title: Surprising intrinsic photostability of the disulfide bridge common in proteins.
abstract: For a molecule to survive evolution and to become a key building block in nature, photochemical stability is essential. The photolytically weak S-S bond does not immediately seem to possess that ability. We mapped the real-time motion of the two sulfur radicals that result from disulfide photolysis on the femtosecond time scale and found the reason for the existence of the S-S bridge as a natural building block in folded structures. The sulfur atoms will indeed move apart on the excited state but only to oscillate around the S-S center of mass. At long S-S distances, there is a strong coupling to the ground state, and the oscillatory motion enables the molecules to continuously revisit that particular region of the potential energy surface. When a structural feature such as a ring prevents the sulfur radicals from flying apart and thus assures a sufficient residence time in the active region of the potential energy surface, the electronic energy is converted into less harmful vibrational energy, thereby restoring the S-S bond in the ground state.
authors.affiliation: Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark.
authors.forename: Anne B
authors.initials: AB
authors.lastname: Stephansen
authors.forename: Rasmus Y
authors.initials: RY
authors.lastname: Brogaard
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Kuhlman
authors.forename: Liv B
authors.initials: LB
authors.lastname: Klein
authors.forename: Jørn B
authors.initials: JB
authors.lastname: Christensen
authors.forename: Theis I
authors.initials: TI
authors.lastname: Sølling
mesh_terms: D004220:Disulfides / Q000737:chemistry*; D008958:Models, Molecular; D055668:Photochemical Processes; D011506:Proteins / Q000737:chemistry*; D013455:Sulfur / Q000737:chemistry
chemical_list: D004220:Disulfides; D011506:Proteins; D013455:Sulfur