Conformational studies on Cu(II) policomplexes of pyridoxal Schiff bases of polypeptides

Structures of Cu(II) complexes of pyridoxal Schiff bases with poly(l-lysine), poly(l-ornithine), and poly(l-α,γ-diaminobutyric acid) were investigated by absorption spectra, CD, and conformational analysis. Although the polypeptides retain their typical right-handed α-helical conformation, opposite Cotton effects were found for the poly(l-lysine) and poly(l-ornithine) polycomplexes in the whole range of wavelengths from 600 to 250 nm. As in the analogous derivatives of salicyladehyde, this effect seems to be due to a stereospecific binding of the square planar Cu(II)-bis-pyridoxylideneimine group to the α-helical matrix. Circular dichroism spectrum of poly(l-α,γ-diaminobutyric acid) polycomplex is similar to that found for poly(l-lysine) derivative, but indicates large tetrahedral distortion of the square-planar coordination of copper ion.