Radical quenching effects

Antioxidants shift the autoaccelerating increase of chemiluminescence intensity to higher time. This is due to reactions 12 and 13 of the Bolland-Gee mechanism (Section 1, Scheme 2) in which peroxyl radicals and hydroperoxides are scavenged until antioxidants InFl and D are consumed. A typical example of such a behavior occurs for samples of PP containing 0.1 %wt. of Irganox 1010 (a sterically hindered phenol) (Figure 18 and Table 4). The presence of antioxidants usually reduces the maximum chemiluminescence intensity [61,62]. This may be explained by the quenching effect of the antioxidant on excited carbonyls, but it may be also related to the mechanism of oxidation of stabilized PP. Stabilizers in... 

As discussed previously, UV-C irradiation increased the phenol and flavonoid content such compounds present high radical-quenching activity by themselves (Robles-Sanchez and others 2007). Few studies have been reported specifically about the effect of UV-C irradiation on antioxidant capacity of treated fruit. However, Fan and others... 

In addition to heat transfer with the wall there may also be chemical effects such as free-radical quenching. Discuss ways in which the analysis could be further extended to include such behavior. Consider the essential role of free radicals, such as atomic H, in sustaining the flame. 

Free radical quenching by extracts of brown ragi was 94% while that by germinated, fermented and white ragi was 22%, 25%, and 5%, respectively. Extracts from foxtail was equally effective while extracts from rice had a free energy quenching activity of 1.8 (Sripriya et al., 1996). Mehta (2006) extracted ragi flour with methanol and added the dried powder to... 

Cyclopentadiene undergoes ionic polymerisation by Friedel-Crafts catalysts32. Its polymerisation by y-rays is markedly suppressed by ammonia or amines but much less by diphenylpicrylhydrazyl or oxygen33. This again points to the ionic rather than the free radical nature of the radiation-induced polymerisation. The quenching effect of ammonia was postulated as due to reactions of the type... 

Radicals add to unsaturated bonds to form new radicals, which then undergo addition to other unsaturated bonds to generate further radicals. This reaction sequence, when it occurs iteratively, ultimately leads to the production of polymers. Yet the typical radical polymerization sequence also features the essence of radical-induced multicomponent assembling reactions, assuming, of course, that the individual steps occur in a controlled manner with respect to the sequence and the number of components. The key question then becomes how does one control radical addition reactions such that they can be useful multicomponent reactions Among the possibilities are kinetics, radical polar effects, quenching of the radicals by a one-electron transfer and an efficient radical chain system based on the judicious choice of a radical mediator. This chapter presents a variety of different answers to the question. Each example supports the view that a multicomponent coupling reaction is preferable to uncontrolled radical polymerization reactions, which can decrease the overall efficiency of the process. 

As an indirect effect of increased metal uptake, the physiological state of the cell can alter and defence mechanisms can be induced. Phytochelatin (metal binding proteins) synthesis and induction of free radical quenching enzymes and metabolites were frequently observed. Especially the latter can protect membranes against oxidative breakdown. 

Evidence is now being obtained that suggests that lycopene may have direct stimulatory effects on the response of the immune system. This may involve an antioxidant action, and it could form the basis of a protective action against cancer and also against human immunodifiency virus (HIV) and acquired immune deficiency syndrome (AIDS). The free radical quenching constant of lycopene was found to be more than double that of [3-carotene and 10 times more than that of a-tocopherol, which makes lycopene s presence in the diet of considerable interest (Di Mascio et al., 1989,1991 Conn et al., 1991 Devasagayam et al., 1992 Ribaya-Mercado et al., 1995). 

As an example, the assay commonly used to measure the direct generation of ROS by nanoparticles is based on the conversion by ROS of the 2,7-dichlorodihydrofluorescein dye into a fluorescent product, 2,7-dichlorofluorescein. There is also a range of fluorescent probes that measure NM-induced ROS production inside the cells, in different intracellular compartments (e.g., dihydrorhoda-mine-1,2,3 in the mitochondria, 2,7-dichlorodihyydrofluorescein diacetate in the cytoplasm, dihydroethidium bromide in the nucleus) [59]. They are all relatively easy to use for quantification in a fluorimeter, multiwall plate reader, or by flow cytometry, but a potential drawback of all these assays is the background caused by particles as well as the fluorescence quenching effects that need to be controlled and taken into account to reliably measure the free radical production [59, 60]. 

In this study, therefore, flow injection analysis-chemiluminescence (FIA-CL) methods to evaluate quenching effects of functional foods against ROS such as singlet oxygen ( 02) and hydroxyl radicals (OH) were developed. The applicabilities of these methods were confirmed by evaluating quenching effects of grape seed extracts and their isolated polyphenols. 

To verify the involvement of free radical reactions in dye ozonation at a high pH, a quenching test was conducted by the use of carbonate as the free radical scavenger (Hoigen J. and Bader H., 1976). The results of the quenching effect is shown in Figure 16,... 

When the humic concentration increases in the solution, humic was not only acted as a hydrogen source but also acted as a free radical scavenger. Judging from the rate retardation when humic is over dosed, it is rational to assume that the quenching effect of humic is dominant under this circumstance, and the concentration of humic in the eq. 77 is in excess and can be assumed to be a constant. Therefore, the eq. 77 can be rewritten to ... 

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