Radiation chemistry specificity

The important role of radicals and radical ions in various branches of chemistry (e.g., electrochemistry, radiation chemistry, macromolecular chemistry), their remarkable physical properties and reactivity, as well as the specific problems in a quantum chemical approach, make this region interesting from the theoretical point of view. 

Since this book is primarily concerned with condensed-phase studies, we do not go into the details of gas-phase radiation chemistry. We will briefly outline some important mechanisms of gas-phase reactions, followed by a presentation of some specific examples and certain theoretical considerations. In Chapter 4, we considered ionization and excitation in some detail. Many of these considerations apply to the gas phase these will not be repeated. We stress that the measurement of the W value is of utmost importance in the... 

Applied radiation chemistry has gained considerable momentum since the late sixties and early seventies, and it would be futile to describe all the progress made in a single chapter. Spinks and Woods (1990) have nicely summarized the synthetic and processing aspects of the field in the latest edition of their book. Proceedings of various international conferences on specific aspects of radiation applications have appeared sporadically in Radiation Physics and Chemistry starting from middle seventies, of which mention may be made of vol. 9 (1977), vol. 14 (1979), vol. 25 (1985), vol. 31 (1988), vol. 34 (1989), vols. 35-36 (1990), vol. 37 (1991), vol. 40 (1992), vol. 42 (1993), and vol. 46 (1995). A... 

By its very nature this book is interdisciplinary. The first eleven chapters delineate the fundamentals of radiation physics and radiation chemistry that are common to all irradiation effects. Chapters 12 and 13 deal with specific liquid systems, while Chapter 14 is concerned with LET effects. Chapters 15 to 18 describe biological and medical consequences of photon and charged-particle irradiation. The rest of the book is much more applied in character, starting with irradiated polymers in Chapter 19 and ending with applications of heavy ion impact in Chapter 27. 

The Electron Excess Center. In their earlier paper Schulte-Frohlinde and Eiben (57) had assigned the line A to the O ion and the other line to the stabilized electron subsequently they have reversed this assignment, and are therefore in agreement with other authors. However, the line with g = 2.0006 has been interpreted in different ways, although all interpretations relate it to the radiation-produced electron. Thus Schulte-Frohlinde and Eiben (57, 58) consider the species responsible for this line to be a stabilized free electron, while Ershov et al. (16) and Henriksen (23) identify it with a solvated electron or a po-laron in the same sense as these two terms are used in the radiation chemistry of water and aqueous solutions. According to the above authors, this species is not found in pure ice because of Reaction 30, whereas in alkaline systems such a reaction should not occur. (Henriksen does not offer any explanation about the specific role of alkali hydroxide in stabilizing the solvated electron. ) Both of these hypotheses can be shown to be incorrect. Thus, if Reaction 30 occurred to any extent in pure ice, one should be able to detect H atoms in neutral ice with a yield of at least as high as the maximum yield of the solvated electrons, viz.. 

It will be convenient to review firstly the evidence for the production of specific excited states in radiation chemistry and then to examine the details of some of their reactions. 

As has been discussed here, the reactions that occur upon radiolysis of dilute solutions of proteins in water are very much dependent upon the amino acid composition of the protein, protein folding (i.e. residues that are surface exposed), the presence of metal catalytic centers and the particular radicals that are generated in solution. As has been illustrated in the last two examples, radiation chemistry can serve as a probe of the redox processes that occur upon catalysis and, under very specific systems, can also serve to generate the substrate for enzyme catalysis. 

Early studies of the radiation chemistry of chlorinated hydrocarbons demonstrated the formation of molecular cations of aromatic hydrocarbons with half-lives of the order of a few micoseconds [26]. In solutions containing two different aromatic solutes, it was possible to measure the rate of electron transfer from the neutral molecule to the radical cation. Some specific examples of other studies are given below. 

Several books on radiation chemistry have appeared recently - - one deals specifically with gases . Two reviews have appeared on the radiation chemistry of hydrocarbons . Radiation chemistry has also been the subject of many articles in Annual Reports of the Chemical Society and Annual Reviews of Physical Chemistry. Two recentcontributionsareby Collinson and Ausloos . Radiation Research Reviews is devoted solely to reviews in this general field, and the first issue contains another review by Ausloos. 

Mossbauer effect Resonance absorption of gamma radiation by specific nuclei arranged in a crystal lattice in such a way that the recoil momentum is shared by many atoms. It is the basis of a form of spectroscopy used for studying coordinated metal ions. The principal application in bioinorganic chemistry is 57Fe. The parameters derived from the Mossbauer spectrum (isomer shift, quadrupole splitting, and the hyperfine cou-... 

Ionizing radiation (y- and X-rays, high energy electrons and other particles) is absorbed by molecules rather indiscriminately, so that most of the energy is absorbed by the solvent and not by the solutes that are present at low concentrations. Thus radiation chemistry involves in most cases the reactions of solvent radicals with the solutes. Deposition of ionizing radiation leads, as the name implies, to ionization of the solvent, i.e. formation of electrons and radical cations. These undergo subsequent processes to form a complex mixture of species. In many solvents, however, the primary events are followed by solvent-specific reactions, which result in the formation of one or two main radicals that can undergo simple reactions with the solute. Thus, despite the complexity of the early events, radiation chemistry may provide a means to study reactions of simple radicals or reduction... 

Since phenols are solid under ambient conditions, few studies were concerned with the radiation chemistry of phenols in the gas phase. An early study demonstrated the acetylation of phenols when irradiated in a specific gaseous mixture. Gas-phase y-irradiation of a mixture of CH3F and CO was found to form the acetyl cation, CHsCO , and to lead to acetylation of substrates . Gaseous phenol, cresols and xylenols present in such a mixture were acetylated mainly at the OH group to form 80-97% aryl acetate. The remaining products, hydroxyacetophenones, were mainly the ortho and para derivatives. 

Clearly, a large subfield of radiation chemistry has grown up around the phenomena observed during radiolysis in the presence of solids. It depends upon the behavior of electrons and holes in solids and their interactions with adsorbed molecules, and therefore has a general connection with catalytic reactions on the same solids. Further developments may reveal points of closer and more specific common interest. 

Suppose we could assume both radiation chemistry and discharge chemistry to be sufficiently developed so that we could examine the components in this kind of detail. The next step would be to make the contrasts suggested in the title of this article. We would select components which in our opinion contribute the major characteristic of the particular branch. We would compare them with each other. We would compare the specifically important and contrasting ways in which they interact in the two cases. Such procedure would appear to be very logical indeed. 

Williams, T. Ff. Specific Elementary Processes in the Radiation Chemistry of Organic Oxygen Compounds. Nature 194, 348 (1962). 

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. 

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