Stability Constants of Mixed Ligand Complexes of Nickel(II) with Adenine and Some Amino Acids.

Naciye Türkel

doi:10.1155/2015/374782

Abstract

Nickel is one of the essential trace elements found in biological systems. It is mostly found in nickel-based enzymes as an essential cofactor. It forms coordination complexes with amino acids within enzymes. Nickel is also present in nucleic acids, though its function in DNA or RNA is still not clearly understood. In this study, complex formation tendencies of Ni(II) with adenine and certain L-amino acids such as aspartic acid, glutamic acid, asparagine, leucine, phenylalanine, and tryptophan were investigated in an aqueous medium. Potentiometric equilibrium measurements showed that both binary and ternary complexes of Ni(II) form with adenine and the above-mentioned L-amino acids. Ternary complexes of Ni(II)-adenine-L-amino acids are formed by stepwise mechanisms. Relative stabilities of the ternary complexes are compared with those of the corresponding binary complexes in terms of Δlog10⁡K, log10⁡X, and % RS values. It was shown that the most stable ternary complex is Ni(II):Ade:L-Asn while the weakest one is Ni(II):Ade:L-Phe in aqueous solution used in this research. In addition, results of this research clearly show that various binary and ternary type Ni(II) complexes are formed in different concentrations as a function of pH in aqueous solution.

Highlights

Metal ions form different complexes with various biological macromolecules or with their synthetic derivatives [1]
Results of this study indicate that stabilities of binary and ternary complexes of Ni(II) with these ligands depend on the pH of the aqueous solution and the structure of the L-amino acids
Nickel can interact with various amino acids and their side chains within the active sites of nickel-based enzymes [2]

Summary

Introduction

Metal ions form different complexes with various biological macromolecules or with their synthetic derivatives [1]. Seven out of the eight nickel-based enzymes produce or use gases in their reactions. These gases are CO, CO2, CH4, H2, and NH3 [2]. Efficacy and the specificity of nickel-based enzymes depend upon the exact coordination of nickel atom within the active site of the enzyme [3]. In the nickel-based superoxide dismutase (Ni-SOD) enzyme, single nickel atom is coordinated via sulfur side chains of two cysteines together with the two atoms of nitrogen from peptide backbone [4]

Methods

Results

Conclusion