Time resolved electron spin resonance of spin correlated micelle confined radical pairs

Tarasov, V. F.; Forbes, Malcolm D. E.

doi:10.1016/s1386-1425(99)00236-x

Cited by 34 publications

(41 citation statements)

References 43 publications

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“…For the both SCRPs, the exchange is slow for the external components of the spectrum of the alkyl radicals (the corresponding differences in the resonance frequencies exceed the colli sion frequencies of the radicals) and fast for the cen tral part. 22 Since the photoreduction rate in the micellar phase is rather low (~10 7 s -1 for benzophenone), the contribution of the triplet polarization mechanism to the ESR spectra of these pairs is small. Therefore, the pairs have the distinctly pronounced APS (see Fig.…”

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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Effect of nitroxide radicals on chemically induced dynamic electron polarization of spin-correlated radical pairs in aqueous micellar solutions of sodium dodecyl sulfate

et al. 2008

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The multispin systems consisting of spin correlated radical pairs (SCRPs) and stable nitroxide radicals, localized in micelles of sodium dodecyl sulfate (SDS), were studied by ESR and pulse laser photolysis techniques. In all the systems studied, the stable nitroxide radicals exert no effect on the shape of the ESR spectra of the SCRPs (in particular, on the shape of their antiphase structure) and on the decay kinetics of the ESR signal of the SCRPs. In the SDS micelles, the electron spin polarization transfer from the nonequilibrium electron spin states of the molecular triplets (SCRP precursors) is the most efficient mechanism of generation of the electron spin polarization in nitroxide radicals. The experimental data also show that the nitroxide radicals and SCRP radicals are most probably distributed uniformly in the micellar phase.

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Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

Effect of nitroxide radicals on chemically induced dynamic electron polarization of spin-correlated radical pairs in aqueous micellar solutions of sodium dodecyl sulfate

et al. 2008

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“…However, as new experimental observations become available, it was gradually recognized that the CFN model fit experimental data only under certain conditions. For example, rather surprisingly, J eff was found to depend on temperature [81,82] and on the chemical structure [83] of the detergent making up the micelle. The model failed to explain the dependence of the width of the spectral lines on micelle's size [82,84,85] or on the length of the hydrocarbon tether [86] connecting two paramagnetic centers in biradicals.…”

Section: History the Closs-forbes-norris (Cfn) Modelmentioning

confidence: 99%

“…The first of these processes causes flip-flop electron spin transitions jαβ; χ〉 $jβα; χ〉 which leads to annealing of the populations of corresponding spin states. The second process provides so-called "dephasing," because it splits the rotation of transverse magnetization of the RP into two components [81] and prevents the generation of ST 0 RPM polarization in subsequent encounters. Figure 16 illustrates the decay of ST 0 RPM polarization due to enforced encounters.…”

Section: The Concept Of the Filled-out Micelle And Enforced Encountersmentioning

confidence: 99%

Investigation of Liquid‐Phase Inhomogeneity on the Nanometer Scale Using Spin‐Polarized Paramagnetic Probes

Tarasov¹,

Forbes²

2017

Properties and Uses of Microemulsions

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The concept, basic physics, and experimental details of time-resolved electron paramagnetic resonance (TREPR) spectroscopy for the study of spin-correlated radical pairs (SCRPs) in heterogeneous media are presented and discussed. The delicate interplay between electron spin wave function evolution (governed by magnetic interactions such as the isotropic electron spin-spin exchange interaction and the electron-nuclear hyperfine interaction) and diffusion (governed by the size and microviscosity of the medium) provides a mechanism for assessing molecular mobility in confined spaces on the nanoscale (e.g., micelles, vesicles, and microemulsions). Experimental examples from micellar SCRPs are used to highlight the dominant features of the TREPR under different degrees of confinement and microviscosity, and spectral simulation methods are described to show how molecular mobility can be quantified.

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“…Rate constants of quenching of the triplet state of 4,4´ dimethylbenzophenone with phenols 4 RC 6 H 4 OH (k q ), escape of phenols and phenoxyl radicals from micelles (k -and k e , respectively), and radical recombination in micelles (k r ) in the zero magnetic field and at B = 0.2 T, the quantum yields of radicals (ϕ R ), and the partition constants of phenols between the micellar and aqueous phases (P MW )* than the diffusion limit (typical collision frequencies for a pair of aromatic reactants in SDS micelles are ν d = (2-5)•10 7 s -1 ). 9,10, 21 The k q value somewhat decreases when electron withdrawing substituents (halogen atoms) are introduced into a phenol molecule but increases sub stantially with an increase in the atomic weight of a halo gen atom (see Table 1, transition from 4 chloro to 4 bromo and 4 iodophenols), indicating the appearance of a new channel of 3 DB quenching. [16][17][18] In an encoun ter complex of 3 DB and RC 6 H 4 OH containing a heavy atom, intersystem crossing is accelerated (external heavy atom effect) in addition to the chemical reaction.…”

Section: Quenching Of the Triplet State Of 44´ Dimethylbenzo Phenonementioning

confidence: 99%

Kinetics of fast reactions of triplet states and radicals under photolysis of 4,4′-dimethylbenzophenone in the presence of 4-halophenols in micellar solutions of sodium dodecyl sulfate in magnetic field

2005

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Quenching kinetics of the 4,4´ dimethylbenzophenone triplet state with para substituted phenol derivatives RC 6 H 4 OH (R = Н, F, Сl, Br, I) was studied by nanosecond laser photolysis in aqueous micellar solutions of sodium dodecyl sulfate. The kinetic data were processed in the framework of a model with the Poisson distribution of phenols between micelles. The partition constants of RC 6 H 4 OH between the aqueous and micellar phases and the rate constants of their escape from a micelle and quenching of the 4,4´ dimethylbenzophenone triplet state with phenols in micelles were obtained. The quenching proceeds with high rate constants through hydrogen atom transfer to form the ketyl and phenoxyl radicals (no radicals are formed in the case of 4 iodophenol), which then recombine in a micelle or escape into the outer aqueous volume. The application of an external magnetic field retards radical pair recombination in a micelle and increases the fraction of radicals escaped into the aqueous phase. The quantum yield of radical pairs decreases 2.5 fold, and the rate of their recombination in micelles in creases 2.5 fold on going from 4 chloro to 4 bromophenol. This is caused by the acceleration of triplet radical pair recombination in the solvent cage.Key words: 4,4´ dimethylbenzophenone, 4 halophenol, laser photolysis, triplet states, hydrogen atom transfer, radical recombination, heavy atom effect, magnetic effect.Researchers are interested in the kinetics of fast pho toinduced reactions in systems containing carbonyl and phenol compounds in micellar solutions due to pro nounced magnetic and spin effects for the recombination of triplet radical pairs (RPs) formed in these reactions. 1-15 Hydrophobic substituted phenols almost completely lo calized in the micellar phase were predominantly used in earlier studied systems. Neither the kinetics of primary processes of quenching of triplet states of carbonyl com pound with phenols and RP formation, nor the kinetic behavior of RPs at different phenol concentrations in micellar solutions were studied. Several kinetic regulari ties observed for RP recombination in micelles, in par ticular, internal heavy atom effect, assume that the corre sponding effect can appear during the primary step. 3,5-10 The effect of a heavy atom on the primary step of radical formation in carbonyl-phenol systems was repeatedly observed in homogeneous solutions. This effect depends on the parameters of the medium. 16-18 It is of interest to study the kinetics of all the processes of radical formation and recombination during photosensitized oxidation of phenols in micellar solutions. A study of the quenching kinetics of the triplet state of a photosensitizer localized in the micellar phase by molecules of hydrophilic phenols, which are distributed between the aqueous and micellar phases, also provides information on the partition con stants. 19 The kinetics of fast processes during photooxida tion of water soluble halosubstituted phenols is also worthy of attention because of the problem of industria...

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Time resolved electron spin resonance of spin correlated micelle confined radical pairs

Cited by 34 publications

References 43 publications

Effect of nitroxide radicals on chemically induced dynamic electron polarization of spin-correlated radical pairs in aqueous micellar solutions of sodium dodecyl sulfate

Effect of nitroxide radicals on chemically induced dynamic electron polarization of spin-correlated radical pairs in aqueous micellar solutions of sodium dodecyl sulfate

Investigation of Liquid‐Phase Inhomogeneity on the Nanometer Scale Using Spin‐Polarized Paramagnetic Probes

Kinetics of fast reactions of triplet states and radicals under photolysis of 4,4′-dimethylbenzophenone in the presence of 4-halophenols in micellar solutions of sodium dodecyl sulfate in magnetic field

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