Metal complexes of poly(alpha-amino acids). A potentiometric and circular dichroism investigation of Cu(II) complexes of poly(L-lysine), poly(L-ornithine), and poly(L-diaminobutyric acid).

The conformational properties of cupric complexes of poly (L-lysine), poly (L-ornithine), and poly(L-di-aminobutyric acid) have been investigated by potentiometric, visible and UV absorption, and circular dichroism (CD) techniques. The three polymers form two kinds of complexes stable at pH <8.5 (type I complexes) and at pH >8.5 (type II complexes). It has been found that in the low pH complexes of poly(L-diaminobutyric acid) at least one deprotonated amido nitrogen is coordinated to cupric ions. Type II complexes involve always amide nitrogens in the coordination sphere of Cu(II). Evidence is presented that the structure of such complexes is not compatible with the α-helical conformation of the peptide backbone. © 1977, American Chemical Society. All rights reserved.