Lamellar packing, polypeptides

Figure 3. Lamellar packing model for polypeptide containing rod-coil diblock copolymers (A) Model for polybuta-diene-b-PBLG diblock copolymer in which the PBLG chains fold in the lamellar layer and adopt hexagonal packing. This corresponds to a SmB mesophase [9]. (B) Model for amphiphilic polypeptide diblock copolymer. Note that the rods are tilted relative the lamella layer normal while maintaining hexagonal close packing with a constant domain D independent of tilt angle.

In the solid state the poly(L-lysine)-dodecyl sulfate complex is invariably organized in a lamellar structure consisting of layers of polypeptide chains alternating with double layers of surfactant molecules arranged tail to tail. However, both the secondary structure adopted by the polypeptide and the packing of the polymethylene chains in the paraffinic phase depend upon the history of the sample. In the powder isolated from synthesis, the structure of the complex is predominantly of /3-sheet with side chains in a liquid-like state characterized by only short-range order. On the contrary, films cast from a chloroform solution in which the polypeptide is in the disordered state exhibit a a-helix conformation of the main chain with side chains also uncrystallized but with the mobility more restricted than in the former case. 

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