Copolypeptides vesicles

From the pioneering studies on block copolypeptide vesicles described above, design criteria were established for successful vesicle formation, namely an... 

Fig. 1 Vesicle construct formed from poly(L-lysine)-i)-poly(L-leucme) polypeptides where the poly(L-leucine) block corresponds to the a-helical hydrophobic segments and the poly (L-lysine) block corresponds to the random coil hydrophilic segments. Note that this is one specific example and not all vesicle constructs have a-helical and random coil blocks. Moreover, the amphiphilic copolymer can be comprised of either a pure block copolypeptide or a macromolecule consisting of a polypeptide and another type of polymer. Adapted from [20] with permission. Copyright 2010 American Chemical Society...

The most general and frequently used method to synthesize long chains of block copolypeptides for vesicle assembly is successive ring opening polymerizations of a-amino acid-Ai-carboxyanhydride (NCA) monomers [18, 20, 21, 39-51]. NCA monomers are readily prepared from commercially available amino acids, most commonly through direct phosgenation [52]. 

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 linear polypeptide hybrid block copolymers and block copolypeptides reported to form vesicles in aqueous solution are listed in Fig. 1. 

Nonionic block copolypeptides made of PEGylated L-lysine and L-leucine residues, PELLys- -PLLeu (Fig. lOh) have also been described [52], The copolymers adopted a rod-like conformation, due to the strong tendency of both segments to form a-helices (CD spectroscopy), and produced a variety of self-assembled structures in aqueous solution. Micrometer vesicles and sheet-like membranes could be obtained for copolymers with fractions of the hydrophobic leucine ranging from 10 to 30mol%. Conventional uncharged block copolymers of this composition would be expected to form spherical or cylindrical micelles. The assembly into bilayers was related to a secondary structure effect, as illustrated in Fig. 12. Accordingly, samples with the same composition but nonhelical chain conformation (CD),... 

Bellomo and co-workers prepared a new type of synthetic vesicle with a high degree of architectural control made of amphiphilic block copolypeptides (Bellomo et al., 2004). The hydrophUic block was made of lysine, augmented with a few water-soluble ethylene glycol units, and the hydro-phobic block was constituted by leucine peptide. The synthetic polymer forms a supramolecular structure highly sensitive to environmental signals... 

These block copolypeptides, where both hydrophilic and hydrophobic segments were a-helical, gave rise to very stiff membranes, as suggested by the large vesicle diameters and lack of fluidity in the sheets that were formed. Further investigation revealed that these membranes were completely insensitive to osmotic stress, a consequence of their impermeability to water, ions, or other small molecules... 

Fig. 5 Structure of amphiphilic glycosylated diblock copolypeptides and their assembly into vesicles. Adapted from [106]...

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