well-suitable for an oxidative nucleobase damage involving PET
steps. Further, we speculated about possible synergistic effects,
as the biological activity of gold-based drug compounds had
already been studied for more than one century ( 218 ). Indeed,
it turned out in the mean time that gold porphyrin complexes
depending on their detailed ligand structures display several
promisingin vitro properties, which seem to indicate a bright
future as drug candidates for variety of therapeutic applications
( 219 ).
The attachment of the pyrenyl substituents in the ligand
periphery of 28 was chosen to supply a functional domain that
could act as an anchor group with a pronounced affinity for
DNA binding and intercalation. This kind of functionalization
of the gold(III) porphyrin core structure also introduced novel
excited state levels, which led to the occurrence of additional
intramolecular CT interactions ( 216 ). Thus, excitation of the
complex 28 with visible light resulted in a direct optical electron
transfer process generating a charge-separated state with a
pyrenyl radical cation functionality in the molecule periphery
and a reduced gold porphyrin center. The redox properties of this
FIG. 24. Structures of cationic gold porphyrins which can bind to
DNA and display photocatalytic nucleobase damage and double-strand
cleavage controlled by visible light absorption (216,217).
PHOTOSENSITIZATION AND PHOTOCATALYSIS 277