Radiation Chemistry Of Aqueous Solutions Research Articles

The role of molecular oxygen in the formation of radiation-engineered multifunctional nanogels

Nanogels are very promising biomedical nanodevices. The classic “radiation chemistry-based” approach to synthetize nanogels consists in the irradiation with pulsed electron beams of dilute, N2O-saturated, aqueous solutions of water-soluble polymers of the “crosslinking type”. Nanogels with controlled size and properties are produced in a single irradiation step with no recourse to initiators, organic solvents and surfactants. This paper combines experimental syntheses, performed with two e-beam irradiation setups and dose-ranges, starting from poly(N-vinyl pyrrolidone) solutions of various concentrations, both in N2O-saturated and air-saturated initial conditions, with the numerical simulations of the radiation chemistry of aqueous solutions of a radical scavanger exposed to the same irradiation conditions used in the experiments. This approach provides a methodology to predict the impact of system and irradiation conditions on the water radiation chemistry, which in turn affect the nanogel features in terms of molecular and physico-chemical properties. In particular, the crucial role of initial and transient concentration of molecular oxygen is revealed. This work also proposes a very simple and effective methodology to quantitatively measure the double bonds formed in the systems from disporportionation and chain scission reactions, competing with inter-/intra-molecular crosslinking.

Building micro and nanosystems with electrochemical discharges

Since the discovery of the electrochemical discharge phenomenon by Fizeau and Foucault, several contributions have expanded the wide range of applications associated with this high current density electrochemical process. The complexity of the phenomenon, from the macroscopic to the microscopic scales, led since then to experimental and theoretical studies from different research fields. This contribution reviews the chemical and electrochemical perspectives where a mechanistic model based on results from radiation chemistry of aqueous solutions is proposed. In addition applications to micro-machining and fabrication of nanoparticles are discussed.

A brief account on radiation chemical studies of antioxidants : Examples from natural phenols, sulfur and selenium compounds

Reactive oxygen species (ROS) is a collective term used for a group of oxidants, which are either free radicals or molecular species capable of generating free radicals. Excessive production of ROS in living cells is a pathological condition known as oxidative stress. These species, depending on their reactivity and oxidizing ability, participate in a variety of chemical reactions and their reactions often cause irreversible chemical changes in biomolecules. Antioxidants are employed to protect the biomolecules from the damaging effects of such free radicals, primarily by their direct reaction. Although free radical reactions involving ROS with antioxidants are studied by several indirect methods, their direct monitoring is possible only by employing fast kinetic methods. Radiation chemistry of aqueous solutions and pulse radiolysis technique in particular has been found to be well suited to probe such reactions. Thus in this article, contributions from radiation chemistry section of BARC on the reactions of biologically important free radicals involved in oxidative stress with antioxidants have been discussed. Reactions of such radicals with curcumin, an antioxidant from turmeric, which was studied extensively in this laboratory using pulse radiolysis technique, has also been presented. In the last three decades, the section has contributed significantly to the understanding of sulfur and selenium based antioxidants. A few recent highlights on these systems using pulse radiolysis have also been compared.

Radiation chemistry of aqueous solutions of hydrazine Part 3. The chain reaction in oxygenated solutions irradiated with 60Co γ-rays

The radiation-induced decomposition by 60Co γ-rays of oxygen saturated aqueous solutions of hydrazine has been measured over the pH range 3.5 to 11.7. A reaction set has been devised which accounts for the experimental observations based on decomposition proceeding by a pH-dependent chain reaction propagated by hydrazil radicals (specifically N2H3) reacting with O2 and the resulting HO2/O2- radicals oxidising hydrazine (N2H5+/N2H4) to hydrazil radicals (N2H4+/N2H3). Chain termination is via the self-reactions of HO2-/O2-. The pH dependence of the chain length is consistent with (a) HO2/O2- having different reactivity towards N2H4/N2H5+ in the propagating step, and (b) the known pH dependence of the termination reaction. The values of the rate constants of the propagation reactions that simulate the experimental data quite well are (in units of d mol-1 s-1): k(HO2+N2H5+)=10; k(HO2+N2H4)=70; k(O2-+N2H5+)=100; k(O2-+N2H4)=2.2; each with an estimated uncertainty of ±10%. There is no evidence that N2H4+ is a chain carrier.

Radiation chemistry of aqueous solutions of hydrazine at elevated temperatures Part 2.—Solutions containing oxygen

The rate of reaction for has been measured by pulse radiolysis up to 110°C in aqueous solutions of hydrazine having a pH of 10.3 at room temperature. The values of the kinetic parameters are k 1 =(3.8±0.1)×10 8 dm3 mol -1 s -1 at 20°C and E act =5.6±2.1 kJ mol -1 . This small activation energy is interpreted in terms of the formation of an intermediate adduct N 2 H 3 O 2 which is in a pre-equilibrium with the reactants and whose stability with respect to dissociation back to the reactants decreases with increasing temperature. The rate of the thermal reaction has also been determined up to 110°C by measuring the decrease in k 1 with increasing age of the oxygenated hydrazine solution in order to monitor the depletion of [O 2 ]. The kinetic parameters are k 12 =(1.2±0.8)×10 -3 dm3 mol -1 s -1 at 20°C and E act =70±5 kJ mol -1 . γ-Radiolysis studies show that N 2 H 4 is destroyed in a short chain reaction in oxygenated hydrazine solutions with G(-N 2 H 4 )∝(dose rate) -0.5 , indicating chain termination by radical–radical reactions. Added EDTA shortens the chain but does not alter the form of the rate law, indicating that metal ions present as impurities accelerate the chain-propagating reactions more than the termination steps. In each case the chain length increases as ca. [N 2 H 4 ] 0.5 .

Radiation chemistry of aqueous solutions of hydrazine at elevated temperatures. Part 1.—Oxygen-free solutions

Rate constants for the reactions of eaq– and ˙OH with N2H4 and N2H5+ in liquid water up to 200 °C have been measured by pulse radiolysis. Linear Arrhenius plots for the reactions of eaq– gave k(20 °C)= 106 and 1.6 × 108 dm3 mol–1 s–1, and Ea= 13.5 and 18.2 kJ mol–1, respectively. H is the product of the reaction with N2H5+. Non-linear Arrhenius behaviour was observed for the reactions of ˙OH with k(20 °C)= 4.5 × 109 and 8.2 × 107 dm3 mol–1 s–1, respectively. The pKa of N2H5+ decreases linearly with temperature from 8.1 at 20 °C to 4.2 at 200 °C. The products of the ˙OH reactions are ˙N2H3 and ˙N2H4+, respectively, and the pKa of ˙N2H4+ also decreases with increasing temperature. The self-reaction of ˙N2H3 shows the same temperature dependence as that of ˙OH with k(20 °C)= 2 × 109 dm3 mol–1 s–1. The product of this reaction is tetrazene. Up to 200 °C the data are consistent with successive eliminations of NH3 to form triazene and then N2. The pH-dependent kinetics of these processes indicate that the decomposition of N3H3 is acid- and base-catalysed over the whole temperature range.

Free radical formation induced by ultrasound and its biological implications

The chemical effects of ultrasound in aqueous solutions are due to acoustic cavitation, which refers to the formation, growth, and collapse of small gas bubbles in liquids. The very high temperatures (several thousand K) and pressures (several hundred atmospheres) of collapsing gas bubbles lead to the thermal dissociation of water vapor into .OH radicals and .H atoms. Their formation has been confirmed by electron spin resonance (ESR) and spin trapping. The sonochemistry of aqueous solutions of gases and of volatile and nonvolatile solutes is reviewed. The similarities and differences between sonochemistry and radiation chemistry of aqueous solutions are explained. Some unusual characteristics of aqueous sonochemistry can be understood by considering the properties of supercritical water. By the use of rare gases with different thermal conductivities, it is possible to distinguish between temperature-dependent processes such as redox reactions initiated by .OH radicals and .H atoms and pressure-dependent processes which lead to polymer degradation and cell lysis. The evidence for free radical formation in aqueous solutions by pulsed ultrasound is discussed. This subject is of interest because it is related to the possible deleterious effects of ultrasonic diagnostic devices. The role of free radicals and of mechanical effects induced by ultrasound in DNA degradation, inactivation of enzymes, lipid peroxidation, and cell killing is reviewed.

Radiolysis of aqueous formaldehyde relevant to cometary environments

The radiation chemistry of aqueous solutions of formaldehyde was studied in order to obtain an insight into the possible role of ionizing radiation on cometary environments. Aqueous solutions of 1.0 mol dm −3 formaldehyde were exposed to γ-radiation in the dose rage from 0.01 to 1200 kGy at 298 K. The radiation chemical yield of decomposition of formaldehyde was determined to be: G(−CH 2(OH) 2) = 26.3±1.2. The high radiation chemical yield of decomposition was explained by a chain reaction initiated by the radical ·CH(OH) 2 with formaldehyde. Computer fitting of the experimental data gives k(·CH(OH) 2 + CH 2(OH) 2) = 8.0×10 1 dm 3 mol −1 s −1. In the computer treatment of experimental findings we used 54 equations to consider the radiolysis of water and 11 reactions for the radiolysis of aqueous formaldehyde. Based on previous estimates of the total dose of ionizing radiation that comets have accumulated over 4.6 billion years, we predict a radiation damage-depth curve of formaldehyde in comet nuclei.

The radiolysis of aqueous solutions containing dithiothreitol and oxidized dithiothreitol

The radiation chemistry of aqueous solutions (pH 1-9) of dithiothreitol (DTT) has been investigated by pulsed and steady-state techniques. From G( H 2 S) in N 2- and N 2O-saturated solutions it was concluded for pH 5–9 that the majority of the solvated electrons and 25–40% of the hydroxyl radicals reacted with DTT to form H 2S. Oxidized dithiothreitol (DTT- ox) was the other major product observed for pH 5–9. However, DTT- ox was not formed when DTT solutions were irradiated at pH 1 and 2. When nitrate ions were added as an electron scavenger over the pH range 5–9, G( DTT- ox) was not affected; at pH 9.0 G( H 2 S) decreased slightly but at pH 5–6, G( H 2 S) was reduced to that arising from the reaction of the hydroxyl radical. The reaction of CO 2 - with DTT- ox was studied at pH 4.6 and pH 9.0. At pH 9.0 the G( DTT)=3.3−0.2 indicated a simple two electron reduction of DTT- ox while at pH 4.6 the G( DTT) >25 implied a chain reaction had occurred.

Some aspects of radiation chemistry of aqueous solutions of neptunium and americium ions

This paper is a review of experimental results obtained by the authors while studying radiation chemistry of alkaline and acid aqueous solutions of neptunium and americium ions. The oxidation of hexavalent neptunium and americium in alkaline solutions up to heptavalent state by ions-radicals O - has been studied. The yields of the formation of neptunium(VII) from γ-radiolysis in the presence of N 2O, K 2S 2O 8, NaBrO have been determined and the mechanism of the process has been proposed. By the pulse radiolysis method with fast spectrophotometrical registration of short-lived species the rate constant of the oxidation of Np(VI) by ion-radical O - has been estimated. The review contains the data on radiolysis of perchloric acid solutions of NpO 2 + and Am 3+ in the presence of N 2O or XeO 3. The pulse radiolysis method has been used for the study of oxidation of Am 3+ up to Am(IV), the disproportionation of Am(IV) and the interaction of Am(IV) with H 2O 2 and HO 2. This mehtod has also been used to obtain ion Am 2+.

Radiation-chemical aspects of chemical evolution and radiation chemistry of simple cyano compounds

The role of ionizing radiation as one of energy sources for chemical evolution processes is examined. The discovery of fossile nuclear reactors in old uranium deposits of Oklo (Africa) suggest that natural nuclear reactors could have have been the sources of abundant, localized, radiation in the past of our planet. A brief survey of radiation chemistry of aqueous solutions of cyanides and simple nitriles is given. Some results obtained at BKI (Vinča) suggest that simple cyano compounds could have been an important raw material for primordial organic synthesis in aqueous medium and ionizing radiation as the source of energy. It has been concluded that the studies of chemical evolution can be a rewarding domain for radiation chemistry to transfer some of its achievements.

Radiation chemistry of aqueous solutions of dicyandiamide

Oxygen-free aqueous solutions of dicyandiamide, DCDA, were exposed to /sup 60/Co ..gamma.. rays or a pulsed 10-MeV electron beam. Fast kinetic spectrophotometry was used for the study of free-radical intermediates, and computer simulation of the reaction mechanism for evaluation of experimental data. The hydrated electron reacts by addition, k(e/sub aq//sup -/ + DCDA) = 1.1 x 10/sup 10/M/sup -1/s/sup -1/; the anion radical (NH/sub 2/C(=NH)NHCN)/sup -/ absorbs in the UV region with lambda/sub max/<255nm and an epsilon (255) of 1150 M/sup -1/cm/sup -1/. It disappears with 2k = 1 x 10/sup 9/M/sup -1/s/sup -1/ by forming a product which absorbs with lambda/sub max/<255nm and an epsilon (255) of 2400 M/sup -1/cm/sup -1/. The hydrogen atom also reacts by addition, k(H + DCDA) = 2.7 x 10/sup 6/ M/sup -1/s/sup -1/, and the radical intermediate has a lambda/sub max/ of 350nm and an epsilon (350) of 1250 M/sup -1/cm/sup -1/; it disappears with 2k greater than or equal to 10/sup 9/M/sup -1/s/sup -1/. Hydroxyl radicals react both by addition and by abstraction, k(OH + DCDA) = 5.6 x 10/sup 6/M/sup -1/s/sup -1/, and two transients with lambda/sub max/ at 450 and 355nm appear. It is estimated that about 90% of OHmore » radicals react by abstraction. It has also been found that the radical-anion SO/sub 4//sup -/ reacts efficiently with DCDA and the product of this reaction, NH/sub 2//sup +/C(=O)NHCN, absorbs light with a lambda/sub max/ of 355nm and epsilon (355) of 1150 M/sup -1/cm/sup -1/. The OH adduct of DCDA has a lambda/sub max/ of 450nm and epsilon (450) of 1700 M/sup -1/cm/sup -1/; it disappears by a second-order process with 2k less than or equal to 4 x 10/sup 9/M/sup -1/s/sup -1/. The search for stable radiolytic products in the kilorad-megarad dose range has shown the presence of only a few smaller molecules and in low yields.« less

The Radiation Chemistry of Aqueous Solutions of Cyanamide

Oxygen-free aqueous solutions of 0.1 M NH2CN (pH 2.4 and 5) were irradiated with y rays (0.01-25 Mrad). The rate constants determined in competition experiments are: k(H + NH2CN) = 6.7 X 106 M-1 sec-', k(eaq- + NH2CN) = 1.5 X 109 M-1 sec-1, and k(OH + NH2CN) = 8.5 X 106 M -sec-1. Radiation-chemical yields were determined for the decomposition of cyanamide molecules and the formation of several radiolytic products. The following compounds were identified in irradiated solutions: H2, CO2, NH3, urea, biuret, arginine, and a -N=N- molecule assigned to methylaminoazoformamide. Possible reactions of secondary free radicals leading to the formation of radiolytic products were considered by taking into account the model of water radiolysis and the measured radiation yields.

Radiation chemistry of aqueous solutions of sodium o-iodhippurate

This paper is an auto-review of experimental results obtained by the authros during the study of radiation chemistry of aqueous solutions of sodium o-iodhippurate. The products of α-radiolysis have been identified. Among them are iodide ion, o-hydroxyhippurate, hippurate, hydrogen peroxide, methylamide of o-iodbenzoic acid etc. Their radiation chemical yields and also the yield of the decomposition of o-iodhippurate under different conditions have been measured. The intermediate products of radiolytic transformations of o-iodhippurate have been detected by pulse-radiolysis method with optical registration of short-lived species. They are OH and H adducts to benzene ring, product of abstraction of iodine by e - aq and H, radical of phenoxyl type in acid medium and peroxide hydroxycylohexadienyl radical in the presence of oxygen. The rate constants of some reactions with their participation have been determined. On the basis of data obtained, the conclusions on the mechanism of radiolytic transformation of o-iodhippurate in aqueous solutions have been made.

The Radiation Chemistry of Aqueous Solutions of Ammonium and Sodium Cyanides in the Megarad Dose Range

to large doses of 60Co -y rays. Radiation-chemical yields were determined for the decomposition of cyanide molecules, as were the total amount of nitrogen in nonvolatile nitrogen-containing radiolytic products, the free ammonia, and the yields of several amino acids released on acid hydrolysis of irradiated samples. Positive biuret reaction was found and its intensity used for an estimation of amide bond yields. Up to 18% of the nitrogen from nonvolatile radiolytic products appears in the amide bond, and up to 14% appears in natural amino acids. The origin of peptidic material is attributed to the polymerization initiated by cyano radicals produced in reactions of cyanides with OH, H, and eaq- species from radiolyzed water.

Kinetics of the Decomposition of Hydrogen Peroxide in the Presence of Aqua‐Pentacyanoferrate (II)

AbstractThe decomposition of hydrogen peroxide has been studied in the presence of a large number of metal ions and their complexes1,2). Interest in radiation chemistry of aqueous solutions where hydrogen peroxide is one of the products and the use of acidic ferrous sulphate solutions as dosimeter in these studies has particularly stimulated the investigation on the kinetics of decomposition of hydrogen peroxide in the presence of Fe+2, Fe+3 and their complexes1,2). Ferrous sulphate solution can be used as a dosimeter under acidic conditions only, as at higher pH the hydrolysis of Fe+2 and Fe+3 interferes. Recent studies3‐6) have shown the possibility of using the aqueous solutions of ferro‐ and ferri‐cyanides over a range of pH as dosimeter. In the studies of ferrocyanide and ferricyanide catalysed decomposition of hydrogen peroxide7‐11), it is suggested that the catalytic properties of hexacyano ferrates are through their hydrated products. The present study aims at studying the interaction of aquapentacyanoferrate11) with hydrogen peroxide over a range of pH, concentration and temperature.

The Radiation Chemistry of Aqueous Solutions of Hydrogen Cyanide in the Megarad Dose Range

at their natural pH and at pH 2.4. The solutions were exposed to high doses of 6Co gamma rays (up to 16 Mrad) causing large decompositions (up to 90%). The decomposition yield, G(-HCN), and the radiation-chemical yields of formation of NH3, HCHO, H2, CO2, and of seven amino acids were determined. Also, the total yields of nitrogen in nitrogen-containing nonvolatile compounds, G(N), were measured. The irradiated solutions exhibited positive biuret reaction and the absorbancies depend on both the dose and the initial pH. Histidine, aspartic acid, threonine, serine, glutamic acid, alanine, and glycine were found in irradiated samples. Glycine was found to be the most abundant among the radiolytically produced amino acids; strong acid hydrolysis increases its yield by one or two orders of magnitude in samples irradiated initially at pH 2.4 as well as at their natural pH. The release of amino acids on hydrolysis and the positive biuret reaction suggest the presence of peptidic material in irradiated samples both at acid and neutral pH's. To account for these findings the formation of polymers (or their segments) having a peptidic structure was taken into consideration. The polymerization reactions were assumed to be initiated by the free radicals which were produced by HCN reactions with H, OH, and ej,- species. It has been concluded that the radiolysis of dilute aqueous

The Radiation Chemistry of Aqueous Solutions of Acetonitrile and Propionitrile in the Megarad Dose Range

A study was made of the radiolytic behavior of dilute, neutral, oxygen-free aqueous solutions of CH/sub 3/CN and C/sub 2/H/sub 5/CN. Small-molecular products were identified as RCHO, NH/sub 3/, CO/sub 2/, and H/sub 2/. The decomposition of nitrile is followed by high yields of formation of the nonvolatile nitrogen-containing compounds, G(N). The ..gamma..-irradiated solutions exhibit a positive biuret reaction. Several amino acids were identified among radiolytic products, and glycine and alanine were found to be the most abundant for CH/sub 3/CN and C/sub 2/H/sub 5/CH, respectively. Their yields increased after strong acid hydrolysis of the irradiated samples. The free radicals formed by reactions of RCN with H, OH, and e/sub aq/- were found to be important for the phenomena observed. It is suggested that the positive biuret reaction, ir spectra, and the release of amino acids on acid hydrolysis provide some evidence on the formation of peptidic materials and might be of interest for the evaluation of the role that ionizing radiation might have played in prebiotic chemical evolution in aqueous media.

Comments on "The aqueous photochemistry …", and "The radiation chemistry of aqueous solutions of sodium 9,10-anthraquinone-2-sulfonate"

Some of the mechanistic conclusions of the title articles are criticized because they are inconsistent with other results available to the present authors. Further, the mechanisms of the title articles would not operate in aerobic systems for which alone the present authors' mechanisms were designed.

Radiation Chemistry of Aqueous Solutions of Propane-Oxygen Mixtures

The aqueous solutions of propane-oxygen mixtures under pressure, on irradiation with 60Co r-rays, yielded hydrogen peroxide, organic hydroperoxides, acetone, propionaldehyde, 1-propanol, 2-propanol, and hydrogen. The G values of these radiation products were determined under various irradiation conditions.The formation of the oxygen-contained compounds was interpreted in terms of reactions of both hydroperoxy and organic peroxy radicals.The formation of hydrogen suggested that the hydrogen atoms might be capable of abstracting hydrogenfrom propane in competition with addition to oxygen.