Real-time probing of a three-electron bonded radical: Ultrafast one-electron reduction of a disulfide biomolecule ultrafast

The primary steps of a one-electron reduction of a disulfide molecule (cyst amine) by the infrared p-like state of an excited hydrated electron have be en investigated by femtosecond laser spectroscopy. The initial electron pho todetachment from chloride ion or phenothiazine is triggered by a two-photo n ultraviolet excitation. In homogeneous aqueous cystamine solution, a subp icosecond univalent reduction of the disulfide molecule by an infrared preh ydrated electron competes with the nonadiabatic relaxation of trapped elect rons (electron solvation process. This presolvation one-electron reduction occurs with a characteristic time of 160 +/- 20 fs at 294 K. Within the ele ctron solvation regime, this elementary redox process is totally achieved i n less than 1 x 10(-12) s and exhibits a probability 9 times higher than th e radiationless relaxation of an infrared excited electron. In aqueous orga nized assemblies (cationic micelles) the partitioning of reactants does not influence the frequency rate of a prehydration reaction but modifies the e arly branching between reactive and nonreactive LR electronic channels. The real-time UV probing of a nascent sulfur-centered radical anion (RStherefo reSR(-))(aq) is discussed in the framework of a two-center-three-electron b ond.