Triazole-Linked Quinoline Conjugate of Glucopyranose: Selectivity Comparison among Zn(2+), Cd(2+), and Hg(2+) Based on Spectroscopy, Thermodynamics, and Microscopy, and Reversible Sensing of Zn(2+) and the Structure of the Complex Using DFT

[Image: see text] A water-soluble triazole-linked quinoline conjugate of glucopyranose (L) has been synthesized and characterized, and its single-crystal X-ray diffraction (XRD) structure has been established. Binding of L toward different biologically relevant metal ions has been studied using fluorescence and absorption spectroscopy in HEPES buffer at pH 7.4. The conjugate L detects Zn(2+) and Cd(2+) with 30 ± 2 and 14 ± 1-fold fluorescence enhancement, respectively, but in the case of Hg(2+), only a fluorescence quench was observed. The stoichiometry of the complex is 1:2 metal ion to the ligand in the case of Zn(2+) and Cd(2+) resulting in [Zn(L)(2)] and [Cd(L)(2)], and it is 1:1 in the case of Hg(2+), as confirmed from their electrospray ionization mass spectrometry (ESIMS) spectra. Zn(2+) shows greater exothermicity over Cd(2+), whereas Hg(2+) shows endothermicity , which supports the differences in their binding strength and the nature of the corresponding complex. L exhibits rod-shaped particles and upon complexation with Zn(2+), it exhibits sphere-like morphological features in scanning electron microscopy (SEM) images. However, clustered aggregates are observed in Cd(2+), whereas the [HgL] complex exhibits small fused spherical structures, and therefore the signature of these ions is seen in microscopy images. The computational studies revealed that the syn-[Zn(L)(2)] complex is stabilized by 9.7 kcal mol(–1) more than that in the case of anti-[Zn(L)(2)] owing to the formation of hydrogen bonds between the two glucosyl moieties within the syn-complex. Among the anions studied, [Zn(L)(2)] is sensitive and selective toward the phosphate ion (H(2)PO(4)(–)) with a minimum detection limit of 16 ± 2 ppb. Similarly, the [HgL] 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(2+) vs H(2)PO(4)(–) and IMPLICATION logic gate was built in the case of Hg(2+) vs CN(–).