Equilibrium Studies of Binary and Mixed-Ligand Complexes of Zinc(II) Involving 2-(Aminomethyl)-Benzimidazole and Some Bi
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Equilibrium Studies of Binary and Mixed-Ligand Complexes of Zinc(II) Involving 2-(Aminomethyl)Benzimidazole and Some Bio-Relevant Ligands M. Aljahdali • Ahmed A. El-Sherif
Received: 24 May 2011 / Accepted: 15 December 2011 / Published online: 21 November 2012 Ó Springer Science+Business Media New York 2012
Abstract Binary and mixed-ligand complexes of zinc(II) involving 2-(aminomethyl)benzimidazole (AMBI) and amino acids, peptides (HL) or DNA constituents have been investigated. Ternary complexes of amino acids or peptides are formed simultaneously. Amino acids form the complex Zn(AMBI)L, whereas amides form two complex species Zn(AMBI)L and Zn(AMBI)(LH-1). The ternary complexes of zinc(II) with AMBI and DNA are formed in a stepwise process, whereby binding of zinc(II) to AMBI is followed by ligation of the DNA constituents. The stability of ternary complexes is quantitatively compared with their corresponding binary complexes in terms of the parameters Dlog10 K, log10 bstat and log10 X. The effect of the side chains of amino acid ligands (DR) on complex formation is discussed. The values of Dlog10 K indicated that the ternary complexes containing aromatic amino acids are significantly more stable than the complexes containing alkyl- and hydroxyalkyl-substituted amino acids. This may be taken as evidence for a stacking interaction between the aromatic moiety of AMBI and the aromatic side chains of the bio-active ligands. The concentration distributions of various species formed in solution were also evaluated as a function of the pH. Keywords 2-(Aminomethyl)-benzimidazole Amino acids Amides DNA constituents Stability constants 1 Introduction Considerable attention has been paid in recent years to the investigation of the complex-forming properties of amino acids, peptides and DNA units because of their outstanding biological M. Aljahdali Department of Chemistry, Faculty of Pharmacy, Northern Border University, Rafha, Saudi Arabia M. Aljahdali Department of Chemistry, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia A. A. El-Sherif (&) Department of Chemistry, Faculty of Science, Cairo University, Cairo, Egypt e-mail: [email protected]
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J Solution Chem (2012) 41:1759–1776
significance [1–7]. It has been shown that the imidazole group of histidine is the most important binding site of zinc(II) and other metal ions in serum albumin [8, 9]. Albumin-bound Zn(II) has been found to account for approximately 98 % of the exchangeable fraction of zinc(II) in blood serum. This fraction is known to be associated with the transport process of zinc(II). It has been suggested [8] that the zinc(II)–albumin interaction can be described by either a simple 1:1 zinc(II)–imidazole interaction or by more than one binding site interacting with zinc(II), leading to mixed ligand complexes. Studies on the formation of mixed ligand complexes give a realization of their growing importance, particularly in their role in biological process. The formation of mixed ligand chelates is a general fea
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