
417Biosensing and Cancer Treatment with Magnetic Nanoparticles
constant K
stab
= 10
44.9
has been determined for the octahedral complex between three cat-
echol units and Fe(III).
50
Interestingly, catecholate groups are found in siderophores (iron-
transporting proteins, e.g., enterobactin,
51
) and in adhesive mussel proteins.
52
Dopamine is chemically not stable when bound to Fe
2
O
3
or Fe
3
O
4
. It slowly undergoes
oxidation. Fe(III) acts as electron acceptor and reacts to Fe(II), which then leaves the nano-
crystal and forms Fe(OH)
2
under physiological conditions. This reaction slows down sig-
nicantly, if the amine group of dopamine is converted into ...