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The oxidation peak potentials (E p) of 31 phenolate, chlorophenolate, and other para-substituted phenolate ions were measured as a function of scan rate, substrate concentration, and pH by cyclic voltammetry in aqueous solution. The one-electron reduction potentials (E red o) of the phenoxyl radical/phenolate ion couples were evaluated from E p and the rate constants for dimerization of the phenoxyl radicals. The dependence of E red o on pH was established, and the relationships that connect E red o with the Brown σ+ constant, the pK a values of the phenols and the protonated phenoxyl radical cations, and the reduction potentials of the protonated radicals were explored.

Publication costs assisted by Natick LaboratoriesThe interactions of hydrated electrons and hydroxyl radicals with a number of sulfhydryl compounds have been studied using the technique of pulse radiolysis. Thioglycolic acid, 0-mercaptopropionic acid, cysteamine, IV-acetylcysteamine, cysteine, iV-acetylcysteine, S-methylcysteine, penicillamine, glutathione, benzyl mercaptan, and thiodiacetic and thiodipropionic acids are among the compounds examined. The reaction rate constants of eacr with these compounds were found to be strongly dependent on the acid-base properties of the sulfhydryl compounds, with the rate decreasing upon deprotonation of both the amino and the mercapto groups. The eaq" were shown to react with RSH to produce quantitatively the Rradical, eaq-+ RSH -* R• + HS~. The reaction rate constants of OH radicals were found to be ~l-3 X 1010 M-1 sec-1 and essentially independent of the ionization constants of the sulfhydryl compounds. The OH radicals form the thiyl radicals, OH + RSH -» RS• + H20. The absorption spectra, extinction coefficients, and decay kinetics of these thiyl radicals have been determined for a number of RSH compounds. The rate constants of the reactions of RS• radicals with RSH and RShave been measured, and the equilibrium constants for RS• + RS-¡=r RSSRhave been calculated for a few systems. The high electrophilicity of the thiyl radical is indicated.

The rate constants for the quenching of the excited states of metal ions and complexes in homogeneous fluid solution are reported in this compilation. Values of kq for dynamic, collisional processes between excited species and quenchers have been critically evaluated, and are presented with the following information, among others, from the original publications, when available: description of the solution medium, temperature at which kq was determined, experimental method, range of quencher concentration used, lifetime of the excited state in the absence of quencher, activation parameters, quenching mechanism. Data collection is complete through the end of 1986, and covers the coordination compounds of 26 metals, including the ions and complexes of the inner-and outer-transition metals, and porphyrin complexes of nontransition metals. Data for 261 excited states quenched by more than 400 inorganic quenchers and 600 organic quenchers have been extracted from almost 500 publications. The introduction to the work contains a discussion of the conceptual background to quenching, including a general treatment of the kinetics, an explanation of the tables, and a list of recent review articles. Uncommon kin~tics mechanisms and equations, usedto obtain the reported values of kq, are discussed in detail as part of the notes to the tables. Indexes of excited states, quenchers, and authors are appended.In this mechanism, kd is the rate constant for the bimolecular diffusional encounter of *S and Q, which can be calculated by use of the Debye-Smoluchowski equation [M. V. Smoluchowski, Phys. Z. 17, 557 (1916); P. Debye, Trans. Electrochem. Soc. 82, 265 (1942) ], andk _ d is the rate con-J.

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