Stability of Binary and Ternary Copper(II) Complexes with 1,10-Phenanthroline, 2,2'-Bipyridyl and Some .ALPHA.-Amino Acids in Aqueous Medium

Abstract

Interactions of certain amino acids with some metal ions have significant consequences in biological systems. Metal ions can act as co-factors in the regulation of enzymatic reactions. Interactions of metal ions with amino acid side chains or with different organic complexes is also essential for many biological events. In this study, the stability constants of 1 : 1 : 1 ternary complexes of Cu(II) with 1,10-phenanthroline (Phen) as the primary ligand, and 2,2'-bipyridyl (Bpy) and some selected alpha-amino acids [(glycine (Gly), leucine (Leu), glutamine (Gln)] as secondary ligands, were identified in I=0.1 M ionic medium at t=(25+/-0.1) degrees C in aqueous solutions, by potentiometry. The protonation constants of the free ligands and the stability constants of the binary and ternary systems were also determined under the same experimental conditions. The protonation constants of all of the ligands and the stability constants of the formed complexes were evaluated by using the BEST computer program. The stabilities of the ternary complexes have been quantitatively compared with those of the corresponding binary complexes in terms of the some parameters. The concentration distributions of the complexes in solution were also evaluated. Species distributions as a function of pH reveal that the MAB ternary complexes predominate over a pH range, where M=Cu(II); A=Phen; B=Bpy, Gly, Leu and Gln.

Cu(II), Co(II), and Ni(II)–Antioxidative Phenolate–Glycine Peptide Systems: An Insight into Its Equilibrium Solution Study

“…In some systems (Cu–GA–G, Cu–GA–GG, Cu–GA–GGG, Ni–GA–G, and Cu–FA–G), Δ log K are negative. These negative values may be the result of the high stability of their binary complexes, reduction in the coordination sites of the metal ions, steric hindrance, and electrostatic effect. − For the FA-GG and FA-GGG systems, Δ log K values have a similar tendency as their corresponding binary complexes. It may occur due to the competition between ligands since FA, GG, and GGG show almost similar chelating abilities toward metal ions.…”

Switching on the Fluorescence Emission of Polypyridine Ligands by Simultaneous Zinc(II) Binding and Protonation

“…The higher stability of the L1 complexes with Cu 2+ and Zn 2+ cannot be ascribed to the different coordination abilities of bpy and phen. In fact, phen is a better chelating agent than bpy and, for instance, the stability constants of the [Cu L ] 2+ complex are 9.1 and 8.08 log unit with L =phen and bpy, respectively …”

Solvent effects on the crystallization and structure of ternary copper(ii) coordination compounds with l-threonine and 1,10-phenanthroline

“…Binding modes at different pH-values of ternary coordination compounds were investigated with different amino acids and heterocyclic bases, including l -threonine and 1,10-phenanthroline [ 24 , 25 ]. It was shown that ternary coordination species [Cu(aa)(N–N)] + (aa = aminoacidate; N–N = 2,2′-bipyridine or 1,10-phenanthroline) are more stable than either [Cu(aa) 2 ] or [Cu(N–N) 2 ] 2+ binary compounds [ 25 , 26 , 27 , 28 ].…”