structural changes on the substrate binding sites of biomimetic
and bioinspired coordination compounds (artificial photoenzymes,
photochemical model enzymes). Already, the first attempts in this
direction have proven to be very promising ( 3 ). As will be shown
later in more detail, most of the other functions of metal sites in
biological systems summarized in Table I can also be reproduced
with bioinspired photochemical model systems.
Efficient light absorption and the population of photoreactive
excited states are the minimum requirements for this novel
approach. The quantum nature of photons furthermore offers a
straightforward strategy to incorporate other interesting pro-
perties such as selectivity, switching, and regulation of light-
responsive processes. Some basic characteristics of the functional
components present in the corresponding bioinorganic and
biomimetic systems will be discussed in the following sections.
A. LIGHTABSORPTION ANDSENSITIZATION
The most fundamental principle of photochemistry, which
actually was discovered by exposing inorganic compounds to sun-
light ( 21 ), states that light must be absorbed by a chemical sub-
stance for a photochemical reaction to occur. We will therefore
start our discussion with a brief overview on some of the natural
chromophores which are known to be involved in photosensory
processes or could be useful for the construction of artificial
photoreactive systems.
FIG. 2. (a) Structure and function ofH.sapiensmanganese super-
oxide dismutase (PDP-code: 1ABM) and (b) synthetic low molecular
weight substitute of MnSOD optimized for therapeutical purposes ( 20 ).
PHOTOSENSITIZATION AND PHOTOCATALYSIS 239