Metal(II) binding ability of a novel N-protected amino acid. A solution-state investigation on binary and ternary complexes with 2,2′-bipyridine

Abstract

The binary and ternary systems 2,2′-bipyridine (bpy)–M(II)–NO 2psglyH 2 (M(II)=Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II); NO 2psglyH 2= N-(2-nitrophenylsulfonyl)glycine) were investigated in aqueous solution by means of potentiometry and electron spectroscopy in order to identify the type, number and stability of the complex species as a function of pH and metal-to-ligand molar ratio. The aim is to evaluate the effect of a substituent on the phenyl ring of the N-sulfonyl amino acids on their coordination properties. The prevailing species in the binary systems is the [ML] (M=Co(II), Ni(II), Cu(II), Cd(II), Pb(II)) where the amino acid molecule is in the dianionic form and coordinates the metal ion through both carboxylic oxygen and deprotonated sulfonamidic nitrogen, while in the Mn(II)- and Zn(II)-containing binary system the only complex species found are those with the amino acid in the monoanionic form. In the ternary 2,2′-bipyridine-containing systems the chelating coordination mode of the dianionic amino acid is maintained with M(II)=Co(II), Ni(II), Cu(II), Cd(II), Pb(II) and the addition of the aromatic base also enables the Zn(II) ion to substitute for the sulfonamide nitrogen-bound hydrogen of NO 2psglyH 2.