Selective recognition of Fe²⁺ in aqueous solution by chalcones

Recognition of metal ions in aqueous media has direct impact for designing new supramolecular hosts for targeting biochemical pathways. In the present work we have studied the binding behavior of three simple chalcones with variation in number of phenolic OH groups. These chalcones showed very good binding capabilities towards metal ions in CH₃OH-H₂O (1:1, v/v) solvent system. The receptors R1 has interacted with all metal ions, which are used in the present study through 2:1 mode of complexation whereas R2 have showed equilibrium between the complexes of 2:1 and 1:1 with few exceptions. The highest association constants (K₂₁) of R1 and R2 for Fe²⁺ is observed as 1.1 × 10⁹ (4) M^-1 and 2.3 × 10⁸ (7) M^-1 respectively by fluorescence titration method. But R3, which is lack of any phenolic OH group, binds all the metal ions through the formation of 1:1 mode of complex formation by exploiting the only one donor site as carbonyl 'O' atom resulting lower association constant for all the metal ions. So intermolecular hydrogen bonding as well as π- π stacking interaction forced the receptors R1 and R2 to arrange in a pseudo cleft orientation for the recognition of metal ions in 2:1 mode of complex formation. The binding behaviour of the receptors with few alkali metal ions (Na⁺, K⁺ and Cs⁺) and alkaline-earth metal ions (Mg²⁺, Ca²⁺ and Ba²⁺) are also studied and observed weak binding nature in compared with the transition metal ions.