unimolecular assembly (micelle). However, this terminology is not entirely consistent because unimolecular micelles in polymer sciences are typically considered
to be composed of dendritic or star-like structures and not linear amphiphiles
[91, 92]. In any case, although the previous section discussed issues that may not
appear immediately relevant to the traditional polymer chemist, this section
briefly reviews recent results that are very interesting with respect to polymer
self-assembly.
4.1 Globular Structures
Peptoids have been used as model compounds for many decades to better understand the behavior of peptides. Recently, Zuckermann et al. designed a peptoid
100-mer to study the coil-to-globule transition [93]. It has been established
that hydrophobic interactions are an important driving force in the folding of
polypeptides in proteins [94–98].
By the reduction to peptoids, Zuckermann and colleagues were able to rule out
any effects of H-bonding and secondary structure on the folding and reduce the
issue to hydrophobic effects [93]. In this work, two different peptoids were
investigated. The first had a regular distribution of the two different repeat units,
whereas the second exhibited a more clustered, protein-like distribution with
different domains. The sequence of the latter was obtained by molecular dynamics
calculations (Fig. 10a). When the coil-to-globule collapse of the two peptoids was
experimentally studied by small-angle X-ray scattering and dye incorporation, it
became clear that the protein-like sequence collapses to a more compact globule
and did so in a more defined manner, that is, the collapse took place in a smaller
window of solvent composition (Fig. 10b). This result should help us to improve
our understanding of protein folding. However, this also demonstrates the importance of polymer definition and polymer microstructure on the aggregation. We
have recently compared the aggregation and endocytosis of random copolymers
and block copolymers. Dynamic light scattering provided evidence that the
aggregates of the random copolymers were smaller but less defined. When we
compared the endocytosis of the copolymers in MCF7-ADR cells, we found a
distinct difference [99]. The random copolymer entered the cells much more readily
than the block copolymer. Similarly, in an in vitro model of the blood–brain barrier,
transport of the dye rhodamine 123 across the barrier was different for block and
random copolymers of otherwise similar composition [100]. Although the
aggregates in this study were about one order of magnitude larger than the globules
studied by Zuckermann, similar effects on the interaction with biological entities
may be observed for the peptoids.
Peptoids for Biomimetic Hierarchical Structures
403
to be composed of dendritic or star-like structures and not linear amphiphiles
[91, 92]. In any case, although the previous section discussed issues that may not
appear immediately relevant to the traditional polymer chemist, this section
briefly reviews recent results that are very interesting with respect to polymer
self-assembly.
4.1 Globular Structures
Peptoids have been used as model compounds for many decades to better understand the behavior of peptides. Recently, Zuckermann et al. designed a peptoid
100-mer to study the coil-to-globule transition [93]. It has been established
that hydrophobic interactions are an important driving force in the folding of
polypeptides in proteins [94–98].
By the reduction to peptoids, Zuckermann and colleagues were able to rule out
any effects of H-bonding and secondary structure on the folding and reduce the
issue to hydrophobic effects [93]. In this work, two different peptoids were
investigated. The first had a regular distribution of the two different repeat units,
whereas the second exhibited a more clustered, protein-like distribution with
different domains. The sequence of the latter was obtained by molecular dynamics
calculations (Fig. 10a). When the coil-to-globule collapse of the two peptoids was
experimentally studied by small-angle X-ray scattering and dye incorporation, it
became clear that the protein-like sequence collapses to a more compact globule
and did so in a more defined manner, that is, the collapse took place in a smaller
window of solvent composition (Fig. 10b). This result should help us to improve
our understanding of protein folding. However, this also demonstrates the importance of polymer definition and polymer microstructure on the aggregation. We
have recently compared the aggregation and endocytosis of random copolymers
and block copolymers. Dynamic light scattering provided evidence that the
aggregates of the random copolymers were smaller but less defined. When we
compared the endocytosis of the copolymers in MCF7-ADR cells, we found a
distinct difference [99]. The random copolymer entered the cells much more readily
than the block copolymer. Similarly, in an in vitro model of the blood–brain barrier,
transport of the dye rhodamine 123 across the barrier was different for block and
random copolymers of otherwise similar composition [100]. Although the
aggregates in this study were about one order of magnitude larger than the globules
studied by Zuckermann, similar effects on the interaction with biological entities
may be observed for the peptoids.
Peptoids for Biomimetic Hierarchical Structures
403