Temperature and (polar) solvent effects on positronium reactions with nitroxyl free radicals

Abbé, J.Ch.; Duplâtre, G.; Haessler, A.; Netto, A. Marques; Veloso, Dorila Piló

doi:10.1021/j150654a027

Cited by 20 publications

(10 citation statements)

References 5 publications

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“…8 For example, a decrease in S is seen in the addition of nitroxyl free radicals to organic substances. 20 From the chemistry of Ps with free radicals, our correlation of the Ϫ⌬S and free radical intensity from the in situ PAS and ESR experiments is consistent. However, it must be emphasized that the ex situ PAS experiments were performed several days after the irradiation while the ex situ ESR spectra were recorded shortly (ϳ 10 min) after the irradiation.…”

supporting

confidence: 62%

Degradation of polymer coating systems studied by positron annihilation spectroscopy. II. Correlation with free radical formation

Cao

Zhang

et al. 1999

J. Polym. Sci. B Polym. Phys.

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supporting

confidence: 62%

Degradation of polymer coating systems studied by positron annihilation spectroscopy. II. Correlation with free radical formation

Cao

Zhang

et al. 1999

J. Polym. Sci. B Polym. Phys.

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“…The rate constant of HTMPO is somewhat higher in MeOH than in water. 15 Similar complicated and solute-dependent solvent dependences have been reported for the reactions of solvated electrons with organic and charged solutes in MeOH-water mixtures. [20][21][22] Solvent viscosity (η) and dielectric permittivity ( ) are the two most important physicochemical parameters affecting the rate of the reactions in solutions.…”

Section: Resultssupporting

confidence: 61%

“…Activation Entropies. The solvent composition dependence of the average activation entropy (∆S q ) of the o-Ps reaction with DMNA and HTMPO 15 are shown in Figure 9 together with the data for the reaction of e swith NO 2 B. 21 ∆S q for DMNA exhibits a maximum also at that particular solvent composition which corresponds to the most ordered structure.…”

Section: Resultsmentioning

confidence: 98%

“…For comparison, Δ H ⧧ values for the reactions of o -Ps with HTMPO and e s - with NO 2 B, activation energies of the solvent viscosity ( E η ) and of the self-diffusion ( E sd ) of MeOH molecules are also shown in Figure . (Δ H ⧧ for HTMPO and NO 2 B, E η , and E sd values were calculated from data in refs , , , and 29, respectively.)…”

Section: Resultsmentioning

confidence: 99%

“…[11][12][13][14] A special group of free radicals, the stable nitroxides, was thoroughly investigated by Abbe ´and co-workers. 15 These compounds play a significant role in the study of biological systems by electron spin resonance (ESR) spectroscopy, using the so-called spin-labeling technique. 16 A molecule originally not bearing any unpaired electron is considered to be spin labeled when a nitroxide bearing molecule is covalently attached to it.…”

Section: Introductionmentioning

confidence: 99%

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Temperature and Solvent Effects on the Reactions of o-Positronium with Nitroso Spin Traps in Methanol−Water Mixed Solvents

Levay

Boros

2004

J. Phys. Chem. A

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Positron annihilation lifetime spectroscopy (PALS) is used to study the reactions of the ortho-positronium (o-Ps) atom with the following nitroso spin traps: nitrosobenzene (NOB), N,N-dimethyl-4-nitroso-aniline (DMNA), and tert-nitroso-butane (t-NOBu). The reaction rate constants (k) are close to the range that corresponds to that of diffusion-controlled reactions and exhibit a similar trend to those reported in the literature for the analogous nitro compounds. The differences between the aromatic and aliphatic nitroso and nitro compounds and the observed substituent effect are in good correlation with the calculated LUMO energies of the molecules. The nucleophilic o-Ps attacks the molecules at their electron deficient aromatic ring. Solvent effects on the reaction rates in methanol-water solvent mixtures exhibit a complex and solute-dependent nature. The reactions are strongly affected by solvent viscosity; however, the expected 1/η versus k variation is valid only for limited ranges of solvent compositions. The dielectric permittivity effect on the reaction rate constants does not follow the expected trend; k values in water are significantly greater than in the less polar methanol. The average activation enthalpies (∆H q and entropies (∆S q ) evaluated for the reaction of o-Ps with DMNA exhibit maxima at a solvent composition which corresponds to the most rigid solvent structure, where the activation energies of the transport processes such as viscosity and self-diffusion have extremes too. The validity of the isokinetic relation between ∆H q and ∆S q shows that the mechanism of the reaction of o-Ps does not depend on the solvent composition. ∆H q exhibits an "Onsager reaction field" type ( -1)/( + 2) dependence on solvent permittivity. The results are compared to literature data for the reactions of o-Ps with stable nitroxide free radicals and reaction of solvated electron with nitrobenzene (NO 2 B) in methanol-water mixtures. The observed similarities and differences are discussed.

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Solvent and temperature effects on positronium annihilation parameters and on its quenching reactions with the free radical HTEMPO

1991

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Temperature and (polar) solvent effects on positronium reactions with nitroxyl free radicals

Cited by 20 publications

References 5 publications

Degradation of polymer coating systems studied by positron annihilation spectroscopy. II. Correlation with free radical formation

Degradation of polymer coating systems studied by positron annihilation spectroscopy. II. Correlation with free radical formation

Temperature and Solvent Effects on the Reactions of o-Positronium with Nitroso Spin Traps in Methanol−Water Mixed Solvents

Solvent and temperature effects on positronium annihilation parameters and on its quenching reactions with the free radical HTEMPO

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