Solvent Effects in the Electron Spin Resonance Spectra of Some Phenoxyl, Nitroxide, and Anilino Radicals

Mukai, Kazuo; Nishiguchi, Hiroaki; Ishizu, Kazuhiko; Deguchi, Yasuo; Takaki, Hideo

doi:10.1246/bcsj.40.2731

Cited by 52 publications

(7 citation statements)

References 22 publications

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“…Then, the ESR spectra were obtained in the presence of TTBP and 2,6-DTBO ( Figure 8 c,d). The observed spectra were assigned to their corresponding phenoxyl radicals (PhO • ) [ 29 , 30 ]. The hfccs were simulated from the measured spectra, which confirm the generation of a PhO • through the PCET involving one or two PTs and one ET between the compounds and O 2 •− .…”

Section: Resultsmentioning

confidence: 99%

Electrochemical and Mechanistic Study of Reactivities of α-, β-, γ-, and δ-Tocopherol toward Electrogenerated Superoxide in N,N-Dimethylformamide through Proton-Coupled Electron Transfer

et al. 2021

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Scavenging of superoxide radical anion (O2•−) by tocopherols (TOH) and related compounds was investigated on the basis of cyclic voltammetry and in situ electrolytic electron spin resonance spectrum in N,N-dimethylformamide (DMF) with the aid of density functional theory (DFT) calculations. Quasi-reversible dioxygen/O2•− redox was modified by the presence of TOH, suggesting that the electrogenerated O2•− was scavenged by α-, β-, γ-TOH through proton-coupled electron transfer (PCET), but not by δ-TOH. The reactivities of α-, β-, γ-, and δ-TOH toward O2•− characterized by the methyl group on the 6-chromanol ring was experimentally confirmed, where the methyl group promotes the PCET mechanism. Furthermore, comparative analyses using some related compounds suggested that the para-oxygen-atom in the 6-chromanol ring is required for a successful electron transfer (ET) to O2•− through the PCET. The electrochemical and DFT results in dehydrated DMF suggested that the PCET mechanism involves the preceding proton transfer (PT) forming a hydroperoxyl radical, followed by a PCET (intermolecular ET–PT). The O2•− scavenging by TOH proceeds efficiently along the PCET mechanism involving one ET and two PTs.

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Section: Resultsmentioning

confidence: 99%

Electrochemical and Mechanistic Study of Reactivities of α-, β-, γ-, and δ-Tocopherol toward Electrogenerated Superoxide in N,N-Dimethylformamide through Proton-Coupled Electron Transfer

et al. 2021

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“…It is well-known that A 0 for a nitroxide spin probe such as 5DSE varies systematically with the solvent polarity, [11][12][13] so the previous work 9,10 showed that as the micelle grew because of increasing [SDS], the polarity sensed by 5DSE decreased.…”

Section: Combining Eqs 1 and 2 Yieldsmentioning

confidence: 99%

Precision Relative Aggregation Number Determinations of SDS Micelles Using a Spin Probe. A Model of Micelle Surface Hydration

et al. 1998

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A spin-probe method is described that can detect changes in the relative aggregation numbers in SDS micelles with a precision of about one molecule. The method is based on the fact that the 14 N hyperfine coupling constant is sensitive to the average fraction of the volume occupied by water in the region of the nitroxide moiety that is located on average near the micelle surface. Defining A 0 (N A ) to be the 14 N hyperfine coupling constant at an aggregation number N A , we find A 0 (N A ) ) A 0 (0) + (∂A 0 /∂N A )N A , where N A is controlled by varying either the SDS or the NaCl concentrations. For the spin probe 5-doxylstearic acid ester(5DSE), by combination of the results of experiments in which the SDS and/or the NaCl concentrations were varied, linear least-squares fits gave A 0 (0) ) (15.498 ( 0.009) G and ∂A 0 /∂N A ) -3.99 ( 0.02 mG/molecule (constant). A 0 (N A ) depends only on the aggregation number despite the fact that a given value of N A may be prepared by choosing different combinations of NaCl and SDS concentrations. This means that, for a given micelle size, neither interactions between micelles nor the ionic strength of the solution influence the value of A 0 . A geometric model, based on a simple model in which a spherical hydrocarbon core is surrounded by a concentric spherical polar shell, is developed to predict the volume fraction of the polar shell occupied by water as a function of N A . This water fraction is written in terms of a hydration number per surfactant molecule, N(H 2 O). A 0 (N A ) is related to N(H 2 O) by employing the nonempirical polarity index introduced by Mukerjee et al. (Mukerjee, P.; Ramachandran, C.; Pyter, R. A. J. Phys. Chem. 1982, 86, 3189). The value of N(H 2 O) decreases as the micelle grows because the volume per surfactant molecule in the polar shell decreases. Once N(H 2 O) is specified at a particular value of N A , no further adjustable parameters enter into the model. The variation with micelle size of the theoretical polarity is in excellent agreement with experiment for values of N(H 2 O) that are comparable to those found from transport properties. The sphere-rod transition is observed as a rather sharp transition in which the detected water volume fraction becomes constant. Detailed future tests of the model are outlined.

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“…The spectrum for TI was broad probably due to the aggregation (association) of TI in the St medium, and that for BHT clearly split into four peaks (1:3:3:1 ratio: hypersplitting constant a H = 11.20 G) by the methyl group at the para position and further split into three peaks (1:2:1 ratio: a H = 1.67 G) by the protons at the meta positions. 17 The spectrum for CHD was somewhat noisy due to the lower concentration of A • than those for TI and BHT. The spectrum split into three peaks (1:2:1 ratio: a H = 42 G) because of the protons at the meta positions and further split into two peaks (1: 1 ratio: a H = 18 G) because of the proton at the central position.…”

Section: Introductionmentioning

confidence: 99%

Phenols and Carbon Compounds as Efficient Organic Catalysts for Reversible Chain Transfer Catalyzed Living Radical Polymerization (RTCP)

et al. 2010

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Simple phenols and hydrocarbons were used as novel and efficient organic catalysts for reversible chain transfer catalyzed living radical polymerization (RTCP). This is the first use of oxygen-and carbon-centered compounds as catalysts of living radical polymerization. The catalysts include such common compounds as phenol itself, phenol-based antioxidants for foods and resins (e.g., 3,5-di-tert-butyl-4hydroxytoluene (BHT)), phenol-based natural antioxidants (e.g., vitamin E), and dienes (e.g., 1,4-cyclohexadiene). Their cheapness, excellent environmental safety, and ease of handing may be quite attractive in practice. The catalysts were highly active and tolerant to functional groups. The required amounts of the catalysts were typically as small as 100-500 ppm, yielding low-polydispersity polymers (M w /M n ∼ 1.1-1.4) at moderate temperatures (40-100 °C), where M w and M n are weight-and number-average molecular weights, respectively. A wide variety of functional monomers with alkyl, aryl, hydroxyl, poly(ethylene glycol), alkylamino, amino, and carboxylic acid groups were adopted to the homo-and copolymerizations. Kinetic studies supported that, mechanistically, the polymerization is based on reversible chain transfer (RT) for these catalysts.

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Solvent Effects in the Electron Spin Resonance Spectra of Some Phenoxyl, Nitroxide, and Anilino Radicals

Cited by 52 publications

References 22 publications

Electrochemical and Mechanistic Study of Reactivities of α-, β-, γ-, and δ-Tocopherol toward Electrogenerated Superoxide in N,N-Dimethylformamide through Proton-Coupled Electron Transfer

Electrochemical and Mechanistic Study of Reactivities of α-, β-, γ-, and δ-Tocopherol toward Electrogenerated Superoxide in N,N-Dimethylformamide through Proton-Coupled Electron Transfer

Precision Relative Aggregation Number Determinations of SDS Micelles Using a Spin Probe. A Model of Micelle Surface Hydration

Phenols and Carbon Compounds as Efficient Organic Catalysts for Reversible Chain Transfer Catalyzed Living Radical Polymerization (RTCP)

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