Abstract: Circular dichroism (CD) spectra of the ternary copper(Ê) complexes with 3,5-diiodo-L-tyrosine (L-I₂tyr), L-tyrosine (L-Tyr), or L-homoserine (L-Hser) and amino acids L-/DL-AA, where AArepresents arginine (Arg), lysine (Lys), asparagine (Asn), glutamine (Gln), or alanine (Ala), have been determined in the d-d region in various ionic strength (I=1.0 or 0.1 mol/L KNO₃) and solvents(H₂O, 50%(U)ethanol-H₂O, or 50%(U)dioxane-H₂O). The spectra exhibit a maximum at 599~623 nm for all the ternary complexes, and the $E for Cu(L-I₂tyr)(L/DL-Arg) and Cu(L-I₂tyr)(L/DL-Lys) are abnormally negative (-0.493~-1.072); the $E for Cu(L-I₂tyr)(L/DL-AA) are obviously more negative than that for Cu(L-Tyr)(L/DL-AA). The possible ligand-ligand interactions in these ternary complexes were discussed, and the structural effects of the iodo groups on the interaction were emphasized.

Key words: Diiodotyrosine, Weak interaction among ligands, Ternary complex