Dinuclear zinc complex for fluorescent indicator-displacement assay of citrate

Two zinc complexes based on 9,10-distyrylanthracene, 1-Zn and 2-Zn, were synthesized for fluorescence indicator-displacement assay of citrate. The fluorescence of the two complexes can be quenched significantly by energy transfer mechanism upon the binding of a common indicator – phenol red (PR). By using the chemo-ensemble of 2-Zn and PR, a linear fluorescence enhancement is observed upon the addition from 0 to 10 μM citrate (R = 0.9947). The detection limit is evaluated to be 0.1 μM on the basis of the 3σb/slope. This approach showed good selectivity over other nine anions including succinate and glutarate. The association constant of 2-Zn with citrate was evaluated to be 9.2 × 105 M−1 by UV-titration. To our knowledge, this affinity was higher than the reported citrate receptors based on electrostatic interaction, hydrogen bonding and copper complexes. Many other diamagnetic metal complexes could be employed in this approach to detect various analytes with improved affinity.