inorganic chemistry

important topics in biomimetic chemistry( 183 ). Detailed knowl-
edge about O 2 activation at metal sites opens the scene for highly
selective bioinspired substrate conversions with novel types of
redox catalysts. These properties are highly relevant for many
environmentally benign technological processes using dioxygen
molecules from ambient air as their only oxidant. The investiga-
tion of functional chemical models for critical reaction inter-
mediates involved in bioinorganic redox processes of reactive
oxygen species is therefore of prime interest for bioinorganic
photochemistry.
Nature uses many different types of metalloproteins for the
binding, transportation, and controlled activation of oxygen
(10,13). An extremely versatile catalyst system is present in the
biochemistry of iron-containing heme enzymes (Fig. 21).
The reaction sequence at the heme active site starts with the
binding of unactivated triplet dioxygen forming the so-called
oxy–heme complexes. The iron center in O 2 -activating heme
enzymes is then thought to be converted into a peroxo anion spe-
cies. It can be protonated to form a ferric hydroperoxo intermedi-
ate usually termed compound 0( 183 ), which is a crucial reactive
species in catalase and peroxidase enzyme catalysis (Fig. 21).
These hydroperoxo intermediates of hemoproteins are important

300 400

Absorbance

500

23

600

Wavelength (nm)

700 800 900

OC CO

Re CO

OO

X

CT

FIG. 20. Electronic spectrum of a rhenium(I) carbonyl complex ( 23 )
featuring an optical charge transfer transition atlmax¼711 nm involv-
ing a coordinated quinone acceptor ligand ( 181 ).

PHOTOSENSITIZATION AND PHOTOCATALYSIS 271