Intramolecular electron transfer in bipyridinium disulfides

Area of Science:

• Electrochemistry
• Organic Chemistry
• Biochemistry

Background:

• Reductive cleavage of disulfide bonds is crucial in biological and chemical systems.
• Understanding the mechanism (stepwise vs. concerted electron transfer) and electron source (intermolecular vs. intramolecular) is key.

Purpose of the Study:

• To investigate the electrochemical reduction mechanisms of 4,4'-bipyridyl-3,3'-disulfide (1) and its di-N-methylated derivative (2(2+)).
• To elucidate the role of redox-active moieties in facilitating disulfide bond cleavage.

Main Methods:

• Cyclic voltammetry in acetonitrile.
• Density Functional Theory (DFT) computations.
• Simulation of electrochemical data.

Main Results:

• Compound 1 shows direct disulfide reduction with a large potential gap between the first and second electron transfers.
• Compound 2(2+) is reduced at the bipyridinium moiety at a less negative potential.
• The second reduction of the bipyridinium in 2(2+) triggers intramolecular electron transfer to cleave the disulfide bond.

Conclusions:

• The redox-active bipyridinium moiety in compound 2(2+) provides an efficient, low-energy pathway for disulfide bond reductive cleavage.
• This intramolecular mechanism circumvents the high negative potential required for direct disulfide reduction.
• The study clarifies distinct mechanisms for disulfide bond reduction based on molecular structure.