Water soluble 8-hydroxyquinoline conjugate of amino-glucose as receptor for La³⁺ in HEPES buffer, on Whatman cellulose paper and in living cells

Abstract

A water-soluble glucopyranosyl conjugate, L, has been synthesized and characterized by different analytical and spectral techniques. The L has been demonstrated to have switch-on fluorescence enhancement of ∼75 fold in the presence of La³⁺ among the nine lanthanide ions studied in the HEPES buffer at pH 7.4. A minimum detection limit of 140 nM (16 ± 2 ppb) was shown by L for La³⁺ in the buffer at physiological pH. The utility of L has been demonstrated by showing its sensitivity toward La³⁺ on Whatman filter paper strips. The reversible and reusable action of L has been demonstrated by monitoring the fluorescence changes as a function of the addition of La³⁺ followed by F^– and HPO₄^2– ions. The complexation of L by La³⁺ was shown by absorption spectra wherein isosbestic behavior was observed. The Job’s plot suggests a 2:1 complex between L and La³⁺, and the same was supported by ESI-MS. The control molecular study revealed the necessity of hydroxy quinoline and the amine group for La³⁺ ion binding and the glyco-moiety to bring water solubility and biocompatibility. The structural features of the [2L+La³⁺] complex were established by DFT computational calculations. The chemo-ensemble, [2L+La³⁺], is shown responsible for providing intracellular fluorescence imaging in HepG2 cells.