Sensing Zn(2+) in Aqueous Solution with a Fluorescent Scorpiand Macrocyclic Ligand Decorated with an Anthracene Bearing Tail

Synthesis of the new scorpiand ligand L composed of a [9]aneN(3) macrocyclic ring bearing a CH(2)CH(2)NHCH(2)-anthracene tail is reported. L forms both cation (Zn(2+)) and anion (phosphate, benzoate) complexes. In addition, the zinc complexes of L bind these anions. The equilibrium constants for ligand protonation and complex formation were determined in 0.1 M NaCl aqueous solution at 298.1 ± 0.1 K by means of potentiometric (pH-metric) titrations. pH Controlled coordination/detachment of the ligand tail to Zn(2+) switch on and off the fluorescence emission from the anthracene fluorophore. Accordingly, L is able to sense Zn(2+) in the pH range 6–10 down to nM concentrations of the metal ion. L can efficiently sense Zn(2+) even in the presence of large excess of coordinating anions, such as cyanide, sulphide, phosphate and benzoate, despite their ability to bind the metal ion.