Radiolysis Of Aqueous Solutions Research Articles

On the Mechanism and Kinetics of Synthesizing Polymer Nanogels by Ionizing Radiation-Induced Intramolecular Crosslinking of Macromolecules.

Nanogels—internally crosslinked macromolecules—have a growing palette of potential applications, including as drug, gene or radioisotope nanocarriers and as in vivo signaling molecules in modern diagnostics and therapy. This has triggered considerable interest in developing new methods for their synthesis. The procedure based on intramolecular crosslinking of polymer radicals generated by pulses of ionizing radiation has many advantages. The substrates needed are usually simple biocompatible polymers and water. This eliminates the use of monomers, chemical crosslinking agents, initiators, surfactants, etc., thus limiting potential problems with the biocompatibility of products. This review summarizes the basics of this method, providing background information on relevant aspects of polymer solution thermodynamics, radiolysis of aqueous solutions, generation and reactions of polymer radicals, and the non-trivial kinetics and mechanism of crosslinking, focusing on the main factors influencing the outcomes of the radiation synthesis of nanogels: molecular weight of the starting polymer, its concentration, irradiation mode, absorbed dose of ionizing radiation and temperature. The most important techniques used to perform the synthesis, to study the kinetics and mechanism of the involved reactions, and to assess the physicochemical properties of the formed nanogels are presented. Two select important cases, the synthesis of nanogels based on polyvinylpyrrolidone (PVP) and/or poly(acrylic acid) (PAA), are discussed in more detail. Examples of recent application studies on radiation-synthesized PVP and PAA nanogels in transporting drugs across the blood–brain barrier and as targeted radioisotope carriers in nanoradiotherapy are briefly described.

Kinetics of Formation of Gaseous Products in γ-Radiolysis of Mixtures Modeling Liquid Radioactive Waste

The kinetics of the formation of gaseous products and variation in the parameters of acidity (pH) and chemical oxygen consumption (COC) are studied in relation to the γ-radiolysis of aqueous solutions of mixtures of formic, oxalic, and nitric acid as the model system of radiolytic transformations of acid components of liquid radioactive waste. It is found that with an increase in the absorbed dose of γ-radiation, the acidity and the COC value both decrease because of the decrease in the concentration of organic acids in the mixture. The gaseous products CO2 and H2 were identified. Their concentrations increase nonlinearly with the absorbed dose. Radiation-chemical yields of H2 and CO2 are calculated. Using data from experiment and the literature on composition of liquid products of radiolysis of aqueous solutions of acids, kinetics of formation of gaseous products are studied using soft KINET (version 4.2.5).

Non-Enzymatic Methylglyoxal Formation From glucose Metabolites and Generation of Superoxide Anion Radical During Methylglyoxal-Dependent Cross-Links Reaction

The paper explores the formation of a-oxoaldehydes during the interaction of glucose metabolites with hydroxyl or alkoxyl radicals. Hydroxyl radicals were generated under radiolysis of aqueous solutions, and alkoxyl radicals (t-BuO) were obtained in the model system tert-butyl hydroperoxide/Fe2+. High-performance liquid chromatography revealed that methylglyoxal was one of the organic products resulting from t-BuO-induced transformations of fructose-1,6-bisphosphate under hypoxic conditions. The interaction of lysine and methylglyoxal one of the main targets of a-oxoaldehydes in proteins was also studied. As chemiluminescence and EPR spectroscopy demonstrated, this reaction generates a methylglyoxal anion radical, a cation-radical of methylglyoxal dialkylamine and a superoxide anion radical. EPR signal of methylglyoxal-derived free radicals was observed in hypoxia, whereas only the trace amounts of these free radicals were recorded in the aerated reaction medium.

Radiolysis of the Glycolaldehyde-Na+Montmor- illonite and Glycolaldehyde-Fe3+Montmorillonite Systems in Aqueous Suspension under Gamma Radiation Fields: Implications in Chemical Evolution

The stability and reactivity of organic molecules with biological and pre-biological significance in primitive conditions are of paramount importance in chemical evolution studies. Sugars are an essential component in biological systems for the different roles that they play in living beings. The objective of the present work is to study the gamma radiolysis of aqueous solutions of glycolaldehyde, the simplest sugar and aqueous suspensions of glycolaldehyde-Na+-montmorillonite and glycolaldehyde-Fe3+Montmorillonite. Our results indicate that the radiolysis of the aqueous solutions of glycolaldehyde (0.03M), oxygen free, mainly produce the linear dimer known as eritriol (122 g/mol) and a sugar-like compound with six carbon atoms (180 g/mol). The experiments with the clay suspensions show that clays can adsorb glycolaldehyde and protect it from gamma irradiation. Additionally, it was observed that depending on the cation present in the clay, the percentage and the product (monomer or cyclic dimer) adsorption was different. In the case of Fe3+ Montmorillonite, this clay catalyzed the decomposition of glycolaldehyde, forming small amounts non-identified products. The analysis of these systems was performed by ATR-FTIR, UV spectroscopy, liquid chromatography (UHPLC-UV), and HPLC coupled to a mass spectrometry.

Formation of isomers in the radiolysis of aqueous solutions of alcohols

Formation of isomers in the radiolysis of aqueous solutions of alcohols

Hydroxyl radical induced transformation of phenylurea herbicides: A theoretical study

Aromatic ring hydroxylation reactions occurring during radiolysis of aqueous solutions are studied on the example of phenylurea herbicides by Density Functional Theory calculations. The effect of the aqueous media is taken into account by using the Solvation Model Based on Density model. Hydroxyl radical adds to the ring because the activation free energies (0.4–47.2kJmol−1) are low and also the Gibbs free energies have high negative values ((−27.4) to (−5.9)kJmol−1). According to the calculations in most of cases the ortho- and para-addition is preferred in agreement with the experimental results. In these reactions hydroxycyclohexadienyl type radicals form. In a second type reaction, when loss of chlorine atom takes place, OH/Cl substitution occurs without cyclohexadienyl type intermediate.

Reactions of aminyl radicals during radiolysis and photolysis of aqueous solutions of amino alcohols and their derivatives

It has been found that the radiolysis of the aqueous solutions of α,β-amino alcohols leads to the formation of degradation products of the parent substances. The experimental data suggest that the degradation process includes the stage of the formation of aminyl radicals, which undergo decomposition with the simultaneous cleavage of -C-C- and -O-H bonds through a five-membered transition state. The radiation-induced degradation of amino alcohols is enhanced in an alkaline medium, in which the amino group is deprotonated, and is blocked via the etherification of the hydroxyl group in the parent substances or the introduction of reducing agents.

Specifics of radiolytic degradation of oxalic acid in aerated aqueous solutions

The radiolysis of aqueous solutions of oxalic acid has been studied. Data on the radiation-chemical transformations of the radiolysis liquid-phase products hydrogen peroxide, formaldehyde, glyoxylic acid, and hydrogen ions are presented. The significant effect of oxygen on the mechanism of radiolysis of oxalic acid, which in particular determines the nonmonotonic buildup of radiolysis products in the absorbed dose range of 0.5 to 2 kGy, has been confirmed.

Rapid Electrochemical Detection of Radiolysis Products in an Aqueous Solution Exposed to Alpha Particle Beams

An electrochemical cell has been developed that allows for the rapid and exhaustive detection of oxygen and/or hydrogen peroxide produced during the radiolysis of aqueous solutions by alpha particle or proton beams. Short, 10–100 s, exposures were sufficient to yield steady-state electrochemical currents proportional to the radiolysisG-factor. The use of thin SiC windows provided a robust means of separating the vacuum environment of the ion-beam accelerator from the aqueous solution at atmospheric pressure with minimal energy loss.

Seedless synthesis of gold nanorods employing isopropyl radicals generated using gamma radiolysis technique

The one step synthesis of short aspect ratio gold nanorods using gamma radiation method by incorporating cetyltrimethyl ammonium bromide (CTAB) as a directing agent is reported in this communication. In present method of synthesis, isopropyl radical is selectively generated in the system by carrying out radiolysis of aqueous solution containing 2.75 × 10−2 mol dm−3 of acetone, 0.2 mol dm−3 isopropanol, 4 × 10−4 mol dm−2 Au1+ and 6 × 10−5 mol dm−3 Ag+. The isopropyl radical brings about the reduction of Au1+ to Au0, which undergoes coalescence with other Au0 resulting in formation of Au nanorods. The formation of nanorods is attributed to slower reaction of isopropyl radical with Au1+. The TEM of as-prepared nanoparticles confirmed the formation of uniform sized nanorods having aspect ratio 3.

Reactions of Hydrated Electrons with Pyridinium Salts in Aqueous Solutions

Rate coefficients for the reactions of the hydrated electron (e(aq)(-)) with pyridinium salts in aqueous solutions have been determined using pulse radiolysis techniques. The rate coefficients for pyridine, 1-hydropyridinium chloride, and 1-hydropyridinium nitrate were observed to be 1.4 x 10(10), 4.5 x 10(10), and 5.3 x 10(10) M(-1) s(-1), respectively. The e(aq)(-) was found to primarily attack the pyridine ring, the proton coordinated to the nitrogen atom, and the nitrate counterion, but not the chloride. Results for the corresponding dimer structures of 4,4'-dipyridyl, 1,1'-dihydro-4,4'-bipyridinium dichloride, and 1,1'-dihydro-4,4'-bipyridinium dinitrate had similar trends for e(aq)(-) attack sites. The rate coefficients for pyridinium salts were lower when the pyridinium nitrogen atom is coordinated to a methyl group rather than to a proton. This reduction is probably due to the increase in electron density of the pyridine ring due to the electron-donating methyl group. Pyridinium salts are not major contributors to the production of molecular hydrogen in the radiolysis of aqueous solutions and actually decrease molecular hydrogen yield due to scavenging reactions of the e(aq)(-). The yield of molecular hydrogen decreases from 0.45 to approximately 0.2 molecule/(100 eV) over the scavenging capacity range for the e(aq)(-) of 10(5)-10(9) s(-1). Absorption spectra of the transient species produced by the reactions of pyridinium salts with OH radical and H atom formed in water radiolysis were observed, and rate coefficients for these reactions were determined.

Glycoside bond cleavage in the radiolysis of aqueous solutions of methylglycosides and disaccharides

The kinetics of formation of methylglycoside and disaccharide radiolysis products resulting from the O-glycoside bond cleavage was studied, and the yields of these products were determined. It was found that oxygen inhibits these processes. The findings suggest that the fragmentation reaction of C’2 radicals plays an important role in the formation of carbohydrate degradation products in the radiolysis of aqueous carbohydrate solutions.

Radiolysis of Aqueous Solutions of Poly(ethylene oxide) at 77 K

Low-temperature (77 K) γ-radiolysis of aqueous solutions of poly(ethylene oxide) was studied by ESR spectroscopy. Trapped electrons, hydroxyl radicals, and -CH2-ĊH-O- radicals were identified as principal paramagnetic products of radiolysis. It was shown that an increase in the polymer concentration in solution led to a growth in number of trapped electrons and -CH2-ĊH-O- macroradicals. The decay of hydroxyl radicals occurring at 110–115 K was accompanied by the formation of -CH2-ĊH-O- macroradicals and partial recombination of hydroxyl radicals. Action of visible light resulted in virtually quantitative transformation of trapped electrons into -CH2-ĊH-O- macroradicals. The radiation-chemical yields of the species trapped at 77 K were estimated and the scheme of radiation-induced chemical processes was suggested.

Role of Excess Electrons in TiO2 Nanoparticles Coated with Pt in Reduction Reactions Studied in Radiolysis of Aqueous Solutions

Surface modification of TiO2 nanocrystallites in aqueous solution was carried out by reduction of chloroplatinic acid with TiO2 electrons (eTiO2-). The TiO2 electrons had been generated through electron injection from 2-propanol radicals, hydrogen atoms, and hydrated electrons produced by γ or pulse radiolysis prior to the addition of the chloroplatinic acid. Upon addition of the latter, Pt0 clusters are produced by multistep reduction of the chloroplatinic acid on the TiO2 surface. The present work concerns the material balance and chemical kinetics of the Pt0 mediated reduction of water and H+ to molecular hydrogen by the TiO2 electron. Pt0 showed no effect on the rate of oxygen reduction, compared to bare TiO2. The effect of surface Pt0 on increasing photocatalytic yields, claimed by a number of laboratories, is apparently due to electron capture by the Pt0 rather than electron removal by oxygen.

Deconvolution of Complex Absorption Spectra Recorded in the Pulse Radiolysis of Aqueous Solutions of 3,5-Dihydroxytolyene

The optical absorption spectra of short-lived species generated in aerated aqueous solutions of 3,5-dihydroxytoluene, a representative of alkylhydroxybenzenes, by the action of single electron beam pulses were recorded. The decay curves recorded at different wavelengths differ from each other, thus suggesting that the transient species react with one another and with water via a complex mechanism and making it possible to discriminate between individual bands characterizing each particular species in the overall spectrum. Two procedures for analyzing complex absorption spectra were employed: (i) with the use of spectra observed at different time delays after the electron pulse and (ii) with deconvolution into a sum of Gaussians.

Effect of copper ions on the radiostability of protein-polyelectrolyte mixtures

Aqueous solution of polyacrylic acid (PAA), poly-N-isopropylacrylamide (PNIPAAm), bovine serum albumin (BSA), superoxide dismutase (SOD) and their mixtures (PAA-BSA, PAA-Cu-BSA, PNIPAAm-BSA, PAA-SOD) were irradiated in the presence of oxygen in neutral media (pH 7.0) with 60Co γ-rays. In addition, aliquots of aqueous solutions of PAA, PAA-Cu2+, BSA and PAA-Cu2+-BSA saturated with N2 and N2O were also irradiated. The decomposition rate of irradiated solutions were measured by UV-visible spectrophotometry, fluorescence spectroscopy, and high performance liquid chromatography (HPLC). Protective effect of copper ions on radiolysis of aqueous solution of PAA-Cu-BSA and conversion of Cu(II) to Cu(I) was observed. The possible mechanism of this phenomenon is discussed.

Radiolysis of Aqueous Solutions of Benzoate Ion: A Radiation Chemistry Experiment for Undergraduates

This investigation describes the chemical effects of ionizing radiation on dilute aqueous solutions of benzoate ion. We have composed an experimental procedure that allows undergraduate chemistry students to identify and to quantitatively determine the amount of the products that are produced. The student investigators determine the absorbed dose that a sample receives when exposed to a 60Co source, irradiate dilute aqueous solutions of benzoate ion, and analyze the resulting mixture of hydroxybenzoate ions using high-performance liquid chromatography. The radiolysis of dilute solutions of benzoate ion results in the formation of a mixture of ortho-, meta-, and para-hydroxybenzoate ions that are readily separated on a C18 μ-Bondapak column. By the use of appropriate calibration curves, the yield (G values) of each of the isomers may be determined and compared.

The Reaction of Superoxide Radicals withS-Nitrosoglutathione and the Products of Its Reductive Heterolysis

Generation of superoxide radicals (0.01-0.1 microm s(-1)) by radiolysis of aqueous solutions containing S-nitrosoglutathione (45-160 microm, pH 3.8-7.3) resulted in loss of this solute at rates varying with solute concentration, radical generation rate, and pH. The results were quantitatively consistent with the loss being attributed to competition between reaction of superoxide with S-nitrosoglutathione (rate constant 300 +/- 100 m(-1) s(-1)) and the pH-dependent disproportionation of superoxide/hydroperoxyl. This rate constant is much lower than previous estimates and seven orders of magnitude lower than the rate constants between superoxide and superoxide dismutase or superoxide and nitric oxide. This indicates that interaction between superoxide and S-nitrosoglutathione is unlikely to be biologically important, contrary to previous suggestions that reaction could serve to prevent the rapid reaction between superoxide and nitric oxide. Reductive homolysis of S-nitrosoglutathione by the carbon dioxide radical anion, a model for biological reductants such as disulfide radical anions, occurred with a rate constant of 7.4 x 10(8) m(-1) s(-1) and produced nitric oxide stoichiometrically. Thiyl radicals were not produced, indicating the alternative homolysis route to generate nitroxyl did not occur.

Copper-Catalyzed Radiolytic Reduction of CO2 to CO in Aqueous Solutions

Radiolysis of aqueous solutions containing CO2 and Cu(II) ions under reducing conditions leads first to reduction of the Cu(II) and then to formation of CO. Experiments under various conditions show that although Cu(II) was often reduced to colloidal Cu(0) particles, formation of CO requires the presence of Cu(I). It also requires that CO2 be first reduced to the •CO2- radical. The •CO2- radical was produced radiolytically by reaction of CO2 with eaq- or by reaction of formate ions with H• and •OH radicals and photochemically by reaction of formate with the acetone triplet. The •CO2- radicals are reduced to CO via addition to Cu(I) and subsequent reaction of the product with another Cu(I). The first reaction produces CuCO2, which undergoes protonation at pH < 4. The reaction of the neutral CuCO2 with Cu(I) leads to reduction of the copper to form Cu2+ and subsequently Cu(0) particles. However, the reaction of the protonated form, CuCO2H+, with Cu(I) leads to oxidation of the copper and formation of CO in the form of the CuCO+ complex. After most of the copper is converted into CuCO+, subsequent reactions involve this species instead of Cu+ and lead to further production of CO. From pulse radiolysis measurements, the rate constants for the reactions of the •CO2- radicals with Cu+ and CuCO+ were found to be ≈ 1 × 109 and (1.5 ± 0.4) × 108 L mol-1 s-1, respectively. The protonated adduct formed by the latter reaction at pH 3.4, Cu(CO)CO2H+, reacts with CuCO+ with a rate constant ≈ 5 × 105 L mol-1 s-1 to produce more CO. It also undergoes first-order decomposition and second-order decay reactions.

Radiolysis of Aqueous Solutions with Pulsed Ion Beams. 4. Product Yields for Proton Beams in Solutions of Thiocyanate and Methyl Viologen/Formate

The yields of radicals from water decomposition produced in the radiolysis of two types of aqueous solutions, thiocyanate and methyl viologen (MV2+), were determined using proton pulses of 5.2 MeV energy. Aerated thiocyanate solutions in the concentration range of 0.001−0.75 M gave yields of (SCN)2•-, formed from scavenging OH radicals, that were lower than those for high-energy electrons and higher than those for 4He ions of 21 MeV energy. The (SCN)2•- yield increased with increasing thiocyanate concentration, but the decay of thiocyanate radicals through intratrack reactions appears to be substantial in proton radiolysis. Methyl viologen radical cations (MV•+) formed by scavenging eaq-, H atoms, and OH radicals were measured in deaerated 0.5 mM MV2+ solutions containing formate. The MV•+ yields agreed with the results of steady-state proton beam radiolysis, which confirms earlier results that this system is a suitable chemical dosimeter for ion beam pulse radiolysis. The yields of MV•+ in deaerated MV2+ solutions containing formate and formate/tertiary butanol were used to determine the yields of OH radicals and the sum of the eaq- and H atom yields. Both sets of yields for proton beams were lower than the corresponding ones for high-energy electrons and higher than those for 21 MeV 4He ions. The predicted hydroxyl radical yields for proton beams increase with increasing scavenging capacity and approach the value found for high-energy electron radiolysis. The sum of the eaq- and H atom yields is about 1.8 molecules/100 eV and nearly independent of the scavenging capacity for OH radical. Intratrack reactions were simulated using a deterministic diffusion kinetic model, and the results qualitatively predict the observed yields in the thiocyanate and the MV2+ solutions.