Reactions of Pyridine Coenzyme Dimers and Monomers with Viologens

El-Sherbini, El Said; Finazzi‐Agrò, Alessandro; Tortorella, Silvano; Casini, Antonio

doi:10.1006/abbi.1998.0669

Cited by 5 publications

(4 citation statements)

References 25 publications

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“…In the proposed alternative mechanism that is described here, the first step in VA side product formation is the attack of O 2 on VA + . The phenomenon that a radical cation readily reacts with O 2 has been shown before [17,18]. Furthermore, there is literature evidence that this reaction is also applicable to VA + .…”

Section: Resultsmentioning

confidence: 70%

On a revised mechanism of side product formation in the lignin peroxidase catalyzed oxidation of veratryl alcohol

Have

Franssen

2001

FEBS Letters

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The O 2 -dependent formation of side products during the oxidation of veratryl alcohol (VA) by lignin peroxidase has previously been proposed to start with the attack of H 2 O on the VA radical cation (VA + ). This initial reaction is unlikely since it would also lead to side product formation in the absence of O 2 , which is not the case. In the current mechanism VA + reacts first with O 2 , whereafter H 2 O attacks. Furthermore, this paper describes an alternative explanation for the inhibitory effect of Mn 2+ on VA side product formation. It is proposed that Mn 2+ reduces reactive intermediates back to VA. ß

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Section: Resultsmentioning

confidence: 70%

On a revised mechanism of side product formation in the lignin peroxidase catalyzed oxidation of veratryl alcohol

Have

Franssen

2001

FEBS Letters

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“…Then, this transition complex undergoes a second electron-transfer process to give the (Ru 2+ −MV +• ) 2 /CB[8] dimer. In the presence of molecular oxygen, the Ru 2+ −MV +• radical dimer are oxidized back to Ru 2+ −MV 2+ , which are “unlocked” from one CB[8] cavity and reassembled as the original Ru−MV 2+ −CB[8] complexes. The above processes have been repeated several times and shown nice reversibility as evidenced by both the broadening of related 1 HNMR peaks and the color change of the solution.…”

Section: Resultsmentioning

confidence: 99%

Host−Guest Chemistry and Light Driven Molecular Lock of Ru(bpy)₃−Viologen with Cucurbit[7−8]urils

et al. 2007

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Host-guest chemistry and photoinduced electron-transfer processes have been studied in the systems containing Ru(bpy)3 complex covalently linked to viologen as a guest molecule and cucurbit[n]urils (n = 7, 8) as host molecules in aqueous solution. The Ru(bpy)3-viologen complex, [Ru(2,2'-bipyridine)2(4-(4-(1'-methyl-4,4'-bipyridinediium-1-yl)butyl)-4'-methyl-2,2'-bipyridine)]Cl4 (denoted as Ru2+-MV2+, 1) was shown to form stable 1:1 inclusion complexes with cucurbit[7]uril (CB[7]) and cucurbit[8]uril (CB[8]). The binding modes are slightly different with CB[7] and CB[8]. CB[7] preferentially binds to part of the viologen residue in 1 together with the butyl chain, whereas CB[8] preferentially encloses the whole viologen residue. Photoinduced intramolecular electron transfer from the excited-state of the Ru moiety to MV2(+) which is inserted into the cavity of the CBs occurred. Long-lived charge-separated states Ru3(+)-MV(+*) were generated with the lifetimes of 280 ns with CB[7] and 2060 ns with CB[8]. This shows that CBs can slow down the charge recombination within supramolecular systems, and the difference in lifetimes seems to be due to the difference in binding modes. In the presence of a sacrificial electron donor triethanolamine, light-driven formation of a dimer of MV(+*) inside the CB[8] cavity was observed. This "locked" molecular dimer can be "unlocked" by molecular oxygen to give back the original form of the molecular dyad 1 with the MV2(+) moiety inserted in the cavity of CB[8]. The processes could be repeated several times and showed nice reversibility.

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“…The nicotinamide adenine radical dimer participates in processes analogous to NADH elementary , and and reaction with methylene blue. In spite of slower diffusion and presumably larger steric hindrance (NAD) 2 reacts as fast or faster than NADH, in keeping with the greater reducing potential of the dimer than NADH [37]. Reactions with CpIII, CpI, and CpII might produce radical (NAD) 2 · .…”

Section: Discussionmentioning

confidence: 99%

Nicotinamide adenine dinucleotide species in the horseradish peroxidase–oxidase oscillator

Kirkor

Scheeline

2000

European Journal of Biochemistry

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NADH chemistry ancillary to the oscillatory peroxidase±oxidase (PO) reaction has been reexamined. Previously, (NAD) 2 has been thought of as a terminal, inert product of the PO reaction. We now show that (NAD) 2 is a central reactant in this system. Although we found traces of the dimer after several hours of the PO reaction, no accumulation of the dimer occurred, regardless of the reaction time or the number of oscillations. (NAD Keywords: horseradish peroxidase catalysis; methylene blue; NAD anomers; NAD dimer; rate constants.Peroxidases are widely distributed floral, fungal and animal heme-containing enzymes. Across the phyla, this class of enzymes participates in oxidations and reductions essential in anti-infectious defenses, hormonal signaling, and in a plants' formation and maintenance of cell walls. In mammals, peroxidases are also implicated in the pathology of inflammation. Horseradish peroxidase has found wide-spread use in a multitude of analytical assays and biosensors [1]. Due to its wide-range of catalytic activity and ready availability, HRP serves as the archetypal peroxidase in investigations of mechanisms of biochemical redox reactions. Even more importantly, pyridine nucleotides are the most common coenzymes in plant and animal cellular metabolism. NADH (Fig. 1) is one of a few substrates that activates both oxidase and peroxidase cycles of peroxidases. In stimulated neutrophils, pyridine coenzymes serve as the source of electrons shuttled by NADH oxidase through the plasma membrane to oxygen, in formation of superoxide radicals and activation of antimicrobial defenses, the chlorinating system of myeloperoxidase among them. The main target of this work is an assessment of the role of (NAD) 2 (Fig. 1) in reaction pathways operating in the horseradish peroxidase-catalyzed oxidation of NADH. A secondary goal concerns establishing the roles of other b-NADH-derived species in the PO reaction. Explorations of reduced nicotinamide adenine dinucleotide (NADH) reaction pathways are notoriously difficult. The difficulty lies in the wide range of transformations and instability of intermediates that can form. It is manifest in a large number of model compounds synthesized to restrict possible transformations. We select the HRP-NADH-O 2 oscillator as, on one hand, a more stringent framework for mechanistic evaluation of the relevant chemistry of NADH, and on the other hand, a medium kinetically enforcing a hierarchy of reaction pathways [2]. The HRP-NADH-O 2 reaction is the most thoroughly studied in the group of peroxidase oscillators [3]. The abstract models of this oscillator emulate its observable PO dynamics with general fidelity. Chemically realistic models, however, have been found lacking in simulating several features of the oscillator [4]. Our current work increases the number of reactions demonstrated to occur in the PO oscillator.In aqueous solutions of moderate acidity, the main transformations of nicotinamide adenine dinucleotide are acidcatalyzed autooxidation, anomerization, and hydration...

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Reactions of Pyridine Coenzyme Dimers and Monomers with Viologens

Cited by 5 publications

References 25 publications

On a revised mechanism of side product formation in the lignin peroxidase catalyzed oxidation of veratryl alcohol

On a revised mechanism of side product formation in the lignin peroxidase catalyzed oxidation of veratryl alcohol

Host−Guest Chemistry and Light Driven Molecular Lock of Ru(bpy)₃−Viologen with Cucurbit[7−8]urils

Nicotinamide adenine dinucleotide species in the horseradish peroxidase–oxidase oscillator

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Reactions of Pyridine Coenzyme Dimers and Monomers with Viologens

Cited by 5 publications

References 25 publications

On a revised mechanism of side product formation in the lignin peroxidase catalyzed oxidation of veratryl alcohol

On a revised mechanism of side product formation in the lignin peroxidase catalyzed oxidation of veratryl alcohol

Host−Guest Chemistry and Light Driven Molecular Lock of Ru(bpy)3−Viologen with Cucurbit[7−8]urils

Nicotinamide adenine dinucleotide species in the horseradish peroxidase–oxidase oscillator

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Host−Guest Chemistry and Light Driven Molecular Lock of Ru(bpy)₃−Viologen with Cucurbit[7−8]urils