Air-Tight Three-Electrode Design of Coaxial Electrochemical-EPR Cell for Redox Studies at Low Temperatures

2001 ◽  
Vol 66 (1) ◽  
pp. 52-66 ◽  
Author(s):  
František Hartl ◽  
Ronald P. Groenestein ◽  
Taasje Mahabiersing
Keyword(s):  
Unpaired Electron ◽  
Low Temperatures ◽  
Radical Anion ◽  
Reference Electrode ◽  
Octahedral Complex ◽  
Electrode Design ◽  
Epr Spectrum ◽  
Weak Point ◽  
Electron Reduction ◽  
Elegant Solution

The weak point of the original Allendoerfer electrochemical-EPR cell has been the reference electrode, placed outside the space-limited electrolysis cavity or not used at all in experiments at low temperatures. We present here an elegant solution to this problem, based on a modified air-tight design of an Allendoerfer cell equipped with a silver-wire pseudoreference electrode. The cell performance is demonstrated on one-electron electrochemical oxidation of heterocyclic 3,6-diphenyl-1,2-dithiine and one-electron reduction of 6-methyl-6-phenylfulvene and the pseudo-octahedral complex fac-[Re(benzyl)(CO)3(dmb)] (dmb = 4,4'-dimethyl-2,2'-bipyridine). In the latter case, the EPR spectrum of the radical anion [Re(benzyl)(CO)3(dmb)]•- points to predominant localization of the unpaired electron on the dmb ligand, in agreement with UV-VIS and IR spectroelectrochemical data.

Erratum: EPR Spectrum of an Azulene Free‐Radical Anion

1962 ◽  
Vol 37 (7) ◽  
pp. 1571-1571 ◽  
Author(s):  
Harmon W. Brown ◽  
Robert C. Jones
Keyword(s):  
Free Radical ◽  
Radical Anion ◽  
Epr Spectrum ◽  
Free Radical Anion

E.S.R. studies of the oxidative coupling of some bisphenols

1975 ◽  
Vol 28 (2) ◽  
pp. 343 ◽  
Author(s):  
SM Colegate ◽  
FR Hewgill ◽  
GB Howie
Keyword(s):  
Carbon Monoxide ◽  
Alkaline Solution ◽  
Unpaired Electron ◽  
Oxidative Coupling ◽  
Radical Anion ◽  
Neutral Solution

E.s.r. spectroscopy and the identification of products show that oxidation of 3,5,3?,5?-tetra-t-butyl-4,4?-dihydroxybenzophenone in neutral solution gives 3,5,3?,5?-tetra-t-butyldipheno-4,4?-quinone. If oxygen is present 2,6-di-t-butyl-p-benzoquinone is also formed. The evolution of carbon monoxide suggests that bis-spirodienones are intermediate in the formation of these products. E.s.r. spectra of radicals produced by oxidation of 3,5,3?,5?-tetra-t-butylbiphenyl-4,4?- dio and 2,6-di-t-butylhydro-quinone have been re-examined. In alkaline solution 3,5,3?,5?-tetra-t-butyl-4,4?-dihydroxybenzo-phenone is oxidized to a radical anion in which the unpaired electron is delocalized over both rings. ��� Attempts to detect unsymmetrical bisaryloxy radicals were unsuccessful, 3?,5?-di-t-butyl-4,4?-dihydroxy-3,5-dimethoxybenzophenone forming only the radical derived from the syringoyl portion, and 2,4?- oxydiphenol ether forming only the 4?-oxy radical. Comparison with the observation of both radicals when a mixture of guaiacol and p- methoxyphenol was oxidized suggests that C-O-C coupling in 2,4?- oxydiphenol proceeds by direct radical pairing.

scholarly journals Electron Paramagnetic Evidence for the ·pf3 Radical Anion

2000 ◽  
Vol 2000 (7) ◽  
pp. 342-343 ◽  
Author(s):  
Martyn C.R. Symons
Keyword(s):  
Radical Anion ◽  
Hyperfine Coupling ◽  
Coupling Constants ◽  
Radical Anions ◽  
Epr Spectrum ◽  
Hyperfine Coupling Constants ◽  
Spectroscopic Evidence ◽  
The Third ◽  
Electron Paramagnetic

Although ·PF2 radicals have been extensively studied there does not seem to be any spectroscopic evidence for ·PF3-radical anions. Here it is proposed that an EPR spectrum previously assigned to ·PF2 radicals is almost certainly due to ·PF3-centres. The 31P and 19F hyperfine coupling constants for these radicals are expected to be very similar. However, the ·PF3-radicals should show an extra coupling to the third 19F nucleus. This is clearly present.

scholarly journals Biomimetic Ketone Reduction by Disulfide Radical Anion

Molecules ◽  
2021 ◽  
Vol 26 (18) ◽  
pp. 5429
Author(s):  
Sebastian Barata-Vallejo ◽  
Konrad Skotnicki ◽  
Carla Ferreri ◽  
Bronislaw Marciniak ◽  
Krzysztof Bobrowski ◽  
...  
Keyword(s):  
Radical Anion ◽  
Radical Mechanism ◽  
Cyclic Ketones ◽  
High Concentration ◽  
Radical Chain ◽  
Ketyl Radical ◽  
Electron Reduction ◽  
The One ◽  
Key Steps ◽  
Radical Chain Reaction

The conversion of ribonucleosides to 2′-deoxyribonucleosides is catalyzed by ribonucleoside reductase enzymes in nature. One of the key steps in this complex radical mechanism is the reduction of the 3′-ketodeoxynucleotide by a pair of cysteine residues, providing the electrons via a disulfide radical anion (RSSR•−) in the active site of the enzyme. In the present study, the bioinspired conversion of ketones to corresponding alcohols was achieved by the intermediacy of disulfide radical anion of cysteine (CysSSCys)•− in water. High concentration of cysteine and pH 10.6 are necessary for high-yielding reactions. The photoinitiated radical chain reaction includes the one-electron reduction of carbonyl moiety by disulfide radical anion, protonation of the resulting ketyl radical anion by water, and H-atom abstraction from CysSH. The (CysSSCys)•− transient species generated by ionizing radiation in aqueous solutions allowed the measurement of kinetic data with ketones by pulse radiolysis. By measuring the rate of the decay of (CysSSCys)•−at λmax = 420 nm at various concentrations of ketones, we found the rate constants of three cyclic ketones to be in the range of 104–105 M−1s−1 at ~22 °C.

Elektronentransfer und Ionenpaar-Bildung, 48 [1] Titrationen von Tetraphenyl-p-benzochinon mit Natrium- und Kaliummetall in aprotischen Lösungen / Electron Transfer and Ion Pair Formation, 48 [ 1 ] Titrations of Tetraphenyl-p-benzoquinone with Sodium and Potassium Metals in Aprotic Solutions

1996 ◽  
Vol 51 (9) ◽  
pp. 1222-1228 ◽  
Author(s):  
Hans Bock ◽  
Markus Kleine
Keyword(s):  
Electron Transfer ◽  
Radical Anion ◽  
Esr Spectra ◽  
Electron Transfer Reaction ◽  
Ion Pair ◽  
Pair Formation ◽  
Reaction Products ◽  
Ion Pair Formation ◽  
Electron Reduction ◽  
Sodium And Potassium

UV/VIS and ESR spectra of electron transfer reaction products in aprotic (cH⊕ < 0,1 ppm) solution can be measured in an especially designed and sealed glass apparatus and provide information on unknown facets of the microscopic pathway through the network of interdependent equilibria. For tetraphenyl-p-benzoquinone in tetrahydrofuran, single-electron reduction by a sodium metal mirror produces a red solution and, unexpectedly, after addition of 2.2.2. cryptand, contact with a potassium metal mirror generates a green (!) one. For both, ESR/ENDOR spectra prove the presence of tetraphenyl-p-benzoquinone radical anion. UV/VIS measurements provide the clue: In the equilibrium revealed by repetetive spectra recording, M·⊖solv + Me⊕solv ⇄ [M·⊖···Me⊖]solv, the radical anion is green (vm = 16900 cm-1) and the contact ion pair red (vm=18900 cm-1 ). On ion pair formation, therefore, the excitation energy of the radical anion increases by 0.25 eV.

The dynamic Jahn—Teller effect in octahedrally co-ordinated d 9 ions

1964 ◽  
Vol 281 (1386) ◽  
pp. 323-339 ◽  
Keyword(s):  
Low Temperatures ◽  
Octahedral Complex ◽  
Nuclear Motion ◽  
Relaxation Processes ◽  
Structure Parameters ◽  
Vibrational States ◽  
Jahn Teller ◽  
Electronic Motion ◽  
Jahn Teller Effect ◽  
High And Low Temperatures

The nature of the electronic-vibrational states of a d 9 ion in an octahedral complex is discussed in term s of an adiabatic model in which th e electronic motion follows the nuclear motion exactly. Expressions for the g-values and the hyperfine structure parameters of the e.s.r. spectrum at high and low temperatures are derived. Relaxation processes and other effects due to the complex being part of a crystal are discussed.

Correlation of the first reduction potential of selected radiosensitizers determined by cyclic voltammetry with theoretical calculations

2011 ◽  
Vol 76 (8) ◽  
pp. 937-946 ◽  
Author(s):  
Miroslav Gál ◽  
Viliam Kolivoška ◽  
Marta Ambrová ◽  
Ján Híveš ◽  
Romana Sokolová
Keyword(s):  
Experimental Study ◽  
Cyclic Voltammetry ◽  
Radical Anion ◽  
Reduction Potential ◽  
Theoretical Calculations ◽  
Dft Method ◽  
Basis Set ◽  
Radical Anions ◽  
Electron Affinities ◽  
Electron Reduction

Radiosensitizers are drugs that make cancer cells more sensitive to radiation therapy. The cytotoxic properties of such compounds are due to the fact that in the cell these compounds undergo one-electron reduction to generate radical anions. Therefore, their theoretical and/or experimental study is of high interest. To determine the correlation between reduction potential determined by cyclic voltammetry measurements and some physicochemical properties of selected radiosensitizers theoretical calculations of electron affinities based on the DFT method with B3LYP functional at the level of 6-311++G** basis set in vacuum were utilized. Very good correlation was found between electron affinities of radiosensitizers and their reduction potential and so called E71 potential that account for the energy necessary to transfer the first electron to an electroactive group at pH 7 in aqueous medium to form a radical anion.

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