Electron Paramagnetic Resonance of Some Sulfur and Selenium Compounds

Windle, J. J.; Wiersema, A. K.; Tappel, Al L.

doi:10.1063/1.1726194

Cited by 63 publications

(15 citation statements)

References 19 publications

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“…The g value of the radical species in Fig. 4E (∼2.0) is consistent with a carbon-rather than thiyl-centered radical (47,48) and is also distinct from the radical formed in the reaction of (Fe II /αKG)-DAOCS with O 2 as well as the radical of the oneelectron oxidized penicillin-G substrate (SI Appendix, Fig. S26).…”

Section: Characterization Of the Fe III Species And Its Reactivity: Esupporting

confidence: 62%

Evaluation of a concerted vs. sequential oxygen activation mechanism in α-ketoglutarate–dependent nonheme ferrous enzymes

Goudarzi

Iyer

Babicz

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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Determining the requirements for efficient oxygen (O2) activation is key to understanding how enzymes maintain efficacy and mitigate unproductive, often detrimental reactivity. For the α-ketoglutarate (αKG)–dependent nonheme iron enzymes, both a concerted mechanism (both cofactor and substrate binding prior to reaction with O2) and a sequential mechanism (cofactor binding and reaction with O2 precede substrate binding) have been proposed. Deacetoxycephalosporin C synthase (DAOCS) is an αKG-dependent nonheme iron enzyme for which both of these mechanisms have been invoked to generate an intermediate that catalyzes oxidative ring expansion of penicillin substrates in cephalosporin biosynthesis. Spectroscopy shows that, in contrast to other αKG-dependent enzymes (which are six coordinate when only αKG is bound to the FeII), αKG binding to FeII-DAOCS results in ∼45% five-coordinate sites that selectively react with O2 relative to the remaining six-coordinate sites. However, this reaction produces an FeIII species that does not catalyze productive ring expansion. Alternatively, simultaneous αKG and substrate binding to FeII-DAOCS produces five-coordinate sites that rapidly react with O2 to form an FeIV=O intermediate that then reacts with substrate to produce cephalosporin product. These results demonstrate that the concerted mechanism is operative in DAOCS and by extension, other nonheme iron enzymes.

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Section: Characterization Of the Fe III Species And Its Reactivity: Esupporting

confidence: 62%

Evaluation of a concerted vs. sequential oxygen activation mechanism in α-ketoglutarate–dependent nonheme ferrous enzymes

Goudarzi

Iyer

Babicz

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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“…Previous work has discussed the difficulties with observing features of the analogous sulfur-based thiyl radical, ,, due to substantial spin–orbit coupling to filled sulfur-based orbitals, with a very broad g zz at the high value of 2.3. With the selenium-based selenyl radical, this broadening and shift to high g -values will be even more pronounced, so that reports of EPR spectra of putative selenyl radicals with substantially lower g zz than thiyl probably arise from other species. Thus, while there are reports of selenium-based free radical systems, to date, there have been no authenticated reports of selenyl radical EPR spectra.…”

Section: Resultsmentioning

confidence: 99%

A Photochemically Generated Selenyl Free Radical Observed by High Energy Resolution Fluorescence Detected X-ray Absorption Spectroscopy

et al. 2018

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Selenium-based selenyl free radicals are chemical entities that may be involved in a range of biochemical processes. We report the first X-ray spectroscopic observation of a selenyl radical species generated photochemically by X-ray irradiation of low-temperature solutions of l-selenocysteine. We have employed high energy resolution fluorescence detected X-ray absorption spectroscopy (HERFD-XAS) and electron paramagnetic resonance (EPR) spectroscopy, coupled with density functional theory calculations, to characterize and understand the species. The HERFD-XAS spectrum of the selenyl radical is distinguished by a uniquely low-energy transition with a peak energy at 12 659.0 eV, which corresponds to a 1s → 4p transition to the singly occupied molecular orbital of the free radical. The EPR spectrum shows the broad features and highly anisotropic g-values that are expected for a selenium free radical species. The availability of spectroscopic probes for selenyl radicals may assist in understanding why life chooses selenium over sulfur in selected biochemical processes.

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“…Finally, for both kinds of excitation, signals at g=2.095 are observed, that emerge with a red discoloration in the samples. We therefore assign them to emerging polyselenides, as found by Sampath [12] in contrast to prior studies [10] . A more detailed EPR analysis is given in Figures S42 to S45.…”

Section: Methodsmentioning

confidence: 89%

Trapping X‐ray Radiation Damage from Homolytic Se−C Bond Cleavage in BnSeSeBn Crystals (Bn=benzyl, CH₂C₆H₅)

et al. 2022

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Irradiation of dibenzyl diselenide BnSeSeBn with X‐ray or UV‐light cleaves the Se−C and the Se−Se bonds, inducing stable and metastable radical states. They are inevitably important to all natural and life sciences. Structural changes due to X‐ray‐induced Se−C bond‐cleavage could be pin‐pointed in various high‐resolution X‐ray diffraction experiments for the first time. Extended DFT methods were applied to characterize the solid‐state structure and support the refinement of the observed residuals as contributions from the BnSeSe⋅ radical species. The X‐ray or UV‐irradiated crystalline samples of BnSeSeBn were characterized by solid‐state EPR. This paper provides insight that in the course of X‐ray structure analysis of selenium compounds not only organo‐selenide radicals like RSe⋅ may occur, but also organo diselenide BnSeSe⋅ radicals and organic radicals R⋅ are generated, particularly important to know in structural biology.

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Electron Paramagnetic Resonance of Some Sulfur and Selenium Compounds

Cited by 63 publications

References 19 publications

Evaluation of a concerted vs. sequential oxygen activation mechanism in α-ketoglutarate–dependent nonheme ferrous enzymes

Evaluation of a concerted vs. sequential oxygen activation mechanism in α-ketoglutarate–dependent nonheme ferrous enzymes

A Photochemically Generated Selenyl Free Radical Observed by High Energy Resolution Fluorescence Detected X-ray Absorption Spectroscopy

Trapping X‐ray Radiation Damage from Homolytic Se−C Bond Cleavage in BnSeSeBn Crystals (Bn=benzyl, CH₂C₆H₅)

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Electron Paramagnetic Resonance of Some Sulfur and Selenium Compounds

Cited by 63 publications

References 19 publications

Evaluation of a concerted vs. sequential oxygen activation mechanism in α-ketoglutarate–dependent nonheme ferrous enzymes

Evaluation of a concerted vs. sequential oxygen activation mechanism in α-ketoglutarate–dependent nonheme ferrous enzymes

A Photochemically Generated Selenyl Free Radical Observed by High Energy Resolution Fluorescence Detected X-ray Absorption Spectroscopy

Trapping X‐ray Radiation Damage from Homolytic Se−C Bond Cleavage in BnSeSeBn Crystals (Bn=benzyl, CH2C6H5)

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Trapping X‐ray Radiation Damage from Homolytic Se−C Bond Cleavage in BnSeSeBn Crystals (Bn=benzyl, CH₂C₆H₅)