Chemistry Reference
In-Depth Information
from
3
O
2
requires excited state energy transfer by the Dexter mechanism. The
3
MLCT state of [Ru(phen)
3
]
2+
, has been shown to produce
1
O
2
from
3
O
2
(Equation
8.28 ).
49
I
[
]
2
+
[
]
2
+
(
)
a
1
(
)
Ru phen
+→
hv
* Ru phen
(8.24)
3
3
k
[
]
2
+
[
]
2
+
1
(
)
3
(
)
* Ru phen
→
isc
* Ru phen
(8.25)
3
3
k
[
]
2
+
[
]
2
+
3
(
)
(
)
* Ru phen
→
nr
Ru phen
(8.26)
3
3
k
2
+
2
+
3
* Ru phen
[
]
→
p
[
]
+
′
(
)
Ru phen
(
)
hv
(8.27)
3
3
k
[
]
2
+
[
]
2
+
3
(
)
3
(
)
1
* Ru phen
+
O
→
en
Ru phen
+
O
(8.28)
2
2
3
3
k
′
1
3
O
nr
→
O
(8.29)
2
2
k
′
1
p
3
O
→+
O
h
′′
(8.30)
2
2
k
1
DNA
+
O
→
rxn
DNA photoproduct
(8.31)
2
Using the steady-state approximation on the [
1
O
2
], the quantum effi ciency of
oxygen mediated photomodifi cation of DNA (F
rxn
) can be described by:
[ ]
++
[
3
k
kk k
O
!
#
k
kkk
[
DNA
]
!
#
en
2
rxn
ΦΦ
rxn
=
(8.31)
isc
]
3
[
]
O
′ + ′ +
xn
DNA
p
nr
en
2
nr
p
r
where F
isc
is the quantum yield of population of the
3
MLCT state,
k
en
is the rate
constant for ES energy transfer to oxygen,
3
O
2
, dissolved in solution and
k
rxn
is the
rate constant for the reaction of
1
O
2
with DNA, where [DNA] is expressed as con-
centration of DNA base pairs. The rate constant
k
en
is determined experimentally
by measuring emission from the
3
MLCT state of [Ru(phen)
3
]
2+
in the absence of
DNA, at different concentrations of
3
O
2
. The rate constant
k
rxn
can be elucidated
from DNA photoproduct analysis or by observing
1
O
2
emission decay.
8.3 Photochemical Reactions of Metal Complexes with DNA
DNA plays important roles in the functioning of cells because it is central to protein
expression (transcription) and cell replication. Damage to DNA manifests itself in
many forms, some of which are detrimental to the integrity of the data stored on
the DNA. Damage to DNA disrupts cell function by causing carcinogenesis, muta-
genesis, apoptosis and cell death. There are several reported mechanisms of excited
state photosensitizer reactions inducing DNA damage.
2,5,50 - 53
Careful design of DNA
photochemical experiments can yield surprising amounts of information about the
mechanism of DNA/metal complex interaction as well as information about the
