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Title: Studies on biologically relevant ternary metal complexes: Part V-Stability of ternary Co(II), Ni(II), Zn(II), and Cd(III) complexes containing bis(imidazol-2-yl)methane as primary ligand and amino acids as secondary ligands
Authors: Rao, A Koteswara
Mohan, M Srinivas
Batbina, Harinath B
Issue Date: Oct-1990
Publisher: NISCAIR-CSIR, India
Abstract: The formation constants of ternary complexes of the type ML2A, where M = Co(II), Ni(II), Zn(II) or Cd(II), L= bis(imidazol-2-yl)methane (BIM) and A= glycine, alanine, valine, norvaline, leucine, norleucine, phenylalanine, tryptophan, serine, threonine, methionine, histidine, aspartic acid, pyrocatechol or ethylenediamine have been determined potentiometrically at 35°C and μ = 0.2 M (KNO3). The stabilities of various ternary metal complexes have been quantitatively compared with those of the corresponding binary complexes (MA) in terms of the parameter log K1 (where log K1 = log K-log K). The relative stabilities of the ternary metal complexes containing amino acids with aromatic side chain have been quantitatively compared with those of the corresponding ternary complexes containing alanine(ALA) in terms of the parameter log K2 which is the constant for the equilibrium: M(A) + ML2(ALA) ML2(A) + M(ALA). The enhanced stability of ternary metal complexes containing phenylalanine or tryptophan is attributed to intramolecular metal ion mediated stacking interactions between the aromatic moieties of amino acids and the imidazole rings of bis(imidazol-2-yl)methane. Ternary complexes containing the tridentate amino acids, aspartic acid and histidine are destabilized to a greater extent due to a combination of statistical effect and the decrease in the denticity of these ligands from tridentate in binary to bidentate in ternary complexes. The relative ability of donor atoms in ligand(A) tobind to [M - (BIM)2]2+ complex is found to increase in the order N - N < -. The factors contributing to the stability of the various ternary complexes have been discussed.
Page(s): 996-1001
ISSN: 0975-0975(Online); 0376-4710(Print)
Appears in Collections:IJC-A Vol.29A(10) [October 1990]

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