Polypeptide copolymers, aggregation

Abstract The aggregation behaviour of biomimetic polypeptide hybrid copolymers and copolypeptides is here reviewed with a particular eye on the occurrence of secondary structure effects. Structure elements like a-helix or / -sheet can induce a deviation from the classical phase behaviour and promote the formation of vesicles or hierarchical superstructures with ordering in the length-scale of microns. Polypeptide copolymers are therefore considered as models to study self-assembly processes in biological systems. In addition, they offer a great potential for a production of novel advanced materials and colloids. 

The phase behaviour of biomimetic polypeptide-based copolymers in solution was described and discussed with respect to the occurrence of secondary structure effects. Evidently, incorporation of crystallisable polypeptide segments inside the core of an aggregate has impact on the curvature of the corecorona interface and promotes the formation of fibrils or vesicles or other flat superstructures. Spherical micelles are usually not observed. Copolymers with soluble polypeptide segments, on the other hand, seem to behave like conventional block copolymers. A pH-induced change of the conformation of coronal polypeptide chains only affects the size of aggregates but not their shape. The lyotropic phases of polypeptide copolymers indicate the existence of hierarchical superstructures with ordering in the length-scale of microns. 

This review covers the literature on the aggregation of (homo)polypeptide hybrid copolymers and copolypeptides in dilute solution, which was published up to June 2005 a recent review on amphiphiles consisting of peptide sequences is given elsewhere in [12]. It was a particular concern to give a comprehensive overview on secondary structure effects in the self-assembly of these copolymers. Briefly presented are also structures in concentrated solutions (lyotropic phases) and in heterophase systems (see also [14]). 

Besides the polypeptide hybrid block copolymers described earlier, there exist a few examples of purely peptide-based amphiphiles and block/random copolymers (copolypeptides) (Fig. 10). In the latter case, both the core and corona of aggregates consist of a polypeptide. Any of the studies reported so far dealt with aggregation in aqueous media. 

Keywords Aggregation, Biohybrid, Biomembrane, Block copolymer, Colloid, Glycopolymer, Polypeptide, Secondary structure, Self-assembly, Vesicle... 

Hydrogen bonding and secondary interactions may not be the origin of aggregation of block copolymers but can cause deviations from the expected phase behavior. An asymmetric block copolymer consisting of a minor polypeptide fraction may... 

Polypeptides are copolymers of amino acids, i.e., different amino acids are joined to each other in a specific sequence. Proteins are naturally occurring polypeptides, usually in aggregation with one or more other polypeptides and/or with other types of molecules or ions. 

Cai C, Wang L, Lin J (2011) Self-assembly of polypeptide-based copolymers into diverse aggregates. Chem Conunun 47 11189-11203... 

Figure 24 Poly(butadiene-/)/ock- L-gliitamate)) copolymers self-assemble into peptosomes. These are vesicular aggregates stabilized by the polypeptide segments. The size of the peptosomes does not depend on the pH that is, the solvating peptide can perform a helix-to-coil transition as illustrated (transition from right to left). Reprinted with permission from Kukula, H. Schlaad, H. Antonietti, M. Forster, S. J. Am. Chem. Soc. 2002, 124,1658. Copyright 2002, American Chemical Society. ...

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