Aqueous solutions of penicillamine (RSH) and penicillamine disulfide (RSSR) have been pulse irradiated at several pH's and the ensuing reactions studied. The rate constant for the reaction of solvated electrons with penicillamine disulfide decreases from 7.3 × 10−9 M−1 s−1 at pH 7 to 0.8 × 109 M−1 s−1 at pH 10. The first-order rate constant for the decomposition of the resulting radical anion, RSSR−, increases from 1.77 × 106 s−1 at pH 7 to 6.5 × 106 s−1 at pH 10. Both of these pH effects are attributed to deprotonation of the two amino groups of the disulfide which have microscopic pK values of 7.9 and 8.5. The equilibrium constant for the reaction[Formula: see text]is (2.31 ± 0.2) × 102 M−1 at pH 8 but increases to 3.04 × 102 M−1 at pH 7 and decreases to 0.96 × 102 M−1 at pH 9. Measured from the kinetics of the build-up of RSSR−, k−2 = 1.83 × 106 s−1 at pH 8.Decay of RSSR− in the presence of RSH follows second-order kinetics at high dose rates and first-order kinetics at low dose rates. At high dose rates two second-order reactions[Formula: see text]appear to be involved with rate constants of 1.7 × 109 M−1 s−1 and 6.4 × 109 M−1 s−1 respectively at pH 8, At low dose rates the decay appears to be due to a pseudo first-order reaction between RSSR− and H2O, k ~ 2 × 103 s−1, with valine (RH) and penicillamine trisulfide (RSSR) as principal products. These products are obtained in similar yields by gamma radiolysis of penicillamine solutions. At pH 5, the thiyl radical decays by second-order kinetics, 2k = (2.85 ± 0.15) × 109 M−1 s−1.Studies of solutions containing penicillamine and methanol showed that penicillamine repairs methanol radicals very efficiently by hydrogen transfer. k = (1.1 ± 0.1) × 108M−1 s−1. The implications of the results for chemical radioprotection are discussed.

Complexed radical cations are formed as transient products in the one-electron oxidation of organic sulphides by hydroxyl radicals. Intermolecular complexes, (R2S .*. SR,) + , are characterized by a 3-electron bond between sulphur atoms of two different molecules, absorption maxima around 500 nm and an equilibrium (R2S)2t + R2S f + R2S. In addition, intramolecular complex formation n + yielding ( ... ) is observed in the oxidation of 1 , 4-di-, 1,3-di-, and 1,3,5-tri-thiane. In these complexes a 3-electron-through-space-bond between two sulphur atoms of the same molecule is established. Absorption maxima are red shifted to 2600 nm. Stabilization of an oxidized sulphur atom can also be effected by hetero-atoms other than sulphur. R2S .*. Br(C1) are formed in the reaction of either R2S with Br2r(CI,T) or the oxidized sulphide with Br-(Cl-). Equilibrium constants for the complexes, spectral and kinetic data on the neutral radicals and radical cations are reported and discussed.

Experimental studies of excess electrons in aqueous glasses and crystalline ice are reviewed. Emphasis is placed on studies of the two main optical absorption bands, the well known visible band, which is similar to that of the solvated electron in water, and the IR band which has λmax [Formula: see text] 2950 nm. Under some circumstances partial conversion of the IR-absorbing species to the visible-absorbing species has been observed. Evidence indicates that the two species are due to electrons trapped in distinctly different physical environments. Two mechanisms have been proposed for the formation of the visible-absorbing electron in crystalline ice, one involving naturally occurring vacancies and the other radiation produced vacancies. Studies of the UV and visible luminescence emitted when ice at low temperature is irradiated are summarized, and the mechanisms suggested for its production are discussed briefly. The studies on excess electrons in aqueous solids seem to the authors to be highly relevant to the more recent studies of electron solvation in water which are done on a much shorter time-scale. These latter studies are reviewed briefly with the aim of elucidating the relevance.Key words: visible-absorbing electrons, IR-absorbing electrons, irradiation of aqueous glasses, irradiation of crystalline ice, electron solvation in water.

The spectra of the trapped electron in 3-methylpentane and 3-methylhexane glasses at 76°K as determined by pulse radiolysis have been found to shift toward the blue on a time scale of mseconds, seconds, and minutes. For 3-methylhexane Xmax is approximately 2000 and 1700 nm at 3 psec and 380 sec, respectively. For 3-methylpentane Xmax is approximately 1900 at 10 psec and shifts to about 1700 nm at 380 sec. The spectra at 380 sec are very similar to those determined by others after 60Co irradiation. Geminate recombination occurs simultaneously with the spectral shifts, but an experiment with added biphenyl indicates that the mechanism involved in the spectral shifts is predominantly molecular reorientation rather than detrapping-retrapping.

The pulse radiolysis of the proteolytic enzyme papain has been studied in nitrogen-purged and N2O-purged aqueous solutions at pH 6.4. The rate constant for reaction of OH with papain is 4.7 × 1010 M−1 s−1. The initial spectrum of the intermediate formed by this radical is consistent with a major fraction of attack at tyrosine residues with smaller proportions reacting at tryptophan and other sites. Subsequent spectral changes are also consistent with the preferential attack of OH on tyrosine. The overall rate constant for reaction of [Formula: see text] with papain is 4.1 × 1010 M−1 s−1 and the spectrum of the electron adduct closely resembles that of the disulfide anion [Formula: see text] However, there is evidence that not all reactions of [Formula: see text] with papain lead to the formation of this species. The results are discussed in the light of deactivation yields for Co60γ radiolysis measured by biochemical techniques.