Reactions with radiation induced

NITROXYL RADICAL REACTIONS WITH RADIATION-INDUCED SPECIES... 

The use of ultrasonic (US) radiation (typical range 20 to 850 kHz) to accelerate Diels-Alder reactions is undergoing continuous expansion. There is a parallelism between the ultrasonic and high pressure-assisted reactions. Ultrasonic radiations induce cavitation, that is, the formation and the collapse of microbubbles inside the liquid phase which is accompanied by the local generation of high temperature and high pressure [29]. Snyder and coworkers [30] published the first ultrasound-assisted Diels-Alder reactions that involved the cycloadditions of o-quinone 37 with appropriate dienes 38 to synthesize abietanoid diterpenes A-C (Scheme 4.7) isolated from the traditional Chinese medicine, Dan Shen, prepared from the roots of Salvia miltiorrhiza Bunge. 

Willson RL (1970) The reaction of oxygen with radiation-induced free radicals in DNA and related compounds. Int J Radiat Biol 17 349-358... 

Michaels HB, Hunt JW (1977a) Radiolysis of the double-stranded polynucleotides poly(A+U) and DNA in the presence of oxygen. Radiat Res 72 32-47 Michaels HB, Hunt JW (1977b) Reaction of oxygen with radiation-induced free radicals on single-stranded polynucleotides. Radiat Res 72 18-31... 

Very primary events in the chemical effect of radiations on matter are excitation and ionization of molecules, which result in the formation of neutral free radicals and radical ions. These reactive species play vital roles in the radiation-induced chemical reactions. As they are paramagnetic with an unpaired electron, electron spin resonance (ESR) spectroscopy has been a useful method for elucidating the mechanism of radiation-induced reactions in solid matter where radical species can be trapped temporarily. Since the early days of the chemical application of ESR, this method has been applied very often to the identification and quantification of free radicals in polymers irradiated by radiation [1]. This is probably because, from the view-point of fundamental research, a variety of free radicals are readily trapped in solid polymers and, from the view-point of applied research, these free radicals have close correlation with radiation-induced crosslinking and degradation of polymers. 

Aqueous heterophase polymerizations may be carried out in microwave ovens because the polar nature of the continuous phase allows for efficient microwave coupling. This dielectric heating is extremely fast as the reaction mixture can be warmed up within about 12 seconds from room temperature to >90 °C. Comparable with radiation induced polymerization pulsed thermal polymerizations (FTP) with alternating hot and cold stages as illustrated in Figure 4 give rise to... 

As stated earlier, the number of possibilities for reaction of these species with radiation-induced radicals is large and the exact mechanism may be different from that suggested by the above reaction. In recent results the in vitro sensitizing action of rhodium carboxylates has been attributed to their thiol binding capacity [58], and this is of interest in view of their known affinity for sulfur-containing cellular constituents (see Chapter 6). The in vitro sensitizing efficiency of the carboxylates follows the order butyrate > propionate > acetate > methoxyacetate, which parallels the antitumour effect and is related to the intracellular uptake. The sensitiza-... 

Radiation induced redox reactions and the fragmentation of constituent ions in ILs are phenomena which have to be known in detail when using ILs in solar cells, electrolytes etc. Anion fragmentation in ILs starts with radiation induced redox reactions. Scission of the oxidized anions is the main fragmentation pathway, in competition with internal proton transfer reactions involving the aliphatic chains of these anions. Perfluorinated anions show a fluoride loss after a dissociative electron attachment. For example CF3SO3 +e -f CF2S03 is a typical re-... 

The bismaleimide can then be polymerized by reaction with additional amine to form polyaininobismaleknide or by radiation-induced homopolymerization to form polybismaleimide (4). 

In terms of atomic spectrometry, NAA is a method combining excitation by nuclear reaction with delayed de-excitation of the radioactive atoms produced by emission of ionising radiation (fi, y, X-ray). Measurement of delayed particles or radiations from the decay of a radioactive product of a neutron-induced nuclear reaction is known as simple or delayed-gamma NAA, and may be purely instrumental (INAA). The y-ray energies are characteristic of specific indicator radionuclides, and their intensities are proportional to the amounts of the various target nuclides in the sample. NAA can thus... 

The quantitative aspects of track reactions are involved some details will be presented in Chapter 7. The LET effect is known for H2 and H202 yields in aqueous radiation chemistry. The yields of secondary reactions that depend on either the molecular or the radical yield are affected similarly. Thus, the yield of Fe3+ ion in the Fricke dosimeter system and the initiation yield of radiation-induced polymerization decrease with LET. Numerous examples of LET effects are known in radiation chemistry (Allen, 1961 Falconer and Burton, 1963 Burns and Barker, 1965) and in radiation biology (Lamerton, 1963). 

In the preceding ten chapters of this book, we have described various important chemical and physical changes brought about by the absorption of ionizing radiation in gaseous and condensed media. Wherever possible, we have tried to elucidate the underlying mechanism with a discussion of the properties and reactivities of the intermediate species. However, the book would remain incomplete without discussion of some of the various uses that have been found for radiation-induced reactions in science and industry. 

Radiation-induced substitution reactions have been reviewed by Wilson (1972) with examples of nitration, nitrosation, sulfochlorination, and others. These generally proceed by a free-radical mechanism. The free radicals are generated by the action of radiation on the reagent, which is present in large excess—for example,... 

---