Peroxy Radical Scavenging Research Articles

Isolation and characterization of alkyl peroxy radical scavenging compound from leaves of Laurus nobilis.

EtOH-soluble fraction from leaves of Laurus nobilis (bay leaves) possessed the highest alkyl peroxy radical (ROO*) scavenging activity among 120 kinds of herbs and edible plants, using the bioassay system which could determine the viability of Staphylococcus aureus 209p by ROO* cytotoxicity. After EtOH-soluble fraction was partitioned with chloroform, ethylacetate, n-butanol and water, the ethylacetate-soluble fraction (L-EA) possessing the highest scavenging activity was further fractionated by Silica gel, Sephadex LH-20 and semi-preparative HPLC analysis on micro-Bondapak C18 reverse phase, and a major flavonol (L-EA-IIa-3-H2) in leaves of L. nobilis was isolated. According to the ultraviolet-visible absorption spectra, L-EA-IIa-3-H2 was thought to be 3,5,7,3'-OH or 3(5),7,3',4'-OH flavonol. After acid hydrolysis of the fraction, L-EA-IIa-3-H2 was found to consist of quercetin and glucose, and was confirmed by one- or two-dimensional (1D or 2D)-NMR to be isoquercitrin. In addition, the ROO* scavenging activity of L-EA-IIa-3-H2 was supported by ESR and its activity was found to be comparable to that of other well-known antioxidants such as epigallocatechin and resveratrol, and higher than that of butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and ascorbic acid.

NO3-initiated oxidation of biogenic hydrocarbons

To test the recent hypothesis of a possible non-photochemical, NO3-initiated production of peroxy radicals, differential optical absorption spectroscopy (DOAS) measurements of NO3 and its precursor species were made at a mediterranean Eucalyptus forest site in the framework of the CEC FIELDVOC'94 project. Our data set is presented in combination with other FIELDVOC'94 results for various important reactants in night-time radical chemistry. Despite a high NO3 production (as calculated from O3 and NO2 measurements), its concentration remained below the detection limit of 6 pptv. This is most likely due to the large abundance of olefins, which are very effective NO3 scavengers. In fact, it is shown that among the known NO3 sinks, the reaction with olefins was by far the most important NO3 loss process during our measurements. It was suggested that this reaction could be a non-photochemical source of peroxy radicals (RO2) and probably OH. Kinetic model calculations based on our observations lead to night-time RO2 concentrations between 108 and 1010 molecule cm−3. While during most nights observed RO2 values were considerably lower, elevated RO2 concentrations in the low ppt range were occasionally found in the late evening, demonstrating the presence of a night-time RO2 source. The data set suggests that heterogeneous scavenging of peroxy radicals (which is not accounted for in our model) may be the dominant night-time sink for peroxy radicals.

Contribution of proanthocyanidins to the peroxy radical scavenging capacity of some Italian red wines.

Highly reactive radicals, ROO(*), were generated from 2, 2'-azobis[2-(2-imidazolin-2-yl)propane] and linoleic acid. The ROO(*) scavenging capacity of some Italian red wines was evaluated following the changes in oxygen consumption. Under the experimental conditions the time course of oxygen consumption shows two typical behaviors: trolox-like (class I) and gallic acid-like (class II). Usually the time course of wine was similar to that of gallic acid. The rate of oxygen consumption was found to decrease exponentially with the amount of wine or gallic acid added to the test solution. On this basis the capacity of red wines to scavenge peroxy radicals was expressed as content of gallic acid (S(GA)). The S(GA) values were found to be correlated to the amount of total proanthocyanidins and total polyphenols of some Italian red wines (p < 0.01). The proanthocyanidins extracted from seeds were shown to make a major contribution to the peroxy radical scavenging capacity of red wines, whereas, interestingly, the chemical class of the low molecular weight tannins reactive to vanillin did not correlate with the S(GA) values.

EFFECT OF THE THERMO-OXIDATION AND NATURAL WEATHER ON THE STRUCTURE, MORPHOLOGY, AND PROPERTIES OF UNSTABILIZED AND HALS-STABILIZED LDPE FILMS

ABSTRACT The aging of unstabilized low density polyethylene (LDPE) films and those stabilized with hindered amine light stabilizers (HALS) was studied as a function of the exposure time to thermo-oxidation at 90°C and to natural weathering. The HALS tested was Tinuvin 783 from Ciba-Geigy and added to the polymer in the concentration of 0.6% (w/w). Modifications in the film characteristics were investigated by using Fourier transform infrared (FTIR), scanning electron microscopy (SEM), wide angle X-ray scattering (WAXS) and mechanical testing. The FTIR spectra showed that the thermo-oxidation led to the formation of ketone groups attributed to hydroperoxide decomposition, whereas in natural weathering ketones and vinyl unsaturations are formed due to Norrish II reactions. The mechanism of stabilization involved in thermo-oxidation of the HALS-stabilized samples may be attributed to the classical radical scavenging of alkyl and peroxy radicals formed during propagation by nitroxyl radicals. The stabilizing activity of Tinuvin 783 in natural weathering may be explained by its capacity to trap the alkyl radicals resulting from the charge transfer complexes reactions between the polymer and oxygen. The effectiveness of Tinuvin 783 as heat and UV stabilizer in LDPE film was confirmed by the slow decline of the elongation at break as found in the exposed samples. The thermo-oxidation and the natural weathering caused the formation of micro-voids on the surfaces of the unstabilized films; the presence of the HALS reduced the number and the size of the micro-voids. WAXS analysis showed that the crystallinity indexes of the unstabilized samples, both thermo-oxidated and exposed to natural weather, increase significantly with the time; for the stabilized samples the increases of the crystallinity resulted less pronounced.

Reperfusion injury of postischemic skeletal muscle is attenuated by the 21-aminosteroids U-74389F and U-74500A independent of iron binding

Lazaroids (21-aminosteroids) are a novel class of compounds that have been shown to limit experimental ischemic injury of varied causes. The mechanism of action is uncertain but may include scavenging of lipid peroxy radicals, iron binding, or direct membrane interaction. The purpose of these experiments was to evaluate the capacity of the lazaroids U-74500A and U-74389F to modify ischemia/reperfusion injury of skeletal muscle in a well-characterized model of high-grade partial ischemia. Nonfasted male Sprague-Dawley rats were anesthetized, a tracheostomy tube was placed, and the carotid artery and jugular vein were cannulated. Animals received heparin (1 unit/gm) and crystalloid (1 ml/hr) intravenously. The baseline group (n = 6) was allowed a 30-minute equilibration period, after which resting transmembrane potential (Em) was measured in a hindlimb muscle. Muscle biopsy specimen was obtained; conjugated diene and thiobarbituric acid reactive substances were measured as indexes of lipid peroxidation. Spectrophotometric determination of plasma iron and unsaturated iron-binding capacity were performed (total iron-binding capacity and percent saturation were calculated). Animals received U-74389F (2 mg/kg, n = 7), U-74500A (2 mg/kg, n = 6), or vehicle only (0.02 mol/L citrate acid/citrate; n = 7) intraarterially before infrarenal aortic clamping was performed for 120 minutes. An additional group of animals received U-74389F (2 mg/kg, n = 7), U-74500A (2 mg/kg, n = 7), or vehicle (n = 11) intraarterially before infrarenal aortic clamping was performed for 120 minutes, followed by reperfusion for 30 minutes. Depolarization of resting Em was noted during ischemia, with partial repolarization on reperfusion, which was enhanced by either lazaroid. As expected, iron delocalization occurred during ischemia and persisted on reperfusion, with U-74500A effectively binding iron, whereas U-74389 did not. Vehicle but not the 21-aminosteroids inhibited lipid peroxidation. High-grade partial ischemia of skeletal muscle is associated with iron delocalization, which persists on reperfusion. Each lazaroid achieved a similar "membranoprotective" effect during reperfusion only despite lack of iron binding by U-74389F, suggesting a direct interaction with the cell membrane. These data support the concept that ischemic injury and reperfusion injury occur through fundamentally different mechanisms.

Aldehyde Dehydrogenase, Aldose Reductase, and Free Radical Scavengers in Cataract

Human lens was found to contain aldehyde dehydrogenase at a level of activity similar to that of bovine lens, namely 1.76 +/- 0.51 IU/g. The enzyme, which appears to be a tetramer of 229 kD, was less susceptible to inhibition by cataractogenic agents than the bovine enzyme. The lipid peroxidation product malondialdehyde was a good substrate of the human lens enzyme. The in vitro aldose reductase reaction, which we have shown is caused by glyceraldehyde-stimulated free-radical NADPH oxidation, is inhibited by the potential anti-cataract agents, bendazac acid and bendazac lysine; these compounds also inhibit ferricytochrome c reduction in the presence of DL-glyceraldehyde and scavenge superoxide radicals. These results are consistent with the hypotheses that aldehyde dehydrogenase is a protective enzyme in the human lens, and that the peroxy radical scavenging effects of bendazac acid and bendazac lysine contribute to their anti-cataract activity.

Phycoerythrin fluorescence-based assay for peroxy radicals: A screen for biologically relevant protective agents

Under the conditions of this assay, antioxidants that react rapidly with peroxy free radicals (e.g., ascorbate, vitamin E analogs, urate), protect phycoerythrin completely from damage by such radicals generated by thermal decomposition of 2,2′-azobis(2-amidinopropane); other compounds provide partial concentration-dependent protection. Change in phycoerythrin fluorescence emission with time provides a measure of the rate of free radical damage. The assay exploits the unusual reactivity of phycoerythrin toward these peroxy radicals. On a molar basis, phycoerythrin reacts with these radicals over 100-fold slower than do ascorbate or vitamin E analogs, but over 60-fold faster than other proteins. Applications of this assay to the estimation of the peroxy radical scavenging capacity of human plasma are described, and to the comparison of the scavenging properties of several proteins and of DNA, of vitamins and their derivatives, of catecholamine neurotransmitters, and of a variety of other low molecular weight biological compounds.

Glutathione status in constituted physiological fluids containing albumin

1. 1. Glutathione (GSH) and cysteine, added to the constituted incubation medium, rapidly disappeared from the medium in the presence of bovine serum albumin (BSA). The major portions of added GSH and cysteine were oxidized. Only a fraction was recovered as cysteine-GSH mixed disulfide in case of GSH. About 15–30% cysteine or GSH were not recovered in the media. 2. 2. The rate of GSH oxidation was linear with time, however, GSH disappearance was not linear with GSH concentrations. 3. 3. Oxidation of GSH to GSSG in the albumin supplemented media was greater under O 2 atmosphere, but was significantly decreased under N 2 atmosphere. 4. 4. Catalase, a peroxy radical scavenger, but not dimethyl pyroline N-oxide (DMPO), N-tertbutyl-2(-2 sulfophenyl)-nitrone (NTBSPN), mannitol or Superoxide dismutase (SOD), decreased BSA mediated GSH oxidation. 5. 5. GSH oxidation was abolished when mono- or divalent metal ions were absent in the BSA supplemented media. 6. 6. Alkaline pH favored and acidic pH inhibited GSH oxidation. GSH oxidation was maximum above pH 7.4. GSH oxidation was minimal in the media containing boiled BSA. 7. 7. A reaction mechanism involving the mixed GSH-BSA disulfide formation, followed by the reduction of these disulfides by GSH and subsequent release of GSSG is proposed.

Polyolefin photo-stabilisation mechanisms. Reactions of tetramethylpiperidine derivatives in model systems

The relative rate of cyclohexyl radical scavenging by oxygen or 4-oxo-2,2,6,6-tetramethylpiperidino-N-oxyl has been measured at 25°C, together with the relative rates of cyclohexyl peroxy radical attack on cyclohexane or substituted hydroxylamines derived from 2,2,6,6-tetramethylpiperidine. These competitive processes are important in the stabilisation of polymers against photo-oxidative destruction by piperidine derivatives. Peroxy radical scavenging by the substituted hydroxylamine appears to be considerably more important than alkyl radical scavenging by the nitroxide, although both processes are essential for prolonged ultra violet (uv) stabilisation of a polymer. However, a comparison of experimental photo-protection with that predicted by the measured rate constant ratios shows that other processes are needed to account entirely for the observed stabilisation. Other factors which may be involved in piperidine photo-protection of polymers include thermal decomposition of the substituted hydroxylamine to reform nitroxide in polar(oxidised) zones and especially the association of nitroxides with hydroperoxide groups (the dominant photo-initiator in degrading polyolefins).

Metal complexes as antioxidants. V. Inhibition of hydrocarbon autoxidation by cupric complexes of dialkyldithiophosphoric and dialkyldithiocarbamic acids

Liquid-phase reactions of alkylperoxy radicals with cupric complexes of dialkyldithiophosphoric and dialkyldithiocarbamic acids have been examined. These complexes have been shown to be extremely efficient peroxy radical scavenging antioxidants for hydrocarbon autoxidation. Initial rates of oxygen absorption by typical hydrocarbons were extremely slow implying inhibition rate constants &gt; 106 M−1 s−1. The initial rate of disappearance of the dithiocarbamate was equal to the rate of chain initiation (Ri) whereas the rate of disappearance of the dithiophosphate was twice as fast as Ri. In both cases the rate of complex disappearance slowed down as the complex was consumed. Autoxidation of styrene commenced as soon as the complex disappeared while cumene did not absorb oxygen for a considerable length of time after complex destruction. Cumylperoxy radicals were converted to α-cumyl alcohol, α-methylstyrene, and acetophenone by reaction with these complexes and the copper ions were eventually precipitated as copper sulphate. In the case of the dithiocarbamate three intermediate cupric complexes were detectee by epr spectroscopy.