An artificial siderophore for the detection of iron(III)

An artificial siderophore in the form of a squaraine dye (1) has been synthesized. The bidentate ligand chelates to Fe(III) between the deprotonated hydroxyl group on the ortho position of the ring adjacent to the carbonyl group of the cyclobutadiene ring. The optical response is due to a subtle geometry change of 1 on chelation to Fe(III). This artificial siderophore forms a 2 : 1 ligand : metal complex, as indicated by a sigmoidal isotherm (K-a = 10(7) M-1). The optical response on the addition of Fe( III) is observed at low concentrations in comparison to other metal salts. The X-ray crystal structure and calculated structures of dye (1) are also included, and will be discussed.