Putting the Disulfide Bridge at Risk: How UV‐C Radiation Leads to Ultrafast Rupture of the S‐S Bond

Abstract

We investigate the ultrafast photoinduced dynamics of the cyclic disulfide 1,2-dithiane upon 200 nm excitation by time-resolved photoelectron spectroscopy and show that the S-S bond breaks on an ultrafast time scale. This stands in stark contrast to excitation at longer wavelengths where the initially excited S state evolves as the wavepacket is guided towards a conical intersection with S by a torsional motion involving a partially broken bond between the sulfur atoms. This process at lower excitation energy allows for efficient (re-)population of S , rendering dithiane intact. At 200 nm, in contrast, the excitation leads to a manifold of higher excited states, S , that are primarily of Rydberg character. We are able to follow the gradual transition from the initially excited state to the dissociative receiver state in real time. The Rydberg states are intersected by a repulsive valence state that mediates a transition to the repulsive S surface. Therefore, we propose that the resulting diradical will eventually break apart on a longer timescale. The findings imply that upon going from UV-B to UV-C light the structural integrity of the disulfide moiety is compromised and proteins irradiated in this range will not be able to reform the initial tertiary structure, leading to loss of function.

Nonstatistical Photoinduced Processes in Gaseous Organic Molecules

“…It is worth noticing that lower wavelengths change the picture a little and leads to decomposition in the gas phase. 72 A time-resolved X-ray study has shown that the time scale for decomposition at lower wavelengths is so long that the system is able to distribute the energy to the surrounding solvent medium. So even here the conclusions stand for what is a saving grace for the S−S bond to maintain its status as a key structural motif in biology.…”

“…From the crossing it is downhill all the way to the initial geometry that can then deactivate in a natural environment via the solvent molecules. It is worth noticing that lower wavelengths change the picture a little and leads to decomposition in the gas phase . A time-resolved X-ray study has shown that the time scale for decomposition at lower wavelengths is so long that the system is able to distribute the energy to the surrounding solvent medium.…”