Chemistry Reference
In-Depth Information
the early 1990s. The interest in developing metallodendrimers [12-18] resulted from
the fact that the introduction of metals into dendritic structures allows access to highly
ordered materials with new magnetic, catalytic, optical, electro- and photochemical,
and biomedical properties as well as reactivity.
In particular, the incorporation of organometallic entities on the surface or within
the dendritic structures represents a stimulating, challenging target in both organo-
metallics and dendrimers research because it provides a unique opportunity for
tailoring organometallic dendrimers to achieve desirable properties for well-defined
applications such as dendritic catalysts, in multielectron redox and photocatalytic
processes, as molecular sensors, and others [19-22].
Dendrimers containing redox-active units are of great importance because the
number of electrochemically active functional groups can be precisely controlled.
Thus, redox-active dendrimers are excellent candidates to play a key role in
understanding biological electron transfer and for use in practical applications such
as catalyst, electron transfer mediators, energy conversion, ion sensors, and in
electronic devices [23-26].
Since 1994, Mor
an and his group, pioneering in the dendrimer research in Spain,
have reported the synthesis of several families of silicon- and nitrogen-based
organometallic dendritic molecules decorated, in most cases, with either ferrocene
or cobaltocenium redox-active moieties as surface functional groups [27-40].
Electrochemical properties of both metallocenes are dominated by a reversible
monoelectronic oxidation (ferrocene) or reduction (cobaltocenium), which can
be easily obtained at very accessible potentials. Some of these dendritic molecules
have been used successfully in the modification of electrode surfaces [41], as electron
transfer mediators in amperometric biosensors [42-44], as exo-receptors for sensing
anions [27,30,36,38,45], and also, as effective guests for the formation of supramo-
lecular complexes with
-cyclodextrin [37,46].
In this chapter, we mainly focus on redox-active organometallic dendrimers, as
well as their properties and electrochemical applications, especially in the field of
molecular recognition and in amperometric biosensors. This chapter will provide
selected references to the work of other groups who are actively working on
metallodendrimers in which reversible redox centers have been attached in any way,
allowing applications to processes that involve the use of the redox functions,
especially in the field of molecular recognition and in amperometric biosensors, but
will primarily focus on our own work in this area.
b
8.2 ORGANOMETALLIC DENDRIMERS AS ION SENSORS
In the last decades the tailored-design and synthesis of host materials for the selective
recognition and sensing of anions, cations, as well as neutral molecules has become a
topic of increasing interest [47]. In particular, the development of molecule-based
anion selective hosts has been a pivotal issue currently receiving considerable
attention and the recognition and sensing of environmentally important anions such
as nitrate and phosphate, as well as the sensing of analytes in biological systems have
