Abstract

Allam Mohan and M. Srinivas Mohan*

Equilibrium studies on mixed ligand complexes MLA and ML2 A containing 1.1:1 or 12:1 molar ratio of NI (II), picolinic acid (L) and one of the following amino acids (A) viz. glycine, alanine, serine, threonine, methionine, phenyl-alanine, tryptophan, tyrosine, lysine or histidine were carried out in aqueous solutions by a pH-metric method and the formation constants are reported at 35.0°C and M = 0.2M (KNO3). The stability of these complexes have been quantitatively compared with the corresponding binary amino acid complexes (MA) in terms of the parameters #log K1 and #log K2 (#log K1, m log KML MLA - log KM MA. # logK2 =log KML2ML2A - log KMMA). Amino acids with an aromatic side chain form stable mixed complexes due to metal ion mediated intramolecular stacking (Interactions between the ligands L and A .The equilibrium between the stacked and unstacked isomers and the percentage of the stacked isomers have been quantified in terms of the parameters KI, and (% MLn A)st. Stacking interactions are found to stabilize the ML2A complexes extensively than the corresponding MLA complexes.

Equilibrium; Quantitatively'; Stacking; Derivatives

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