Long-range electron transfers between very slowly diffusing tetracyanoquinodimethane and its radical anion in poly(ether) solutions

1992 ◽  
Vol 96 (14) ◽  
pp. 5886-5893 ◽  
Author(s):  
T. T. Wooster ◽  
M. Watanabe ◽  
Royce W. Murray
Keyword(s):  
Long Range ◽  
Radical Anion ◽  
Electron Transfers

Proton-Regulated Electron Transfers from Tyrosine to Tryptophan in Proteins: Through-Bond Mechanism versus Long-Range Hopping Mechanism

2009 ◽  
Vol 113 (52) ◽  
pp. 16681-16688 ◽  
Author(s):  
Xiaohua Chen ◽  
Laibin Zhang ◽  
Liang Zhang ◽  
Jun Wang ◽  
Haiying Liu ◽  
...  
Keyword(s):  
Long Range ◽  
Hopping Mechanism ◽  
Electron Transfers ◽  
Bond Mechanism

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.

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.

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