Abstract
The sensing properties of naphthaldimine-glucofuranose conjugates 1 and 2 towards metal ions were investigated by 1H NMR titration, Fourier-transform infrared spectroscopy (FTIR), absorbance, and fluorescence spectroscopic methods. The absorbance and fluorescence studies indicated that compound 1 formed coordination with Fe2+ and Cu2+ ions in dimethyl sulfoxide (DMSO) through color changes yellow to brown and colorless, respectively. The Job's plots using absorbance data showed metal-ligand binding ratio is 1:1 for both cases. The formation of 1-Fe2+ and 1-Cu2+ complexes have been analyzed by absorption and emission spectroscopy, high-resolution mass spectrometry (HRMS) data, FTIR, 1H NMR titration experiment, and density functional theory (DFT) calculations. The detection limits of naphthaldimine sugar conjugate 1 towards Fe2+/Cu2+ were calculated from UV-vis and fluorescence data according to the standard method. The sugar-naphthaldimine conjugate 2 has been used to establish the binding mode of 1 with Fe2+ or Cu2+ ions in DMSO.
Highlights
The design and synthesis of optical sensors to recognize biologically essential metal ions such as Cu2+, Fe2+, Fe3+, Mn2+, Zn2+, Ca2+, Na+, and K+ have gained much attention in supramolecular chemistry.[1]
The recognition properties of 1 and 2 towards metal ions were investigated by absorbance and fluorescence spectroscopic measurements, FTIR, 1H NMR titration, and mass spectrometry
(i) 1H NMR titration of 1 with Fe2+ ions, (ii) Job's plot, and ESI-MS data of sensor with Fe2+ and Cu2+ ions (Supporting information, Fig. S8, and Fig. S9), (iii) UV-vis. and fluorescence measurements of compound 2 (Supporting information, Fig. S7 and Fig. 10b), FTIR studies (Supporting information, Fig. S10), we proposed that two hydroxyl groups and imine N atom of sensor 1 formed a tridentate complex with Fe2+ or Cu2+ ions in DMSO after deprotonation of aromatic -OH group (Fig. S8/9)
Summary
The design and synthesis of optical sensors to recognize biologically essential metal ions such as Cu2+, Fe2+, Fe3+, Mn2+, Zn2+, Ca2+, Na+, and K+ have gained much attention in supramolecular chemistry.[1]. It was extracted from the literature that different types of sensors have been developed for selective differentiation of Pb2+ and Hg2+,[32] Cu2+ and Hg2+,[33,34] Mg2+ and Zn2+,[35] Au3+ and Hg2+,[36] Zn2+ and Cu2+,[37] and Cd2+, Hg2+ and Pb2+[38] by changing of tested media. These studies informed that solvent has a major role in the selection of metal ions by a sensor. It is worth mentioning that this is the second example of a sugar-modified solvent-controlled sensor for the detection of metal ions.[34]
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