Intramolecular Electron Transfer in Bipyridinium Disulfides

Abstract

Reductive cleavage of disulfide bonds is an important step in many biological and chemical processes. Whether cleavage occurs stepwise or concertedly with electron transfer is of interest. Also of interest is whether the disulfide bond is reduced directly by intermolecular electron transfer from an external reducing agent or mediated intramolecularly by internal electron transfer from another redox-active moiety elsewhere within the molecule. The electrochemical reductions of 4,4'-bipyridyl-3,3'-disulfide (1) and the di-N-methylated derivative (2(2+)) have been studied in acetonitrile. Simulations of the cyclic voltammograms in combination with DFT (density functional theory) computations provide a consistent model of the reductive processes. Compound 1 undergoes reduction directly at the disulfide moiety with a substantially more negative potential for the first electron than for the second electron, resulting in an overall two-electron reduction and rapid cleavage of the S-S bond to form the dithiolate. In contrast, compound 2(2+) is reduced at less negative potential than 1 and at the dimethyl bipyridinium moiety rather than at the disulfide moiety. Most interesting, the second reduction of the bipyridinium moiety results in a fast and reversible intramolecular two-electron transfer to reduce the disulfide moiety and form the dithiolate. Thus, the redox-active bipyridinium moiety provides a low energy pathway for reductive cleavage of the S-S bond that avoids the highly negative potential for the first direct electron reduction. Following the intramolecular two-electron transfer and cleavage of the S-S bond the bipyridinium undergoes two additional reversible reductions at more negative potentials.

Sulfur‐Containing Molecules Grafted on Carbon Nanotubes as Highly Cyclable Cathodes for Lithium/Organic Batteries

“…The first reduction peak can be assigned to the one‐electron reduction of the disulfide bond to the radical anion. The second peak can be attributed to the reduction of the radical anion in a dianion by a second electron ,. This signal confirms both the grafting and the electrochemical activity of molecules on the nanotubes.…”

2,2′‐Bipyridine Equipped with a Disulfide/Dithiol Switch for Coupled Two‐Electron and Two‐Proton Transfer

“…Inspired by nature, organic molecules have been designed that make use of the dithiol/disulfide switch for multiple electron storage in material science. In that context, dithiins appear to be particularly promising, and their electrochemistry has been studied in detail; recently reported systems A – C relevant to the present work are shown in Figure . Questions of general interest address the sequence of events during disulfide reduction and how S−S bond breakage is correlated with electron injection and protonation, as well as the combination with potential internal electron transfer processes involving other reducible moieties such as the viologen part in C .…”

Geometrical and optical benchmarking of copper(II) guanidine–quinoline complexes: Insights from TD‐DFT and many‐body perturbation theory (part II)

“…This approach is used here in conjunction with Becke–Johnson damping that seems to provide a physically correct short‐range description of the electron correlation even with unmodified standard functionals . This model has recently been applied to various challenging problems such as electron transfer, agostic interactions, and transorganometallic species…”