Interquinone Electron Transfer in Photosystem I As Evidenced by Altering the Hydrogen Bond Strength to the Phylloquinone(s)

2010 ◽  
Vol 114 (28) ◽  
pp. 9300-9312 ◽  
Author(s):  
Stefano Santabarbara ◽  
Kiera Reifschneider ◽  
Audrius Jasaitis ◽  
Feifei Gu ◽  
Giancarlo Agostini ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Electron Transfer ◽  
Bond Strength ◽  
Photosystem I ◽  
Hydrogen Bond Strength

A molecular mediator for reductive concerted proton-electron transfers via electrocatalysis

Science ◽  
2020 ◽  
Vol 369 (6505) ◽  
pp. 850-854 ◽  
Author(s):  
Matthew J. Chalkley ◽  
Pablo Garrido-Barros ◽  
Jonas C. Peters
Keyword(s):  
Hydrogen Bond ◽  
Electron Transfer ◽  
Bond Strength ◽  
Hydrogen Evolution ◽  
Redox Mediator ◽  
Cathodic Reduction ◽  
Hydrogen Bond Strength ◽  
Brönsted Acid ◽  
Nitrogen Hydrogen Bond ◽  
Electron Transfers

Electrocatalytic approaches to the activation of unsaturated substrates via reductive concerted proton-electron transfer (CPET) must overcome competing, often kinetically dominant hydrogen evolution. We introduce the design of a molecular mediator for electrochemically triggered reductive CPET through the synthetic integration of a Brønsted acid and a redox mediator. Cathodic reduction at the cobaltocenium redox mediator substantially weakens the homolytic nitrogen-hydrogen bond strength of a Brønsted acidic anilinium tethered to one of the cyclopentadienyl rings. The electrochemically generated molecular mediator is demonstrated to transform a model substrate, acetophenone, to its corresponding neutral α-radical via a rate-determining CPET.

Redshift or Adduct Stabilization—A Computational Study of Hydrogen Bonding in Adducts of Protonated Carboxylic Acids

2009 ◽  
Vol 15 (2) ◽  
pp. 239-248 ◽  
Author(s):  
Solveig Gaarn Olesen ◽  
Steen Hammerum
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonds ◽  
Bond Strength ◽  
Bond Length ◽  
Carboxylic Acids ◽  
Computational Study ◽  
Proton Affinities ◽  
Oh Groups ◽  
Hydrogen Bond Strength ◽  
Length Changes

It is generally expected that the hydrogen bond strength in a D–H•••A adduct is predicted by the difference between the proton affinities (Δ PA) of D and A, measured by the adduct stabilization, and demonstrated by the infrared (IR) redshift of the D–H bond stretching vibrational frequency. These criteria do not always yield consistent predictions, as illustrated by the hydrogen bonds formed by the E and Z OH groups of protonated carboxylic acids. The Δ PA and the stabilization of a series of hydrogen bonded adducts indicate that the E OH group forms the stronger hydrogen bonds, whereas the bond length changes and the redshift favor the Z OH group, matching the results of NBO and AIM calculations. This reflects that the thermochemistry of adduct formation is not a good measure of the hydrogen bond strength in charged adducts, and that the ionic interactions in the E and Z adducts of protonated carboxylic acids are different. The OH bond length and IR redshift afford the better measure of hydrogen bond strength.

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