A New Family of Macrocyclic Polyamino Biphenolic Ligands: Acid-Base Study, Zn(II) Coordination and Glyphosate/AMPA Binding.

In this study, the ligands 23,24-dihydroxy-3,6,9,12-tetraazatricyclo[17.3.1.1(14,18)]eicosatetra-1(23),14,16,18(24),19,21-hexaene, , and 26,27-dihidroxy-3,6,9,12,15-pentaazatricyclo[20.3.1.1(17,21)]eicosaepta-1(26),17,19,21(27),22,24-hexaene, , were synthesized: they represent a new class of molecules containing a biphenol unit inserted into a macrocyclic polyamine fragment. The previously synthesized is obtained herein with a more advantageous procedure. The acid-base and Zn(II)-binding properties of and were investigated through potentiometric, UV-Vis, and fluorescence studies, revealing their possible use as chemosensors of H and Zn(II). The new peculiar design of and afforded the formation in an aqueous solution of stable Zn(II) mono (LogK 12.14 and 12.98 for and , respectively) and dinuclear (LogK 10.16 for ) complexes, which can be in turn exploited as metallo-receptors for the binding of external guests, such as the popular herbicide glyphosate (-(phosphonomethyl)glycine, PMG) and its primary metabolite, the aminomethylphosphonic acid (AMPA). Potentiometric studies revealed that PMG forms more stable complexes than AMPA with both - and -Zn(II) complexes, moreover PMG showed higher affinity for than for . Fluorescence studies showed instead that the -Zn(II) complex could signal the presence of AMPA through a partial quenching of the fluorescence emission. These studies unveiled therefore the utility of polyamino-phenolic ligands in the design of promising metallo-receptors for elusive environmental targets.