Heteroatom-Centered Radicals - Free-Radical-Induced DNA Damage and Its Repair - page 141

tion even by reducing radicals such as the H atom and α -hydroxyalkyl radicals

(Schuchmann et al. 2000).

In addition to the complexation by the parent, the sulfide radical cation can un-
dergo a deprotonation at a neighboring carbon [cf. reaction (51)]. Also, in the
case of thiourea, deprotonation at nitrogen in basic solution competes with a
complexation by the parent (Wang et al. 1999). This reaction is, of course, not
given by its N , N , N -tetramethyl derivative.

The sulfide radical cation can also complex with neighboring hydroxy, alk-
oxy and carboxylate groups (e.g., Glass et al. 1984; Asmus et al. 1985; Chatgilia-
loglu et al. 1985; Mahling et al. 1987; Pogocki and Schöneich 2002). The reaction
with the latter that gives rise to a sulfuranyl radical is shown in reaction (52).

′ , N ′

All these radical cations are fairly strong oxidants. For example, the monomeric
methionine radical cation is likely to propagate oxidative damage in peptides
(Rauk et al. 2000). Yet in cellular systems, thiourea has radiation-protective
properties (Bacq 1965). This may be accounted for considering that the oxida-
tive power of its dimeric radical is not high enough to oxidize even G; it reacts
only reasonably fast when G is deprotonated (Schuchmann et al. 2000), and this
is a non-relevant situation in DNA.
Obviously, these sulfur-centered radical cations are good sinks for O 2 • − , and,
for example, disulfide radical cations give rise to sulfoxides in a very fast reac-
tion [reaction (53), k = 1.6 10 10 dm 3 mol − 1 s − 1 ; Bonifacic et al. 2000b]. ×

R 2 SSR 2 • + + O 2 • − → 2 R 2 S=O (53)

References

Adams GE, McNaughton GS, Michael BD (1967) The pulse radiolysis of sulphur compounds, part I.
Cysteamine and cystamine. In: Johnson GRA, Scholes G (eds) The chemistry of ionization and
excitation. Taylor and Francis, London, pp 281−293
Adams GE, McNaughton GS, Michael BD (1968) Pulse radiolysis of sulphur compounds, part 2.
Free radical 'repair' by hydrogen transfer from sulfhydryl compounds. Trans Faraday Soc
64:902−910