Formation of Reactive Free Radicals in an Aqueous Environment - Free-Radical-Induced DNA Damage and Its Repair - page 32

the presence and absence of a reductant is markedly different (John and Doug-
las 1996) pointing to different mechanisms. While the Fe 2+ desferal complex,
a highly effective chelation drug in iron overload diseases, does not undergo
Fenton-type reactions, its Cu, Co and Ni complexes are capable of cleaving DNA
(Joshi and Ganesh 1994).

The DNase activity of o -phenanthroline-Cu 2+ complex bound to DNA in the
presence of H 2 O 2 is also triggered by thiols (Chap. 12).

2.5.3
Manganese

Manganese(II) is normally not readily autoxidized, but when it is complexed
by, e.g., nitrilobis(methylenephosphonic acid) ready autoxidation by O 2 occurs
(Nowack and Stone 2000). Whether under such conditions • OH are set free as
in the autoxidation of EDTA-complexed Fe(II) (Yurkova et al. 1999), is not yet
know.

2.6
Ozone

Ozone is widely used for the disinfection of drinking water (Ellis 1991), and es-
pecially in the case of viruses there is a considerable likelihood that the nucleic
acids are the main target (Roy et al. 1981). Ozone has been reported to be weakly
mutagenic (Dubeau and Chung 1982; Dillon et al. 1992; Rodrigues et al. 1996),
and DNA damage is reported for plants and human tissues (Fetner 1962; Huber
et al. 1971; Floyd et al. 1989). In its reaction with DNA, a part of the DNA damage
is due to • OH (van der Zee et al. 1987). This may potentially be due to its reaction
with A, for which there is increasing evidence that • OH are generated at one stage
of the reaction sequence (Ishizaki et al. 1984; Theruvathu et al. 2001a). Thus,
ozone may be included into the reagents that cause DNA damage by a free-radi-
cal pathway, although most of the ozone reactions that have been studied so far
are non-radical in nature.
Ozone is a strongly electrophilic reagent (for a compilation of rate constants,
see Neta et al. 1988), and in its reaction with aromatic compounds its rate of
reaction strongly depends on the electron-donating/withdrawing power of the
substituent ( 3.1; Hoigné and Bader 1983). A similarly dramatic substitu-

ent effect is observed with olefins, where the reaction rate constant varies by as
much as eight orders of magnitude on going from tetramethyl- to tetrachloro-
ethene [Dowideit and von Sonntag 1998;for the rate constants of ozone with the

ρ = −