Hydroxyls radicals, generation

Hydroxyl radicals, generated from hydrogen peroxide and titanium trichloride, add to the sulfur atom of 2-methylthiirane 1-oxide leading to the formation of propene and the radical anion of sulfur dioxide (Scheme 102) (75JCS(P2)308). 

In an unusual example of displacement of fluonne by hydroxyl, hydroxyl radicals attack fluorinated benzenes Hexafluorobenzene is the least reactive The hydroxyl radical generates the pentafluorocyclohexadienonyl radical from it [13] (equation 13) These unstable species are detected spectroscopically Their disap-... 

Van Zyl JM, BJ van der Walt (1994) Apparent hydroxyl radical generation without transition metal catalysts and tyrosine nitration during oxidation of the anti-tubercular drug, isonicotinic acid hydrazide. Biochem Pharmacol 48 2033-2042. 

By combining these reactions, hydroxyl radicals, generated with the photocatalyst and the electron transfer reagent, should react with methane to produce m yl radicals. In our... 

Smith, C., Mitchinson, M.J., Amoma, O. and Halliwell, B. (1992). Stimulation of lipid peroxidation and hydroxyl radical generation by the contents of human atherosclerotic lessions. Biochem. J. 286, 901-905. 

Aruoma, 0.1. and Halliwell, B. (1987). Superoxide-dependent and ascorbate-dependent formation of hydroxyl radicals from hydrogen peroxide in the presence of iron. Are lactoferrin and transferrin promoters of hydroxyl radical generation. Biochem. J. 241, 273-278. 

Hard, S. and Kanner, J. (1989). Haemoglobin and myoglobin as inhibitors of hydroxyl radical generation in a model system of iron redox cycle. Free Rad. Res. Commun, 6, 1-10. 

Shimizu N, Ogino C, Dadjour M, Ninomiya K, Fujihira A, Sakiyama K (2008) Sonocatalytic facilitation of hydroxyl radical generation in the presence of Ti02. Ultrason Sonochem... 

Tan, D. X., Manchester, L. C., Reiter, R. J. et al. (1998). A novel melatonin metabolite, cyclic 3-hydroxymelatonin a biomarker of in vivo hydroxyl radical generation. Biochem. Biophys. Res. Comm. 253, 614-20. 

Chiueh, C.C., Miyake, J., Peng, M.T. Role of dopamine autoxidation, hydroxyl radical generation, and calcium overload in underlying mechanisms involved in MPTP-induced parkinsonism. Adv. Neurol. 60 251, 1993. 

There is an irreversible enzymatic inactivation reaction, which occurs during the oxidation of the cyclizable and noncyclizable diphenols to oquinones. This inactivation process has been interpreted as being the result of a direct attack of an o-quinone on a nucleophilic residue (His) near the active enzyme center or of an attack of a copper-bound hydroxyl radical generated by the Cu(I)-peroxide complex. However, the latter hypothesis seems to be more probable, because inactivation also occurs in the presence of reducing agents that remove the o-quinones generated. 

This assay measures the ability of antioxidant components in test materials to inhibit the decline in (3-phycoerythrin ((3-PE) fluorescence that is induced by 2,2 -azobis(2-amidinopropane) dihydrochloride (AAPH) as peroxyl radical generator (ORACroo.X H202-Cu2+ as hydroxyl radical generator (ORACho.X and Cu2+ as a transition metal oxidant (ORACcu)-... 

The thermodynamic functions (AH, AS, AG(298 K)) of hydrogen peroxide reactions with transition metal ions in aqueous solutions are presented in Table 10.1. We see that AG(298K) has negative values for reactions of hydroxyl radical generation with Cu1+, Cr2+, and Fe2+ ions and for reactions of hydroperoxyl radical generation with Ce4+, Co3+, and Mn3+. 

Formation of hydroxyl radicals has been suggested in many studies, which are considered in subsequent chapters in connection with the mechanisms of lipid peroxidation and protein and DNA destruction as well as the mechanisms of free radical pathologies. Furthermore, hydroxyl radical generation occurs under the conditions of iron overload and is considered below. 

Recent studies suggest that many factors may affect hydroxyl radical generation by microsomes. Reinke et al. [34] demonstrated that the hydroxyl radical-mediated oxidation of ethanol in rat liver microsomes depended on phosphate or Tris buffer. Cytochrome bs can also participate in the microsomal production of hydroxyl radicals catalyzed by NADH-cytochrome bs reductase [35,36]. Considering the numerous demonstrations of hydroxyl radical formation in microsomes, it becomes obvious that this is not a genuine enzymatic process because it depends on the presence or absence of free iron. Consequently, in vitro experiments in buffers containing iron ions can significantly differ from real biological systems. 

However, subsequent studies demonstrated that the formation of hydroxyl radicals, even if it takes place during lipid peroxidation, is of no real importance. Beloqui and Cederbaum [11] have found that although the glutathione-glutathione peroxidase system suppressed hydroxyl radical generation during the oxidation of 4-methylmercapto-2-oxo-butyrate, it exhibited a much smaller effect on microsomal lipid peroxidation. Therefore, hydroxyl radical formation is apparently unimportant in this process. Other authors also pointed out at an unimportant role of hydroxyl radicals in the initiation of microsomal lipid peroxidation [12 14], For example, it has been shown that Fe(EDTA), a most efficient catalyst of hydroxyl radical formation by the Fenton reaction, inhibited microsomal and liposomal lipid peroxidation, while the weak catalysts of this reaction Fe(ADP) and Fe(ATP) enhanced it [13]. 

Figure 6.9 Abstraction of a phenolic hydroxyl proton by a hydroxyl radical generated by Fenton s reaction with hydrogen peroxide.

Elegant work by Van der Hoff [60] seems to suggest that it is the latter, or more correctly there is a Gaussian distribution about the midpoint of a chain. However, as to whether the main chains are primarily broken by ultrasonic action is still open to question since it is possible that the main chain scissions are secondary effects due to chemical reactions initiated by unstable intermediates, such as free radicals or ions, produced by sonication. For example McKay [61] has shown that hydroxyl radicals, generated by the oxidation of Fe by H2O2, are the cause of chain scission in polyacrylamide molecules in aqueous solution. 

Figure 1. Degradation (Q) of 17 gL dehydropolymerizate (0) from [2-l C]coniferyl alcohol by hydroxyl radicals generated from 1 M H2O2/IO mM FeS04. Sephadex LH20/DMF elution profiles adapted and redrawn fi om reference 12.

Related three-electron bond radical-cations 1 are formed from dialkyl sulphides by oxidation with hydroxyl radicals generated using pulse radiolysis [2]. An isoe-lectronic three-electron bond between two nitrogen atoms in 2 is formed by reduc-... 

The results presented here suggest a new mechanism of toxicity for PM 5 based on sustained hydroxyl radical generation by the semiquinone radicals present in PM 5. Because a substantial fraction of the fine particles in the atmosphere arises from combustion sources (9), it is possible that the deleterious health effects associated with PM2 5 can be at least partially ascribed to radicals associated with combustion-generated particulate matter. 

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