Development of zinc detection system with novel zinc-fluorophores

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Quantitative analysis of trace zinc(II) ion with a selective analytical reagent has become extremely important for environmental and biological applications. While remarkable development has been made for other biologically important divalent metal ions, in particular calcium(II) ion, with several selective fluorophores such as Quin-2 and Fura-2, there have been few zinc(II)-selective analytical reagents available for biological research on zinc(II) ion. Currently, the most widely used probes for detecting intracellular zinc(II) ion are 8-aminoquinoline sulfonamide derivatives such as Zinquine. Recently, fluorescein-appended zinc(II) chelates such as azacrownfluorone have been developed as improved proves for understanding the zinc(II) chemistry in biological systems. While working on elucidation of intrinsic properties of zinc(II) ion in the catalytic sites of zinc enzymes by use of macrocyclic polyamine complexes (e.g., zinc(II) complexes with 1,5,9-triazacyclododecane ([12]aneN_3) a … More nd 1,4,7,10-tetraazacyclododecane (cyclen)), we have discovered unique acid properties of zinc(II) ion. One of the most outstanding zinc(II) properties is a strong affinity to aromatic sulfonamides, as illustrated by formation of the strong bonds between the deprotonated sulfonamide N^- anions and zinc(II) in the macrocyclic polyamines at physiological pH. On the basis of these findings, we have designed 5-dimethylamino-naphthalene-1-sulfonic acid [2-(1,4,7,10-tetraazacyclododec-1-yl)-ethyl]-amide (dansylamidoethyl-cyclen) that serves as a novel type of zinc(II)-fluorophore by forming a highly fluorescent 1:1 complex with zinc(II) ion at physiological pH. The zinc(II) dissociation constant is much smaller than intracellular zinc(II) concentrations, which is a drawback on the dynamic analysis of intracellular zinc(II) ion. In order to shift the analytical range to the higher concentrations (I.e., biological conditions), we have designed some zinc-fluorophores (e.g., dansylamidoethyl-[12]aneN_3) having a larger K_d value. In this study we deterimined the synthetic method and characterization of those novel fluorophores and those zinc(II) complexes. Less