Synthesis of triazole linked fluorescent amino acid and carbohydrate bio-conjugates: a highly sensitive and skeleton selective multi-responsive chemosensor for Cu(ii) and Pb(ii)/Hg(ii) ions

Abstract

A set of triazole-based chromogenic and fluorescent chemosensors with amino acid/carbohydrate–fluorophore conjugates have been designed and synthesized. The metal cation-sensing properties of glycine–anthracene, C₂₄H₂₄O₄N₄ (3), glycine–pyrene C₂₆H₂₄O₄N₄ (4), glucose–anthracene, C₃₂H₃₃O₁₀N₃ (5) and glucose–pyrene, C₃₄H₃₃O₁₀N₃ (6) bio-conjugates have been studied systematically. The significant changes in their absorption spectra are accompanied by a strong color change from light yellow to brown for 3 and 4 and colorless to greenish blue for 5 and 6. Receptors 3 and 4 have potential in the “naked eye” detection of Cu²⁺ and 5 and 6 for Pb²⁺/Hg²⁺ ion. The receptors 3 and 4 show fluorescence diminution following Cu²⁺ coordination within the limit of detection at 0.89 parts per billion (ppb) and this is unprecedented, whereas the receptors 5 and 6 present drastic fluorescence quenching upon addition of Hg²⁺ and Pb²⁺ within the limit of detection at 4 and 2 ppb respectively. Interestingly, their fluorescence and colorimetric responses are preserved in the presence of water that can be used for the selective colorimetric detection of these ions in aqueous environments. Along with the spectroscopic data, combined ¹H NMR titration of the complexes and the DFT studies suggest the proposed coordination modes.