Abstract

P. Venkataih and M. Srinivas Mohan*

The influence of the bidentate anionic oxygen donor ligands oxalic acid (Ox) pyrocatechol (Pyr) and 4-nitroatechol (NPyr) on the binding of Cu(11) with various amino acids was investigated by evaluating the formation constants of ternary metal complexes MLA where M = Cu(ll), L = Ox/Pyr/NPyr and A = alanine, phenylalanine, trytophan, serine, theronine, methionine, tryosine, lysine, histidine or asparctic acid at 35°C and μ=0.2 (KN03). The ternary formation constants were quantitatively compared with the corresponding binary Cu(ll) -amino acid complexes (determined under identical experimental conditions) in terms of the parameter ΔLog K. The amino acids were found to interact more strongly with the binary Cu(ll)-Ox complex relative to the Cu(ll) -Pyt or NPyr complexes. Ternary complexes containing histidine are appreciable stabilized while asparctic acid forms complexes of low stability. Amongst the ternary Ox-Cu(ll)-amino acid complexes, phenylalanine, tryptophan and tryosine which possess an aromatic side chain form relatively more stable complexes. The various factors influencing the stability are discussed in terms of statistical, electrostatic, π-bonding and stacking interactions.

Oxygen; Series; Amino

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