EPR and DFT Study on the Stabilization of Radiation-Generated Methyl Radicals in Dehydrated Na-A Zeolite

Danilczuk, Marek; Pogocki, Dariusz; Lund, A.; Michalik, J.

doi:10.1021/jp063506y

Cited by 13 publications

(9 citation statements)

References 54 publications

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“…The rapid tumbling of the • CH 3 radical seen here at ∼40 K and above has commonly been observed at liquid nitrogen temperatures and above, as illustrated by a few examples: • CH 3 in frozen solutions of solvents ranging from nonpolar to aqueous; at 77 K generated by X-irradiation of CH 3 I; at 210 K trapped in zeolite cages; and as transiently generated through photolysis of MeCob in aqueous solution at 284 K . In this last case, the lines of the quartet at 280 K are extremely narrow, thus demonstrating the expected enhanced rotational mobility near ambient temperatures.…”

Section: Resultssupporting

confidence: 57%

Photoinduced Electron Transfer in a Radical SAM Enzyme Generates an S-Adenosylmethionine Derived Methyl Radical

et al. 2019

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Radical SAM (RS) enzymes use S-adenosyl-L-methionine (SAM) and a [4Fe-4S] cluster to initiate a broad spectrum of radical transformations throughout all kingdoms of life. We report here that low-temperature photoinduced electron transfer from the [4Fe-4S] 1+ cluster to bound SAM in the active site of the hydrogenase maturase RS enzyme, HydG, results in specific homolytic cleavage of the S-CH 3 bond of SAM, rather than the S-C5′ bond as in the enzymecatalyzed (thermal) HydG reaction. This result is in stark contrast to a recent report in which photoinduced ET in the RS enzyme pyruvate formate-lyase activating enzyme cleaved the S-C5′ bond to generate a 5′-deoxyadenosyl radical, and provides the first direct evidence for homolytic S-CH 3 bond cleavage in a RS enzyme. Photoinduced ET in HydG generates a trapped • CH 3 radical, as well as a small population of an organometallic species with an Fe-CH 3 bond, denoted Ω M. The • CH 3 radical is surprisingly found to exhibit rotational diffusion in the HydG active site at temperatures as low as 40 K, and is rapidly quenched: whereas 5′-dAdo • is stable indefinitely at 77 K, • CH 3 quenches with a half-time of ~2 min at this temperature. The rapid quenching and rotational/translational freedom of • CH 3 shows that enzymes would be unable to harness this radical as a regio-and stereospecific H atom abstractor during catalysis, in contrast to the exquisite control achieved with the enzymatically generated 5′-dAdo • .

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Section: Resultssupporting

confidence: 57%

Photoinduced Electron Transfer in a Radical SAM Enzyme Generates an S-Adenosylmethionine Derived Methyl Radical

et al. 2019

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“…Similar EPR signals with A iso (Ag) = 13.0 mT have been observed in γ-irradiated frozen solution of methanol and in glassy ethanol [25]. [19,29,30]. However, due to the complexity of adsorbate-zeolite systems, the application of very sophisticated ab initio or density functional theory (DFT) methods for the calculations of magnetic parameters require quite substantial computational effort.…”

Section: Introductionmentioning

confidence: 53%

Interaction of CH2OH with silver cation in Ag–A/CH3OH zeolite: A DFT study

Danilczuk

Pogocki

Lund

2009

Chemical Physics Letters

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“…The best overall agreement between experimental and calculated values was obtained for the B3LYP hybrid functional and EPR-III basis sets combination. This approach has been proven to give reliable results for the Ag(C 2 H 4 ) 2 or Na + ···CH 3 complexes stabilized in SAPO-11 molecular sieve and 4A zeolite, respectively [64,65].…”

Section: Computationsmentioning

confidence: 98%

Monomer- and polymer radicals of vinyl compounds: EPR and DFT studies of geometric and electronic structures in the adsorbed state

Lund

Danilczuk

2012

Spectrochimica Acta Part A: Molecular and Biomolecular Spectros

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Electron paramagnetic resonance (EPR) spectroscopy was applied to study the paramagnetic species formed from styrene, 1,1-diphenylethylene, α-methylstyrene, β-methylstyrene and methylmethacrylate adsorbed on amorphous silica gel after -irradiation at 77 K. Radicals formed by the hydrogen atom addition at the vinyl group of the monomers were observed in all samples. The hydrogen atoms were shown to originate to a large extent from the adsorbent by using silica gel with deuterated silanol groups. An EPR spectrum assigned to a propagating radical was observed at increased temperature for samples containing methylmethacrylate (MMA). The structures of the adsorption complexes, the respective hyperfine coupling constants and the adsorption energies were calculated by applying DFT quantum chemical methods. The reaction between an MMA molecule and the MMA radical and the structure of the propagating radical was modeled. The calculated hyperfine coupling constants for all radicals confirmed the assignment of the experimental spectra.3

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EPR and DFT Study on the Stabilization of Radiation-Generated Methyl Radicals in Dehydrated Na-A Zeolite

Cited by 13 publications

References 54 publications

Photoinduced Electron Transfer in a Radical SAM Enzyme Generates an S-Adenosylmethionine Derived Methyl Radical

Photoinduced Electron Transfer in a Radical SAM Enzyme Generates an S-Adenosylmethionine Derived Methyl Radical

Interaction of CH2OH with silver cation in Ag–A/CH3OH zeolite: A DFT study

Monomer- and polymer radicals of vinyl compounds: EPR and DFT studies of geometric and electronic structures in the adsorbed state

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