Reactivity of Peroxy Radicals Coordinated to Vitamin B12 Studied by Electron Spin Resonance Spectroscopy

2004 ◽  
Vol 69 (11) ◽  
pp. 2091-2097 ◽  
Author(s):  
Alexander Tkáč ◽  
Eva Hanušovská
Keyword(s):  
Peroxy Radical ◽  
Resonance Spectroscopy ◽  
Vitamin B ◽  
Sterically Hindered Phenols ◽  
Peroxy Radicals ◽  
Oh Groups ◽  
Biological Targets ◽  
Hindered Phenols ◽  
Phenoxy Radicals ◽  
Radical Attack

One-electron transfer from chelated Co(II)(3d7) of vitamin B12 (cyanocobalamine) to tert-butylhydroperoxide forms at ambient temperature in non-polar solvents peroxy radicals stabilized by π-coordination to Co(III)(3d6) of the oxidized vitamin. In the absence of oxygen, the peroxy radicals manifest themselves as singlet ESR lines at g = 2.0174. After addition of sterically hindered phenols, apart from the decreased original singlet line, a new signal of stable phenoxy radicals, formed by H-abstraction from the phenols, is observed. Phenoxy radicals generated from unhindered phenols remain stabilized by σ-coordination to the cobalt(III) centre, giving rise to an ESR signal split into eight lines due to interaction of the unpaired electron with the magnetic moment of the 59Co nucleus (I = 7/2) of vitamin B12. Large molecules with unhindered OH groups, such as testosterone or cholesterol cannot be coordinated after the primary radical attack and the generated radicals disappear by recombination. By this technique, the sensitivity of biological targets to primary peroxy radical attack as well as the efficiency of different antioxidants (vitamin E, Stobadine) can be tested.

scholarly journals A Low-Viscosity BisGMA Derivative for Resin Composites: Synthesis, Characterization, and Evaluation of Its Rheological Properties

Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 338
Author(s):  
Ali Alrahlah ◽  
Abdel-Basit Al-Odayni ◽  
Haifa Fahad Al-Mutairi ◽  
Bashaer Mousa Almousa ◽  
Faisal S. Alsubaie ◽  
...  
Keyword(s):  
Substantial Reduction ◽  
Triethylene Glycol ◽  
High Viscosity ◽  
Resin Matrix ◽  
Resonance Spectroscopy ◽  
Dental Resin ◽  
Triethylene Glycol Dimethacrylate ◽  
Oh Groups ◽  
Low Viscosity ◽  
13C Nuclear Magnetic Resonance

This study aimed to synthesize new bisphenol A-glycidyl methacrylate (BisGMA) derivatives, targeting a reduction in its viscosity by substituting one of its OH groups, the leading cause of its high viscosity, with a chlorine atom. Hence, this monochloro-BisGMA (mCl-BisGMA) monomer was synthesized by Appel reaction procedure, and its structure was confirmed using Fourier transform infrared spectroscopy, 1H and 13C-nuclear magnetic resonance spectroscopy, and mass spectroscopy. The viscosity of mCl-BisGMA (8.3 Pa·s) was measured under rheometry conditions, and it was found to be more than 65-fold lower than that of BisGMA (566.1 Pa·s) at 25 °C. For the assessment of the viscosity changes of model resins in the presence of mCl-BisGMA, a series of resin matrices, in which, besides BisGMA, 50 wt % was triethylene glycol dimethacrylate, were prepared and evaluated at 20, 25, and 35 °C. Thus, BisGMA was incrementally replaced by 25% mCl-BisGMA to obtain TBC0, TBC25, TBC50, TBC75, and TBC100 blends. The viscosity decreased with temperature, and the mCl-BisGMA content in the resin mixture increased. The substantial reduction in the viscosity value of mCl-BisGMA compared with that of BisGMA may imply its potential use as a dental resin matrix, either alone or in combination with traditional monomers. However, the various properties of mCl-BisGMA-containing matrices should be evaluated.

Research changes in the properties of butadiene-nitrile rubber under various aging conditions

2021 ◽  
pp. 009524432110290
Author(s):  
Mariya L Davydova ◽  
Aytalina F Fedorova
Keyword(s):  
Accelerated Aging ◽  
Physical And Mechanical Properties ◽  
Exposure Period ◽  
Climatic Conditions ◽  
Nitrile Rubber ◽  
Sterically Hindered Phenols ◽  
Loading Mode ◽  
Hindered Phenols ◽  
The Republic ◽  
Butadiene Nitrile Rubber

This article represents the results of a study of changes in the properties of vulcanizates based on BNR-18 butadiene-nitrile rubber containing as stabilizers the experimental spatially hindered phenols Stafen, CO3, CO4, and industrial antioxidant 6PPD, after accelerated aging (100°C 96 h) and aging under full-scale exposure in extreme climatic conditions of the Republic of Sakha (Yakutia) during 2 years. In winter, the air temperature reached—48°C, in summer—+36.1°C. It is shown that the experimental sterically hindered phenols more effectively under natural exposure conditions. They are characterized by the most stability in terms of strength throughout the entire exposure period. Under conditions of accelerated aging, the vulcanizate containing the industrial antioxidant 6PPD is characterized by the greatest stability of physical and mechanical properties. According to the viscoelastic characteristics obtained in the dynamic loading mode, the contribution of the presented stabilizers in maintaining resistance to temperature and deformation effects compared with unstabilized rubber is confirmed.

The Influence of Irradiation Temperature on U.V. Induced Defect Creation in Dry Silica

1985 ◽  
Vol 61 ◽  
Author(s):  
R. A. B. Devine ◽  
C. Fiori ◽  
J. Robertson
Keyword(s):  
Oxygen Vacancy ◽  
Peroxy Radical ◽  
Irradiation Temperature ◽  
Threshold Temperature ◽  
Peroxy Radicals ◽  
Oxygen Hole ◽  
Spin Resonance ◽  
Dependent Growth ◽  
Dose Dependent ◽  
Annealing Curve

ABSTRACTElectron spin resonance measurements have been carried out on samples of Suprasil Wl (dry silica) subjected to ultraviolet laser radiation (λ = 248 nm, E = 5 eV/photon). Studies have been made for fixed irradiation temperature (room) variable accumulated ultraviolet dose and fixed accumulated dose (3000 J/cm2) at various irradiation temperatures in the range 110 K to 335 K. Three principal defect centers are observed. Non-bridging oxygen hole centers are created at all temperatures in the range studied with slightly higher efficiency at room temperature (ration 300 K/150 K ∼ 2.5). Comparison of the dose dependent growth curve of the 4.8 eV absorption and its isochronal annealing curve with those for the oxygen hole center clearly identify the origin of the absorption band with this defect. A threshold temperature ∼ 200 K is found for oxygen vacancy creation consistent with results on single crystalline quartz. Post irradiation annealing at 593 K eliminates the vacancy centers and the peroxy radical resonance appears. Its growth as a function of accumulated ultraviolet dose and irradiation temperature supports the hypothesis that peroxy radicals form by the trapping of diffusing, molecular oxygen at the oxygen vacancy center.

Absolute rate constants for hydrocarbon autoxidation. VI. Alkyl aromatic and olefinic hydrocarbons

1967 ◽  
Vol 45 (8) ◽  
pp. 793-802 ◽  
Author(s):  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Hydrogen Atom ◽  
Steric Hindrance ◽  
Rate Constants ◽  
Peroxy Radical ◽  
Electron System ◽  
Chain Termination ◽  
The Self ◽  
Hydrogen Atom Abstraction ◽  
Peroxy Radicals ◽  
Absolute Rate

Absolute rate constants have been measured for the autoxidation of a large number of hydrocarbons at 30 °C. The chain-propagating and chain-terminating rate constants depend on the structure of the hydrocarbon and also on the structure of the chain-carrying peroxy radical. With certain notable exceptions which are mainly due to steric hindrance, the rate constants for hydrogen-atom abstraction increase in the order primary < secondary < tertiary; and, for compounds losing a secondary hydrogen atom, the rate constants increase in the order unactivated < acyclic activated by a single π-electron system < cyclic activated by a single Π-system < acyclic activated by two π-systems < cyclic activated by two π-systems. The rate constants for chain termination by the self-reaction of two peroxy radicals generally increase in the order tertiary peroxy radicals < acyclic allylic secondary  [Formula: see text] cyclic secondary  [Formula: see text] acyclic benzylic secondary < primary peroxy radicals < hydroperoxy radicals.

scholarly journals Diel peroxy radicals in a semi industrial coastal area: nighttime formation of free radicals

2012 ◽  
Vol 12 (8) ◽  
pp. 19529-19570 ◽  
Author(s):  
M. D. Andrés-Hernández ◽  
D. Kartal ◽  
J. N. Growley ◽  
V. Sinha ◽  
E. Regelin ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Trace Gases ◽  
Peroxy Radical ◽  
Industrial Area ◽  
Diurnal Variations ◽  
Peroxy Radicals ◽  
Industrial Emissions ◽  
Air Masses ◽  
Volatile Organic ◽  
Organic Trace

Abstract. Peroxy radicals were measured by a PeRCA (Peroxy Radical Chemical Amplifier) instrument in the boundary layer during the DOMINO (Diel Oxidant Mechanisms In relation to Nitrogen Oxides) campaign at a coastal, forested site influenced by urban-industrial emissions in Southern Spain in late autumn. Total peroxy radicals (RO2* = HO2 + ΣRO2) generally showed a daylight maximum between 10 and 50 pptv at 13:00 UTC, with an average of 18 pptv over the 15 days of measurements. Emissions from the industrial area of Huelva often impacted the measurement site at night during the campaign. The processing of significant levels of anthropogenic organics leads to an intense nocturnal radical chemistry accompanied by formation of organic peroxy radicals at comparable levels to those of summer photochemical conditions with peak events up to 60–80 pptv. The RO2 production initiated by reactions of NO3 with organic trace gases was estimated to be significant but not sufficient to account for the concentrations of RO2* observed in air masses carrying high pollutant loading. The nocturnal production of peroxy radicals seems therefore to be dominated by ozonolysis of volatile organic compounds. RO2* diurnal variations were consistent with other HO2 measurements available at the site. HO2/RO2* ratios generally varied between 0.3 and 0.4 in all wind directions. Occasional HO2/RO2* ≥ 1 seemed to be associated with periods of high RO2* variability and with RO2 interferences in the HO2 measurement in air masses with high RO2 load.

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