Metal Complexes of Poly(α-amino acids). Conformational Aspects of the Interaction between Cupric Ions and Poly(L-histidine)¹

The interaction between cupric ions and poly(L-histidine) under various experimental conditions has been investigated by potentiometric, visible absorption, and circular dichroism techniques. In addition to the low- and high-pH forms described by Levitzki et al.2 a new complex has been detected, which is formed with poly(L-histidine) in the ordered structure. Moreover, at very low Cu/peptide ratios, a species is observed, the optical rotatory properties of which are time dependent and slowly transform into the CD pattern typical of the low-pH complex. From the spectroscopic properties, a structure has been proposed for the new complexes.