Hydroxyl radicals generation mechanisms

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. 

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. 

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. 

Manevich Y, Held KD, Biaglow JE (1997) Coumarin-3-carboxylic acid as a detector for hydroxyl radicals generated chemically and by gamma radiation. Radiat Res 148 580-591 Maples KR, Johnson NF (1992) Fiber-induced hydroxyl radical formation correlation with mesothelioma induction on rats and humans. Carcinogenesis 13 2035-2039 MarkG, Korth H-G, Schuchmann H-P, von Sonntag C (1996) The photochemistry of aqueous nitrate revisited. J Photochem Photobiol A Chem 101 89-103 Maskos Z, Rush JD, Koppenol WH (1990) The hydroxylation of the salicylate anion by a Fenton reaction and v-radiolysis a consideration of the respective mechanisms. Free Rad Biol Med 8 153-162... 

The superoxide oxide radical interacts with nitric oxide to produce peroxynitrite at a rate which three times faster than the rate at which superoxide dismutase utilizes superoxide (Beckman, 1994). Peroxynitrite is capable of diffusing to distant places in neural cells where it induces lipid peroxidation and may be involved in synaptosomal and myelin damage (Van der Veen and Roberts, 1999). After protonation and decomposition, peroxynitrite produces more hydroxyl radicals. This mechanism of hydroxyl radical generation is not dependent on redox active metal ions and may be involved in initiating lipid and protein peroxidation in vivo (Warner et al., 2004). 

Shi, X. and N.S. Dalai. 1993. Vanadate-mediated hydroxyl radical generation from superoxide radical in the presence of NADH Haber-Weiss vs. Fenton mechanism. Arch. Biochem. Biophys. 307 336-341. 

Robertson [28] proposed that an additional possibility was that the destruction of the substrates may be mediated by hydroxyl radicals generated via the superoxide radical anion produced at the conduction band. This is subsequently hydrated or deuterated by the solvent. This may be rate determining since the O2 has to be generated at the conduction band prior to interaction with the solvent and subsequent formation of OH or OD" species. Therefore the kinetic isotope effect could be due to the interaction of the solvent with the superoxide species rather than the attack on the toxin. If this is the case it was suggested that a similar kinetic isotope effect would be observed no matter what substrate was being destroyed. Further kinetic isotope studies will help elucidate the potential of this proposed mechanism. 

Single- and double-strand scission of DNA, together with hydroxylation of constituent bases, are changes characteristic of oxygen-radical attack on DNA. An important mechanism is site-specific hydroxyl-radical generation, catalysed... 

The photocatalytic destruction of haloaliphatic compounds has been studied in detail by Hoffmann and co-workers [107,108]. A detailed study of the mechanism of the photocatalytic destruction of chloroform using Ti(>2 was investigated by Kormann et al. [107]. The process was believed to be initiated by hydrogen abstraction by the hydroxyl radicals generated on the surface of the TiC>2 (Eqs. 27-32). The chloroform radical subsequently reacts with oxygen forming trichloromethanol oxidation to trichloroformaldehyde and ultimately complete mineralisation. 

As Table 9.4 shows, most of these hydroxyl radical generating reactions are rather slow, so it can be challenging to make accurate measurements on them. In particular, the NO3 reaction has yielded results that vary quite dramatically from one lab to the other.51 It seems rather unlikely that a uniform method can be taken to explain the rates of these reactions, given that a variety of mechanisms are involved. 

We may note that the mechanisms of reactions included in the last two types are, in general, not the same for paraffins, on the one hand, and aromatic hydrocarbons, on the other hand, even if the products of these reactions are of the same type. For example, alcohols and phenols may be obtained from alkanes and arenes respectively by the reaction in air with hydroxyl radicals generated by the action of a metal complex. However, in the case of alkane, an alcohol can be formed by the reduction of alkyl peroxide, whereas hydroxyl is added to an arene with subsequent oxidation of a radical formed. Hence follows the possibility that arenes and alkanes may exhibit different reactivities in each specific reaction. 

Murphy, G. (1950). Similitude in Engineering. Ronald Press Company, New York. Mutaftschiev, B. (2001). The Atomistic Nature of Crystal Growth. Springer, Berlin. Narayanasamy, J., Kubicki, J.D. (2005). Mechanism of hydroxyl radical generation from a silica surface Molecular orbital calculations. Journal of Physical Chemistry B, 109,... 

Scheme 3.25 Proposed mechanism for hydroxyl radical generation from hydrogen peroxide catalyzed by the redox centers of G.

Figure 21.17 Mechanism of hydroxyl radical generation by daunorubicin.

Although alternative ionic mechanisms have been formulated," the essential feature of the reaction, namely the generation of free hydroxyl radicals, is now generally accepted." ... 

The degree of dissociation is very small but the diphenylcyanomethyl radical is sufficiently reactive to induce polymerization in styrene. Methyl radicals or hydrogen atoms bring about polymerization of vinyl monomers in the gas phase.Hydrogen peroxide in the presence of ferrous ions initiates polymerization in the aqueous phase or in aqueous emulsions through generation of hydroxyl radicals according to the Haber-Weiss mechanism... 

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