Radiolysis and free-radical chemistry

In applications of water radiolysis to free radical chemistry, it is particularly convenient to use aqueous solutions saturated with N2O, where is converted to OH via reactions (27) and (28) [59] ... 

A general review of pulse radiolysis studies on electron transfer in solution is presented together with some recent unpublished data. Electron transfer processes occurring in irradiated solutions of metal ions, inorganic anions, and various aliphatic and aromatic organic compounds are discussed with respect to general redox phenomena in radiation and free radical chemistry. Specific topics include the measurement of peroxy radical formation, the use of nitrous oxide in alkaline radiation chemistry, and cascade electron transfer processes. Some implications of the kinetics of electron transfer are discussed briefly. 

The free-radical chemistry of polyhydric alcohols in deoxygenated solutions has been extensively investigated by using radiolysis and ra-... 

Much of basic free-radical chemistry of DNA and its constituents have been elucidated with the help of radiation techniques. This requires one to address briefly the properties of the H atom and the hydrated electron, eaq , which are important intermediates in the radiolysis of water (Chap. 2.2). 

Schuchmann MN, von Sonntag C (1982) Flydroxyl radical induced oxidation of diethyl ether in oxygenated aqueous solution. A product and pulse radiolysis study. J Phys Chem 86 1995-2000 Schuchmann MN, Schuchmann H-P, Knolle W, von Sonntag J, Naumov S, Wang W-F, von Sonntag C (2000) Free-radical chemistry of thiourea in aqueous solution, induced by OFI radical, FI atom, a-hydroxyalkyl radicals, photoexcited maleimide, and the solvated electron. Nukleonika 45 55-62... 

The reduction and oxidation of radicals are discussed in Chapter. 6.3-6.5. That in the case of radicals derived from charged polymers the special effect of repulsion can play a dramatic role was mentioned above, when the reduction of poly(U)-derived base radicals by thiols was discussed. Beyond the common oxidation and reduction of radicals by transition metal ions, an unexpected effect of very low concentrations of iron ions was observed in the case of poly(acrylic acid) (Ulanski et al. 1996c). Radical-induced chain scission yields were poorly reproducible, but when the glass ware had been washed with EDTA to eliminate traces of transition metal ions, notably iron, from its surface, results became reproducible. In fact, the addition of 1 x 10 6 mol dm3 Fe2+ reduces in a pulse radiolysis experiment the amplitude of conductivity increase (a measure of the yield of chain scission Chap. 13.3) more than tenfold and also causes a significant increase in the rate of the chain-breaking process. In further experiments, this dramatic effect of low iron concentrations was confirmed by measuring the chain scission yields by a different method. At present, the underlying reactions are not yet understood. These data are, however, of some potential relevance to DNA free-radical chemistry, since the presence of adventitious transition metal ions is difficult to avoid. 

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. 

For the detection of free-radical-induced DNA damage and its repair, biochemical techniques are increasingly applied. It would exceed the allocated space to discuss these techniques here, and the reader is referred to the original literature. However, to assist biologists and biophysicists, some of the chemical techniques for measuring typical DNA lesions are discussed. Most of the kinetic data concerning the free-radical chemistry of DNA and its model systems has been obtained by pulse radiolysis. This technique is only available in a few laboratories worldwide. For this reason, it will be described in some detail here. 

Radiolysis of alkane liquids fits the classical picture of radiation chemistry, namely, large yields of ions are initially produced which on recombination give rise to excited states and other products. Much radiation chemistry of alkanes is also interpreted in terms of free radicals. The exact connection between the three reactive regimes of excited states, ions, and free radicals is not always clearly established. 

The largest contribution of radiation chemical techniques to general free-radical chemistry has been made in aqueous solution because they provide a very convenient way of generating an enormous variety of highly reactive species which cannot readily be generated by thermal or photochemical methods. In particular, the technique of pulse radiolysis has provided a wealth of kinetic and mechanistic information in inorganic, organic, and biochemistry [4,5]. 

In this way the radiolysis of water provides a ready source of one-electron redox agents that can be finely tuned in terms of reduction potential and electric charge, and this has been widely used in obtaining kinetic and mechanistic data for free radical chemistry in aqueous solution [5]. 

One of the topics to which Radiation Chemistry has made many significant and highly visible contributions is that of free radical chemistry . An interesting group within organic radicals is that where the spin is located on a heteroatom. Such radicals often exhibit quite different properties as compared to C-centered radicals owing to the influence of lone electron pairs on their overall electronic structure. Research on these transients flourished particularly since the advent of time-resolved techniques such as pulse radiolysis and flash photolysis which allowed their direct detection on real time. Because of their electronic structure hetero-centered radicals most often exhibit intense and thus easily detectable optical absorptions in the UV, visible and near-IR. 

In studies of this kind, methods developed in radiation chemistry and photochemistry are often applied The methods of pulse radiolysis and flash photolysis allow one to investigate the mechanism of reactions in which free radicals, electrons and positive holes are the intermediates. In order to understand the mechanisms of processes that occur on colloidal particles it is important to know how free radicals... 

It is now clearly demonstrated through the use of free radical traps that all organic liquids will undergo cavitation and generate bond homolysis, if the ambient temperature is sufficiently low (i.e., in order to reduce the solvent system s vapor pressure) (89,90,161,162). The sonolysis of alkanes is quite similar to very high temperature pyrolysis, yielding the products expected (H2, CH4, 1-alkenes, and acetylene) from the well-understood Rice radical chain mechanism (89). Other recent reports compare the sonolysis and pyrolysis of biacetyl (which gives primarily acetone) (163) and the sonolysis and radiolysis of menthone (164). Nonaqueous chemistry can be complex, however, as in the tarry polymerization of several substituted benzenes (165). 

Adams GE, McNaughton GS, Michael BD (1967) The pulse radiolysis of sulphur compounds, part I. Cysteamine and cystamine. In Johnson GRA, Scholes G (eds) The chemistry of ionization and excitation. Taylor and Francis, London, pp 281 -293 Adams GE, McNaughton GS, Michael BD (1968) Pulse radiolysis of sulphur compounds, part 2. Free radical repair by hydrogen transfer from sulfhydryl compounds. Trans Faraday Soc 64 902-910... 

One of the overlooked aspects of the radiolysis process is that the underlying chemistry is relatively well understood. This chapter will examine the chemistry of free radical generation by radiation, those reactions of radicals with pollutants, which result in mineralization, and the kinetics of reaction from a process chemistry point of view. Two currently operational e-beam processes will be presented. 

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