Chemistry Reference
In-Depth Information
The coupling of Ru polyazine chromophores to a
cis -
Pt
II
Cl
2
site provides a
forum to attach a DNA photocleavage unit to a DNA covalent binding unit. This
attachment provides a means to deliver the Ru polyazine chromophore to the DNA
target. An example of such a complex, [{(bpy)
2
Ru(dpp)}
2
Ru(dpp)PtCl
2
]
6+
, binds to
DNA through the Pt(II) centre and photocleaves DNA via an oxygen-mediated
pathway.
78
Oxygen independent photocleavage of DNA.
Swavey, Holder and Brewer exam-
ined the DNA photocleavage ability of polyazine bridged mixed-metal supramole-
cules. The supramolecules were constructed with two Ru(II) or two Os(II) light
absorber subunits connected to a central
cis
- Rh
III
Cl
2
moiety.
42,44
A wide array of
supramolecules constructed with a dpp molecular bridge produced nicks in super-
coiled circular plasmid DNA with
450 nm light photolysis. The gel showing the
photocleavage of DNA by a member of this series, [{(bpy)
2
Ru(dpp)}
2
RhCl
2
]
5+
, is
shown in Figure 8.19. The mechanism of DNA photocleavage is unclear, but this
complex functions as a DNA photocleavage agent in the presence or absence of
dissolved
3
O
2
. DNA photocleavage is proposed to result from intramolecular ES
electron transfer quenching of the
3
MLCT state by the
cis
- RhCl
2
center. The result-
ant metal to metal charge transfer (
3
MMCT) state has a formally oxidized Ru centre
and a formally reduced Rh centre, both of which are capable of mediating DNA
cleavage in the absence of
3
O
2
. Importantly, nicks in the DNA backbone caused by
most types of photocleavage often are irreparable by the repair enzyme DNA ligase.
53
>
no
MC
MC
+h
N N
Ru
II
Cl
Cl
Rh
III
N
N
MC
ν
Ru
II
N
NN
N
N
N
N
N
N
N
N N
MC = [{(bpy)
2
Ru(dpp)}
2
RhCl
2
]Cl
5
Form II
Form I
λ
pUC18 DNA
Array of 5W LEDs
Figure 8.19
Photograph of electrophoresis gel showing the effi cient photocleavage of
pUC18, supercoiled circular plasmid DNA (Form I), with the metal complex [{(bpy)
2
Ru
(dpp)}
2
RhCl
2
]Cl
5
, generating open circular pUC18 DNA (Form II)
[bpy = 2,2
-bipyridine, dpp = 2,3-bis(2-pyridyl)pyrazine]. DNA was photolysed with 460 nm
centred light from a 5W LED (inset image). From left to right the lanes are: lambda DNA/
HindIII digest molecular weight marker (
′
), pUC18 DNA without treatment with metal
complex (no MC), pUC18 DNA incubated with metal complex in the dark at 5:1 base pairs
to metal complex (MC), and pUC18 DNA photolysed in the presence of metal complex at
5:1 base pairs to metal complex (MC+
h
λ
)
ν
