The Reverse of the ‘Repair’ Reaction of Thiols: H-abstraction at Carbon by Thiyl Radicals

Summary

Thiyl radicals (RS^·) formed by the reaction of radiolytically generated OH radicals with thiols, e.g. 1,4-dithiothreitol (DTT), react with cis- and trans-2,5-dimethyltetrahydrofuran by abstracting an H atom in the α-position to the ether function (k ≈ 5 × 10³ dm³ mol⁻¹ s⁻¹). The so-formed planar ether radical is ‘repaired’ by the thiol (k = 6 × 10⁸ dm³ mol⁻¹ s⁻¹) thereby regenerating a cis- or trans-2,5-dimethyltetrahydrofuran molecule. In this reaction a thiyl radical is reproduced. Thus trans-2,5-Me₂THF from cis-2,5-Me₂THF and vice versa are formed in a chain reaction: at a dose rate of 2·8 × 10⁻³ Gy s⁻¹ and a trans-2,5-Me₂THF concentration of 1 × 10⁻² mol dm⁻³ using DTT as the thiol, G(cis-2 5-Me₂THF) = 160 has been found. The chain reaction is very sensitive to impurities and also to disulphides such as those radiolytically formed. 2,5-Me₂THF can be regarded as a model for the sugar moiety of DNA where the C(4′)-radical is known to lead to DNA strand breakage. The possible role of cellular thiols in the repair of the C(4′) DNA radical, and also the conceivable role of thiyl radicals inducing DNA strand breakage, are discussed.

• chemical repair
• thiyl radicals
• chain reaction
• 2,5-dimethyl-tetrahydrofuran
• DNA model