Elsevier

Tetrahedron Letters

Volume 55, Issue 49, 3 December 2014, Pages 6623-6626
Tetrahedron Letters

Imidazole and imine coated ZnO nanoparticles for nanomolar detection of Al(III) and Zn(II) in semi-aqueous media

https://doi.org/10.1016/j.tetlet.2014.10.080Get rights and content

Abstract

Imidazole and imine-linked dipodal receptors were decorated on the surface of ZnO nanoparticles. Cation binding assays of these chemosensors showed that receptors 5 and 6 had high selectivity for Al(III) and Zn(II) ions, respectively. The detection limit for Al(III) with receptor 5 was 11 nM, and the detection limit for Zn(II) ion with receptor 6 was 23 nM.

Introduction

Recently, organic–inorganic hybrid chemosensors that recognize metal ions have gained considerable attention.1, 2, 3, 4, 5, 6 Ease of preparation, a low detection limit, and a broad detection range are advantageous features of organic–inorganic hybrid chemosensors. Aluminum is the third most abundant element in the earth’s crust, and trace amounts of aluminum are required for various normal human biological processes.7 However, excessive intake of aluminum may cause Parkinson’s disease, Alzheimer’s disease, and amyotrophic lateral sclerosis.8, 9, 10 In addition, Aluminum hinders the growth of plants.11 Zinc is another essential transition metal in human physiology,12, 13 playing roles in multiple biological processes including as an essential element of antioxidants and cofactors, gene transcription, neural signal transmission, regulation of metallo-enzymes, and apoptosis.14, 15, 16, 17 A deficiency in zinc may lead to growth retardation, diarrhea, impotence, and delayed sexual maturation.18, 19, 20 Therefore, it is essential to develop chemosensors for the detection of Al(III) and Zn(II) ions.

Fluorogenic chemosensors have enjoyed substantial interest due to their widespread applications in medical and environmental areas. Most of the reported chemosensors for Al(III) and Zn(II) have complex structures that require multistep synthetic routes.21, 22, 23, 24, 25, 26, 27, 28 Therefore, it is essential to develop sensors, which can be easily prepared and have a broad detection range, low detection limit, and a high binding constant.

We previously reported the preparation of dipodal imine-linked ZnO-coated chemosensors, which when decorated with compounds 2 and 3 showed high selectivity for Mg(II)29 and Co(II),30 respectively. To extend the scope of this methodology, two different organic ligands were attached to the surface of ZnO nanoparticles (ZnO-NPs). The best results were obtained using 1-methyl-3-carboxymethylimidazole (1) along with ligands 2 or 3 as shown in Figure 1. Receptors 5 and 6 exhibited selective affinity toward Al(III) and Zn(II), respectively.

Section snippets

Results and discussion

Ligands 1, 2, and 3 were synthesized by literature methods, and the ZnO-NPs were prepared via a sol-gel method.30, 31, 32 Decoration of the organic ligands on the surface of ZnO-NPs was performed through an in situ method. Receptor 4 was obtained by reaction of ligand 1 with Zn(NO3)2 and NaOH. The 1H NMR spectrum of receptor 4 was similar to that of ligand 1 except for signal broadening due to the presence of ZnO-NPs. Transmission electron microscopy (TEM) analysis showed that the modified

Conclusions

Members of a new class of chemosensors 4, 5, and 6, have been prepared. Receptor 5 showed high selectivity for Al(III) ions with a detection limit of 11 nM, whereas receptor 6 selectively recognized Zn(II) with a detection limit of 23 nM. Receptors 5 and 6 displayed sensitive and selective recognition of Al(III) and Zn(II), respectively, even in the presence of other metal ions.

Acknowledgments

This work was supported by the India-Korea Joint Program of Cooperation in Science &Technology (NRF-2011-0027710) and by a CSIR, India Project Grant (01(2417)/10 EMR-II).

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