Electron spin resonance study of peroxy labels in a copolymer of tetrafluoroethylene-hexafluoropropylene

Schlick, Shulamith; Chamulitrat, Waleé; Kevan, Larry

doi:10.1021/j100266a027

Cited by 21 publications

(5 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The spectrum could be observed superimposed on that of the starting glycyl radical for samples exposed to air for less than 20 s (data not shown), suggesting that the new radical signal evolves as the glycyl radical disappears. The g values for this signal are similar to those for peroxyl radicals (19) including alkyl and sulfur peroxyl groups, though individual values for g y and g z could not be resolved (18,(20)(21)(22).…”

Section: Resultsmentioning

confidence: 55%

Dioxygen Inactivation of Pyruvate Formate-Lyase: EPR Evidence for the Formation of Protein-Based Sulfinyl and Peroxyl Radicals

et al. 1998

View full text Add to dashboard Cite

We here report EPR studies that provide evidence for radical intermediates generated from the glycyl radical of activated pyruvate formate-lyase (PFL) during the process of oxygen-dependent enzyme inactivation, radical quenching, and protein fragmentation. Upon exposure of active PFL to air, a long-lived radical intermediate was generated, which exhibits an EPR spectrum assigned to a sulfinyl radical (RSO*). The EPR spectrum of a sulfinyl radical was also generated from the activated C418A mutant of PFL, indicating that Cys 418 is not the site of sulfinyl radical formation. Exposure of the activated C419A mutant or C418AC419A double mutant to air on the other hand, resulted in a new EPR spectrum that we assign to the alpha-carbon peroxyl radical (ROO*) of the active-site glycine, G734. These findings suggest that C419 is the site of sulfinyl radical formation and that replacement of this cysteine with alanine results in the accumulation of the carbon peroxyl radical. The results also support the proposal that the peroxyl radical and the sulfinyl radical are intermediates in the oxygen-dependent inactivation and cleavage of the protein. Moreover, these observations are consistent with the hypothesis that C419 and G734 are in close proximity in the activated enzyme and may participate in a glycyl/thiyl radical equilibrium. A mechanism that accounts for the formation of the radical intermediates is proposed.

show abstract

Section: Resultsmentioning

confidence: 55%

Dioxygen Inactivation of Pyruvate Formate-Lyase: EPR Evidence for the Formation of Protein-Based Sulfinyl and Peroxyl Radicals

et al. 1998

View full text Add to dashboard Cite

show abstract

“…The principal values of the g tensor are in the range of values determined for peroxy radicals in various systems. 25,26 The dynamic effect was demonstrated by the reproducibility of the spectra as the temperature is cycled in the range 290-320 K.…”

Section: Resultsmentioning

confidence: 99%

“…The variation of the line shapes with temperature is identical to that predicted by the "cubic jump" mechanism described in our studies of dynamics in peroxy radicals: interconversion between three sites by rotation about an axis that is equally inclined (at the magic angle of 54.7°) to the principal axes of the g tensor. 25,26 The model corresponds to rotation around the body diagonal of a cube. Calculated spectra as a function of the mean lifetime, τ, of all sites (Figure 7 in ref 26) reproduce accurately the temperature variation of the spectra given in Figure 3B.…”

Section: Resultsmentioning

confidence: 99%

Nafion Perfluorinated Membranes Treated in Fenton Media: Radical Species Detected by ESR Spectroscopy

2004

Self Cite

View full text Add to dashboard Cite

ESR spectroscopy was used to detect and identify radicals in Nafion perfluorinated membranes exposed to the Fenton reagent based on Ti3+ (TiCl3 + H2O2). This method allowed monitoring the disappearance of the ESR signal from Ti3+ during reaction. The initially formed radical was HOO•, with magnetic parameters g 1 = 2.0261, g 2 = 2.0088, g 3 = 2.0031 (g iso = 2.0127), and a 1 = 5 G at 200 K. The disappearance of this radical above 220 K was accompanied by the appearance of a mixture of peroxy radicals TiOO• and superoxide radicals O2 -. The O2 - radicals were observed only in the dry Nafion after treatment and were stable up to 370 K; the g-tensor components are g 1 = 2.0190, g 2 = 2.0092, and g 3 = 2.0036 (g iso = 2.0106) at 300 K. In samples swollen by the hydrogen peroxide solution, signals from the TiOO• radicals predominated, with g-tensor components g 1 = 2.0228, g 2 = 2.0092, and g 3 = 2.0046 (g iso = 2.0122) at 200 K. A dynamical process lead to averaging of the g anisotropy of TiOO• radicals in the temperature range 220−320 K. The dynamics mechanism was identified with the “cubic jump” model: rotation of the O−O fragment about an axis equally inclined to the principal directions of the g tensor. A broad signal (line width ≈ 84 G, g = 2.0023) appeared in slightly dried samples after ≈14 days and increased in intensity after 92 days; this signal is thought to represent fluorinated alkyl radicals, formed by attack of oxygen radicals on the polymer chain. In the Fenton reagent (in the absence of Nafion) radicals are detected only for high concentrations of hydrogen peroxide, 30% w/v. In addition, the HOO• radicals formed are less stable, and the peroxy radicals TiOO• are the only species detected at and above 200 K. The presence of the Nafion membranes has important effects on both the type of radicals formed and their thermal stability.

show abstract

“…Further improvements are possible, for example, by assuming the presence of several species with distinct (but similar) g values. At any rate, it seems that a large portion of the EPR spectrum can be attributed to radicals with principal g values typical of an alkoxyl (R 1 R 2 R 3 CO • ) radical47 or a peroxyl (R 1 OO • ) radical,25, 32, 34, 35, 48–50 the latter being the most obvious candidate. The absence of strong proton hyperfine interactions is also an argument in favor of this assignation, although beta proton hyperfine interactions of alkoxyl species strongly depend on the local conformation and can be small enough to match experiment 47…”

Section: Resultsmentioning

confidence: 99%

New cheek swab technique may detect lung cancer

Printz¹

2011

Cancer

View full text Add to dashboard Cite

Electron paramagnetic resonance (EPR) measurements were performed on poly‐ε‐caprolactone (PCL) films at different stages of the postplasma‐grafting process. PCL films prepared by solvent casting (SC) or electrospinning (ESP) yield very similar EPR spectra after Ar‐plasma treatment and subsequent exposure to air, but the EPR signal is much stronger in the PCL‐ESP films. The free radicals appear to be mainly, and possibly exclusively, oxygen centered. The radicals generated by UV irradiation in PCL‐ESP films were studied in situ with EPR, using a UV‐LED (λ = (285 ± 5) nm). Their EPR spectrum is distinctly different from the plasma‐induced signal, indicative of carbon‐centered radicals, and appears to be independent of the plasma pretreatment. UV‐induced homolytic splitting of (hydro)peroxide bonds was not observed. Both the plasma‐ and UV‐induced radicals decay at room temperature (RT), even in an inert atmosphere. This study demonstrates the potential of electrospun films and UV‐LEDs for the study of plasma‐ and UV‐generated free radicals with EPR in polyesters, and raises questions with respect to the validity of some generally accepted molecular mechanisms underpinning the postplasma grafting technique for polyesters. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

show abstract

Electron spin resonance study of peroxy labels in a copolymer of tetrafluoroethylene-hexafluoropropylene

Cited by 21 publications

References 1 publication

Dioxygen Inactivation of Pyruvate Formate-Lyase: EPR Evidence for the Formation of Protein-Based Sulfinyl and Peroxyl Radicals

Dioxygen Inactivation of Pyruvate Formate-Lyase: EPR Evidence for the Formation of Protein-Based Sulfinyl and Peroxyl Radicals

Nafion Perfluorinated Membranes Treated in Fenton Media: Radical Species Detected by ESR Spectroscopy

New cheek swab technique may detect lung cancer

Contact Info

Product

Resources

About