Photoinduced formation of hydrogen peroxide in aqueous solutions of adenine derivatives at 77 K

The amount of hydrogen peroxide in aqueous solutions of adenine (A), adenosine (Ado), cytidine (Cyt), and thymine (T) containing 0.1 M NaCl and irradiated with near-UV light at 77 K is determined. It is established by comparing the results to data obtained earlier that the amount of H₂O₂ detected in the defrosted samples following identical irradiation falls in the order Ado > adenosine-5′-diphosphate (ADP) > A >> Cyt. The formation of H₂O₂ was not detected for T. The formation of H₂O₂ in solutions of adenine derivatives was observed when the samples were irradiated with light having wavelengths in the ranges λ = 240–400 nm and 290–450 nm. The latter covers only the long wave absorption range of these compounds. It is shown that the change in the intensity of irradiation that strongly affected the intensity оf EPR signals of irradiated samples prior to defrosting affected the amount of detected H₂O₂ only slightly, and the effect was not unidirectional. The results from determining H₂O₂ in the samples of adenine derivatives are compared to estimates of the content of free peroxyl radicals, obtained by analyzing EPR spectra. Plausible mechanisms of the processes are discussed.     

Effect of temperature on hydrogen peroxide photolysis in aqueous solutions

The photolysis of hydrogen peroxide in dilute aqueous solution (1 × 10⁻⁴ M) at various temperatures (15–85°C) and pH (ph 2.5–7) was studied by flash photolysis. The rate of oxygen production under continuous photolysis conditions was measured at room temperature. The rate constants and activation parameters are reported. Evidence for the formation of complexes between hydrogen peroxide and intermediate radicals is presented. The liquid phase data are discussed and compared with those available for the gas phase.     

Effect of bicarbonate ions on photodecomposition of sodium dodecyl sulfate in aqueous solutions containing hydrogen peroxide

Effect exerted by bicarbonate ions on decomposition of sodium dodecyl sulfate in the presence of hydrogen peroxide under the action of UV light was studied.     

Interaction of positronium with Co2+ and Cu2+ ions in aqueous solutions

Interactions of positronium in aqueous solutions of Co²⁺ and Cu²⁺ ions have been investigated at room temperature (297 K) at varying concentrations using both lifetime and Doppler broadening of annihilation radiation techniques. In the case of Co²⁺, the results indicate spin conversion reaction alone. However, in the case of Cu²⁺, oxidation is predominant with a small contribution of spin conversion reaction. The corresponding rate constants have been evaluated.     

Sorption of Na+, Ca2+ ions from aqueous solution onto unbleached kraft fibers-kinetics and equilibrium studies

The sorption of Na+ and Ca2+ from aqueous solutions onto unbleached kraft fiber was investigated. The sorption kinetics was found to be highly dependent on pH, initial concentration, and temperature. The sorption rate increased as the initial concentration and pH were increased. Thermodynamic and kinetic results indicated that the sorption of Na+ and Ca2+ onto kraft fiber was exothermic, reversible, and spontaneous with activation energies of 11.0 and 23.3 kJ/mol, respectively. The sorption kinetics followed a pseudo-second-order model and the equilibrium data followed the Langmuir isotherms. The fiber sorption capacities calculated from the Langmuir isotherms were similar to the fiber charges determined by potentiometric titration at pH > 7.     

Decomposition of hydrogen peroxide in aqueous solutions at elevated temperatures

Decomposition of hydrogen peroxide in high-purity water has been measured at temperatures ranging 100 to 280°C in a laboratory test loop. A first-order decomposition kinetics has been observed in all cases, but the decomposition rates were found to vary widely, depending on the material used in the reaction chamber. In a 4 mm ID stainless steel tubing, the decomposition rate constant is determined to be k = 2 × 10⁵ exp(?14800/RT). This decomposition rate is approximately 100 times faster than that observed in a Teflon tubing. The variation of decomposition rate in different reaction chambers is attributed to the heterogeneous catalytic effects. There is no evidence of reaction between H₂ and H₂O₂ in the highpurity water at temperatures up to 280°C.     

Adsorption of the Cu<Superscript>2+</Superscript> ions from aqueous solutions on the active carbon oxidized with hydrogen peroxide and impregnated with nitrogen-containing compounds

Adsorption of the copper ions from aqueous solutions, benzene, and water on the active carbon obtained by chemical activation from walnut shells was studied. The active carbon was additionally oxidized with hydrogen peroxide and then impregnated with nitrogen-containing compounds. As a result of impregnation with melamine, a secondary porosity is formed within the oxidized active carbon, leading to an increase in the specific surface of the sorbent. A modified carbon surface is heterogeneous, and the carbons themselves exhibit catalytic activity in the oxidation of luminol and decomposition of hydrogen peroxide.     

Kinetics of Ca2+ complexation with some carbohydrates in aqueous solutions

For solutions of four saccharides in water with alkaline-earth chlorides added ultrasonic attenuation spectra between 100 kHz and 2 GHz are reported and compared to those for carbohydrate solutions without salt. Calcium chloride does not alter the relaxation times in the spectra of D-glucose and D+-maltose solutions, reflecting the exocyclic hydroxymethyl group rotation, a saccharide-saccharide association, and, with the disaccharide, also motions of both rings of a molecule relative to one another. The spectra of D-xylose and D-fructose solutions are substantially changed by the salts. With both saccharides an additional term with relaxation time around some nanoseconds exists which is assigned to a rearrangement of a carbohydrate-cation complex. Other relaxation terms of these saccharide solutions are also subject to noticeable changes by the salt, indicating specific carbohydrate-cation interactions. The ultrasonic spectra show that such interactions may exist also with carbohydrates which do not display the particular hydroxyl group sequences that are considered to promote complexation with cations.     

Kinetics and mechanism of the reactions of uracil with hydrogen peroxide in aqueous solutions

The kinetics of the reactions of 5-hydroxy-6-methyluracil and 6-methyluracil with hydrogen peroxide in aqueous solutions has been investigated. The reactions proceed via two competitive mechanisms, namely, free-radical and nonradical ones. The iron ions present in water as impurities make possible the free-radical mechanism.     

Uptake of methacrolein into aqueous solutions of sulfuric acid and hydrogen peroxide

Multiphase acid-catalyzed oxidation by hydrogen peroxide has been suggested to be a potential route to secondary organic aerosol (SOA) formation from isoprene and its gas-phase oxidation products, but the kinetics and chemical mechanism remain largely uncertain. Here we report the first measurement of uptake of methacrolein into aqueous solutions of sulfuric acid and hydrogen peroxide in the temperature range of 253-293 K. The steady-state uptake coefficients were acquired and increased quickly with increasing sulfuric acid concentration and decreasing temperature. Propyne, acetone, and 2,3-dihydroxymethacrylic acid were suggested as the products. The chemical mechanism is proposed to be the oxidation of carbonyl group and C═C double bonds by peroxide hydrogen in acidic environment, which could explain the large content of polyhydroxyl compounds in atmospheric fine particles. These results indicate that multiphase acid-catalyzed oxidation of methacrolein by hydrogen peroxide can contribute to SOA mass in the atmosphere, especially in the upper troposphere.     

The determination of hydrogen peroxide in aqueous solutions by square wave voltammetry

Hydrogen peroxide in aqueous solutions can be determined directly by square wave voltammetry. The method is applicable to samples with a large range of pH in matrices ranging from distilled de-ionized water to sea-water. Its dynamic range extends from 0.5 to at least 1000 microM and the precision is about +/-6% at 2.5 microM and +/-2% at 215 microM. In comparison to DC and differential pulse polarography, by using square wave voltammetry the scan time is reduced from minutes to a fraction of a second, the sensitivity is increased by several-fold and the dynamic range has been greatly expanded at both the lower and the upper end by at least an order of magnitude. The low detection limit allows this method to be applied to the determination of H(2)O(2) in some samples of rainwater.     

Removal of Pb2+ and Cd2+ ions from aqueous solutions using guanidine modified hydrogels

In this study, experimental measurements have been made on the batch adsorption of cadmium and lead ions from aqueous solutions using poly(guanidine modified 2‐acrylamido‐2‐methylpropan sulfonic acid/acrylic acid/N‐vinylpyrrolidone/2‐Hydroxyethyl methacrylate), P(AMPSG/AAc/NVP/HEMA) hydrogels. The guanidyl end group bearing AMPSG monomer was synthesized from the reaction of AMPS and guanidine. The hydrogels were prepared by UV‐curing technique. The morphology of the dry H10‐hydrogel sample was examined by SEM. The influence of the uptake conditions, such as pH, functional monomer per cent, contact time, initial feed concentration, and foreign metal ions on the metal ion binding capacity of hydrogel, was also tested. The selectivity of the hydrogel toward the different metal ions tested was Hg(II) > Pb(II) > Au(III) > Cd(II). The adsorption isotherm models were applied to the experimental data, and it was seen that the Langmuir isotherm model was the best fit for the adsorption of Cd(II) and Pb(II) ions on P(AMPSG/AAc/NVP/HEMA) hydrogel. It was found that adsorbed lead and cadmium ions on P(AMPSG/AAc/NVP/HEMA) hydrogel can be effectively desorbed by acid leaching and the regenerated P(AMPSG/AAc/NVP/HEMA) hydrogel can be reused almost five times less without any loss of adsorption capacity. Copyright © 2009 John Wiley & Sons, Ltd.