G. Tripathi, T. Tobien
Mar 16, 2001
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Influential Citations
6
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Journal
Journal of Physical Chemistry A
Abstract
Kinetic and structural properties of the intramolecular sulfur−nitrogen bond (>S∴NH2+•−) in aqueous 3-(methylthio)propylamine (3-MTPA) radical cation have been examined as a model for the cyclized radical state of l-methionine, an essential aminoacid in protein biosynthesis. The •OH radical reacts with amine-protonated 3-MTPA at a rate constant of 8.3 × 109 M-1 s1, primarily by addition at the sulfur site. Intramolecular hydrogen abstraction and water elimination from the •OH adduct (3-MTPAH+−OH• → 3-MTPA+• + H2O) occurs at a rate of 9.4 × 107 s-1, forming the radical cation. The Raman scattering of 3-MTPA+•, excited in resonance with its broad 390-nm absorption on the microsecond times, exhibits a surprisingly simple spectrum dominated by a strongly enhanced S∴N stretching vibration at 288 cm-1, observed for the first time. This observation provides vibrational spectroscopic evidence of intramolecular bonding in 3-MTPA+• and shows that the 390-nm absorption of the radical is almost completely confined to...