Scavenging Of Hydrated Electrons Research Articles

Mechanism of multibubble sonochemiluminescence of Ru(bpy)32+ in neutral aqueous solutions

The effect of hydrated electron scavengers, Cd2+, NO3−, (CH3)2CO, and OH radical scavengers, Cl−, I−, on the intensity of Ru(bpy)32+ ion sonochemiluminescence observed in neutral aqueous solutions of Ru(bpy)3Cl2 was studied. The variation trends in the luminescence intensity due to the action of the scavengers indicated three main reactions sufficient to explain the sonochemiluminescence in a neutral medium. These reactions are the Ru(bpy)32+ reduction and oxidation with the H atom and the OH radical, respectively, and disproportionation of the Ru(bpy)3+ and Ru(bpy)33+ ions thus formed, giving rise to the multibubble sonochemiluminescence emitter, namely, the electronically excited ∗Ru(bpy)32 ion.

Organic-Gelatin-Free Nanocomposite Fricke Gel Dosimeter.

We report a nanocomposite Fricke gel (NC-FG) dosimeter prepared using only Fe2+ and nanoclay in water, without any organic gelling agents. This dosimeter gels due to its thixotropic properties and exhibits linear energy transfer (LET)-independent radiological properties under carbon ion beam irradiation. The radiation sensitivity of this dosimeter was 1.8 [s-1 kGy-1], which is three times higher than that reported previously (0.6 [s-1 kGy-1]) for a similar dosimeter containing gelatin. The Fe3+ yield was determined to be 0.19 μmol/J by evaluating the difference in spin-lattice relaxivity between Fe3+ and Fe2+. A further increase in the radiation sensitivity was observed upon addition of the hydrated electron scavenger N2O, suggesting the reduction of Fe3+ by a hydrated electron. LET-dependent variations of the contributions of OH radicals and hydrated electrons compensate each other in the oxidation yield of NC-FG. This is the main mechanism of the suppression of LET effects in the Bragg peak compared to conventional Fricke dosimeters. The radiation-induced oxidation yield G(Fe3+) can be described by the stoichiometric equation {G(Fe3+) = G(OH) - G(eaq-) + 2G(H2O2) + G(H)} with the reported LET dependence of the primary yield of water decomposition radicals. The calculated results are in approximate agreement with the absolute value of the experimental oxidation yield of NC-FG. The effects of the addition of small amounts of radical scavengers (nitrate, selenate, or cadmium) are also evaluated. The sensitivity was divided into two types, and influences of intermediate radicals after scavenging reaction are indicated.

Evaluation of the potential of p-nitrophenol degradation in dredged sediment by pulsed discharge plasma

Hazardous pollutants in dredged sediment pose great threats to ecological environment and human health. A novel approach, named pulsed discharge plasma (PDP), was employed for the degradation of p-nitrophenol (PNP) in dredged sediment. Experimental results showed that 92.9% of PNP in sediment was smoothly removed in 60 min, and the degradation process fitted the first-order kinetic model. Roles of some active species in PNP degradation in sediment were studied by various gas plasmas, OH radical scavenger, hydrated electron scavenger and O2·− scavenger; and the results presented that O3, OH radical, eaq− and O2·− all played significant roles in PNP removal, and eaq− and O2·− mainly participated in other oxidising active species formation. FTIR analysis showed that PNP molecular structure was destroyed after PDP treatment. The main degradation intermediates were identified as hydroquinone, benzoquinone, phenol, acetic acid, NO2− and NO3−. PNP degradation pathway in dredged sediment was proposed. It is expected to contribute to an alternative for sediment remediation by pulse discharge plasma.

Radiolysis of an aqueous [11C]iomazenil solution

Summary Radiolysis of [11C]iomazenil was investigated in an aqueous solution. Preparation of [11C]iomazenil with [11C]CH3I produced a good radiochemical yield, however, its radiochemical purity was always less than 90 without additives. This poor radiochemical purity was attributed to radiolysis of [11C]iomazenil. The degradation of [11C]iomazenil via radiolysis was markedly facilitated in the presence of HCOONa (strong selective hydroxyl radical and hydrogen atom scavenger). On the other hand, the radiolysis was suppressed effectively in the presence of NaNO3 (selective hydrated electron scavenger), suggesting participation of hydrated electrons in the radiolysis of [11C]iomazenil. LC/MS analysis of the degradation product suggested that the major degradation product by radiolysis had a molecular weight of 285 corresponding to the deiodinated compound. The present study showed that a decrease in the radiochemical purity of [11C]iomazenil was attributed to the radiolysis via the deiodination reaction by hydrated electron.

Decomposition of an aqueous solution of [ 11C]Ro 15-4513: implication of hydrated electrons in the radiolysis of [ 11C]Ro 15-4513

An aqueous solution of [ 11C]Ro 15-4513 underwent decomposition to give a few radioactive degradation products. The major degradation product corresponded to that of authentic Ro 15-4513 with 60Co radiolysis, which showed a molecular weight of 301 (M+H). The structure of this degradation product was estimated to have an amine group instead of an azido group on Ro 15-4513. Radiolysis of Ro 15-4513 was not suppressed by the addition of selective hydroxyl radical scavenger (MeOH, HCOO -), in contrast, it was suppressed effectively in the presence of a selective hydrated electron scavenger (NaNO 3), suggesting that hydrated electrons would play an important role in the radiolysis of [ 11C]Ro 15-4513.

Sonochemistry of aqueous solutions: EPR and spin trapping studies of radical intermediates

The primary free radical species produced in the sonolysis of aqueous argon-saturated solutions (i.e., H, OH, and O2–) and in N2-containing aqueous solutions (H, OH, O2–, NO) can be identified by electron paramagnetic resonance (EPR) combined with spin trapping. The EPR experiments using cadmium(2+) ions as hydrated electron scavengers show that no detectable level of hydrated electrons is formed in the sonolysis of argon-saturated water at neutral pH. The temperature dependence of the semi-classical treatment of the kinetic isotope effect for H and D formation by O–H and O–D bond scission in 1:1 H2O–D2O mixtures was used to estimate the effective temperatures (2000–4000 K using phenyl t-butyl nitrone spin traps) in collapsing cavitation bubbles. At low concentrations of nonvolatile solutes (e.g., acetate ions, amino acids, and sugars) only radicals formed by H-abstraction were observed. At high concentrations, pyrolysis radicals such as methyl radicals from acetate, amino acids, and sugars could also be spin trapped. For volatile organic solutes, the effect of the vapor pressure of the solute on the effective value of gamma (the ratio of Cp/Cv) in the cavitation bubble is the major determinant of radical yields.

Diffusion-kinetic modelling of the cooperative effect of scavengers on the scavenged yield of the hydroxyl radical

The scavenger concentration dependence of the scavenged yield of the hydroxyl radical produced by the high-energy electron radiolysis of deaerated, and of nitrous oxide saturated, aqueous solutions is modelled using deterministic diffusion-kinetic methods. These calculations provide a simple, but valuable, method for estimating the scavenged yield of the hydroxyl radical in a variety of systems containing both hydroxyl radical and hydrated electron scavengers. The scavenging of hydroxyl radicals in an aqueous solution usually can be divided into two components: the yield that would be scavenged by the hydroxyl radical scavengers in the absence of any hydrated electron scavenger and an additional contribution arising from the cooperative effect of the hydrated electron scavenger. Hydrated electron scavengers reduce the amount of intraspur e–aq+ OH reaction and so increase the amount of hydroxyl radical scavenged by a given concentration of hydroxyl radical scavenger. The yield of scavenged hydroxyl radicals in nitrous oxide solution is not well represented by the sum of the yield of oxide radical anions produced by the nitrous oxide scavenging of the hydrated electron and the radiation-induced yield of hydroxyl radicals that would be scavenged if the hydrated electron scavenging reaction did not produced hydroxyl radicals. In nitrous oxide solutions a small modification to reflect the increase in intraspur reactions of hydroxyl radicals is necessary.

Production of 3- N-[ 11C]methylspiperone with high specific activity and high radiochemical purity for PET studies: Suppression of its radiolysis

3- N-[ 11C]methylspiperone( 11C-NMS, molecular weight = 409 for 12C-NMS) has been prepared automatically with high specific activity (37 ± 18 GBq/μmol at EOS) for the measurement of dopamine D2 receptors in the human brain with a positron camera. It was observed that the radiochemical purity of 11C-NMS decreased from 97.8% (in HPLC eluate) to 83.5% (in saline, after the dispensing procedure, at 29 min from EOS), and to 79.9% in a further 59 min and that another 11C-labelled compound with a molecular weight of 425 (as a 12C-labelled compound) was formed. It was also observed that an aqueous solution of carrier methylspiperone (NMS) decomposed on 60Co irradiation and, using the same analytical conditions, gave the compound with the same retention time and the same molecular weight as 11C-NMS gave. The G-value of NMS decomposition by 60Co irradiation was estimated to be about two in an aqueous solution. The decomposition of 11C-NMS was suppressed remarkably by the addition of hydroxyl radical scavengers such as potassium iodide, and accelerated slightly by a hydrated electron scavenger such as sodium nitrate. Therefore, it was assumed that the hydroxyl radical generated by the radiolysis of water played an important role in the decomposition of 11C-NMS in the aqueous solution. Polysolvate-80 and ethyl alcohol were used as i.v. injectable additives to protect 11C-NMS against decomposition. In 47 routine productions, 2.7 ± 1.7 GBq of 11C-NMS aqueous solutions ready for i.v. injection have been produced at 98.3 ± 1.0% radiochemical purity using an automated synthesis apparatus. The products were used for clinical purposes with a positron camera and animal experiments.

265 nm laser flash spectroscopy of indoles in the presence of nitroxide radicals. A model for probing protein—membrane interactions

Nitroxide spin labels are good triplet quenchers and hydrated-electron scavengers, as evidenced by 265 nm laser flash spectroscopy of indoles and in particular tryptophan (Trp), the chromophoric residue of proteins. These quenching and scavenging abilities depend on the Trp exposure in proteins, on environmental factors such as intercalation in micelles and on the structure of the nitroxide.

Radiolysis of Fremy's Salt in the Presence of Some Hydrated Electron Scavengers in Alkaline Aqueous Solution

AbstractFremy's salt, ON(SO3)22−, was irradiated with γ‐rays in deaerated alkaline aqueous solutions in the presence of NO3−, N2O. In the presence of N2O an increase of the G(‐ON(SO3)22− = G from 6.1 to about 6.7 was observed within a limited range of concentration, while with NO3− the change is gradual. This is consistent with NO2 and OH produced, respectively, in the reaction of eaq− with Fremy's salt, taking place in one‐electron‐equivalent processes, and with the assumption that pairs of radicals may originate from water molecules.