1,2,3-triazol-1,4-diyl-fluoroionophores for Zn2+, Mg2+ and Ca2+ based on fluorescence intensity enhancements in water

Abstract

Herein, we represent cation-responsive fluorescent probes for the divalent cations Zn2+, Mg2+ and Ca2+, which show cation-induced fluorescence enhancements (FE) in water. The Zn2+-responsive probes Zn1, Zn2, Zn3 and Zn4 are based on o-aminoanisole-N,N-diacetic acid (AADA) derivatives and show in the presence of Zn2+ FE factors of 11.4, 13.9, 6.1 and 8.2, respectively. Most of all, Zn1 and Zn2 show higher Zn2+ induced FE than the regioisomeric triazole linked fluorescent probes Zn3 and Zn4, respectively. In this set, ZN2 is the most suitable probe to detect extracellular Zn2+ levels. For the Mg2+-responsive fluorescent probes Mg1, Mg2 and Mg3 based on o-aminophenol-N,N,O-triacetic acid (APTRA) derivatives, we also found that the regioisomeric linkage influences the fluorescence responds towards Mg2+ (Mg1 +100 mM Mg2+ (FEF =13.2) and Mg3+100 mM Mg2 + (FEF =2.1)). Mg2 shows the highest Mg2+-induced FE by a factor of 25.7 and an appropriate Kd value of 3 mM to measure intracellular Mg2+ levels. Further, the Ca2 +-responsive fluorescent probes Ca1 and Ca2 equipped with a 1,2-bis(o-aminophenoxy)ethane-N,N,N’,N’-tetraacetic acid (BAPTA) derivative show high Ca2+-induced FEs (Ca1 (FEF =22.1) and Ca2 (FEF =23.0)). Herein, only Ca1 (Kd = 313 nM) is a suitable Ca2+ fluorescent indicator to determine intracellular Ca2+ levels.