the sensitization of related CO-releasing molecules (CORMs) into
the red and NIR spectral region to be able to better match the
phototherapeutic window of mammalian tissue ( 213 ).
IV. Selected ApplicationsDespite the obvious versatility of light-activated key steps and
their numerous advantages for the biomimetic modeling of natu-
ral systems, up to now, only very few examples are known, where
such types of photosensitized processes have been successfully
combined to complete reaction cycles with reasonable catalytic
turnovers ( 6 ). In the last section, we are therefore briefly
presenting two case studies which describe some recent work
performed in our own group focusing on bioinspired catalytic sys-
tems that can be controlled and driven by visible light.
A. TOWARDARTIFICIALENDONUCLEASEACTIVITY
Synthetic compounds able to induce selective damage or scis-
sion of DNA strands in a controlled fashion are of prime interest
for molecular biology and genetic engineering and for the design
of specific diagnostic or chemotherapeutic agents. Therefore,
chemical nuclease mimics have actually been among the first
examples of bioactive model compounds triggered by light( 214 ).
The interactions with DNA or nucleobases observed with most
of these systems, however, are not operating in a catalytic way,
and a reversible regulation of DNA strand cleavage activity with
chemically modified restriction enzymes has only recently been
reported ( 215 ). Natural endonucleases are acting as a kind of
molecular scissors which can recognize short DNA sequences
and cut the phosphodiester bonds of the double helix close to
their target sites, which leads to a complete double-strand
cleavage.
Several years ago, we have started to explore the possibilities
of selective catalytic nucleic acid damage and light-triggered
DNA cleavage with bioinspired metalloporphyrin photocatalyts
( 216 ). In this context, the cationic porphyrinato gold complex 28
shown in Fig. 24 was synthesized as a novel type of potentially
tumor localizing electron transfer sensitizer. The choice of the
high-valent central metal and the additional aromatic sub-
stituents was guided by several reasons. First of all, gold(III)
porphyrins were already established as excellent electron
acceptors, which should make their low-lying excited states
276 GÜNTHER KNÖR AND UWE MONKOWIUS