph Dependence ◽  
Monomeric Species ◽  
Order Of Magnitude ◽  
Computer Based

The oxidation of ferrihaems by H2O2 was studied as a model for haem catabolism. Rates of ferrihaem oxidation were evaluated by using a new computer-based method that measures the loss in catalytic activity of the ferrihaem during oxidation. For protoferrihaem, deuteroferrihaem, coproferrihaem and mesoferrihaem, oxidation proceeded via the monomeric species and no dimer contribution was detectable. The pH-dependence of oxidation was studied in the range 6.5–11. Within experimental error, the data were compatible with an inverse linear dependence on [H+]. This was interpreted in terms of attack by HO2- on monomeric ferrihaem. The specific second-order rate constants for oxidation of monomeric species by HO2- were of the same order of magnitude for all the ferrihaems, and were in the sequence coproferrihaem greater than protoferrihaem greater than mesoferrihaem congruent to deuteroferrihaem. A model is suggested involving formation of a ferrihaem monomerperoxide complex, which may either dissociate with the formation of a peroxidatic intermediate or be involved in an intramolecular oxidation of the ferrihaem. Haem catabolism may occur via the same or a similar intermediate.

scholarly journals The role of methoxy substituents in regulating the activity of selenides that serve as spirodioxyselenurane precursors and glutathione peroxidase mimetics

2016 ◽  
Vol 94 (4) ◽  
pp. 305-311 ◽  
Author(s):  
David J. Press ◽  
Thomas G. Back
Keyword(s):  
Hydrogen Peroxide ◽  
Catalytic Activity ◽  
Glutathione Peroxidase ◽  
Methoxy Group ◽  
Steric Effects ◽  
Disulfide Formation ◽  
Excess Hydrogen ◽  
Meta Position ◽  
Methoxy Groups

A series of o-(hydroxymethyl)phenyl selenides containing single or multiple methoxy substituents was synthesized, and the rate at which each compound catalyzed the oxidation of benzyl thiol to its disulfide with excess hydrogen peroxide was measured. This assay provided the means for comparing the relative abilities of the selenides to mimic the antioxidant selenoenzyme glutathione peroxidase. The mechanism for catalytic activity involves oxidation of the selenides to their corresponding selenoxides with hydrogen peroxide, cyclization to spirodioxyselenuranes, followed by reduction with two equivalents of thiol to regenerate the original selenide with concomitant disulfide formation. A single p-methoxy group on each aryl moiety afforded the highest catalytic activity, while methoxy groups in the meta position had little effect compared to the unsubstituted selenide, and o-methoxy groups suppressed activity. The installation of multiple methoxy groups on each aryl moiety provided no improvement. These results can be rationalized on the basis of dominating mesomeric and steric effects of the p- and o-substituents, respectively.

Dual role of hydrogen peroxide on the oxidase-like activity of nanoceria and its application for colorimetric hydrogen peroxide and glucose sensing

RSC Advances ◽  
2016 ◽  
Vol 6 (65) ◽  
pp. 59939-59945 ◽  
Author(s):  
Ruochen Guo ◽  
Yanru Wang ◽  
Shaoxuan Yu ◽  
Wenxin Zhu ◽  
Fangqing Zheng ◽  
...  
Keyword(s):  
Hydrogen Peroxide ◽  
Catalytic Activity ◽  
Cerium Oxide ◽  
Glucose Sensing ◽  
Dual Role ◽  
Cerium Oxide Nanoparticles ◽  
Oxide Nanoparticles ◽  
Chromogenic Substrate

Nanoceria (cerium oxide nanoparticles) exhibits excellent catalytic activity towards chromogenic substrate 3,3,5,5-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2), which has been reported.

scholarly journals Catalase model systems. Decomposition of hydrogen peroxide catalysed by mesoferrihaem, deuteroferrihaem, coproferrihaem and haematoferrihaem

1978 ◽  
Vol 174 (3) ◽  
pp. 893-900 ◽  
Author(s):  
H Hatzikonstantinou ◽  
S B Brown
Keyword(s):  
Mechanism Of Action ◽  
Rate Constants ◽  
Inverse Relationship ◽  
Ph Dependence ◽  
Catalytic Decomposition ◽  
Order Rate Constant ◽  
Model Systems ◽  
Ph Variation ◽  
Order Of Magnitude ◽  
Decomposition Of H2o2

The catalytic decomposition of H2O2 by deuteroferrihaem, mesoferrihaem, coproferrihaem and haematoferrihaem was studied as a model for the mechanism of action of catalase. For haematoferrihaem, anomalous but reproducible results were obtained, which could not be adequately explained. For each of the other ferrihaems studied, both monomeric and dimeric species catalysed decomposition, although the activity of monomer (aM) was much greater than that of dimer (aD). The pH variation of aD in the range 6.5–11 was consistent with an inverse dependence on [H+]1/2. The molecular mechanism whereby such a dependence could be achieved is not apparent. A study of the pH-dependence of aM in the range 6.5–11 revealed a linear inverse relationship with [H+]. This is interpreted in terms of attack by HO2- on ferrihaem monomer. The specific pH-independent rate constants for this reaction were in the order coproferrihaem greater than protoferrihaem greater than or equal to mesoferrihaem congruent to deuteroferrihaem. The order of magnitude of these rate constants is the same as that for catalysis by Fe(H2O)63+ and the second-order rate constant for decomposition of H2O2 by catalase. The implications on the mechanism of action of catalase are discussed.

scholarly journals The Direct Synthesis of Hydrogen Peroxide over AuPd Nanoparticles: An Investigation into Metal Loading

2021 ◽  
Author(s):  
Joseph Brehm ◽  
Richard J. Lewis ◽  
David J. Morgan ◽  
Thomas E. Davies ◽  
Graham J. Hutchings
Keyword(s):  
Hydrogen Peroxide ◽  
Catalytic Activity ◽  
Oxidation State ◽  
Direct Synthesis ◽  
Catalytic Performance ◽  
Metal Loading ◽  
Subsequent Degradation ◽  
Small Nanoparticles

AbstractThe direct synthesis of H2O2 from molecular H2 and O2 over AuPd catalysts, supported on TiO2 and prepared via an excess chloride co-impregnation procedure is investigated. The role of Au:Pd ratio on the catalytic activity towards H2O2 formation and its subsequent degradation is evaluated under conditions that have previously been found to be optimal for the formation of H2O2. The combination of relatively small nanoparticles, of mixed Pd-oxidation state is shown to correlate with enhanced catalytic performance. Subsequently, a detailed study of catalytic activity towards H2O2 synthesis as a function of AuPd loading was conducted, with a direct correlation between catalytic activity and metal loading observed. Graphic Abstract

Condensation of α,ω-siloxane diols with aminoalkyl- (alkoxy)silanes

e-Polymers ◽  
2013 ◽  
Vol 13 (1) ◽  
Author(s):  
Magdalena Lubkowska ◽  
Wlodzimierz A. Stanczyk ◽  
Krystyna Rozga-Wijas
Keyword(s):  
Chain Length ◽  
Silicon Atom ◽  
Rate Constants ◽  
Second Order ◽  
Order Rate ◽  
Siloxane Oligomers ◽  
Order Of Magnitude ◽  
Kinetics Of

Abstract Kinetics of condensation of individual siloxane diols HO[(CH3)2SiO]xSi(CH3)2OH (x=3,5,6 and 9) with aminoalkyl-alkoxysilanes (RO)2SiR’(CH2)3NHR’’ (R = CH3, CH2CH3; R’ = CH3, OR; R’’ = H, (CH2)2NH2) is described. The second order rate constants point to the significant effect of the siloxane diols chain length on reactivity, which increases for higher homologues (almost an order) of magnitude on coming from x=3 to x=9. The role of substituents at silicon atom is discussed. Three novel functional siloxane oligomers (substrates) are described and characterized.

Quenching of the singlet and triplet state of benzene by halogenated alkanes in the vapor phase

1982 ◽  
Vol 60 (13) ◽  
pp. 1767-1774 ◽  
Author(s):  
H. A. Khwaja ◽  
G. P. Semeluk ◽  
I. Unger
Keyword(s):  
Charge Transfer ◽  
Triplet State ◽  
Vapor Phase ◽  
Linear Dependence ◽  
Rate Constants ◽  
Singlet State ◽  
Quenching Rate ◽  
Order Of Magnitude ◽  
Halogenated Alkanes ◽  
Klein’S Model

The second order rate constants (kq) for the quenching of the singlet state of benzene by several halogenated alkanes (viz. CH2Br2, CCl4, CH3CCl3, CHCl3, CHF3, CH3Cl, CH3F, CH2F2, CH2Cl2, CFCl3, CF2Cl2, CF3Cl, CF4) in the vapor phase have been measured. For CCl4, CHCl3, CH2Cl2, and CH3Cl, which were previously studied by Das Gupta and Phillips, there is satisfactory agreement between the kq values obtained in the separate investigations. The linear dependence of the electron affinity of quencher with the corresponding quenching rate constants supports an exciplex mechanism in accordance with Klein's model. Charge transfer occurs from benzene to halogenated alkane and is greater for the chloro alkanes than for mixed fluoro–chloro alkanes. In the case of the triplet state of benzene, whose behaviour was monitored using the sensitized emission of biacetyl technique, quenching effects were at best one order of magnitude smaller and probably involve more than one bimolecular process.

Role of the K-Channel in the pH-Dependence of the Reaction of CytochromecOxidase with Hydrogen Peroxide†

Biochemistry ◽  
2001 ◽  
Vol 40 (32) ◽  
pp. 9695-9708 ◽  
Author(s):  
Catherine Pecoraro ◽  
Robert B. Gennis ◽  
T. V. Vygodina ◽  
A. A. Konstantinov
Keyword(s):  
Hydrogen Peroxide ◽  
Ph Dependence ◽  
K Channel

The role of copper ions in hydrogen peroxide bleaching: Their origin, removal, and effect on pulp quality

TAPPI Journal ◽  
2012 ◽  
Vol 11 (7) ◽  
pp. 37-46 ◽  
Author(s):  
PEDRO E.G. LOUREIRO ◽  
SANDRINE DUARTE ◽  
DMITRY V. EVTUGUIN ◽  
M. GRAÇA V.S. CARVALHO
Keyword(s):  
Hydrogen Peroxide ◽  
Copper Ions ◽  
Peroxide Bleaching ◽  
Metals Removal ◽  
Peroxide Decomposition ◽  
Equipment Corrosion ◽  
And Performance ◽  
And Control ◽  
Main Effects

This study puts particular emphasis on the role of copper ions in the performance of hydrogen peroxide bleaching (P-stage). Owing to their variable levels across the bleaching line due to washing filtrates, bleaching reagents, and equipment corrosion, these ions can play a major role in hydrogen peroxide decomposition and be detrimental to polysaccharide integrity. In this study, a Cu-contaminated D0(EOP)D1 prebleached pulp was subjected to an acidic washing (A-stage) or chelation (Q-stage) before the alkaline P-stage. The objective was to understand the isolated and combined role of copper ions in peroxide bleaching performance. By applying an experimental design, it was possible to identify the main effects of the pretreatment variables on the extent of metals removal and performance of the P-stage. The acid treatment was unsuccessful in terms of complete copper removal, magnesium preservation, and control of hydrogen peroxide consumption in the following P-stage. Increasing reaction temperature and time of the acidic A-stage improved the brightness stability of the D0(EOP)D1AP bleached pulp. The optimum conditions for chelation pretreatment to maximize the brightness gains obtained in the subsequent P-stage with the lowest peroxide consumption were 0.4% diethylenetriaminepentaacetic acid (DTPA), 80ºC, and 4.5 pH.

Catalytic Activity of Binary and Triple Systems Based on Redox Inactive Metal Compound, LiSt and Additives of Monodentate Ligands-Modifiers: DMF, HMPA and PhOH, in Selective Ethylbenzene Oxidation with Dioxygen

2016 ◽  
Vol 10 (3) ◽  
pp. 259-270
Author(s):  
Ludmila Matienko ◽  
◽  
Larisa Mosolova ◽  
Vladimir Binyukov ◽  
Gennady Zaikov ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Triple System ◽  
Metal Compound ◽  
Ethylbenzene Oxidation ◽  
Catalytic Systems ◽  
Triple Systems ◽  
Lithium Compound ◽  
Mechanism Of Catalysis ◽  
Monodentate Ligands

Mechanism of catalysis with binary and triple catalytic systems based on redox inactive metal (lithium) compound {LiSt+L2} and {LiSt+L2+PhOH} (L2=DMF or HMPA), in the selective ethylbenzene oxidation by dioxygen into -phenylethyl hydroperoxide is researched. The results are compared with catalysis by nickel-lithium triple system {NiII(acac)2+LiSt+PhOH} in selective ethylbenzene oxidation to PEH. The role of H-bonding in mechanism of catalysis is discussed. The possibility of the stable supramolecular nanostructures formation on the basis of triple systems, {LiSt+L2+PhOH}, due to intermolecular H-bonds, is researched with the AFM method.

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