Singlet Oxygen's Potential Role as a Nonoxidative Facilitator of Disulfide S –S Bond Rotation

A density functional theory study provides evidence that singlet oxygen binds to 1,2-dimethyldisulfane to form a peroxy intermediate. Mechanistic detail is provided for the singlet oxygen reaction, where a reduced energy for rotation about the S–S bond is found prior to departure of molecular oxygen. Notably, this disulfide O2-capture and release reaction is reminiscent of alkenes and polyenes that form peroxy intermediates, thereby facilitating their  cis-trans isomerizations. AbstractThe role of singlet oxygen potentially mediating increased conformational flexibility of a disulfide was investigated. Density functional theory (DFT) calculations indicate that the singlet oxygenation of 1,2-dimethyldisulfane produces a peroxy intermediate. This intermediate adopts a structure with a longer S –S bond distance and a more planar torsional angleθ (C –S–S–C) compared with the nonoxygenated 1,2-dimethyldisulfane. The lengthened S–S bond enables a facile rotation about the torsional angle in the semicircle region 0° <  θ <  210°, that is ~5 kcal mol−1 lower in energy than the disulfane. The peroxy intermediate bears nO → σS –S and nO → σ*S –S interactions that stabilize the S –O bond but destabilize the S–S bond, which contrasts with stabilizing nS → σ*S –S hyperconjugative effects in the disulfane S –S bond. Subsequent departure of O2 from the disulfane peroxy intermediate is reminiscent of peroxy intermediates ...

Source: Photochemistry and Photobiology - October 19, 2022 Category: Science Authors: Oliver Turque, Ryan M. O'Connor, Alexander Greer Tags: Special Issue Research Article Source Type: research