Synthesis and characterisation of new fluorescent Na+ and K+ indicators

Article abstract of DOI:10.1016/S0040-4020(99)00167-2

The synthesis of new fluorescent indicators for Na⁺, Benz-15-5 or Diaz- 15-5, and for K⁺, Benz-18-6 or Diaz-18-6, respectively, is reported. They consist of a benzocrown or a diazacrown ether linked to a pyrazoline fluorophore substituted with carboxylate groups to ensure water solubility. They were obtained via reaction of an α,β-unsaturated ketone with an aryl hydrazine. The fluorescence intensity of Benz-15-5 is nearly insensitive to Na⁺. Benz- 18-6 displays a four-fold selectivity for K⁺ over Na⁺, with a dissociation constant of 3.6 mM for the K⁺: indicator complex. Diaz-15-5 and Diaz-18-6 have only a weak affinity for monovalent cations, so that they only can be used for the determination of high Na⁺ and K⁺ concentrations.