Search

Ion pair receptors typically contain two separate binding sites, for the metal and the anion respectively. Here we report a less synthetically demanding approach, whereby we prepared a family of ion pair sensors based on a rhodamine fluorescent scaffold containing a tunable cation binding motif. When exposed to ion pairs, a competition for the metal ion is established between these ligands and anions. Structural and spectroscopic evidence showed that anions bind through weaker secondary interactions in the metal's outer coordination sphere and their presence influences the optical spectroscopic properties of the coordination complex in distinctive ways. The relationship between the binding site's metal affinity and its tunable properties, and the sensors' discriminatory power for anions was explained as a function of the metal ion's binding preferences. These effects were also exploited to discriminate cations and anions concurrently through multivariate data analysis methods.

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 ratio 1 ligand ratio 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.