Hydrated electron optical production

Shortly after the discovery of the hydrated electron. Hart and Boag [7] developed the method of pulse radiolysis, which enabled them to make the first direct observation of this species by optical spectroscopy. In the 1960s, pulse radiolysis facilities became quite widely available and attention was focussed on the measurement of the rate constants of reactions that were expected to take place in the spurs. Armed with this information, Schwarz [8] reported in 1969 the first detailed spur-diffusion model for water to make the link between the yields of the products in reaction (7) at ca. 10 sec and those present initially in the spurs at ca. 10 sec. This time scale was then only partially accessible experimentally, down to ca. 10 ° sec, by using high concentrations of scavengers (up to ca. 1 mol dm ) to capture the radicals in the spurs. From then on, advancements were made in the time resolution of pulse radiolysis equipment from microseconds (10 sec) to picoseconds (10 sec), which permitted spur processes to be measured by direct observation. Simultaneously, the increase in computational power has enabled more sophisticated models of the radiation chemistry of water to be developed and tested against the experimental data. 

Table I. Optical Production of Hydrated Electron from Aromatic Compounds in Aqueous Solution...

Table III. Correlation of Optical Hydrated Electron Production with Gat-Phase...

The nitroform ion has a characteristic absorption at 366 nm with an extinction coefficient of 1,02 x 10 1 mole" cm". At this wavelength, the absorption due to the hydrated electron is weak. It is possible, therefore, to measure in the same experiment the decrease in optical density at 720 nm due to the hydrated electron with the corresponding increase in optical density at 366 nm due to the production of the nitroform ion and thus to determine the extinction coefficient of the hydrated electron. The spectrum broadens slightly and F max shifts towards lower energies with increasing temperature. 

Photolysis of solutions of C6o(OH)ig at low solute concentration leads to [C6o(OH)i8] by electron transfer from Me2C(OH) radicals or from hydrated electrons, and this has enabled the reduction potential of the C6o(OH)ig/ [C6o(OH)ig] couple to be estimated. The kinetics of the photoreduction of hexanal using RhCl(PMe3)2CO as catalyst have been measured and the feasibility of a photocatalytic synthesis of hexanol from pentane, CO, and H2 in the presence of rhodium complexes has been demonstrated. Irradiation of a chiral bimolecular crystal of acridine and R-(-)- or S-(+)-2-phenylpropionic acid induces photodecarboxylation followed by stereoselective condensation to give a mixture of three optically active products, and the 3-0-S-methyl dithiocarbo-nate derivatives of oleanolic and ursolic methyl esters have been used as models for the photodeoxygenation of alcohols. ... 

Reactions of H Atoms. - In the radiolysis of water, the hydrated electron Caq and the OH- and H- radicals are the primary radiolysis products. Whereas the reactivity of hydrated electrons and OH- radicals with scavenger molecules S can be easily studied by optical methods (pulse radiolysis), TR EPR is the unique method which can be used to study the reactivity of hydrogen atoms. Bartels et investigated the temperature dependence of the hydrogen... 

The course of chemical reactions in irradiated proteins is determined hy factors that influence the reactivity of the primary free radicals, the kind of protein radicals formed, and the decay of these protein radicals to stable products. To understand these reactions, basic radiation chemical concepts are considered, chemical changes in several representative proteins irradiated under different conditions are compared, and results from optical and electron spin resonance studies on model systems are presented. Among the reactions described are those involving cation, anion, and a-carbon radicals of amino acids and peptides. Analogous reactions common to proteins are then summarized. These mechanistic considerations have important implications for the irradiation of hydrated muscle proteins at — 40°C and for radiation sterilization of foods. 

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