Absolute rate constants for the formation of nitrogen-centred radicals from chloramines/amides and their reactions with antioxidants

Pattison, David I.; Davies, Michael J.; Asmus, K.‐D.

doi:10.1039/b202526d

Cited by 21 publications

(23 citation statements)

References 41 publications

(54 reference statements)

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“…It seems clear therefore that the same assignments attributable to carboncentred free radicals can be made in the current study on HACl and HepCl, providing support for the 1,2 hydrogen shift mechanism proposed by Davies and co-workers [19] as shown in reaction 8 and in more detail in Scheme 2 in which a chloride ion is eliminated by one-electron reductants to form a nitrogen-centred radical in the first instance followed by rapid re-arangement to form a C-2 radical on the glucosamine moiety. Both EPR data and ion-exchange chromatography to detect chloride in the one-electron reduction of glycosaminoglycan chloramides as well as in pulse radiolysis studies of the reaction of the hydrated electron with chloramines and amides confirm that chloride ion is produced in yields of 100% [47,63]. …”

Section: Reduction By the Hydrated Electronmentioning

confidence: 82%

“…The rate constants for the reaction of the hydrated electron can be compared to those measured for the small model molecule, NH 2 Cl, where values of 2.2 x 10 10 M -1 s -1 were found [25,26]. Pulse radiolysis has also been used to measure hydrated electron reaction rates with chloramines and chloramides of amino acid related models, where rate constants in the range, 10 9 M -1 s -1 to 10 10 M -1 s -1 were found [28].…”

Section: Reduction By the Hydrated Electronmentioning

confidence: 99%

“…Pulse radiolysis studies of the simplest chloramine, NH 2 Cl, showed that it reacts with the hydrated electron at diffusion-controlled rates (k= 2.2 x 10 10 M -1 s -1 ) [25,26]. In more recent pulse radiolysis studies of the chloramines and chloramides of amino acid derivatives [27] and of chloro-and bromo-derivatives of model compounds, such as Nbromoglutarimide (NBG) and N-bromosuccinimide (NBS) [28], hydrated electrons were also shown to react at near diffusion-controlled rates. In the latter study, superoxide radicals were also reacted with NBG and NBS and found to follow complex chain reaction pathways.…”

Section: Introductionmentioning

confidence: 99%

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One-electron oxidation and reduction of glycosaminoglycan chloramides: A kinetic study

Sibanda

Parsons

Houée-Levin⊥

et al. 2013

Free Radical Biology and Medicine

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Hypochlorous acid and its acid-base counterpart, hypochlorite ions, produced in inflammatory conditions, may produce chloramides of glycosaminoglycans, the latter being significant components of the extracellular matrix (ECM). This may occur through the binding of myeloperoxidase directly to the glycosaminoglycans.The N-Cl group in the chloramides is a potential selective target for both reducing and oxidising radicals, leading possibly to more efficient and damaging fragmentation of these biopolymers relative to the parent glycosaminoglycans. In this study,the fast reaction techniques of pulse radiolysis and nanosecond laser flash photolysis have been used to generate both oxidizing and reducing radicals to react with the chloramides of hyaluronan (HACl) and heparin (HepCl).The strong reducing formate radicals and hydrated electrons were found to react rapidly with both HACl and HepCl with rate constants of (1-1.7) x 10 8 M -1 s -1 and (0.7-1.2) x 10 8 M -1 s -1 for formate radicals and 2.2 x 10 9 M -1 s and 7.2 x 10 8 M -1 s -1 for hydrated electrons, respectively. The spectral characteristics of the products of these reactions were identical and were consistent with initial attack at the N-Cl groups, followed by elimination of chloride ions to produce nitrogencentred radicals, which re-arrange subsequently and rapidly to produce C-2 radicals on the glucosamine moiety supporting an earlier EPR study by Rees et 3 This is the first study therefore to conclusively demonstrate that reducing radicals react rapidly with glycosaminoglycan chloramides in a site-specific attack at the N-Cl groups, probably to produce a 100 % efficient biopolymer fragmentation process. Although less reactive, carbonate radicals, which may be produced in vivo via reactions of peroxynitrite with serum levels of carbon dioxide ,also appear to react in a highly site-specific manner at the N-Cl group. It is not yet known if such site-specific attacks by this important in vivo species lead to a more efficient fragmentation of the biopolymers than would be expected for attack by the stronger oxidising species, the hydroxyl radical. It is clear however that the N-Cl group formed in inflammatory conditions in the extracellular matrix does present a more likely target for both reactive oxygen species and for reducing species than the N-H groups in the parent glycosaminoglycans. Graphical abstract4

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Section: Reduction By the Hydrated Electronmentioning

confidence: 82%

Section: Reduction By the Hydrated Electronmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

One-electron oxidation and reduction of glycosaminoglycan chloramides: A kinetic study

Sibanda

Parsons

Houée-Levin⊥

et al. 2013

Free Radical Biology and Medicine

View full text Add to dashboard Cite

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“…Pulse radiolysis studies of the simplest chloramine, NH 2 Cl, showed that the hydrated electron reacts with it at diffusioncontrolled rates (k= 2.2 x 10 10 M -1 s -1 ) [23,24]. In more recent pulse radiolysis studies of chloramines and chloramides of amino acid derivatives [25] and of chloro-and bromoderivatives of model compounds such as N-bromoglutarimide (NBG) and Nbromosuccinimide (NBS) [26], hydrated electrons were also shown to react at near diffusion-controlled rates. In the latter study, superoxide radicals were also reacted with NBG and NBS and found to follow complex chain reaction pathways.…”

Section: Introductionmentioning

confidence: 99%

Reaction of superoxide radicals with glycosaminoglycan chloramides: a kinetic study

Parsons

Sibanda

Heyes

et al. 2013

Free Radical Biology and Medicine

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Hypochlorous acid and its acid-base counterpart, hypochlorite ions, produced in inflammatory conditions, may produce chloramides of glycosaminoglycans, perhaps through the binding of myeloperoxidase directly to the glycosaminoglycans. The N-Cl group in the chloramides is a potential target for reducing species such as Cu(I) and superoxide radicals. Laser flash photolysis has been used here to obtain, for the first time, the rate constants for the direct reaction of superoxide radicals with the chloramides of hyaluronan and heparin. The rate constants were in the range 2.2 -2.7 x 10 3 M -1 s -1 . The rate constant for the reaction with the amino acid, taurine, was found to be much lower at 3.5 -4.0 x 10 2 M -1 s -1 . This demonstration that superoxide anion radicals react directly with hyaluronan and heparin chloramides may support the mechanism first proposed by Rees et al, Biochem. J. 381: 175-184; for an efficient fragmentation of these glycosaminoglycans in the extracellular matrix under inflammatory conditions. 3

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“…18 The ease of formation of N-centered radicals has been reported for a series of chloramines, which play an important role in environmental chemistry and biochemistry. [19][20][21][22][23] Once formed, the N-centered radical 1a can undergo fast protonation yielding the radical cation 1b. The most stable form of 1b adopts a chair conformation of the piperidine ring .…”

Section: Resultsmentioning

confidence: 99%

The chemical fate of paroxetine metabolites. Dehydration of radicals derived from 4-(4-fluorophenyl)-3-(hydroxymethyl)piperidine

et al. 2013

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Quantum chemical calculations have been used to model reactions which are important for understanding the chemical fate of paroxetine-derived radicals in the environment. In order to explain the experimental observation that the loss of water occurs along the ( photo)degradation pathway, four different mechanisms of radical-induced dehydrations have been considered. The elimination of water from the Ncentered radical cation, which results in the formation of an imine intermediate, has been calculated as the most feasible process. The predicted energy barrier (ΔG # 298 = 98.5 kJ mol −1 ) is within the barrier limits set by experimental measurements. All reaction intermediates and transition state structures have been calculated using the G3(MP2)-RAD composite procedure, and solvent effects have been determined using a mixed (cluster/continuum) solvation model. Several new products, which comply with the available experimental data, have been proposed. These structures could be relevant for the chemical fate of antidepressant paroxetine, but also for biologically and environmentally related substrates.

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Absolute rate constants for the formation of nitrogen-centred radicals from chloramines/amides and their reactions with antioxidants

Cited by 21 publications

References 41 publications

One-electron oxidation and reduction of glycosaminoglycan chloramides: A kinetic study

One-electron oxidation and reduction of glycosaminoglycan chloramides: A kinetic study

Reaction of superoxide radicals with glycosaminoglycan chloramides: a kinetic study

The chemical fate of paroxetine metabolites. Dehydration of radicals derived from 4-(4-fluorophenyl)-3-(hydroxymethyl)piperidine

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