Hydroxyl-Radical-Induced Reactions

In the present chapter, it will be shown that in the polynucleotides reactions take place that are not apparent on the nucleotide level (Chap. 10). The increasing number of reactions available to polymer-derived radicals (Chap 9) renders the free-radical chemistry of polynucleotides and ODNs more complex than that of the corresponding nucleotides. Nevertheless, our understanding of mechanistic details is not on a much lower level, because with polymers the pulse radiolysis technique (Chap. 13.3) provides additional information. 

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Janik I, Ulanski P, Flildenbrand K, Rosiak JM, von Sonntag C (2000) Hydroxyl-radical-induced reactions of poly(vinyl methyl ether) a pulse radiolysis, EPR and product study in deoxygenated and oxygenated aqueous solutions. J Chem Soc Perkin Trans 2 2041-2048 Jayson GG, Stirling DA, Swallow AJ (1971) Pulse- and X-radiolysis of 2-mercaptoethanol in aqueous solution. Int J Radiat Biol 19 143-156... 

Hankiewicz E (1995) Hydroxyl radical-induced reactions in polyadenylic acid as studied by pulse radiolysis II. Reactions of primary radicals with oxidants. Bull Pol Acad Sci Chem 43 41-49 Hankiewicz E (1996) Hydroxyl radical-induced reactions in polyadenylic acid as studied by pulse radiolysis - Part III. Consecutive reactions. Radiat Phys Chem 47 61-65 Hankiewicz E (1998) Hydroxyl radical-induced reactions in polyadenylic acid as studied by pulse radiolysis. IV. Reactions of primary radicals with reductants. Bull Pol Acad Sci Chem 46 455-464 Hankiewicz E, Bothe E, Schulte-Frohlinde D (1992) Hydroxyl radical-induced reactions in polyadenylic acid as studied by pulse radiolysis, part. I. Transformation reactions of two isomeric OH-adducts. Free Rad Res Commun 16 391-400... 

The results of this study strongly suggest that purified peptides can prevent oxidative damage to DNA when the DNA is exposed to OH generated by the Fenton reaction. With the purified peptide of protective activity against DNA oxidation, a clear dose-dependent effect was observed. In this result, the effect of purified peptide was to protect hydroxyl radical-induced DNA damage. 

Vieira AJSC, Steenken S (1990) Pattern of OH radical reaction with adenine and its nucleosides and nucleotides. Characterization of two types of isomeric OH adduct and their unimolecular transformation reactions. J Am Chem Soc 112 6986-6994 Vieira AJSC, Steenken S (1991) Pattern of OH radical reaction with N6,N6,9-trimethyladenine. Dehy-droxylation and ring-opening of isomeric OH-adducts. J PhysChem 95 9340-9346 Vieira AJSC, Candeias LP, Steenken S (1993) Hydroxyl radical induced damage to the purine bases of DNA in vitro studies. J Chim Phys 90 881-897... 

Hildenbrand K, Schulte-Frohlinde D (1989) E.S.R. studies on the mechanism of hydroxyl radical-induced strand breakage of polyuridylic add. Int J Radiat Biol 55 725-738 Hildenbrand K, Schulte-Frohlinde D (1997) Time-resolved EPR studies on the reaction rates of per-oxyl radicals of poly(acrylic acid) and of calf thymus DNA with glutathione. Re-examination of a rate constant for DNA. Int J Radiat Biol 71 377-385 Hildenbrand K, Mirtsch S, Schulte-Frohlinde D (1993) H-NMR studies of y-irradiated polynucleotides and DNA in N20-saturated aqueous solutions. Release of undamaged and modified bases. Radiat Res 134 283-294... 

Hydroxyl radical induced strand scission is used for probing of the ribose moiety. The probe is insensitive to local conformations and not useful for detailed structural predictions however, the nonselective reactivity and small size makes hydroxyl radical probing a powerful approach for footprinting proteins on RNA. Recently methods have been developed where the hydroxyl radicals are generated locally by attaching the iron ion, which catalyses the radical formation in the Fenton reaction, to specific sites on RNA binding proteins. RNA located in the neighborhood of the tethered Fe2+ will then be modified selectively.7,8... 

Table 9 gives a list of the principal VOCs, which includes mainly the hydrocarbons and oxygenated molecules, as well as the relative reactivity of these VOCs with the free hydroxyl radical. The reactions which are induced by OH lead to the degradation of the pollutants OH appears thus to be a cleansing agent for the troposphere but the reactions of OH with the primary pollutants can also form other pollutants, which will be called secondary pollutants. 

Polymer is degraded by heat, energy, UV or residues of catalyst and generates alkyl radicals. This alkyl radical reacts with oxygen and form peroxy radicals. These peroxy radicals abstract hydrogen from other polymer and forms alkyl radicals and hydroperoxide. The decomposition of hydroperoxide to alkoxy and hydroxyl radicals induces additional decomposition of the polymer chain. In order to stop the radical chain reaction of degradation, stabilisers such as phenolic antioxidant, phosphites, thioether and hindered amine light stabilisers (HALS) are added. 

This reaction mechanism has yet to be confirmed. Indeed, the second reaction product shown in the reaction (1). i.e., sulfenic acid RSOH, has never been detected experimentally [15]. This is not surprising since most such species are known to be unstable. However, sulfenic acids, formed as intermediates were suggested to be a source of sulfinyl radicals during the course of hydroxyl radical-induced oxidation of thiols and disulfides [16]. 

Li, K., Crittenden, J. Computerized pathway elucidation for hydroxyl radical-induced chain reaction mechanisms in aqueous phase advanced oxidation processes. Environ. Sci. Technol. 43, 2831-2837 (2009)... 

Hard et al (reference 110, 125, and submitted to/. Geophys, Res. 1991) have developed a system for the chemical conversion of HO2 to HO via the reaction HO2 + NO —> HO -I- N02. The hydroxyl radical is then measured by their low-pressure laser-induced-fluorescence instrument. Their multi-sample-channel LIF PAGE system is thus capable of simultaneous measurements of [HO ] (directly) and [H02 ] (by conversion to HO ). 

Glucose may auto-oxidize (like other alphahydroxy-aldehydes) and generate hydroxyl radicals in a transition-metal-catalysed reaction, and induce both fragmentation and conformational changes in glycated proteins (Hunt et al., 1990). 

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