Page 81 - Book of Invited & Keynotes Talks

th
8 Biannual Conference on Chemistry - CHEM 08

Thermodynamics and Equilibrium Studies of Binary and Ternary
Complexes of Zn(II) Involving 1-H-Benzimidazole-2-carboxylic
Acid and Some Bio-Active Ligands

Mohamed S. Mansour,Fakiha El-Taib Heakal, Ahmed A. El-Sherif ∗

Department of Chemistry, Faculty of Science, Cairo University, Egypt.

ABSTRACT

Binary and mixed-ligand complexes of zinc(II) involving 1-H-benzimidazole-2-
carboxylic acid (BCA) and amino acids, peptides (HL),dicarboxylic acid or DNA
constituents have been investigated. The stepwise stability constants of BCA with some
selected bivalent transition metal ions were also determined in 0.1 mol.dm NaNO3. In
-3
terms of the nature of metal ion, the complex stability follows the trend Cu > Ni >
2+
2+
Co > Zn , which is in agreement with the Irving-Williams’ order of metal ions. The
2+
2+
thermodynamic parameters for Zn(II)-BCA complex as arepresentative example of
M(II)-BCA complex formation were derived and discussed. Amino acids form the
complex Zn(BCA)L, whereas amides form two complex species Zn(BCA)L and
Zn(BCA)(LH-1). The stability of ternary complexes was quantitatively compared with
their corresponding binary complexes in terms of the parameters Δlog10 K, log10 βStat and
log10 X. The effect of the side chains of amino acid ligands (ΔR) on complex formation
was discussed. The values of Δlog10 K indicate 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 an evidence for a
stacking interaction between the aromatic moiety of BCA 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 pH. The structure of the M(II) complexes
have been geometrically optimized and the result of molecular parameters support the
experimental formation constants of these complexes.

Keywords: 1-H-Benzimidazole-2-carboxylic acid ; Amino acids; Amides; DNA
constituents; Stability constants.

∗ Corresponding author. e-mail:-aelsherif72@yahoo.com; Tel No. 0020235676636, 0020106086652

BOOK OF INVITED SPEAKERS & KEYNOTES CHEM 08 (2020) Page 81