Hydroxyl Radical comparison

Shiloh H, lancu TC, Bauminger E, Link G, Pinson A, Hershko C (1992) Defer-oxamine-induced iron mobilization and redistribution of myocardial iron in cultured rat heart cells studies of the chelatable iron pool by electron microscopy and Mossbauer spectroscopy. J Lab Clin Med 119 429-437 Singh S, Hider RC (1988) Colorimetric detection of the hydroxyl radical comparison of the hydroxyl-radical-generating ability of various iron complexes. Anal Biochem 171 47-54... 

Atrazine is successively transformed to 2,4,6-trihydroxy-l,3,5-triazine (Pelizzetti et al. 1990) by dealkylation of the alkylamine side chains and hydrolytic displacement of the ring chlorine and amino groups (Figure 1.3). A comparison has been made between direct photolysis and nitrate-mediated hydroxyl radical reactions (Torrents et al. 1997) the rates of the latter were much greater under the conditions of this experiment, and the major difference in the products was the absence of ring hydroxylation with loss of chloride. 

Another important effect observed when reactions take place in the liquid phase is associated with the solvation of the reactants. Theoretical comparison showed that the collision frequencies of the species in the gas and liquid phases are different, which is due to the difference between the free volumes. In the gas phase, the free volume is virtually equal to the volume occupied by the gas species (FfwT), while in the liquid phase, it is much smaller than the volume of the liquid species (V < V). Since the motion and collision of the species occur in the free volume, the collision frequency in the liquid is higher than in the gas by the amount (V/Vf)U3 [32,33]. The activation energies for the reactions of radicals and atoms with hydrocarbon C—H bonds in the gas and the liquid phases are virtually identical, and that in the liquid is independent of the solvent polarity. This also applies to the parameter bre, which can be seen from the following examples referring to the interaction of the hydroxyl radical with hydrocarbons [30] ... 

The subscripts 1 and g in Equation (6.38) refer to the liquid and gas phases, respectively. The results of the comparison are presented in Table 6.10. If the HO + YH reaction takes place in an aqueous solution and not in the gas phase, the parameter bre and hence the activation energy increase. This is associated with the solvation of the reactants and the need to overcome the solvation shell by the reacting component in order to effect the elementary step. The contribution of AEso is particularly large in the reaction of the hydroxyl radical with aldehydes. 

Figure 7 Comparison of experimental and predicted values of G(p2) from hydroxyl radical scavenging as a function of the scavenger power fcu[S2]. S2 = HCOJ ( ) Fe(CN)g (A). The full and broken lines are the best fits of Eqs. (16) and (17) without any restriction on the parameters (see text). (From Ref 54.)...

Winterbourn, C. C. (1979). Comparison of superoxide with other reducing agents in the biological production of hydroxyl radicals. Biochem. J. 182, 625-628. 

This comparison is only theoretical. In reality a high production of OH° can lead to a low reaction rate because the radicals recombine and are not useful for the oxidation process. Also not considerd are the effects of different inorganic and/or organic compounds in the water. Various models to calculate the actual OH-radical concentration can be found in the literature, some are described in Chapter B 5, Further information concerning the parameters which influence the concentration of hydroxyl radicals is given in Section B 4.4, as well as a short overview about the application of ozone in AOPs in Section B 6.2. 

A systematic dependence of reaction order on temperature and pH is not visible, n varies between one and two. Different experimental conditions and/or missing details about these conditions as well as different analytical methods make a comparison of these results impossible. Staehelin and Hoigne (1985) proposed a possible explanation for the second order reaction (n = 2). Since in clean water ozone not only reacts with the hydroxide ions but also with the intermittently produced hydroxyl radicals (see Chapter A 2), it behaves like a promoter and the decay rate increases with the square of the liquid ozone concentration. This is supported by the results obtained by Gottschalk (1997). She found a second order decay rate in deionized water, compared to a first order decay rate in Berlin tap water, which contains about 4 mg L DOC and 4 mmol LT1 total inorganic carbon. Staehelin and Hoigne (1982) also found first order in complex systems. 

Masten S J, Hoignd J (1992) Comparison of Ozone and Hydroxyl Radical-Induced Oxidation of Chlorinated Hydrocarbons in Water, Ozone Science Engineering 14 197-214. 

By a comparison of the calculated values for the OH° concentration according to equation 5-4 and 5-6 in connection with 5-11 it was shown that the initiation term was not negligible and the simplified model not appropriate. Thus, the authors defined a hydroxyl radical initiating rate 8 that includes all possible initiating reactions, calculated by the OH° concentration difference between the experiment and the model. 

It is important to note that both H202 and Fe2+ have to be overdosed to maintain a steady-state concentration of hydroxyl radical and to obtain a satisfactory approximation of the mathematical model with the experimental data. When H202 and Fe2+ concentrations are 5 x 10-3 M and 2 x 1th4 M, respectively, the relative rate constants of 2-chlorophenol (2-CP) and 2,4,6-TCP with respect to 2,4-DCP can be calculated. The oxidation and dechlorination constants of 2,4-DCP were found to be 0.995 1/min (fc4) and 0.092 1/min (k2), as reported in a previous study (Tang and Fluang, 1996). For comparison, Table 6.1 summarizes all the kinetic constants as determined in this study and in the related literature. 

Masten, S.J. and Hoigne, J., Comparison of ozone and hydroxyl radical-induced oxidation of chlorinated hydrocarbons in water, Ozone Sci. Eng., 14, 197-213, 1992. 

Comparison of Hammett s Correlations for Elementary Hydroxyl Radical Reactions and UV/H02... 

A comparison of the kinetic rate constants for elementary hydroxyl radical and UV/Ti02 is provided in Figure 9.24. The slopes of the Hammett correlations for the hydroxyl radical data and UV/TiOz are both negative. This suggests a similarity in the reaction mechanism that is supported by a comparison of these correlations. 

Ortmans I, Moucheron C, Kirsch-De Mesmaeker A (1998) Ru(ll) polypyridine complexes with a high oxidation power. Comparison between their photoelectrochemisty with transparent SnC>2 and their photochemistry with desoxyribonucleic acids. Coord Chem Rev 168 233-271 Ozawa T, Ueda J, Flanaki A (1993) Copper(ll)-albumin complex can activate hydrogen peroxide in the presence of biological reductants first ESR evidence for the formation of hydroxyl radical. Biochem Mol Biol Int 29 247-253... 

Bailey SM, Fauconnet A-L, Reinke LA (1997) Comparison of salicylate and d-phenylalanine for detection hydroxyl radicals in chemical and biological reactions. Redox Rep 3 17-22 Balasubramanian B, Pogozelski WK, Tullius TD (1998) DNA strand breaking by the hydroxyl radical is governed by the accessible surface areas of the hydrogen atoms of the DNA backbone. Proc Natl Acad Sci USA 95 9738-9743... 

When irradiated with UV light in aqueous solution, hydrated ferric ions are photoreduced to ferrous ions with the production of hydroxyl radicals. Thus, the photolysis (>290nm) of aqueous solutions of atrazine, ametryn, prometryn, and prometon in the presence of ferric perchlorate or ferric sulfate was greatly enhanced in comparison to direct photolysis (Larson et al., 1991). In the absence of oxygen or in stream water, photoreaction rates were... 

Hojo Y, Kobayashi T, Shigemitsu Y, et al. 1998. Aluminum(3)-induced brain toxicity and hydroxyl radical generation Comparison with trimethyltin. Eisei Kagaku 44 10. 

As shown in Fig. 10.3C, comparison with hydroxyl radical footprinting data on the same RNA, under identical experimental condition, revealed that while both native and nonnative tertiary contacts are formed during the first compaction phase, only native tertiary contact formation drives the ribozyme to its folded structure in the second phase. The slightly larger global dimension observed in 1.5 M Na+ as compared to that in 10 mM Mg2+ indicates the inability of monovalent ions, even at sufficiently high concentrations, to fully compact this RNA to its native shape. 

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