Sensitized photooxidation of s-methylglutathione in aqueous solution: intramolecular (S∴O) and (S∴N) bonded species.
Nanosecond laser flash photolysis was used to generate sulfur radical cations of the thioether, S-methylglutathione (S-Me-Glu), via the one-electron oxidation of this thioether by triplet 4-carboxybenzophenone. The purpose of this investigation was to follow the neighboring group effects resulting from the interactions between the sulfur radical cationic sites and nearby lone-pair electrons on heteroatoms within the radical cation, especially the electron lone-pairs on heteroatoms in the peptide bonds. The tripeptide, S-Me-Glu, offers several possible competing neighboring group effects that are characterized in this work. Quantum yields of the various radicals and three-electron bonded (both intramolecular and intermolecular) species were determined. The pH dependence of photoinduced decarboxylation yields was used as evidence for the identification of a nine-membered ring, sulfur-nitrogen, three-electron bonded species. The mechanisms of the secondary reactions of the radicals and radical cations were characterized by resolving their overlapping transient-absorption spectra and following their kinetic behavior. In particular, sulfur-oxygen and sulfur-nitrogen three-electron bonded species were identified where the oxygen and nitrogen atoms were in the peptide bonds.
Faculty of Chemistry, Adam Mickiewicz University, 61-614 Poznan, Poland. piotrf@amu.edu.pl
Piotr
P
Filipiak
Gordon L
GL
Hug
Krzysztof
K
Bobrowski
Tomasz
T
Pedzinski
Halina
H
Kozubek
Bronislaw
B
Marciniak
D001577:Benzophenones / Q000737:chemistry; D004583:Electrons; D005978:Glutathione / Q000031:analogs & derivatives* / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009584:Nitrogen / Q000737:chemistry; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D010455:Peptides / Q000737:chemistry; D010782:Photolysis; D011789:Quantum Theory; D013455:Sulfur / Q000737:chemistry; D014867:Water / Q000737:chemistry*
C530484:4-carboxybenzophenone; D001577:Benzophenones; D010455:Peptides; D014867:Water; D013455:Sulfur; D005978:Glutathione; D009584:Nitrogen; C017514:S-methyl glutathione; D010100:Oxygen