| Abstract
| - Two new fluorescent sensors for Zn2+ that utilize fluorescein as a reporting group, Zinpyr-1 andZinpyr-2, have been synthesized and characterized. Zinpyr-1 is prepared in one step via a Mannich reaction,and Zinpyr-2 is obtained in a multistep synthesis that utilizes 4‘,5‘-fluorescein dicarboxaldehyde as a keyintermediate. Both Zinpyr sensors have excitation and emission wavelengths in the visible range (∼500 nm),dissociation constants (Kd1) for Zn2+ of <1 nM, quantum yields approaching unity (Φ = ∼0.9), and cellpermeability, making them well-suited for intracellular applications. A 3- to 5-fold fluorescent enhancementis observed under simulated physiological conditions corresponding to the binding of the Zn2+ cation to thesensor, which inhibits a photoinduced electron transfer (PET) quenching pathway. The X-ray crystal structureof a 2:1 Zn2+:Zinpyr-1 complex has also been solved, and is the first structurally characterized example of acomplex of fluorescein substituted with metal binding ligands.
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