A fluorescent di-zinc(II) complex of bis-calix[4]arene conjugate as chemosensing-ensemble for the selective recognition of ATP

Abstract

A triethylene glycol di-imine locked triazole linked bis-calix[4]arene conjugate L has been synthesised and characterised. Conjugate L exhibits high fluorescence enhancement towards Zn²⁺ among the 13 metal ions studied down to a lower detection limit of ∼12 ppb. The absorption and visual colour change experiments differentiated the Zn²⁺ from the other metal ions studied. The isolated zinc complex, [Zn2L] has been used as a chemo-sensing ensemble for the recognition of anions based on their binding affinities towards Zn²⁺. [Zn₂L] was found to be sensitive and selective towards phosphate-bearing species and in particular to adenosine triphosphate (ATP²⁻) among the other 20 anions studied as observed based on the changes occurred in the fluorescence intensity. The selectivity of the ATP²⁻ has been shown on the basis of the changes observed in the emission and absorption spectral studies. The lowest detectable concentration for ATP²⁻ with the chemo-sensing ensemble [Zn2L] is 348 ppb in methanol. The fluorescence quenching by the phosphate-based anions has been modelled by molecular mechanics studies and found that the anions possessing two or more phosphate moieties can only bridge between the two zinc centres, and hence those possessing only one phosphate moiety (H₂PO₄₋ and AMP²⁻) are ineffective.