[en] In the radiolysis of N₂O-saturated aqueous solutions the ^·OH radicals in their reactions with polymers give rise to polymer-derived radicals. The kinetics of the formation and decay of these radicals are reviewed. Once a larger number of radicals are formed on one polymer molecule, e.g. upon pulse radiolysis, close-by radicals recombine more rapidly while the more distant ones survive for much longer times. Intermolecular cross-linking (between two polymer chains, increase in molecular weight) and intramolecular cross-linking (formation of small loops, no increase in polymer weight) are competing processes, and their relative yields thus depend on the dose rate and polymer concentration. Hydrogen-transfer reactions within the polymer, e.g. transformation of a secondary radical into a tertiary one, are common and facilitated by the high local density of reactive sites. Due to repulsive forces, the lifetime of radicals of charged polymers is substantially increased. This enables even relatively slow β-fragmentation reactions to become of importance. In the case of poly(methacrylic acid) this even leads to an unzipping, and the situation of equilibrium polymerisation is approached. Heterolytic β-fragmentation is possible when adequate leaving groups are available, e.g. in polynucleotides and DNA. In the presence of O₂, chain scission occurs via oxyl radicals as intermediates

[en] Hydroxyl radicals have been reacted with benzene. The major product is phenol. At low dose rate (γ-radiolysis) it is formed in 53% yield with respect to the OH radical yield. This value increases to 93% in alkaline solution (pH 12.3). With deuteriated benzene it is reduced to 39%. In addition, more than fifteen different ring-opened and fragment products are formed. A good material balance (based on primary OH radical yield and oxygen consumption) was obtained. At high dose rate (pulse radiolysis) the major products are phenol, hydroquinone and cyclohexa-2,5-diene-1,4-diol. An important intermediate is the HO₂^./O₂^.-radical. Its rate of formation has been followed by us radiolysis using tetranitromethane as a scavenger as well as conductimetrically (build-up of H⁺/O₂^.-). The results have been interpreted. (Author)

No abstract available

[en] Final products formed by radiolysis of pyrimidinic bases and mechanisms of the reactions are examined. G values of products found by gamma radiolysis of uracyl in solution 2.10^-4M, saturated by a mixture N₂O and O₂ (4/1) at pH of 3.0, 6.5 and 10.0 are given

[en] Only a small percentage of the DNA damage set by ionizing radiation in the living cell manifests itself as lethal. It is now increasingly accepted that clustered lesions may constitute the kind of damage that the repair enzymes cannot adequately deal with. The question is raised as to whether damage amplification reactions (radical transfer reactions) may contribute to these clustered lesions, and examples of such damage amplification reactions are given. In one example a purine is involved. With 2'-deoxy adenosine and 2'-deoxy guanosine it is shown that these purine nucleosides undergo unexpected radical reactions. Evidence for the radical transfer from the purine to the sugar moiety is provided by the formation of the 5'-aldehydes. These products have been assayed with 2-thiobarbituric acid (TBA), a reagent commonly applied to the detection of malonaldehyde. TBA-reactive material has also been assayed in γ-irradiated DNA, about one-third of this is free malonaldehyde, while the major part of the TBA-reactive material remains bound to the DNA. In contrast, bleomycin-treated DNA yields practically no free malonaldehyde, and the major TBA-reactive products are identified as the thymine and adenine base propenals. (Author)

[en] This preview discusses the possible future application of ionizing radiation in the study of the free-radical chemistry of some aqueous systems. With respect to the present state of knowledge in the area of chemistry related to radiobiology, ionizing-radiation damage to DNA will continue to be a major focus. It is noted that the purine-base, free-radical chemistry is still poorly understood, as is the chemistry of the direct effect of ionizing radiation on DNA. The role of transition metal ions, their interaction with hydrogen peroxide and the superoxide radical are areas of increasing interest, as are other reactions of the superoxide radical. The eventual chemical effects, on DNA, of the reactions of these species resemble those of the action ionizing radiation and are therefore apt to be studied radiation chemically. In contaminated water pollution control, procedures termed 'advanced oxidation processes' are gaining in importance. (author)

[en] In the past, radiation chemistry has made considerable contributions to our present knowledge of free-radical chemistry. This was largely due to the pulse radiolysis technique which has been established some 25 years ago. Although it is true that one of its most notable contributions, the establishment of reliable rate constants for the reactions of the water radicals (OH, H and e_aq^-) with a host of organic and inorganic compounds is losing in importance because this technique has provided us with a body of many excellent data and a picture of the reactivity of various classes of compounds has now emerged, there are developments in the pulse radiolysis technique itself which will make possible another breakthrough in free-radical research. These recent developments are briefly discussed. (author). 56 refs

[en] This review includes G value tables of radiation products of γ-radiolysis of aqueous solutions of ethylene glycol, D-glucose, poly(U) and uracil. There is an extensive bibliography concerning the investigation of a wide range of model systems of radiation induced DNA strand breaks. (U.K.)

[en] In the present paper the radiation chemistry of aqueous solutions is reviewed. Areas of active research are pointed out and an attempt is made to assess future research trends in this field. Special emphasis is laid on fundamental aspects, rather than on technical applications. Thus the versatility of the pulse radiolysis technique is briefly described. The primary process occurring in the radiolysis of water are presented and techniques for converting the primary water radicals into radicals of interest are discussed. Special chapters deal with peroxyl radicals, as well as with the free radical chemistry of nucleic acids, proteins, carbohydrates, lipids, and sulfur compounds. Studies on unusual oxidation states of transition metal ions are briefly mentioned. (author). 152 refs, 1 tab

No abstract available