Ferric complexes of acetoacetyl derivatives of poly(L-lysine), poly(L-ornithine), and poly(L-diaminobutyric acid). II. Conformational properties in solution. Evidence for a stereospecific complex formation

The conformational properties of ferric complexes of poly(N^ε-acetoacetyl-L -lysine), poly(N^δ-acetoacetyl-L -ornithine), and poly(N^γ-acetoacetyl-L -diaminobutyric acid) were investigated in 1:1 water/dioxane by CD techniques. Optical activity was found in the visible and in the uv absorption region of the polymeric complexes. The conformation of the peptide backbone was always that of a right-handed α-helix, and was found independent of the degree of complexation, at least up to a degree of binding of 20%. In the absorption region of the side-chain chromophores the optical activity is substantially affected by complex formation. In all three cases a splitting of the ligand π → π* transition centered at 257 nm is observed. These data suggest a stereospecific complex formation. From the signs of the splitting it also appears that the chirality of the poly(N^δ-acetoacetyl-L -ornithine) complex is opposite that of the other two polymers.