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 ZnII that absorbs intensely in the visible region (λmax = 414 nm; ε = 1.8(4) × 104 M−1 cm−1; pH 7.3). Its affinity for ZnII (KD = 5.9(3) × 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 ZnII binding affinities of the soluble metal-binding domains of two plant metal-transporting proteins.