In biology, lipids are well known for their ability to assemble into spherical vesicles. Proteins, in particular virus capsids, can also form regular vesicle-like structures, where the precise folding and stable conformations of many identical subunits directs their self-assembly. Functionality present on these subunits also controls their disassembly within the cellular environment, for example, in response to a pH change. Here, we report the preparation of diblock copolypeptides that self-assemble into spherical vesicular assemblies whose size and structure are dictated primarily by the ordered conformations of the polymer segments, in a manner similar to viral capsid assembly. Furthermore, functionality was incorporated into these molecules to render them susceptible to environmental stimuli, which is desirable for drug-delivery applications. The control of assembly and function exhibited in these systems is a significant advance towards the synthesis of materials that can mimic the precise three-dimensional assembly found in proteins.

Sodium hyaluronate NaHA in phosphate-buffered saline behaves as a typical polyelectrolyte in the highsalt limit, as Newtonian viscosities are observed over a wide range of shear rates. There is no evidence of intermolecule hydrogen bonding causing gel formation in NaHA solutions without protein present. The concentration dependences of viscosity, relaxation time, and terminal modulus are consistent with observations on flexible, neutral polymers in good solvents, which are known to be in the same universality class as flexible polyelectrolytes in the presence of excess salt.

Water soluble alpha-helical polypeptides were used to prepare silica coated hexagonal single crystal platelets in concentrated solutions. To our knowledge, there is no other instance where polymer single crystals, typically formed under high dilution, can be grown in a bulk material. This unprecedented self-assembly process relies on complex cooperative interactions where silica condensation mediates the growth of polypeptide crystals, which in turn template silica overgrowth. The helices were also used to align samples giving monoliths composed of highly oriented layers of platelets. Overall, this procedure allows preparation of composites with good structural order and complexity via a simple biomimetic process.

The aqueous, lyotropic liquid-crystalline phase behavior of the alpha-helical polypeptide, poly(N(epsilon)-2-[2-(2-methoxyethoxy)ethoxy]acetyl-lysine) (1), has been studied using optical microscopy and X-ray scattering. Solutions of optically pure 1 were found to form cholesteric liquid crystals at volume fractions that decreased with increasing average chain length. At very high volume fractions, the formation of a hexagonal mesophase was observed. The pitch of the cholesteric phase could be varied by a mixture of enantiomeric samples L-1 and D-1, where the pitch increased as the mixture approached equimolar. The cholesteric phases could be untwisted, using either magnetic field or shear flow, into nematic phases, which relaxed into cholesterics upon removal of field or shear. We have found that the phase diagram of 1 in aqueous solution parallels that of poly(gamma-benzyl glutamate) in organic solvents, thus providing a useful system for liquid-crystal applications requiring water as solvent.

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