Hydroxyl radical induced decarboxylation of amino acids. Decarboxylation vs bond formation in radical intermediates

Steffen, L. Kraig; Glass, Richard S.; Sabahi, M.; Wilson, George S.; Schoeneich, Christian; Mahling, Sabine; Asmus, K.‐D.

doi:10.1021/ja00006a035

Cited by 76 publications

(67 citation statements)

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“…As in the case of the methionine-derived species, the decay of NB-(S;N) ± is attributed to a decarboxylation process, yielding the corresponding C-centered a-amino radical [12,15]. Our mechanistic conclusion on the sulfur-nitrogen coupling is further supported by an earlier study of ours in which we had reported on the oxidation of the sulfurcontaining stereoisomer of NB(S) with the amino group in the 2-exo and the carboxyl group in the 2-endo position [23]. In this case, the oxidized sulfur could interact only with the carboxyl group and, in a to-be-expected contrast with our present system, the resulting transient was much longer lived (t 1/2 26 ls) and showed a much more blue-shifted absorption at 340 nm.…”

Section: Nb-(s∴n) ± / Nb-(se∴n) ± Nb-(s∴n) + / Nb-(se∴n) +supporting

confidence: 78%

Theoretical calculations and experimental data on spectral, kinetic and thermodynamic properties of Se∴N and S∴N three-electron-bonded, structurally stabilized σ2σ* radicals

et al. 2009

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A complementary quantum mechanical and experimental study has been undertaken on the reactivity, formation and properties of Se;N and S;N r 2 /r* three-electron-bonded radical species, generated upon one-electron oxidation of selenomethionine, methionine and structurally related compounds. The quantum chemical calculations were based on density functional theory (DFT) hybrid B3LYP and BHandHLYP methods with basis sets ranging from 6-31G(d) to 6-311?G(d,p). Solvent effects, which play an important role concerning structure and energy of ground and excited states, were taken into account as dielectric continuum as well as explicit water molecules. They fully confirm new and previously obtained experimental results concerning the Vis/near-UV absorptions and thermodynamic stability. Special emphasis was put on a comparison between selenium and sulfur. The calculations clearly confirm the higher thermodynamic stability of the Se;N radical species relative to the S;N ones, and also corroborate the observed much higher kinetic stability of the former. Concerning optical absorptions, the calculations predict the Se;N transients to exhibit a blue-shift by about 20 nm relative to the S-based analogues, confirming the few experimental data available so far. The theoretical study includes a comparison of various calculation levels and the influence of the solvent environment, by comparison with vacuum. New experimental data within the scope of this study have been obtained on intramolecularlyformed S;N radical cation moieties, structurally stabilized by a rigid norbornane backbone. The methionine-related species, with an endo-2-amino, exo-2-carboxyl, and endo-6 methylthio substitution, for example, exhibits almost identical optical and kinetic stability properties as the corresponding species from free methionine. Its optical absorption depends on the protonation state of the carboxyl group, with k max at 410 nm for the carboxylate (zwitterionic) form and at 390 nm for the overall cationic form with the protonated carboxyl group. The fast exponential decays with t 1/2 of 490 ns and 2 ls pertain to the decarboxylation of the respective species. A much longer-lived S;N species with t 1/2 [ 500 ls and second order decay kinetics (k max 465 nm) was obtained from an endo-2-cyclohexylamino norbornane analogue which does not carry a carboxyl group. The methionine-based S;N species is not stable anymore in vacuum and in low polarity solvents. This is explained by a decrease in stabilization energy of the 3-e-bond and a faster electron transfer from the carboxylate into the cationic 3-e-center. In conclusion, selenium enhances the thermodynamic and kinetic stability of its radical transients, relative to the sulfur analogues.

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Section: Nb-(s∴n) ± / Nb-(se∴n) ± Nb-(s∴n) + / Nb-(se∴n) +supporting

confidence: 78%

Theoretical calculations and experimental data on spectral, kinetic and thermodynamic properties of Se∴N and S∴N three-electron-bonded, structurally stabilized σ2σ* radicals

et al. 2009

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“…30 nm deviation from the experimental data obtained in aqueous solution (see Table 1). 23 The calculated energy band is essentially described by a oneelectron transition between the occupied σ and the singly occupied σ* molecular orbitals, as evident by the weighting coefficients displayed in Table 1. The ZINDO/S calculation of the UV absorption of radicals 1a •+ and 1a aq…”

Section: Radicals From Exo-2-amino-endo-6-(methylthio)bicyclo-[221]mentioning

confidence: 87%

“…35 nm, bringing the computed bands very close to the experimentally observed value (see Table 1). 23 Radical 1a •+ exhibits a vibrational frequency of ca. 755 cm -1 , which can be assigned to the S-O bond-stretching mode.…”

Section: Radicals From Exo-2-amino-endo-6-(methylthio)bicyclo-[221]mentioning

confidence: 99%

Computational Characterization of Sulfur−Oxygen Three-Electron-Bonded Radicals in Methionine and Methionine-Containing Peptides: Important Intermediates in One-Electron Oxidation Processes

2003

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Density functional theory and semiempirical methods were employed to characterize the structure and properties of sulfur-oxygen-bonded radical cations formed during the one-electron oxidation of various organic sulfides and methionine-containing peptides. In general, all of the examined sulfur-oxygen bonds can be described as two-center, three-electron-bonded systems. The usefulness of approximate computational approaches (SCC-DFTB, AM1 and PM3) for the reliable description of three-electron-bonded species was examined.

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“…For example, the OH radical has been implicated in decarboxylation of amino acids (Steffen et al, 1991) and organic acids (Zafiriou et al, 1990). Goldstone et al (2002) showed that the OH radical (generated by radiolysis) reacted with humic substances (Suwannee River fulvic and humic acids) to produce DIC with an efficiency of ~0.3 mol CO 2 (mol of OH radical) −1 .…”

Section: B Dic Photoproduction and Photochemical Oxygen Consumption mentioning

confidence: 99%

Marine Photochemistry of Organic Matter

Mopper

Kieber

Stubbins

2015

Biogeochemistry of Marine Dissolved Organic Matter

142

134

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Hydroxyl radical induced decarboxylation of amino acids. Decarboxylation vs bond formation in radical intermediates

Cited by 76 publications

References 1 publication

Theoretical calculations and experimental data on spectral, kinetic and thermodynamic properties of Se∴N and S∴N three-electron-bonded, structurally stabilized σ2σ* radicals

Theoretical calculations and experimental data on spectral, kinetic and thermodynamic properties of Se∴N and S∴N three-electron-bonded, structurally stabilized σ2σ* radicals

Computational Characterization of Sulfur−Oxygen Three-Electron-Bonded Radicals in Methionine and Methionine-Containing Peptides: Important Intermediates in One-Electron Oxidation Processes

Marine Photochemistry of Organic Matter

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