Theoretical and Electrochemical Analysis of Dissociative Electron Transfers Proceeding through Formation of Loose Radical Anion Species:  Reduction of Symmetrical and Unsymmetrical Disulfides

2002 ◽  
Vol 124 (25) ◽  
pp. 7529-7538 ◽  
Author(s):  
Sabrina Antonello ◽  
Rois Benassi ◽  
Giovanna Gavioli ◽  
Ferdinando Taddei ◽  
Flavio Maran
Keyword(s):  
Radical Anion ◽  
Electrochemical Analysis ◽  
Electron Transfers ◽  
Anion Species

Distonic radical anion species in cysteine oxidation processes

2020 ◽  
Vol 22 (31) ◽  
pp. 17554-17558
Author(s):  
Zhengbo Qin ◽  
Gao-Lei Hou ◽  
Zheng Yang ◽  
Marat Valiev ◽  
Xue-Bin Wang
Keyword(s):  
Radical Anion ◽  
Cysteine Oxidation ◽  
Homo Energy ◽  
Oxidation Processes ◽  
Oxidation Step ◽  
Anion Species

In contrast to the first reversible oxidation step being associated with sulfinate species, a novel distonic radical anion, •OS–CH2CH(NH2)–COO− has been identified with an inverted SOMO–HOMO energy order that can be restored via protonation.

scholarly journals Elektronentransfer und Kontaktionen-Bildung, 45 [1, 2] Strukturänderungen bei der Einelektronen-Reduktion von Tetraphenylbutatrien zum Radikalanion und bei der Zweifach-Deprotonierung von Tetraphenyl-butin-2 zum Tetraphenylbutatrien-Dianion / Electron Transfer and Contact Ion Pair Formation, 45 [1,2] Structural Changes on Single Electron Reduction of Tetraphenylbutatriene to its Radical Anion and on Twofold Deprotonation of Tetraphenylbutyne-2 to the Tetraphenylbutatriene Dianion

1996 ◽  
Vol 51 (10) ◽  
pp. 1381-1390 ◽  
Author(s):  
H. Bock ◽  
C. Arad ◽  
C. Näther ◽  
I. Göbel ◽  
A. John ◽  
...  
Keyword(s):  
Radical Anion ◽  
Structural Changes ◽  
Ion Pair ◽  
Single Electron ◽  
Single Crystal Structures ◽  
Contact Ion Pair ◽  
Dark Violet ◽  
Electron Reduction ◽  
Triple H ◽  
Electron Transfers

Tetraphenylbutatriene is reduced under aprotic conditions to its ESR/ENDOR-spectroscopically characterized radical anion and to its dianion, with both electron transfers quasireversible according to cyclovoltammetric measurements. The alkali cation salts, the red contact ion pair [(H5C6)4C4·⊖][Na⊕ (H3COCH2CH2OCH3)3] and the dark violet contact ion triple [(H5C6)4C4⊖⊖][Li⊕(H3COCH2CH2OCH3)3]2 can be prepared by single electron reduction at a sodium metal mirror or by twofold de-protonation of 1,1,4,4-tetraphenylbutyne-2 using lithium-n-butyl. Their single crystal structures as well as that of the parent acetylene have been determined at low temperatures. The essential structural changes observed are the twisting of both molecular halves (H5C6)2CC relative to each other with increasing negative charge. The simultaneously resulting bond alternancy >C = C = C = C< → >C⊖ - C ≡ C⊖ - C < within the cumulene chain is discussed based on MNDO calculations for the structures determined.

Photophysical and Electrochemical Properties of New Bacteriochlorins and Characterization of Radical Cation and Radical Anion Species

2002 ◽  
Vol 106 (20) ◽  
pp. 5105-5113 ◽  
Author(s):  
Shunichi Fukuzumi ◽  
Kei Ohkubo ◽  
Yihui Chen ◽  
Ravindra K. Pandey ◽  
Riqiang Zhan ◽  
...  
Keyword(s):  
Electrochemical Properties ◽  
Radical Cation ◽  
Radical Anion ◽  
Anion Species

Radical-mediated dehydration reactions in anaerobic bacteria

2005 ◽  
Vol 386 (10) ◽  
pp. 951-959 ◽  
Author(s):  
Wolfgang Buckel ◽  
Berta M. Martins ◽  
Albrecht Messerschmidt ◽  
Bernard T. Golding
Keyword(s):  
Radical Anion ◽  
Anaerobic Bacteria ◽  
Basic Amino Acid ◽  
Hydroxyl Group ◽  
Reductive Activation ◽  
Ketyl Radical ◽  
Dehydration Reactions ◽  
Amino Acid Side Chains ◽  
Acyl Coa Dehydrogenases ◽  
Electron Transfers

AbstractMost dehydratases catalyse the elimination of water from β-hydroxy ketones, β-hydroxy carboxylic acids or β-hydroxyacyl-CoA. The electron-withdrawing carbonyl functionalities acidify the α-hydrogens to enable their removal by basic amino acid side chains. Anaerobic bacteria, however, ferment amino acids via α- or γ-hydroxyacyl-CoA, dehydrations of which involve the abstraction of a β-hydrogen, which is ostensibly non-acidic (pKca. 40). Evidence is accumulating that β-hydrogens are acidified via transient conversion of the CoA derivatives to enoxy radicals by one-electron transfers, which decrease the pKto 14. The dehydrations of (R)-2-hydroxyacyl-CoA to (E)-2-enoyl-CoA are catalysed by heterodimeric [4Fe-4S]-containing dehydratases, which require reductive activation by an ATP-dependent one-electron transfer mediated by a homodimeric protein with a [4Fe-4S] cluster between the two subunits. The electron is further transferred to the substrate, yielding a ketyl radical anion, which expels the hydroxyl group and forms an enoxy radical. The dehydration of 4-hydroxybutyryl-CoA to crotonyl-CoA involves a similar mechanism, in which the ketyl radical anion is generated by one-electron oxidation. The structure of the FAD- and [4Fe-4S]-containing homotetrameric dehydratase is related to that of acyl-CoA dehydrogenases, suggesting a radical-based mechanism for both flavoproteins.

scholarly journals Protonated paramagnetic redox forms of di-o-quinone bridged with p-phenylene-extended TTF: A EPR spectroscopy study

2016 ◽  
Vol 12 ◽  
pp. 2450-2456 ◽  
Author(s):  
Nikolay O Chalkov ◽  
Vladimir K Cherkasov ◽  
Gleb A Abakumov ◽  
Andrey G Starikov ◽  
Viacheslav A Kuropatov
Keyword(s):  
Density Distribution ◽  
Spin Density ◽  
Epr Spectroscopy ◽  
Radical Anion ◽  
Copper Cation ◽  
Chemical Oxidation ◽  
Spin Density Distribution ◽  
Coordination Sites ◽  
Redox Forms ◽  
Anion Species

The chemical oxidation and reduction processes of deprotonated, direduced o-quinone-exTTF-o-quinone in protic solvents were studied by EPR spectroscopy. The formation of relatively stable paramagnetic protonated redox forms of the parent triad was very surprising. The character of spin-density distribution in the semiquinone–quinone and semiquinone–catechol redox forms indicates that the p-phenylene-extended tetrathiafulvalene connector provides a quite effective electronic communication channel between dioxolene coordination sites. It was found that the deprotonated, direduced o-quinone-exTTF-o-quinone is capable to reduction of the metal copper in solution. The radical anion species formed in this reaction exists in solution as a solvent-separated ion pair with a copper cation. A character of spin-density distribution in a radical anion species leads to the conclusion that the ligand corresponds to type III of the Robin–Day classification.

Planar defects in ordered (Ga,In)P

1988 ◽  
Vol 46 ◽  
pp. 902-903
Author(s):  
S. McKernan ◽  
C. B. Carter ◽  
D. Bour ◽  
J. R. Shealy
Keyword(s):  
Electron Diffraction ◽  
Vapor Phase ◽  
Growth Direction ◽  
High Density ◽  
Ordered Structure ◽  
Planar Defects ◽  
Diffraction Patterns ◽  
Ternary Semiconductors ◽  
Anion Species ◽  
Metallic Vapor

The growth of ternary III-V semiconductors by organo-metallic vapor phase epitaxy (OMVPE) is widely practiced. It has been generally assumed that the resulting structure is the same as that of the corresponding binary semiconductors, but with the two different cation or anion species randomly distributed on their appropriate sublattice sites. Recently several different ternary semiconductors including AlxGa1-xAs, Gaxln-1-xAs and Gaxln1-xP1-6 have been observed in ordered states. A common feature of these ordered compounds is that they contain a relatively high density of defects. This is evident in electron diffraction patterns from these materials where streaks, which are typically parallel to the growth direction, are associated with the extra reflections arising from the ordering. However, where the (Ga,ln)P epilayer is reasonably well ordered the streaking is extremely faint, and the intensity of the ordered spot at 1/2(111) is much greater than that at 1/2(111). In these cases it is possible to image relatively clearly many of the defects found in the ordered structure.

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