Chemistry Reference
In-Depth Information
+
====
N-(CH
2
)
2
-CO
2
-CH
2
-CH
3
R
1
R
2
R
3
R
4
PyP
4
=
MnTEt
Est
M
Mn
+
====
R
1
R
2
R
3
R
4
N-(CH
2
)
2
-CO
3
N-(CH
2
)
2
-OH
N-(CH
2
)
3
-CH
3
=
H
2
TPrPyP4
M
H
2
R
1
+
====
R
1
R
2
R
3
R
4
M
=
H
2
H
2
TEtOHPyP4
+
NN
N
=
=
=
=
R
1
R
2
R
3
R
4
Co TButPyP4
M
=
Co(III)
R
2
R
4
+
N
R
1
R
1
R
1
R
1
=
R
2
R
2
R
2
R
2
=
R
3
=
N-CH
3
N-CH
3
N-CH
3
N-CH
3
=
R
4
=
H
2
TMPyPIpP4
CO
2
-
CH
2
-
CO N
N
M
H
2
+
=
=
R
3
=
R
4
=
=
N
M
H
2
TMPyPIpP4
R
3
CO
2
-
CH
2
-
CO N
cis
-H
2
+
=
=
=
R
3
R
3
=
=
R
4
M
H
2
CO
2
-
CH
3
H
2
TMPyCMP4
+
=
=
=
=
R
4
=
M
H
2
CO
2
H
H
2
TMPyCP4
Fig. 8 Structure of several porphyrin derivatives
changes for the two Ni porphyrins upon addition of [poly(dA-dT)] suggest that
partial intercalation is not occurring because models indicate that it would be
difficult to accommodate the bulkier
N
-alkyl substituents.
Kim and coworker [
106
] based on their CD, LD, and contact energy transfer
measurements on H
2
TMPyP4, H
2
TButPyP4, CoTMPyP4, and CoTButPyP4
concluded that the length of the side chain does not affect the binding geometry
of porphyrin. In fact, non-metallo-porphyrins are confirmed to be intercalated to
poly(dG-dC), while they bind to the minor groove of the poly(dA-dT). They
demonstrated that the binding geometries of metalloporphyrins are different when
complexed with poly(dA-dT) and poly(dG-dC) although both can be considered
as groove binding; in particular, the metalloporphyrin-poly(dG-dC) complexes
exhibited 30-40
angle between the molecular plane of the porphyrin and the
polynucleotide helix axis, while the angle between the transition moment of the
drug and the helix axis of poly(dA-dT) is 45-50
as observed for most minor groove-
binding drugs. For these reasons, they proposed that porphyrins may be located in the
major groove of poly(dG-dC). Finally, they showed that the excited energy can be
transferred from the nucleobases even to the porphyrin which is known to bind to
the “outside” of the polynucleotide. In contrast to the strong energy transfer from
nucleobases to the bound porphyrin observed for the non-metallo-porphyrin-poly
(dA-dT) complex, the excited energy of the nucleobases was not transferred to
porphyrins when Co(III) was present. Two factors, distance and relative orientation,
may affect the efficiency of the energy transfer. Since the orientations of the
porphyrin in the presence and absence of the central metal were similar when
bound to poly(dA-dT), the difference in the fluorescence energy transfer may be
attributed to the distance between the porphyrin and nucleobases. The central
octahedral metal complex may inhibit the deep insertion of porphyrin from the
groove. Similar to the poly(dA-dT) case, the metalloporphyrin-poly(dG-dC)
complexes exhibit a null energy transfer, indicating that the metalloporphyrin mole-
cule is quite distant from the nucleobases. It is not surprising that a strong energy
transfer occurs for the intercalated porphyrin because, by definition, porphyrin is in
contact with the nucleobases.
