The Paramagnetism of the Semiquinone of Phenanthrenequinone-3-sulfonate

Michaelis, Leonor; Boeker, G. F.; Reber, R. K.

doi:10.1021/ja01268a058

Cited by 31 publications

(7 citation statements)

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“…Indeed, the early study reported an overall decrease in the magnetic susceptibility of a solution with concentration as a result of dimerization. 27 Overall, this suggests that reaction (2) is the predominant dimerization mechanism probed here: if dimers are formed via reaction (3), we might expect increased overall concentration to increase the dimer concentration and either to have little effect on radical concentration or, if reaction (2) also operates, to decrease radical concentration. The implication of the dimerization for our study is that the apparent comproportionation reaction (eq 1) equilibrium constanti.e., that determined by measuring the radical concentrationnow depends on the initial AQ 2− concentration.…”

Section: Resultsmentioning

confidence: 71%

“…21−26 This overall concentration effect on the maximal radical concentration of quinones was studied as early as the 1930s. 27 As the EPR spectra are consistent with a single EPRactive spin system, the dimer does not appear to be paramagnetici.e., it does not consist of two weakly coupled (but still paramagnetic) spin S = 1 / 2 AQ 3−• monomers. Thus, the orientation and distance between two AQ 3−• monomers must be such that a stronger coupling between the two unpaired electrons results, leading to a total spin of S = 0, i.e., a dimer that is EPR inactive.…”

Section: Resultsmentioning

confidence: 88%

“…This effect suggests that, besides the comproportionation reaction (eq ) proposed in previous work, , additional reaction equilibria exist, which result in lower AQ 3–• fractional concentrations at higher concentrations. The strongest candidates for this are the dimerization equilibria, which have been shown to be important in quinone-based systems. − This overall concentration effect on the maximal radical concentration of quinones was studied as early as the 1930s . As the EPR spectra are consistent with a single EPR-active spin system, the dimer does not appear to be paramagnetici.e., it does not consist of two weakly coupled (but still paramagnetic) spin S = 1 / 2 AQ 3–• monomers.…”

Section: Results and Discussionmentioning

confidence: 99%

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CoupledIn SituNMR and EPR Studies Reveal the Electron Transfer Rate and Electrolyte Decomposition in Redox Flow Batteries

et al. 2021

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We report the development of in situ (online) EPR and coupled EPR/NMR methods to study redox flow batteries, which are applied here to investigate the redox-active electrolyte, 2,6-dihydroxyanthraquinone (DHAQ). The radical anion, DHAQ 3−• , formed as a reaction intermediate during the reduction of DHAQ 2− , was detected and its concentration quantified during electrochemical cycling. The fraction of the radical anions was found to be concentration-dependent, the fraction decreasing as the total concentration of DHAQ increases, which we interpret in terms of a competing dimer formation mechanism. Coupling the two techniquesEPR and NMRenables the rate constant for the electron transfer between DHAQ 3−• and DHAQ 4− anions to be determined. We quantify the concentration changes of DHAQ during the "high-voltage" hold by NMR spectroscopy and correlate it quantitatively to the capacity fade of the battery. The decomposition products, 2,6-dihydroxyanthrone and 2,6-dihydroxyanthranol, were identified during this hold; they were shown to undergo subsequent irreversible electrochemical oxidation reaction at 0.7 V, so that they no longer participate in the subsequent electrochemistry of the battery when operated in the standard voltage window of the cell. The decomposition reaction rate was found to be concentration-dependent, with a faster rate being observed at higher concentrations. Taking advantage of the inherent flow properties of the system, this work demonstrates the possibility of multi-modal in situ (online) characterizations of redox flow batteries, the characterization techniques being applicable to a range of electrochemical flow systems.

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Section: Resultsmentioning

confidence: 71%

Section: Resultsmentioning

confidence: 88%

Section: Results and Discussionmentioning

confidence: 99%

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CoupledIn SituNMR and EPR Studies Reveal the Electron Transfer Rate and Electrolyte Decomposition in Redox Flow Batteries

et al. 2021

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“…This property appears to be common to all melanins regardless of source (531). Since paramagnetism arises in molecules containing unpaired electrok, it follows that these melanins are probably semiquinones (532) or related free radicals. A high order of free radical resonance energy is necessary to stabilize such substances.…”

Section: C I Ciimentioning

confidence: 99%

Comparative Biochemistry of the Phenolase Complex

1955

Advances in Enzymology - And Related Areas of Molecular Biology

158

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“…The transitory existence of semiquinone free radicals has been demonstrated magnetically by Michaelis [25], who studied the concentration of these substances as a function ·of time, and in some cases by a process that might be called "magnetic titration," that is, the change of susceptibility during the quantitative addition of an oxidizing or reducing agent. A typical example of a reaction that may be 1<60 studied in situ magnetically is the slow reduction of dichromate with glucose in dilute solution.…”

Section: Magnetic Measurements On Reacting Systemsmentioning

confidence: 99%

Applications of magnetochemistry to polymers and polymerization

Selwood¹

1948

J. RES. NATL. BUR. STAN.

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After a brief review of fundamental definitionE, experimental methods, theoretical and semiempirical res ults on diamagnetic s ubstances, two topics are considen~d: First, st udies of the diamagnetic anisotropy of crystalline and oriented materials. Using solid naphthalene as an illustration , it is shown how to obtain the principal molecular s usceptib ilities from the meas urcd parameters of the si ngle crystal and t he molec ular orientat ions in the unit cell as derived from X-ray st udies. Conversely, the direction cosines for solid diphenyl a re calculated from the measured macroscop ic s usceptibilit ies and the s usceptibilities of the molecule. R es ults recently obtained on the anisotropy of eellulose, protcin fib ers, and stretched rubber indicate the value of s uch methods, part icularl y for ori ented polymcrs containing aromatic groups, because of the large eff ects of the latter. Next, attention is devoted to the paramagnetism of oxygen and free radicals t hat can be ut ilized as a meas ure of the concentration of t he species. Radical concentrations as low as 10-6 mole per liter may be estimated by m eans of a modification of the Gouy-balance. It has bccn employed in a s tudy of the t hermal polymerization of styrene at 66° C. From the changes in diam agnetism in the course of thc r eaction , thc rate of consumption of oxygen present is determincd. Assnming this to be du e to combination with styre ne rad icals, t he rate of thermal init iation is estimated to be 3.8 X 10_14 mol I liter sec-I. However, . in order to obtain by magnetic methods directly the free radical concent ration in ordinary chain polymerization processes, t he sensitivity would have to be improved by several orders of magnitude.

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The Paramagnetism of the Semiquinone of Phenanthrenequinone-3-sulfonate

Cited by 31 publications

References 0 publications

CoupledIn SituNMR and EPR Studies Reveal the Electron Transfer Rate and Electrolyte Decomposition in Redox Flow Batteries

CoupledIn SituNMR and EPR Studies Reveal the Electron Transfer Rate and Electrolyte Decomposition in Redox Flow Batteries

Comparative Biochemistry of the Phenolase Complex

Applications of magnetochemistry to polymers and polymerization

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