Triazole-Linked Quinoline Conjugate of Glucopyranose: Selectivity Comparison among Zn, Cd, and Hg Based on Spectroscopy, Thermodynamics, and Microscopy, and Reversible Sensing of Zn and the Structure of the Complex Using DFT.

A water-soluble triazole-linked quinoline conjugate of glucopyranose () has been synthesized and characterized, and its single-crystal X-ray diffraction (XRD) structure has been established. Binding of toward different biologically relevant metal ions has been studied using fluorescence and absorption spectroscopy in HEPES buffer at pH 7.4. The conjugate detects Zn and Cd with 30 ± 2 and 14 ± 1-fold fluorescence enhancement, respectively, but in the case of Hg, only a fluorescence quench was observed. The stoichiometry of the complex is 1:2 metal ion to the ligand in the case of Zn and Cd resulting in [Zn()] and [Cd()], and it is 1:1 in the case of Hg, as confirmed from their electrospray ionization mass spectrometry (ESIMS) spectra. Zn shows greater exothermicity over Cd, whereas Hg shows endothermicity , which supports the differences in their binding strength and the nature of the corresponding complex. exhibits rod-shaped particles and upon complexation with Zn, it exhibits sphere-like morphological features in scanning electron microscopy (SEM) images. However, clustered aggregates are observed in Cd, whereas the [Hg] complex exhibits small fused spherical structures, and therefore the signature of these ions is seen in microscopy images. The computational studies revealed that the -[Zn()] complex is stabilized by 9.7 kcal mol more than that in the case of -[Zn()] owing to the formation of hydrogen bonds between the two glucosyl moieties within the -complex. Among the anions studied, [Zn()] is sensitive and selective toward the phosphate ion (HPO ) with a minimum detection limit of 16 ± 2 ppb. Similarly, the [Hg] can act as a secondary sensor for CN while also exhibiting reversibility. Based on the input-output characteristics, INHIBIT logic gate was built in the case of Zn vs HPO and IMPLICATION logic gate was built in the case of Hg vs CN.