Photochemistry and Photophysics of Coordination Compounds

Photochemistry and Photophysics of Coordination Compounds: Chromium 57
Fig. 16 Quenching of [Cr(phen)3] 3+ steady-state emission in air-saturated 50 mM Tris-
HCl buffer (pH 7.4) by calf thymus B-DNA (22 ◦ C)
scission) from agarose gel electrophoresis studies of [Cr(phen)3] 3+ bound
to supercoiled ΦX174 RF plasmid DNA following photolysis at 350 nm (see
Fig. 17) (Barnett et al., unpublished observations). In such studies, the detection
of open-circular DNA following photolysis is clear evidence for a single
strand break in the DNA [116].
Fig. 17 Photoactivated cleavage at pH 7.4 of 5 µM ΦX174 plasmid DNA by 200 µM
[Cr(phen)3] 3+ following irradiation at 350 nm (Rayonet). Samples were subjected to electrophoresis
on 1% agarose gels for 3 hat 70 V, followed by staining with ethidium
bromide
It is also noteworthy that while photodamage in the analogous Ru(II) cases
is dramatically decreased in the absence of O2 (consistent with a singlet O2
pathway), photodamage by [Cr(phen)3] 3+ is considerably greater under a N2
atmosphere (Barnett et al., unpublished observations). Since many cancer