OH radical scavenger

Nishimura and coworkers57-59 studied the y-radiolysis of aqueous solutions of sulfoxide amino acids. Sulfoxide amino acids are the precursors of the flavors of onions (S-propyl-L-cysteine sulfoxide, S-methyl-L-cysteine sulfoxide and S-(l-propenyl)-L-cysteine sulfoxide) and garlic (S-allyl-L-cysteine sulfoxide). In studies on sprout inhibition of onion by /-irradiation it was found that the characteristic flavor of onions became milder. In the y-radiolysis of an aqueous solution of S-propyl-L-cysteine sulfoxide (PCSO)57,58 they identified as the main products alanine, cysteic acid, dipropyl disulfide and dipropyl sulfide. In the radiolysis of S-allyl-L-cysteine sulfoxide (ACSO) they found that the main products are S-allyl-L-cysteine, cysteic acid, cystine, allyl alcohol, propyl allyl sulfide and diallyl sulfide. The mechanisms of formation of the products were partly elucidated by the study of the radiolysis in the presence of N20 and Br- as eaq - and OH radicals scavengers, respectively. 

The monoterpene ketones menthone and isomenthone [159, 166] exhibited OH- radical scavenging activity. Depending on the method employed, different activities for anethole have been reported [153, 169]. 

Chemical reactions in UV/ozone process are a series of slow and fast reactions. The reaction time is determined by the time taken to complete the sequence of reactions. In the presence of OH radical scavengers, the oxidative efficiency of OH radicals will be reduced. For example, bicarbonate and carbonate ions usually play a dominant role as OH radical scavengers, because they present at concentrations of several millimoles per liter and react with OH radicals with rate constants as high as 1.1 x 107 L/mol/cm and 3.9 x 108 L/mol/cm for bicarbonate and carbonate, respectively. 

Valota A, Ballarini F, Friedland W, Jacob P, Ottolenghi A, Paretzke HG (2003) Modelling study on the protective role of OH radical scavengers and DNA higher-order structures in induction of single and double strand breaks by gamma-radiation. Int J Radiat Biol 79 643-653... 

Adhikary A, Bothe E, Jain V, von Sonntag C (1997a) Inhibition of radiation-induced DNA strand breaks by Hoechst 33258 OH-radical scavenging and DNA radical quenching. Radioprotection 32 0-89-0-90... 

Siddiqi MA, Bothe E (1987) Single- and double-strand break formation in DNA irradiated in aqueous solution Dependence on dose and OH radical scavenger concentration. Radiat Res 112 449-463... 

Due to the marked differences in second order rate constants fe.oH,M the reaction of Eq. 6-25 is far more important for OH radical scavenging than the reaction of Eq. 6-26. 

An interesting example of selectivity with respect to hydrogen abstraction by hydroxyl radicals is demonstrated in Fig. 6-25. 2-Propanol is an effective OH radical scavenger that is used in many kinetic studies (e.g. Hislop and Bolton,... 

Fig. 8.19 Fundamental processes influencing the efficiency of the H2O2-UV AOP in aqueous phase. M substrate or other parameter (TOC, AOX. etc.), NAbs absorbing molecule that competes with H2O2 for photons, S,- OH radical scavengers, L VUV/UV/VIS lamp, Q quartz sleeve of the photoreactor, total...

One suitable scavenging system is the use of 0.5 mM methyl viologen (MV ) in the presence of frrf-butanol as OH radical scavenger, under neutral pH condition. Another is the use of 0.5 mM 4,4 -bipyridyl (4,4 -bpy) together with frrf-butanol in alkaline solution (pH > 11). In both cases, ideally only e reacts or 4,4 -bpy to form radical cation MV or radical 4,4 -bpyH, with fairly strong absorption at 605 and -540 nm, respectively. The temperature-dependent G(e/) from 25 to 400°C at a fixed pressure of 25 MPa is shown in Fig. 3(a). G(e q) increases with temperature up to 300°C, which agrees well with the previous reports, then it decreases to a minimum... 

Wherever necessary, the OH radical reactions can be eliminated by using tertiary butanol [Eq. (20)] as OH radical scavenger, where the resultant tertiary butanol radicals are often not very reactive. 

FIG. 2. Normalized concentrations of e aq (upper half) and OH radicals (scavenged by SCN, lower half) vs. concentration of several size silica particles. The upper and lower solid curves are the increase in density and decrease of water volume with Si02 loading, respectively. 

Compared to MTBE the elimination of TAME, DIPE, and ETBE at 10 xg/L from a highly alkaline tap water showed no better removal, whereas in a softer surface water the elimination efficiencies were 60% for the alternative ethers compared to 40% for MTBE. This effect was attributed to the higher amount of OH radical scavenging species in the tap water [70]. 

In the presence of 10 3M isopropyl alcohol, an OH radical scavenger, G(HN02) is markedly enhanced as shown in Figure 9. This enhancement requires us to reject the hypothesis of Pikaev, Glazunov, and Yakubovich (20) that the increase in G(HN02) with increase in sodium nitrate concentration is caused by the reaction of nitrate ion with OH radical... 

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