[Show abstract][Hide abstract] ABSTRACT: Many solutes, added to water in amounts of a few mol%, cause an increase in the yield of solvated electrons (es−) measured by pulse radiolysis. A pulse radiolysis study of tert-butanol (tBuOH) in D2O has been carried out to investigate this phenomenon. Detailed measurements of the yield, measured as Gεmax(es−), and the deeay of solvated electrons were made at 6, 25, and 46 °C over the range 0–5mol% tBuOH. The maximum Gεmax(es−) occurs at about 1 mol% tBuOH, but the exact concentration depends on the temperature of the sample and the time after the pulse at which the measurement is made. Three factors are examined as contributing to the increased Gεmax(es−) in the presence of tBuOH and certain other solutes. They are (i) the change in viscosity produced by the added solute, (ii) the scavenging of OH radicals by the solute, thereby reducing the reaction of OH with es− and (iii) the possibility that the addition of the solute leads to an increase in the thermalization distance of the secondary electrons. It is concluded that effects (i) and (ii) are sufficient to explain the existing experimental data.
Canadian Journal of Chemistry 02/2011; 64(8):1548-1552. · 0.96 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The yield and reaction kinetics of trapped electrons, and , in several ethylene glycol/D2O glasses have been studied from 6–72 K by pulse radiolysis. An increased D2O concentration is believed to increase the concentration of IR-traps thereby leading to a greater and to decrease the concentration of VIS-traps thereby increasing the stability of . The yield and stability of are also increased by lowering the temperature. A redetermination of (1.3 × 104 M−1 cm−1 at 1800 nm) confirms earlier values.
Canadian Journal of Chemistry 02/2011; 61(1):189-193. · 0.96 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Pulse radiolysis of 9.5 M LiCl/D2O glass at 6 K produces both types of trapped electrons, evis− and eir−, just as it does at 75 K. However, going from 75 K to 6 K increases the initial yield of eir− and decreases its decay rate, while the yield of evis− decreases and its decay rate increases. These results are attributed to fast trap-to-trap tunnelling of evis− from unrelaxed traps at 6 K and slower tunnelling from deeper traps at 75 K while the eir− traps seem to relax within 100 ns even at 6 K. In 12 M LiCl/D2O at 4–10 K the initial evis− band with λmax = 625 nm decays considerably over minutes revealing a stable band with λmax = 695 nm. The stimulation spectrum and absorption spectrum of this stable band indicate a bound–free transition of 2.0 eV and a bound–bound transition of 1.8 eV. Similar measurements of evis− at 77 K indicate a bound–free transition of 2.6 eV and a bound–bound transition of 2.1 eV. Tryptophan was photolyzed in 9.5 M LiCl/D2O at 2 K to produce eir−.
Canadian Journal of Chemistry 02/2011; 57(12):1488-1499. · 0.96 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The simultaneous interaction of solvated electrons with strongly solvating water molecules and weakly solvating dimethylsulfoxide (DMSO) molecules has been studied by pulse radiolysis. In all DMSO/H2O mixtures investigated the solvated electrons have a single absorption band with a maximum intermediate between that of pure DMSO (λmax > 1500 nm) and that of water (λmax = 720 nm). There is a nearly linear relationship between the photon energy of λmax and the bulk dielectric constant, indicating that the optical properties of solvated electrons in the mixtures are not dominated by the water. A minimum is observed in the variation of Gεmax with DMSO/H2O composition which may be associated with intermolecular structure. In mixtures containing > 0.2 mole fraction DMSO the solvated electrons have half-lives of 11–18 ns.The radiation produced oxidizing species in DMSO has a half-life of 1–4 µs and an absorption band centered at 600 nm. This species seems to be present in all DMSO/H2O mixtures.Pure DMSO gives a free-ion yield in the range 1.2 to 1.8, as determined separately for the oxidizing and reducing species by bromide and anthracene scavenging experiments respectively. This free-ion yield is in keeping with the dielectric constant of DMSO of 46. The yields in fully deuterated DMSO are ~30% higher than in the protonated material.
[Show abstract][Hide abstract] ABSTRACT: In a pulse radiolysis study of crystalline D2O ice, an intense infrared absorption band with λmax > 2350 nm has been found at low temperatures, in addition to the well-known visible absorption band of the trapped electron. The infrared band is also attributed to trapped electrons, partly because of its similarity to the electron absorption band found recently in some D2O glasses at low temperatures. The effects of temperature, dose per pulse, accumulated dose, and added NH4F, HF, and ND3 on the yields and decay kinetics of both bands have been investigated. It is concluded that the electron trap giving rise to the visible band is a vacancy which at low temperatures is radiation-produced by a two-step spur process. At temperatures close to the melting point the vacancy-trap probably exists before the radiation pulse at equilibrium concentration. The electron trap which gives rise to the infrared band is thought to be a cavity that occurs naturally in the perfect lattice. For previously unirradiated samples the infrared band decays by a second order process which is remarkably fast The decay reaction is probably neutralization by D2O+. Doping with NH4F increases the yield of the infrared absorption and greatly decreases its decay rate. The total yield of localized electrons in irradiated crystalline D2O is higher than has been generally recognized.
[Show abstract][Hide abstract] ABSTRACT: The yields and decay rates of two types of localized excess electrons, absorbing in the visible (e−vis) and in the infrared (e−ir), have been compared in four pulse-irradiated H2O glasses and their D2O analogues, and in irradiated H2Oand D2O ice crystals, all at 73 K. If it is assumed that extinction coefficients of e−vis and e−ir at 650 nm and 1800 nm, respectively, are independent of isotopic substitution for both glasses and ice, the G's for both types of localized electrons are lower in all the H2O solids studied than in the corresponding D2O solids. The largest effect of isotopic substitution was found in the lifetime of e−vis in the crystal; at 73 K the inital half-life for decay of e−vis is approximately 14 times longer in D2O than in H2O ice. Even at 6 K the decay of e−vis in H2O ice is very rapid with an initial half-life of about 75 ns.
[Show abstract][Hide abstract] ABSTRACT: 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 with papain is 4.1 × 1010 M−1 s−1 and the spectrum of the electron adduct closely resembles that of the disulfide anion However, there is evidence that not all reactions of 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.
Canadian Journal of Chemistry 02/2011; · 0.96 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The authors of a recent paper (Claridge Mackonis et al 2007 Phys. Med. Biol. 52 5469-82) measured cell survival in spatially modulated radiation fields. They claim to have identified two new types of radiation-induced bystander effect. We conclude that their claims are not supported by their data.
Physics in Medicine and Biology 04/2009; 54(5):L11-3; author reply L15-21. · 2.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Absorbed doses determined with a sealed water calorimeter operated at 4 degrees C are compared with the results obtained using ionization chambers and the IAEA TRS-398 code of practice in a 10 MV photon beam (TPR(20,10) = 0.734) and a 175 MeV proton beam (at a depth corresponding to the residual range, R(res) = 14.7 cm). Three NE 2571 and two FC65-G ionization chambers were calibrated in terms of absorbed-dose-to-water in (60)Co at the Swedish secondary standard dosimetry laboratory, directly traceable to the BIPM. In the photon beam quality, calorimetry was found to agree with ionometry within 0.3%, confirming the k(Q) values tabulated in TRS-398. In contrast, a 1.8% deviation was found in the proton beam at 6 g cm(-2) depth, suggesting that the TRS-398 tabulated k(Q) values for these two ionization chamber types are too high. Assuming no perturbation effect in the proton beam for the ionization chambers, a value for (w(air)/e)(Q) of 33.6 J C(-1) +/- 1.7% (k = 1) can be derived from these measurements. An analytical evaluation of the effect from non-elastic nuclear interactions in the ionization chamber wall indicates a perturbation effect of 0.6%. Including this estimated result in the proton beam would increase the determined (w(air)/e)(Q) value by the same amount.
Physics in Medicine and Biology 04/2006; 51(6):1503-21. · 2.70 Impact Factor