The captodative effect

Viehe, H. G.; Janousek, Z.; Merényi, R.; Stella, Lucien

doi:10.1021/ar00113a004

Cited by 714 publications

(405 citation statements)

References 54 publications

(4 reference statements)

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“…Structure 2, which has the radical located on the α-carbon, is much higher in energy than structure 1 (63.6 kJ mol -1 ). This is not unexpected as in the anion the α-carbon radical is not stabilized by the captodative effect [60][61][62]. Figure 5a shows the experimentally generated IR spectrum for N-Ac-Cys radical anion and its comparison to the calculated spectra for the two lowest energy isomers of the radical anion, the sulfur and the α-carbon radicals (Figure 5b, c, respectively).…”

Section: Radical Anion Of N-acetyl-cysteinementioning

confidence: 77%

Structure and Reactivity of theN-Acetyl-Cysteine Radical Cation and Anion: Does Radical Migration Occur?

Osburn

Berden

O’Hair

et al. 2011

J. Am. Soc. Mass Spectrom.

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The structure and reactivity of the N-acetyl-cysteine radical cation and anion were studied using ion-molecule reactions, infrared multi-photon dissociation (IRMPD) spectroscopy, and density functional theory (DFT) calculations. The radical cation was generated by first nitrosylating the thiol of N-acetyl-cysteine followed by the homolytic cleavage of the S-NO bond in the gas phase. IRMPD spectroscopy coupled with DFT calculations revealed that for the radical cation the radical migrates from its initial position on the sulfur atom to the α-carbon position, which is 2.5 kJ mol -1 lower in energy. The radical migration was confirmed by time-resolved ion-molecule reactions. These results are in contrast with our previous study on cysteine methyl ester radical cation (Osburn et al., Chem. Eur. J. 2011, 17, 873-879) and the study by Sinha et al. for cysteine radical cation (Phys. Chem. Chem. Phys. 2010, 12, 9794-9800) where the radical was found to stay on the sulfur atom as formed. A similar approach allowed us to form a hydrogen-deficient radical anion of N-acetyl-cysteine, (M -2H)•-. IRMPD studies and ion-molecule reactions performed on the radical anion showed that the radical remains on the sulfur, which is the initial and more stable (by 63.6 kJ mol -1 ) position, and does not rearrange.

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Section: Radical Anion Of N-acetyl-cysteinementioning

confidence: 77%

Structure and Reactivity of theN-Acetyl-Cysteine Radical Cation and Anion: Does Radical Migration Occur?

Osburn

Berden

O’Hair

et al. 2011

J. Am. Soc. Mass Spectrom.

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“…On formation, the radical resides on the sulfur atom (the distonic structure). Both Zhao et al [36] and Ryzhov et al [22], calculated that the most stable structure was the result of hydrogen atom transfer from the α-carbon giving an α-radical stabilized by the captodative effect [37]. Nevertheless, gas-phase IR spectroscopy by Fornarini and co-workers revealed the long-lived distonic structure of the radical [28].…”

Section: Ms3: Cid-ecd Of S-nitrosylated Peptidesmentioning

confidence: 99%

The Radical Ion Chemistry of S-Nitrosylated Peptides

Jones

Winn

Cooper

2012

J. Am. Soc. Mass Spectrom.

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The radical ion chemistry of a suite of S-nitrosopeptides has been investigated. Doubly and triply-protonated ions of peptides NYCGLPGEYWLGNDK, NYCGLPGEYWLGNDR, NYCGLP-GERWLGNDR, NACGAPGEKWAGNDK, NYCGLPGEKYLGNDK, NYGLPGCEKWYGNDK and NYGLPGEKWYGCNDK were subjected to electron capture dissociation (ECD), and collisioninduced dissociation (CID). The peptide sequences were selected such that the effect of the site of S-nitrosylation, the nature and position of the basic amino acid residues, and the nature of the other amino acid side chains, could be interrogated. The ECD mass spectra were dominated by a peak corresponding to loss of• NO from the charge-reduced precursor, which can be explained by a modified Utah-Washington mechanism. Some backbone fragmentation in which the nitrosyl modification was preserved was also observed in the ECD of some peptides. Molecular dynamics simulations of peptide ion structure suggest that the ECD behavior was dependent on the surface accessibility of the protonated residue. CID of the S-nitrosylated peptides resulted in homolysis of the S-N bond to form a long-lived radical with loss of • NO. The radical peptide ions were isolated and subjected to ECD and CID. ECD of the radical peptide ions provided an interesting comparison to ECD of the unmodified peptides. The dominant process was electron capture without further dissociation (ECnoD). CID of the radical peptide ions resulted in cysteine, leucine, and asparagine side chain losses, and radical-induced backbone fragmentation at tryptophan, tyrosine, and asparagine residues, in addition to charge-directed backbone fragmentation.

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“…Conversely, with the bulky, poorly nucleophilic tert-amyloxide only the second equilibrium comes into play. The oxidation of the carbanion, presumably with atmospheric oxygen, leads to a radical 4b stabilized by the capto-dative effect [8][9][10][11] ; dimerization of 4b gives 8.…”

Section: Methodsmentioning

confidence: 99%

Rearrangement of a 3-acyloxyamino-1,5-diketone into enamine and pyrrole: a mechanistic study

Uncuţa¹,

Bartha²,

Tănase³

et al. 2006

Arkivoc

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The paper reports on the diversity of products obtained from a 3-acyloxyamino-1,5 diketone in reaction with bases, the distribution of products being correlated with the nature of the base and the solvent. Like other derivatives of β-hydroxyamino ketones, this compound reacts to form a 2-acylaziridine. Unusually, however, the aziridine undergoes ring-opening with carbon-carbon bond breaking to yield a β-ketoenaminone as isolable product. A minor path occurring with carbon-nitrogen bond breaking gives an α-acylpyrrole. In a further reaction the ketoenaminone forms a dimer which is characterized by X-ray crystallography.

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The captodative effect

Cited by 714 publications

References 54 publications

Structure and Reactivity of theN-Acetyl-Cysteine Radical Cation and Anion: Does Radical Migration Occur?

Structure and Reactivity of theN-Acetyl-Cysteine Radical Cation and Anion: Does Radical Migration Occur?

The Radical Ion Chemistry of S-Nitrosylated Peptides

Rearrangement of a 3-acyloxyamino-1,5-diketone into enamine and pyrrole: a mechanistic study

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