Chemistry Reference
In-Depth Information
Figure 7.1 Schematic representation of a selection of different possible MSP architectures.
However, such systems are not discussed here given their lack of traditional
polymer-like properties.
MSPs differ in a number of ways from more conventional polymers in that their
formation (or change in structure) occurs though supramolecular assembly and as
such does not require the use of an initiator or catalyst. Furthermore, the presence
of supramolecular motifs as an integral part of the polymer can impart a dynamic
nature onto these materials. The reversibility of the kinetically labile metal-ligand
coordination bonds establishes a continual binding equilibrium and potentially
allows the development of stimuli-responsive systems. For example, a change in
environmental conditions, such as temperature, concentration, pH, and so forth,
can alter the amount of metal ions complexed to the ligand, which in turn can dras-
tically affect the properties of the material. This is in contrast to most conventional
covalent polymer systems, where environmental conditions have distinctly less
effect on polymer properties. Another feature of these systems is that the resulting
material can also utilize the functionality inherent in the metal ions. Especially of
interest are those functionalities such as fluorescence, catalysis, conductivity, mole-
cular binding/sensing, and so on, where coordination can alter the properties of
the metal ion.
Figure 7.2 Schematic representation of alginate cross-linking with divalent cations and the
chemical structure of the constituent repeat units, guluronate (G) and mannuronate (M).
Carboxylate groups present along the backbone (largely from the G residues) interact with
multivalent cations to yield metal ion cross-linked gels.
