scholarly journals Lawsone Derivatives as Efficient Photopolymerizable Initiators for Free-Radical, Cationic Photopolymerizations, and Thiol—Ene Reactions

Polymers ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 2015
Author(s):  
Christine Elian ◽  
Vlasta Brezová ◽  
Pauline Sautrot-Ba ◽  
Martin Breza ◽  
Davy-Louis Versace
Keyword(s):  
Free Radical ◽  
Paramagnetic Resonance ◽  
Ene Reactions ◽  
Ene Reaction ◽  
Free Radical Photopolymerization ◽  
Abstraction Reaction ◽  
Epoxy Monomer ◽  
Iodonium Salt ◽  
Epr Spin Trapping ◽  
Electron Paramagnetic

Two new photopolymerizable vinyl (2-(allyloxy) 1,4-naphthoquinone, HNQA) and epoxy (2-(oxiran-2yl methoxy) 1,4-naphthoquinone, HNQE) photoinitiators derived from lawsone were designed in this paper. These new photoinitiators can be used as one-component photoinitiating systems for the free-radical photopolymerization of acrylate bio-based monomer without the addition of any co-initiators. As highlighted by the electron paramagnetic resonance (EPR) spin-trapping results, the formation of carbon-centered radicals from an intermolecular H abstraction reaction was evidenced and can act as initiating species. Interestingly, the introduction of iodonium salt (Iod) used as a co-initiator has led to (1) the cationic photopolymerization of epoxy monomer with high final conversions and (2) an increase of the rates of free-radical polymerization of the acrylate bio-based monomer; we also demonstrated the concomitant thiol–ene reaction and cationic photopolymerizations of a limonene 1,2 epoxide/thiol blend mixture with the HNQA/Iod photoinitiating system.

Investigation of Antioxidant Activity of Pomegranate Juices by Means of Electron Paramagnetic Resonance and UV-Vis Spectroscopy

2015 ◽  
Vol 98 (4) ◽  
pp. 866-870 ◽  
Author(s):  
Violetta Kozik ◽  
Krystyna Jarzembek ◽  
Agnieszka Jędrzejowska ◽  
Andrzej Bąk ◽  
Justyna Polak ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Free Radical ◽  
Epr Spectroscopy ◽  
Antioxidant Properties ◽  
Free Radical Scavenger ◽  
Pomegranate Juice ◽  
Radical Scavenger ◽  
Paramagnetic Resonance ◽  
Vis Spectroscopy ◽  
Electron Paramagnetic

Abstract Pomegranate fruit (Punica granatum L.) is a source of numerous phenolic compounds, and it contains flavonoids such as anthocyanins, anthocyanidins, cyanidins, catechins and other complexes of flavonoids, ellagitannins, and hydrolyzed tannins. Pomegranate juice shows antioxidant, antiproliferative, and anti-atherosclerotic properties. The antioxidant capacity (TEAC) of the pomegranate juices was measured using electron paramagnetic resonance (EPR) spectroscopy and 1,1-diphenyl-2-picrylhydrazyl (DPPH•) as a source of free radicals, and the total phenolic (TP) content was measured using UV-Vis spectroscopy. All the examined pomegranate juices exhibited relatively high antioxidant properties. The TEAC values determined by means of EPR spectroscopy using Trolox (TE) as a free radical scavenger were in the range of 463.12 to 1911.91 μmol TE/100 mL juice. The TP content measured by the Folin-Ciocalteu method, using gallic acid (GA) as a free radical scavenger, widely varied in the investigated pomegranate juice samples and ranged from 1673.62 to 5263.87 mg GA/1 L juice. The strongest antioxidant properties were observed with the fresh pomegranate juices obtained from the fruits originating from Israel, Lebanon, and Azerbaijan. Correlation analysis of numerical data obtained by means of EPR spectroscopy (TEAC) and UV-Vis spectroscopy (TP) gave correlation coefficient (r) = 0.90 and determination coefficient (r2) = 0.81 (P <0.05).

Free radical metabolites in myocardium during ischemia and reperfusion

1991 ◽  
Vol 261 (4) ◽  
pp. L81-L86 ◽  
Author(s):  
Enno K. Ruuge ◽  
Alexander N. Ledenev ◽  
Vladimir L. Lakomkin ◽  
Alexander A. Konstantinov ◽  
Marina Yu. Ksenzenko
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Free Radical ◽  
Low Temperature ◽  
Coenzyme Q ◽  
Heart Tissue ◽  
Paramagnetic Species ◽  
Spectral Parameters ◽  
Paramagnetic Resonance ◽  
Oxygen Paradox ◽  
Electron Paramagnetic

Low-temperature electron paramagnetic resonance (EPR) spectroscopy and spin traps were used to measure paramagnetic species generation in rat hearts and isolated mitochondria. The hearts were freeze-clamped at 77 K during control perfusion by the Langendorff procedure, after 20–30 min of normothermic ischemia or 10–30 s of reperfusion with oxygenated perfusate. All EPR spectra measured at 4.5–50 K exhibited signals of both mitochondrial free radical centers and FeS proteins. The analysis of spectral parameters measured at 243 K showed that free radicals in heart tissue were semiquinones of coenzyme Q10 and flavins. The appearance of a typical “doublet” signal at g = 1.99 in low-temperature spectra indicated that a part of ubisemiquinones formed a complex with a high potential FeS protein of succinate dehydrogenase. Ischemia decreased the free radical species in myocardium ≈50%; the initiation of reflow of perfusate resulted in quick increase of the EPR signal. Mitochondria isolated from hearts during control perfusion and after 20–30 min of ischemia were able to produce superoxide radicals in both the NADH-coenzyme Q10 reductase and the bc1 segments of the respiratory chain. The rate of oxyradical generation was significantly higher in mitochondria isolated from ischemic heart. electron paramagnetic resonance; oxygen paradox; oxyradicals; rat heart; semiquinones

Quantitative Electron Paramagnetic Resonance: The Importance of Matching the Q-Factor of Standards and Samples

2001 ◽  
Vol 55 (10) ◽  
pp. 1375-1381 ◽  
Author(s):  
Richard L. Blakley ◽  
Dwight D. Henry ◽  
Walter T. Morgan ◽  
William L. Clapp ◽  
Carr J. Smith ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Free Radicals ◽  
Free Radical ◽  
Spin Trapping ◽  
Microwave Energy ◽  
Q Factor ◽  
Paramagnetic Resonance ◽  
Tert Butyl ◽  
Electron Paramagnetic ◽  
Stable Free Radicals

Electron paramagnetic resonance (EPR) quantification of free radicals from different samples facilitates comparison of free radical concentrations. Stable free radicals, such as 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), in a suitable solvent (e.g., benzene) can be used as a quantification standard. Free radicals found in samples can be shorter lived than radicals in prepared standards and require stabilizing spin-trapping agents such as N-tert-butyl-α-phenylnitrone (PBN) in an appropriate solvent (e.g., benzene). Analysis in our laboratory showed that free radicals from spin-trapped samples quantified against a standard of TEMPO in benzene displayed large differences among identical samples measured on either a Micro-Now 8300, Micro-Now 8400, or Bruker EMX EPR instrument. The Bruker instrument reported that the typical TEMPO in benzene standard had a Q-factor of ∼4400 while the Q-factor of our PBN-containing samples was ∼2500. (The Q-factor is inversely proportional to the amount of dissipated microwave energy in an EPR cavity.) By placing the TEMPO standard in a PBN/benzene solvent matrix we were able to match the Q-factor of our standards and samples, resulting in each of the three EPR instruments giving the same quantified free radical yields for the samples. This result points out the importance of matching the Q-factor between samples and standards for any quantitative EPR measurement.

Active oxygen and their scavengers in rice seeds (Oryza sativacv. IET 4094) aged under tropical environmental conditions

1997 ◽  
Vol 7 (3) ◽  
pp. 253-260 ◽  
Author(s):  
S. Nandi ◽  
S. Sen-Mandi ◽  
T.P. Sinha
Keyword(s):  
Free Radical ◽  
Active Oxygen ◽  
Prolonged Storage ◽  
Paramagnetic Resonance ◽  
Oxygen Scavenging ◽  
Enzyme Superoxide Dismutase ◽  
Rice Seeds ◽  
Scavenging Enzymes ◽  
Macromolecular Damage ◽  
Electron Paramagnetic

AbstractElectron paramagnetic resonance studies of high vigour (99% viable) and low vigour (38% viable) dry embryos of rice seeds (Oryza sativaL.) stored in a natural (warm and humid) environment were carried out. Loss in viability due to hot and humid conditions was found to be correlated with a decrease in free radical levels. The free radicals could be carbon-based and derived from quinones. Presence of the active oxygen scavenging enzyme, superoxide dismutase (EC 1.15.1.1) in embryos isolated from dry seeds showed a positive corrrelation with the state of vigour or viability. Anodic peroxidase (EC 1.11.1.7) activity in imbibed seeds also declined with the decline in vigour and viability. It is concluded that the deterioration of cells in the embryonic axis depends on the balance between free radical accumulation and the activity of active oxygen-scavenging enzymes which constitutes the active oxygen scavenging system (AOSS) during early imbibition. During prolonged storage under hot and humid conditions, cumulative effects of macromolecular damage due to oxidative chain products, compounded with the loss of enzyme activity, result in the final catastrophe, the death of the embryo.

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