Polarity of the Transition State Controls the Reactivity of Related Charged Phenyl Radicals Toward Atom and Group Donors

Tichy, Shane E.; Thoen, Kami K.; Price, Jason M.; Ferra, Joseph J.; Petucci, Chris; Kenttämaa, Hilkka I.

doi:10.1021/jo001634r

Cited by 42 publications

(40 citation statements)

References 53 publications

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“…This was attributed to the great calculated EA v (6.53 eV at the B3LYP/6-31+G(d)+ZPVE level of theory) of this radical compared to those of the other phenyl radicals (5.11 – 5.82 eV at the B3LYP/6-31+G(d)+ZPVE level of theory). 58 These findings further emphasize the importance of the ionic surface in controlling the barrier height in radical abstraction reactions, in agreement with the work by Donahue et al 130 …”

Section: Properties and Reactivitysupporting

confidence: 86%

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Properties and Reactivity of Gaseous Distonic Radical Ions with Aryl Radical Sites

et al. 2013

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Section: Properties and Reactivitysupporting

confidence: 86%

“…This model has been used in a number of experimental studies to explain relative rates of radical reactions, including several reviewed here. 50,52,56,58,62,67 …”

Section: Properties and Reactivitymentioning

confidence: 99%

Properties and Reactivity of Gaseous Distonic Radical Ions with Aryl Radical Sites

et al. 2013

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“…Polar effects (i.e., polarization of the transition state) play a major role in controlling these reactions [5][6][7]. However, no such studies have been reported for the analogous biradicals.…”

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confidence: 99%

Reactivity of aromatic σ,σ-biradicals toward riboses

Adeuya

Yang

Amegayibor

et al. 2006

J. Am. Soc. Mass Spectrom.

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The gas-phase reactions of sugars with aromatic, carbon-centered ,-biradicals with varying polarities [as reflected by their calculated electron affinities (EA)] and extent of spin-spin coupling [as reflected by their calculated singlet-triplet (S-T) gaps] have been studied. The biradicals are positively charged, which allows them to be manipulated and their reactions to be studied in a Fourier-transform ion cyclotron resonance mass spectrometer. Hydrogen atom abstraction from sugars was found to be the dominant reaction for the biradicals with large EA values, while the biradicals with large S-T gaps tend to form addition/elimination products instead. Hence, not all ,-biradicals may be able to damage DNA by hydrogen atom abstraction. The overall reaction efficiencies of the biradicals towards a given substrate were found to be directly related to the magnitude of their EA values, and inversely related to their S-T gaps. The EA of a biradical appears to be a very important rate-controlling factor, and it may even counterbalance the reduced radical reactivity characteristic of singlet biradicals that have large S-T gaps. . These intermediates are believed to irreversibly damage double-stranded DNA via hydrogen atom abstraction from a sugar moiety in each strand [2]. Therefore, a better understanding of the factors controlling the reactivity of these biradicals toward sugars is important.Solution [3] and gas-phase [4] studies on the reactivity of neutral and charged phenyl radicals have confirmed that these monoradicals can abstract hydrogen atoms from sugars as well as from the sugar moiety in nucleosides and dinucleoside phosphates. Polar effects (i.e., polarization of the transition state) play a major role in controlling these reactions [5][6][7]. However, no such studies have been reported for the analogous biradicals.The magnitude of the singlet-triplet (S-T) gap has been proposed earlier [8] as the major reaction rate controlling factor for aromatic ,-biradicals with singlet ground states. As the magnitude of the S-T gap increases, the reaction efficiency for hydrogen atom abstraction from simple substrates has been observed to decrease, presumably because of the energetically high cost of uncoupling the biradical's electrons in the transition state [8,9]. Biradicals with large S-T gaps appear to avoid this penalty by undergoing nucleophilic or electrophilic (nonradical) addition reactions [10]. Recent gas-phase studies have shown that in addition to S-T gap effects [9], reactions of biradicals with simple organic substrates are also sensitive to polar effects (which is reflected by the biradical's calculated vertical electron affinity, EA) [11]. Here, we report an examination of the reactivity of several ,-biradicals (Scheme 1) toward various sugars, and show that these reactions are also affected by the S-T gap and the EA of the biradical.

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“…Previous studies have suggested that the polarity of the transition state of a charged phenyl radical depends on the electrophilicity of the radical [11]. As the electrophilicity increases, the transition states for its reactions become more polar, which leads to lower transition state energies [12].…”

Section: Introductionmentioning

confidence: 99%

Gas-phase Reactivity of meta-Benzyne Analogs Toward Small Oligonucleotides of Differing Lengths

Widjaja

Max

Jin

et al. 2017

J. Am. Soc. Mass Spectrom.

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Abstract. The gas-phase reactivity of two aromatic carbon-centered σ,σ-biradicals (meta-benzyne analogs) and a related monoradical towards small oligonucleotides of differing lengths was investigated in a Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer coupled with laser-induced acoustic desorption (LIAD). The mono-and biradicals were positively charged to allow for manipulation in the mass spectrometer. The oligonucleotides were evaporated into the gas phase as intact neutral molecules by using LIAD. One of the biradicals was found to be unreactive. The reactive biradical reacts with dinucleoside phosphates and trinucleoside diphosphates mainly by addition to a nucleobase moiety followed by cleavage of the glycosidic bond, leading to a nucleobase radical (e.g., base-H) abstraction. In some instances, after the initial cleavage, the unquenched radical site of the biradical abstracts a hydrogen atom from the neutral fragment, which results in a net nucleobase abstraction. In sharp contrast, the related monoradical mainly undergoes facile hydrogen atom abstraction from the sugar moiety. As the size of the oligonucleotides increases, the rate of hydrogen atom abstraction from the sugar moiety by the monoradical was found to increase due to the presence of more hydrogen atom donor sites, and it is the only reaction observed for tetranucleoside triphosphates. Hence, the monoradical only attacks sugar moieties in these substrates. The biradical also shows significant attack at the sugar moiety for tetranucleoside triphosphates. This drastic change in reactivity indicates that the size of the oligonucleotides plays a key role in the outcome of these reactions. This finding is attributed to more compact conformations in the gas phase for the tetranucleoside triphosphates than for the smaller oligonucleotides, which result from stronger stabilizing interactions between the nucleobases.

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Polarity of the Transition State Controls the Reactivity of Related Charged Phenyl Radicals Toward Atom and Group Donors

Cited by 42 publications

References 53 publications

Properties and Reactivity of Gaseous Distonic Radical Ions with Aryl Radical Sites

Properties and Reactivity of Gaseous Distonic Radical Ions with Aryl Radical Sites

Reactivity of aromatic σ,σ-biradicals toward riboses

Gas-phase Reactivity of meta-Benzyne Analogs Toward Small Oligonucleotides of Differing Lengths

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