Pulse radiolysis, description

Pulse radiolysis requires access to an electron accelerator or similar device. This requirement usually restricts work to specialized laboratories. Thorough descriptions of the experimental apparatus and protocols have been given.23,24... 

An almost complete description of both OH radical-mediated and one-electron oxidation reactions of the thymine moiety (3) of DNA and related model compounds is now possible on the basis of detailed studies of the final oxidation products and their radical precursors. Relevant information on the structure and redox properties of transient pyrimidine radicals is available from pulse radiolysis measurements that in most cases have involved the use of the redox titration technique. It may be noted that most of the rate constants implicating the formation and the fate of the latter radicals have been also assessed. This has been completed by the isolation and characterization of the main thymine and thymidine hydroperoxides that arise from the fate of the pyrimidine radicals in aerated aqueous solutions. Information is also available on the formation of thymine hydroperoxides as the result of initial addition of radiation-induced reductive species including H" atom and solvated electron. 

The shift of the spectrum has been well discussed previously. The early pulse radiolysis data suggested that the kinetics at 1300 nm [28] matched the kinetics in the blue [16], which led to the description of the kinetics as a two-state problem. However, the results measured by Chase and Hunt, where the kinetics at 1050 nm were considerably slower than the kinetics at 500 and 1300 nm, suggested that the kinetics were more... 

It is from these perspectives that we have reviewed the pulse radiolysis experiments on polymers and polymerization in this article. The examples chosen for discussion have wide spread interest not only in polymer science but also in chemistry in general. This review is presented in six sections. Section 2 interprets the experimental techniques as well as the principle of pulse radiolysis the description is confined to the systems using optical detection methods. However, the purpose of this section is not to survey detail techniques of pulse radiolysis but to outline them concisely. In Sect. 3, the pulse radiolysis studies of radiation-induced polymerizations are discussed with special reference to the initiation mechanisms. Section 4 deals with applications of pulse radiolysis to the polymer reactions in solution including the systems related to biology. In Sect. 5 reaction intermediates produced in irradiated solid and molten polymers are discussed. Most studies are aimed at elucidating the mechanism of radiation-induced degradation, but, in some cases, polymers are used just as a medium for short-lived species of chemical interest We conclude, in Sect. 6, by summarizing the contribution of pulse radiolysis experiments to the field of polymer science. 

Detection systems for nanosecond and microsecond pulse radiolysis are mostly the same, but that for picosecond measurement is somewhat different. The description is confined here to nanosecond and microsecond systems and a brief explanation to the picosecond system will be given in the following subsection. 

In many cases the product S is itself a free radical (S ), or a hyper-reduced metal ion, which in turn reacts in one-electron gain or loss processes. It is not surprising, then, that radiation-chemical methods are widely used in the study of electron-transfer processes. Of particular value is the technique of pulse radiolysis which permits reactions to be studied on timescales ranging from seconds down to picoseconds, so that even the most reaetive speeies ean be studied. It is this technique and its applications that form the subject matter of this chapter which begins with an outline of the radiation chemistry of water and other solvents. Next there is a historical view of pulse radiolysis, some of the landmark discoveries are discussed, followed by a description of the principal features of a pulse radiolysis facility and the various methods of detecting and measuring transient speeies. The chapter ends with some examples of data capture and analysis, and methods of sample preparation. 

It is clear from the foregoing descriptions that pulse radiolysis provides a very versatile way of generating one-electron redox reagents under a wide range of solvent conditions that can be finely tuned to accommodate the reactions of interest. 

A brief description of the major components of a pulse radiolysis system will be given in the following whenever possible, references will be given to the original papers where the specific solutions adopted in the various laboratories are described in detail. 

In addition to the references cited above, the following publications also contain descriptions of various aspects of pulse radiolysis and/or its applications. 

This chapter will begin by delineating the capabilities of the two techniques, radiolysis and laser photoexcitation, for examination of factors that regulate ET rates. We will begin with a list summarizing the capabilities of the two techniques. Descriptions will be supplemented by reference to published work and examples from pulse radiolysis experiments in our laboratory, along with a brief description of the experimental setup. In this discussion we shall see... 

For a more thorough description of pulse radiolysis see Pulse Radiolysis, Tabata, Y. Ed., CRC Press, Boston, 1991... 

The aqueous chemistry of NO has been extensively studied. Nitric oxide has a modest solubility of 1.9 mM in water under 1 atm of NO. Descriptions of its reactivity have tended to be highly variable. Recent work indicates that NO is not highly reactive, despite having an unpaired electron, but reacts with O2 to form reactive species. Traces of Oj are the probable source of different conclusions about the reactivity of NO. It should be noted that there have been some recent studies of the general properties of species involved in these sterns, such as the pulse radiolysis of NO, the pK, values of HNOj and 1 0, the reduction potential of NO. and the AGf of ONOjH. ... 

The identification and physicochemical characterization of 2three-electron bonded species, in general, but particularly of those based on the participation of sulfur has enormously benefitted from the availability of sensitive time-resolved techniques [71] such as the radiation chemical method of pulse radiolysis or photochemical laser flash equipment. Valuable information has also been gathered from ESR measurements under steady-state flow conditions [68] as well as in low temperature solid matrices [70, 72, 73]. In addition, excellent high level calculations have provided a good theoretical description of these species. [74-81]. 

From kinetic analyses of these systems. Barker was able to determine the rate constants for the reactions of ethanol and methanol with both OH- and H-radicals. Values of k were equal for each alcohol, with magnitudes of 2.4 x 10 moP liter s for the reactions with atomic hydrogen and 1.0 x 10 moP liter s for those with the OH- radicals. The constants agree well with pulse radiolysis data, and these chemical reactivity studies provide some of the best evidence for the presence of the solvated electron. The original references should be consulted for a detailed description of these results. 

Detailed accounts of the development of radiation chemistry and its tools can be found elsewhere. The purpose of this chapter is to describe the basic characteristics of continuous and pulsed sources of ionizing radiation for radiolysis studies, and to provide a broad overview of the present and near-future status of radiolysis instrumentation worldwide, for the benefit of readers who would like to use these powerful techniques to advance their own research. It is inevitable under the circumstances that some facilities may be missed and that future developments will soon render this overview out-of-date, however the substantial progress that has been made in the years since the previous reviews appeared [14-16] merits description here. 

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