Radicals In Aqueous Solution Research Articles

ChemInform Abstract: The Reactions of HO2/O2‐ Radicals in Aqueous Solution

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ESR study of the dynamics of adsorbed nitroxide radicals on porous surfaces in the dehydration process

The dynamics of 3-carbamoyl-2,2,5,5-tetramethyl-3-pyrrolin-1-yloxy (Tempyo), 4-oxo-2,2,6,6-tetramethyl-1-piperin-yloxy (4-oxo-Tempo) and 4-acetamide-2,2,6,6-tetramethyl-1-piperidin-yloxy (4-acetamide-Tempo) nitroxide radicals in aqueous solutions adsorbed on hydrophilic and hydrophobic SiO 2, Al 2O 3 and NaY zeolites with respect to dehydration degree were studied by ESR spectroscopy. The viscosity and the correlation times for the rotational motion of the adsorbed radicals depend on the dehydration degree, the nature of the support surfaces and the characteristics of the spin probe molecules.

Structure and Magnetic Properties of Glycine Radical in Aqueous Solution at Different pH Values

A recently developed quantum mechanical approach devoted to the study of unstable species in solution was applied to the radicals resulting from the homolytic breaking of the Cα−Hα bond of glycine in aqueous solution at different pH values.The computational protocol includes density functional calculations, simulation of the solvent by a mixed discrete-continuum approach, and averaging of spectroscopic properties over the most important vibrational motions. In vacuo computations provide reliable results for the zwitterionic form when using hybrid Hartree−Fock/density-functional methods with purposely tailored basis sets. Under the same conditions, disappointing results are obtained for the magnetic properties of neutral and, especially, anionic forms. Although the modifications of the structure and the magnetic properties of these species induced by the solvent are well reproduced by either a continuum model or a supermolecule approach, quantitative results can be obtained only by a mixed discrete-continu...

ChemInform Abstract: Kinetic Studies of Organic Peroxyl Radicals in Aqueous Solutions and Mixed Solvents

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Ab initio study of ionic solutions by a polarizable continuum dielectric model

A new implementation of a recently developed formalism to describe chemical systems in ionic solutions is presented. It allows ab initio calculations at the Hartree–Fock and density functional levels on closed and open shell systems, taking into account the ionic atmosphere effects at not too large concentrations. Test calculations on simple systems are compared to experimental data and to values obtained by numerical integration of the Poisson–Boltzmann equation. A more complex system, namely the glycine radical in aqueous solution, is also analyzed.

Formation and reactivity of carboxyphenyl radicals in aqueous solution

Carboxyphenyl radicals were generated in aqueous solutions by reacting the solvated electron with ortho-, meta- and para-chlorobenzoate. These radicals were found to add to chlorobenzoates and abstract hydrogen atoms from a H-atom donor. It was concluded that the rate constants for the addition of carboxyphenyl radicals to chlorobenzoate depend on steric hindrance, since ortho-carboxyphenyl radical adds to 2-chlorobenzoate [ k add=(1.0±0.2)×10 6 dm 3 mol −1 s −1] an order of magnitude slower than para-carboxyphenyl radical to 4-chlorobenzoate [ k add=(1.0±0.2)×10 7 dm 3 mol −1 s −1]. The products of these addition reactions were detected by GC-MS. All three carboxyphenyl radical isomers abstract a H-atom from 4-methoxybenzen thiol at the same rate [ k H-aps∼1×10 9 dm 3 mol −1 s −1], i.e. the position of the carboxylate group seems not to influence the rate of the H-abstraction reaction.

The equilibrium between the oxidation of hydrogen peroxide by oxygen and the dismutation of peroxyl or superoxide radicals in aqueous solutions in contact with oxygen

The equilibrium O2 + HO2− + OH− = 2O2− + H2O, which plays an important role in the chemistry of H2O2 in aqueous media, including H2O2 bleaching of wood pulps and other materials, has been overlooked in the literature. Usually only the backward reaction is considered. We have calculated the equilibrium constant of this reaction from literature data on reversible electrochemical cell measurements without a liquid junction. Re-analysis of these data reveals the reason for a long-standing discrepancy between experiments and predictions based on thermal and equilibria data of the National Bureau of Standards: since HO2− is in equilibrium with O2−, the actual HO2− concentration is less than that assumed. We find that the standard redox potential of the oxygen/superoxide couple is −0.137 V, different from the widely quoted literature value of −0.33 V in irradiated solutions. Re-evaluation of pulse radiolysis equilibria on duroquinone-superoxide yields a redox potential for the O2(g)/O2(aq)− couple of ca. −0.13 V. The standard Gibbs energy of formation of the superoxide radical is found to be 13.18 kJ mol−1 (3.15 kcal mol−1) and that of the peroxyl radical −14.69 kJ mol−1 (−3.51 kcal mol−1).

Investigation of the NH2 radical in aqueous solution up to 200°C by pulse radiolysis

The absorption spectrum of ˙NH2 has been measured in aqueous solutions of ammonia at pH 10.3 and ambient temperature. It exhibits two bands with λmax at 530 nm, e530 = 8.6 ± 0.1 mol−1, and ca. 230 nm, e230 = 23.2 ± 1.2 mol−1. ˙NH2 is produced in the reaction ˙OH + NH3(aq) → ˙NH2 + H2O with k = (8.0 ± 1.3) × 107 d mol−1 s−1 at 25 °C and Eact = 11.4 ± 0.5 kJ mol−1. The self-reaction of ˙NH2 occurs with 2k = (3.6 ± 0.6) × 109 d mol−1 s−1 at 25 °C and Eact = 11.6 ± 0.5 kJ mol−1. This temperature dependence indicates that the reaction rate is influenced by the rate of diffusion, and the relatively low value of 2k (25 °C) is rationalised by including a spin statistical factor of 0.25 in the expression for the rate constant. The reaction ˙NH2 + N2H4 has k = (1.18 ± 0.03) × 107 d mol−1 s−1 at 18.5 °C and Eact = 8.2 ± 0.7 kJ mol−1. Some implications of these data for the coolant chemistry of water-cooled nuclear power reactors are noted.

Intrinsic and Environmental Effects in the Structure and Magnetic Properties of Glycine Radical in Aqueous Solution

The electron spin resonance (ESR) spectrum of the radicals derived from glycine in aqueous solution has not been reproduced satisfactorily until now, even by refined quantum mechanical approaches. ...

Free Radical Reactions in Aqueous Solutions: Examples from Advanced Oxidation Processes for Wastewater from the Chemistry in Airborne Water Droplets

Inorganic chemistry involving free radicals in aqueous solutions can be important in environmental processes. A common free radical reaction in aqueous solution is electron transfer, especially to the hydroxyl radical and to ozone. Hydrogen peroxide and free radicals related to it act as weak acids, so both their neutral and deprotonated forms must be considered in reactions. In Advanced Oxidation Processes, the hydroxyl radical concentration in water is greatly increased by reactions involving ozone and/or ultraviolet light. Irradiation of solid titanium dioxide can also be used to generate the radicals. The hydroxyl radicals are used in the Processes to initiate the oxidation of dissolved organic pollutants. Free radical reactions also play an important role in the chemistry of water droplets suspended in air in clouds and fogs. The radicals arise indirectly from the photoionization of dissolved organic compounds such as aldehydes and from the iron-catalyzed decomposition of dissolved hydrogen peroxide. They oxidize dissolved sulfur dioxide and certain organic compounds.

The fate of peroxyl radicals in aqueous solution

The reactions of peroxyl radicals occupy a central role in oxidative degradation. Under the term Advanced Oxidation Processes in drinking-water and wastewater processing, procedures are summarized that are based on the formation and high reactivity of the OH radical. These react with organic matter (DOC). With O2, the resulting carbon-centered radicals O2 give rise to the corresponding peroxyl radicals. This reaction is irreversible in most cases. An exception is hydroxycyclohexadienyl radicals which are formed from aromatic compounds, where reversibility is observed even at room temperature. Peroxyl radicals with strongly electron-donating substituents eliminate O2.−, those with an OH-group in a-position HO2.. Otherwise organic peroxyl radicals decay bimolecularly. The tetroxides formed in the first step are very short-lived intermediates and decay by various pathways, leading to molecular products (alcohols, ketones, esters and acids, depending on the precursor), or to oxyl radicals, which either fragment by scission of a neighbouring C-C bond or, when they carry an a-hydrogen, undergo a (water-assisted) 1,2-H-shift.

Pulse radiolysis study of one-electron reduction of safranine T

The one-electron reduction of safranine T by hydrated electrons and various reducing organic radicals in aqueous solution has been studied by the technique of nanosecond pulse radiolysis. The absorption spectrum of the transient semireduced safranine formed in these reactions exhibited λmax at 400 and 650 nm with molar absorption coefficient values of 6.88×103 and 9.9×103 d mol-1 cm-1 respectively and decayed obeying a second-order rate law with a bimolecular rate constant of 0.97×109 d mol-1 s-1 at neutral pH. It has two pKa values of 3.0 and 8.5. The rate constants for the formation of semireduced safranine species by the reactions of most of the reducing radicals with the dye were very high and nearly diffusion controlled. The one-electron reduction potential of safranine T was estimated to be -0.35±0.02 V vs. NHE at pH 5. Reaction of H atoms with SF+ at acidic pH was also studied. The results obtained have been discussed with respect to the possibilities of different modes of H-atom reactions with safranine T.

The fate of peroxyl radicals in aqueous solution

The reactions of peroxyl radicals occupy a central role in oxidative degradation. Under the tenn Advanced Oxidation Processes in drinking-water and wastewater processing, procedures are summarized that are based on the formation and high reactivity of the OH radical. These react with organic matter (DOC). With O2, the resulting carbon-centered radicals O2 give rise to the corresponding peroxyl radicals. This reaction is irreversible in most cases. An exception is hydroxycyclohexadienyl radicals which are formed from aromatic compounds, where reversibility is observed even at room temperature. Peroxyl radicals with strongly electron-donating substituents eliminate O2-, those with an OH-group in a-position HO2,. Otherwise organic peroxyl radicals decay bimolecularly. The tetroxides fonned in the first step are very short-lived intermediates and decay by various pathways, leading to molecular products (alcohols, ketones, esters and acids, depending on the precursor), or to oxyl radicals, which either fragment by scission of a neighbouring C-C bond or, when they carry an a-hydrogen, undergo a (water-assisted) 1,2-H-shift.

How Easily Oxidizable Is DNA? One-Electron Reduction Potentials of Adenosine and Guanosine Radicals in Aqueous Solution

How Easily Oxidizable Is DNA? One-Electron Reduction Potentials of Adenosine and Guanosine Radicals in Aqueous Solution

ChemInform Abstract: Rate Constants for Reactions of Aliphatic Carbon‐Centered Radicals in Aqueous Solution

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Guanidino compounds generate reactive oxygen species.

Methylguanidine, guanidinoacetic acid and guanidinosuccinic acid are endogenous substances in body tissues. Extremely high levels of these substances are known to be related to the pathogenesis of epilepsy and renal failure such as uremia. In this study it was demonstrated that methylguanidine, guanidinoacetic acid and guanidinosuccinic acid, and arginine generate hydroxyl radicals in aqueous solution. These findings suggest that a high level of guanidino compounds accumulating near or within cells such as neurons (in an epileptogenic focus) or nephrons (in uremic patients) may cause free radical damage leading to these clinical disorders. Arginine may have a similar role in the pathogenesis of hyperarginemia.

Rate Constants for Reactions of Aliphatic Carbon-Centered Radicals in Aqueous Solution

Absolute rate constants for reactions of aliphatic carbon-centered radicals in aqueous solutions have been compiled and evaluated from the literature. Rate constants are included for reactions of radicals with inorganic and organic compounds and for decay by radical–radical reactions. The radicals were generated by radiolysis, photolysis, or other techniques, and their rate constants were determined generally by kinetic spectrophotometry. The tables include data for over 2,500 reactions of 373 radicals from 740 literature references.

Reactivity of [Co III W12O40]5? with organic radicals in aqueous solution. Evidence for an electron transfer mechanism

The rate constants for reaction of the [12-tungstocobaltate(III)]5– ion [CoIIIW12O40]5– in aqueous solution with a large number of carbon-centered cyclic and acyclic radicals, among them radicals of the alkyl, α-hydroxyalkyl, α-alkoxyalkyl, α-amidoalkyl and benzyl type, have been measured by pulse radiolysis. Except for methyl and ethyl radical and α-carboxyalkyl radical anions, the radicals react with rates of the order (1–5)× 109 dm3 mol–1 s–1, which corresponds to or is close to diffusion control. From a comparison with oxidants that are able to react by ligand transfer, the oxidant [CoIIIW12O40]5– is concluded to react by electron transfer.

Fluoride Elimination upon Reaction of Pentafluoroaniline with H, and OH Radicals in Aqueous Solution

Reduction of pentafluoroaniline (PFA) leads to rapid fluoride elimination to form the aminotetrafluorophenyl radical. This radical undergoes rapid intramolecular electron transfer from the amino group to the phenyl radical site and protonates at the latter site to form the tetrafluoroaniline radical cation or its deprotonated form (pKa = 2.3). Oxidizing radicals such as and oxidize PFA to the pentafluoroaniline radical cation. The pKa = 1.9 of the pentafluoroaniline radical cation is 3.6 units lower than that expected from the substituent effects of fluorine atoms. Addition of OH to PFA is followed by rapid HF elimination to yield the aminotetrafluorophenoxyl radical. In acidic solution, however, the reaction of OH leads to formation of the pentafluoroaniline radical cation. Fluoride elimination upon reduction and upon OH addition to PFA was confirmed by determination of fluoride ion yield.

N-Hydroxypyridine-2(1H)-thione: Not a Selective Generator of Hydroxyl Radicals in Aqueous Solution

<i>N</i>-Hydroxypyridine-2(1<i>H</i>)-thione: Not a Selective Generator of Hydroxyl Radicals in Aqueous Solution