Electron spin resonance evidence for intra- and intermolecular. sigma. sigma. * bonding in methionine radicals: Relative stabilities of S-Cl, S-Br, S-N, and S-S three-electron bonds
- Oakland Univ., Rochester, MI (United States)
An electron investigation of three-electron {sigma}{sigma}* bond formation in methionine, methionine peptides, and model structures in frozen aqueous solutions is presented. Irradiation of 12 M LiCl or 6.3 M LiBr solutions at 77K results in the Cl{sub 2}{sm bullet}{sup {minus}} and Br{sub 2}{sm bullet}{sup {minus}} radicals, respectively. These species are found to attack the methionine sulfur atom to form halogen adducts. Further annealing results in the more stable intermolecularly bonded disulfide radical adduct, S{sm bullet}{sub +}-S<. Experiments performed to compare the stabilities of the various three-electron bonded species show the following order in increasing stability: >S{sm bullet}-O{sup +}<, Cl{sm bullet}-Cl{sup {minus}}, >S{sm bullet}-Br, >S{sm bullet}{sup +}-NH{sub 2}, >S{sm bullet}{sup +}-S<. UV-vis spectra of the various intermediates taken suggest that the species identified in this work are those identified in previous pulse radiolysis investigations in aqueous solutions at ambient temperatures. Results found for methionine peptides and model structures are similar to those found for methionine with the exception that intramolecular bond formation in the peptides was not a facile. Each of the radical species found are analyzed for hyperfine splitting and g values. Ab initio molecular orbital calculations of optimized geometries and hyperfine splittings and g values. Ab initio molecular orbital calculations of optimized geometries and hyperfine couplings for model compounds for Cl{sm bullet}-S<, >S{sm bullet}{sup +}-NH{sub 2}, and >S{sm bullet}{sup +}-S< bonding are presented. The calculations clearly show the localized {sigma}{sigma}* nature of the bonding and further predict that the S{sm bullet}-N species is stable toward deprotonation from the amine group.
- OSTI ID:
- 7017519
- Journal Information:
- Journal of Physical Chemistry; (United States), Journal Name: Journal of Physical Chemistry; (United States) Vol. 95:17; ISSN 0022-3654; ISSN JPCHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
ALKALI METAL COMPOUNDS
AMINO ACIDS
AQUEOUS SOLUTIONS
BROMIDES
BROMINE COMPOUNDS
CARBOXYLIC ACIDS
CHEMICAL BONDS
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHLORIDES
CHLORINE COMPOUNDS
COMPARATIVE EVALUATIONS
DECOMPOSITION
DISPERSIONS
DRUGS
ELECTRON SPIN RESONANCE
EVALUATION
HALIDES
HALOGEN COMPOUNDS
HYPERFINE STRUCTURE
LIPOTROPIC FACTORS
LITHIUM BROMIDES
LITHIUM CHLORIDES
LITHIUM COMPOUNDS
LITHIUM HALIDES
MAGNETIC RESONANCE
METHIONINE
MIXTURES
MOLECULAR ORBITAL METHOD
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
PEPTIDES
PROTEINS
RADIATION EFFECTS
RADICALS
RADIOLYSIS
RESONANCE
SOLUTIONS