Metalloenzyme catalysts participate as key compounds in some
of the most important biochemical processes of life on earth
including nitrogen fixation, respiration, and oxygenic photosyn-
thesis ( 15 ). To imitate such natural chemical processes and to
develop new compounds which are able to mimic biological mat-
erials in their structures or functions are the primary goals of
biomimetic chemistry ( 16 ). Especially, the construction of robust
chemical systems acting as artificial enzyme models (synzymes,
chemzymes) has always been attracting considerable interest in
the field (17,18), as these synthetic counterparts could replace
the role of natural enzymes in various applications such as cata-
lytic substrate conversion, bioanalytics, or medicinal chemistry.
A representative example is the development of N 5 -macrocyclic
transition metal complexes, which are able to act as functional
mimics of superoxide dismutase (SOD) enzymes ( 19 ). The com-
plex 1 shown in Fig. 2 efficiently catalyzes the conversion of
O 2 into peroxide and dioxygen with a rate nearly approaching
that of the native manganese redox enzyme MnSOD ( 20 ).
It is important to note, however, that synthetic bioinorganic
model compounds, which can compete with the reactivity of their
natural counterparts, are still extremely rare. This is probably
due to the fact that despite huge efforts devoted to this topic, a
real breakthrough in simulating the crucial role of the protein
matrix which surrounds the native reaction centers has not yet
been accomplished.
To mimic the extremely efficient and selective chemistry of
biocatalysts in the absence of their dynamic protein environment,
novel routes have to be explored(5,6). In this context, we have
started to impose light-induced electronic, energetic, and
TABLE I
CLASSIFICATION OFMETALSITES INBIOLOGY.aBasic role Typical functions and metal ions involved
Structural Stabilization of protein configuration (Ca, Mg, Fe, Zn)
Redox Transfer of electrons or atoms (V, Mn, Fe, Co, Ni, Cu, Mo, W)
Catalytic Turnover of substrates (V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, W)
Photochemical Light-harvesting and solar energy conversion (Ca, Mg, Mn,
Zn)
Binding Small molecule coordination, transport, and release (Fe,
Ni, Cu)
Storage Uptake and storage of metal ions, storage of dioxygen (Fe)
Regulation Switch of protein function (Fe)
aAdapted from Refs.(13) and (14).238 GÜNTHER KNÖR AND UWE MONKOWIUS