Synthesis and characterization of the zinc(ii)-fluorophore, 5-dimethylaminonaphthalene-1-sulfonic acid [2-(1,5,9-triazacyclododec-1-yl)ethyl]amide and its zinc(ii) complex

Abstract

A new zinc(II)-fluorophore, 5-dimethylaminonaphthalene-1-sulfonic acid [2-(1,5,9-triazacyclododec-1-yl)ethyl]amide (HL) has been synthesized and characterized. The spectrophotometric and potentiometric pH-titration study disclosed a 1 ∶ 1 zinc(II) complexation with a stability constant, K(ZnL) of 10^1.3 (= [ZnL]a_H⁺/[Zn²⁺][HL]) at 25 °C with I = 0.10 (NaCl) in aqueous solution, where L is the dansylamide deprotonated ligand. The fluorescence intensity of ZnL at 538 nm (excitation at 320 nm) is 5.2 times greater than that of the ligand (HL·H⁺ form) in aqueous solution at pH 7.8 and 25 °C with I = 0.10 (NaCl). The X-ray crystal analysis of the zinc(II) complex [ZnL(ClO₄)·EtOH] showed a four-coordinate zinc(II) with three nitrogen atoms of the macrocyclic triamine and the dansylamide N⁻ anion.