Evaluation of formation constants of complexes of a biologically active compound (LAMI) with lanthanons

The proton-ligand formation constant of 2-(2'-lepidylazo)-N-methylisatin (LAMI) and metal-ligand formation constants of its complexes with lanthanons(3) have been determined potentiometrically at different ionic strengths (0,02, 0,05, 0,1 and 0,15 M NaClO4) in 75% aqueous dioxan medium. The method of Bjerrum and Calvin, as modified by Irving and Rossotti, has been used to find values of n-bar and pL. The stability constants and the values of Smin have been calculated. The formation constants logβn for the complexes have been found to increase with the increase in atomic number of the lanthanon. The order was found to be: La < Pr < Nd < Sm < Y < Tb < Dy < Ho. (Author)