Solution properties of synthetic polypeptides. Synthesis and conformational properties of poly(N 08-acetoacetyl-L-lysine), poly(N\u3b4-acetoacetyl-L-ornithine), and poly(N\u3b3-acetoacetyl-L-diaminobutyric acid) in aqueous solution

Poly(N-acetoacetyl-L-lysine) (PALL), poly(N\u3b4-acetoacetyl-L-ornithine) (PALO), and Poly(N\u3b3-acetoacetyl-L-diaminobutyric acid) (PADB) have been synthesized by reaction of poly(L-lysine), poly(L-ornithine), and poly(L-diaminobutyric acid) with diketene in aqueous solution at pH 3c9. All polymers are water soluble at pH >3.5, the order of solubility being PALL < PALO < PADB. With time PALL tends to become insoluble in water probably because of the formation of \u3b2 structures. The conformational properties of three polymers have been investigated by uv absorption and circular dichroism techniques. In acid or neutral aqueous solution the polymers assume the right-handed \u3b1-helical conformation, while the random coil form is predominant in alkaline solution. The conformation of the peptide backbone does affect appreciably the optical activity of the side-chain chromophores in all the three polymers. In the case of PADB the side-chain groups have also substantial perturbing effects on the CD pattern of the backbone