Thermodynamic Investigation and Mixed Ligand Complex Formation of 1,4-Bis-(3-aminopropyl)-piperazine and Biorelevant Ligands

Ahmed A El-Sherif,Mohamed R Shehata,Mohammad H Barakat,Mohamed M Shoukry

doi:10.1155/2012/984291

Ahmed A El-Sherif, Mohamed R Shehata + Show 2 more

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https://doi.org/10.1155/2012/984291

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Journal: Bioinorganic Chemistry and Applications	Publication Date: Jan 1, 2012
Citations: 14	License type: CC BY 3.0

Affiliation: Cairo University

Abstract

Thermodynamic parameters for protonation of 1,4-bis(3-aminopropyl)-piperazine (BAPP) and its metal complexation with some divalent metal ions were determined in aqueous solution at constant ionic strength (0.1 M NaNO3) using a potentiometric technique. The order of –ΔG0 and –ΔH0 was found to obey Co2+ < Ni2+ < Cu2+ > Zn2+, in accordance with the Irving-Williams order. The formation equilibria of zinc (II) complexes and the ternary complexes Zn(BAPP)L, where L = amino acid, amides, or DNA constituents), have been investigated. Ternary complexes are formed by a simultaneous mechanism. The concentration distribution of the complexes in solution was evaluated as a function of pH. Stoichiometry and stability constants for the complexes formed are reported and discussed. The stability of ternary complexes was quantitatively compared with their corresponding binary complexes in terms of the parameter Δlog K.

Highlights

Metal complexes of biologically important ligands are sometimes more effective than free ligands [1]
Mixed ligand complexes have a key role in biological chemistry [2] because the mixed chelation occurs commonly in biological fluids as millions of potential ligands are likely to compete for metal ions in vivo [3]
The study of ternary complexes of transition metal ions with amino acids, peptides, or DNA units has been the focus of increasing research effort [7,8,9,10], which has revealed the role of metal ions at the molecular level

Summary

Introduction

Metal complexes of biologically important ligands are sometimes more effective than free ligands [1]. In view of the above facts and in continuation of our published work on the formation equilibria of amino acids [19, 20], amides [21, 22], and DNA units [23, 24], we report the protonation constants of the free ligand (BAPP) and the stepwise stability constants for its complexes with a number of 3d divalent metal ions (Zn2+, Co2+, Ni2+, and Cu2+) and the thermodynamics of these systems This was done through calculation of stability constants for their complexes at different temperatures.

Experimental

Results and Discussion

Conclusions