Circular dichroism investigation of the (L lysine)n-Cu(II) (1:1) systems with n = 4 and n = 25.

The study of the (L Lys)n-Cu(II) (1:1) system with n = 4 and n = 25 using circular dichroism (CD) data has provided evidence indicating the formation of two complexes in a two-step process. In the first of these complexes, obtained at pH 6.6, the alpha-amino terminal group and the adjacent deprotonated amide nitrogen are bound to the metal. In the second, additional amino nitrogens of side chains lie at the other two corners of the coordination square. A comprehensive investigation of changes occuring in spectral patterns when coordination takes place enables the assignment of three bands that are characteristic to each type of nitrogen coordination.