Side-chain interactions and conformation in alpha-helical poly(gamma-phenacyl L-glutamate). Aggregation in dilute solutions.

The behavior of alpha-helical poly(gamma-phenacyl L-glutamate) (PPLG) has been studied by hydrodynamic, optical rotation, dielectric, and nmr measurements in different solvents. Special attention has been paid to side-chain interactions which depend on the ease of solvation of the phenacyl chromophore. Thus, in hexafluoro-2-propanol the circular dichroism spectrum is very similar to that usually observed for an alpha helix, and hydrogen bonding was shown to occur between the solvent and phenacyl CO group. In other heliocogenic solvents, side chain-side chain interactions occur. In dimethylformamide and pyridine they give rise at low temperature and low concentrations to an aggregation phenomenon whose molecular mechanism implies a molecular weight dependent folding of the molecules. Models for the side-chain conformation are proposed for the polymer in the solid state on the basis of infrared dichroism.