Coordination properties of N-p-tolylsulfonyl-L-glutamic acid toward metalII -: Part 2.: Solution study on binary and ternary 2,2′-bipyridine containing systems

The binary and ternary systems 2,2'-bipyridine (bipy)-M-tsglu [M=Cu-II, Cd-II, Zn-II or Pb-II, tsglu=N-p-tolylsulfonyl-L-glutamic acid, hereafter abbreviated LH3] were investigated in aqueous solution by means of polarography, electronic spectroscopy and potentiometry, in order to identify the type, number and stability of complex species, as a function of pH and metal to ligand molar ratio. The prevailing species in the binary systems is the [ML](-) [M=Cu-II, Cd-II, (PI)-I-II] where the amino acid molecule is in the trianionic form and coordinates the metal ion through both the carboxylic groups and deprotonated sulfonamidic nitrogen. This coordination mode is also maintained in the ternary bipy containing systems. The addition of the aromatic base in the metal coordination, stabilizes the [M(bipy)L](-) species [M=Cu-II, Cd-II] with respect to the binary ones, while it enables the Zn-II ion to substitute for the sulfonamide nitrogen-bound hydrogen of tsglu. (C) 1999 Elsevier Science Ltd. All rights reserved.