A water-soluble bis(thiosemicarbazone) ligand. a sensitive probe and metal buffer for zinc

The first member of a water-soluble family of bis(thiosemicarbazone) ligands is reported. It forms a 1:1 complex with Zn(II) that absorbs intensely in the visible region (lambda(max) = 414 nm; epsilon = 1.8(4) x 10(4) M(-1) cm(-1); pH 7.3). Its affinity for Zn(II) (K(D) = 5.9(3) x 10(-9) M at pH 7.3) was determined by competition with ligand ethylene glycol O,O'-bis(2-aminoethyl)-N,N,N',N'-tetraacetic acid. Its potential application as a chromophoric probe was demonstrated by estimation of the Zn(II) binding affinities of the soluble metal-binding domains of two plant metal-transporting proteins.