- Adduct Formation and Absolute Rate Constants in the Displacement Reaction of Thiyl Radicals with Disulfides
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The displacement reaction of thiyl radicals with disulfides is shown to proceed via a transient adduct radical by using time-resolved pulse radiolysis techniques.The relatively long-lived adduct (t1/2 > 100 μs) formed in the forward reaction of the equilibrum RS. + RSSR . is suggested to be a sulfuranyl radical with the unpaired electron located in an antibonding ?* orbital within a trisulfide bridge.These species exhibit optical absorptions in the UV, e.g., λmax = 375 +/- 10 nm and ε = (3.4 +/- 0.4)*103 M-1 cm-1 for the all-methylated radical, and have been identified in aqueous and methanolic solutions.Equilibrum constants of K = 180 +/- 30 and 60 +/- 20 M-1 have been evaluated for the systems with R = CH3 and cysteine residue, respectively, via two different methods.The corresponding forward reactions occur with k(RS. + RSSR) = 3.8*106 and 7.7*105 M-1 s-1, respectively.
- Bonifacic, M.,Asmus, K.-D.
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p. 6286 - 6290
(2007/10/02)
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