Reusable anion detection kit: An aqueous medium anion detection

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Abstract

Test paper coated with reduced Schiff base 1, can selectively detect fluoride and acetate ions in aqueous medium. With such a drastic color change, detection can be achieved by just using the naked-eye, unaided by any optical instrument. Interestingly, the test paper can be re-used several times after washing with 3% HCl and distilled water respectively.

Introduction

For decades, significant progress have been made in understanding the coordination chemistry of various metal ions with Schiff bases or reduced Schiff bases in order to develop the applications in catalysis [1], asymmetric synthesis [2], epoxidation [3], molecular separation and the biomedical field [4], [5]. However, reduced Schiff base as anion receptor has been confined to only in a few studies [6]. This relatively unexplored utilization is due to the fact that interactions between metal and reduced Schiff bases are in general stronger than the hydrogen bond interactions between anions and reduced Schiff bases.

The reason behind utilizing reduced Schiff bases over Schiff bases include (a) more flexibility around the Csingle bondN single bond, (b) the presence of secondary amine moiety that enhances hydrogen bond donor–acceptor functionalities and (c) that helps to overcome hydrolysis of the Schiff base. Moreover, reduced Schiff bases are easy to synthesize and purify compared to other chemosensor [7], [8].

Recently more and more work has been reported on the development of fluorescent and colorimetric sensors for anions but unfortunately, most of these experiments were carried out in non-aqueous medium which are far away from practical applications [9], [10], [11], [12].

Here, we report an easily synthesized and purification of reduced Schiff-base 1, which was coated on a test paper (test kits) and can recognize biologically important F and AcO anions in aqueous sample by naked-eye color changes without the need of any spectroscopic instruments. Interestingly, the test kits can be re-used several times for the detection of anions after washing with aqueous HCl (3%) solution and distilled water.

Section snippets

Reagents

All reagents and solvents were used as received from commercial sources without further purification. The anions, tetrabutylammonium fluoride hydrate (98%), tetrabutylammonium chloride hydrate (98%), tetrabutylammonium bromide (98%), tetrabutylammonium iodide (98%), tetrabutylammonium dihydrogenphosphate (97%), tetrabutylammonium acetate (97%), and Whatman 40 filter papers were purchased from Sigma–Aldrich Chemical Company. Tetrabutylammonium hydrogensulphate (97%) was purchased from

Results and discussion

Compounds 1 and 2 have been synthesized by reduction of the Schiff base prepared from the derivative of salicylaldehyde and o-phenylenediamine with NaBH4 in MeOH (Scheme 1) [15], [16], [17]. Reduction of Schiff base was confirmed by the disappearance of the characteristic peak of Cdouble bondN at 1641 cm−1. Compound 1 was characterized by NMR, IR, mass and X-ray single crystal structure (Supporting information, Figs. S1–S3 and Table S1). Single crystal X-ray diffraction studies indicate that 1 was

Conclusions

In summary, we have demonstrated an easily prepared reduced Schiff base 1, which has supramolecular host-guest complexing ability, confirmed by X-ray single crystal analysis, can selectively detect F and AcO ions without any spectroscopic instrumentation. We predict that the yellow color is developed in the presence of fluoride/acetate ions due to the formation of 1:1 hydrogen bonded complex between 1 and fluoride/acetate ion, which facilitates the charge transfer between the phenolic oxygen

Acknowledgments

This work is supported by grants from DST, India (Project No. SR/S1/PC/26/2008) and CSIR, India (Project No. 01(2161)07/EMR-II) to NG. SD and SJ would like to acknowledge UGC for fellowship. MAA thank to the VC of AU for giving him permission to work at CU.

Sasanka Dalapati received his B.Sc. (Hons) in pure chemistry from Ramakrishna Mission Vidyamandira, Belure (C.U.), in 2006 and M.Sc. in physical chemistry from University College of Science and Technology (C.U.) in 2008. Now he is working in the Department of Chemistry, University of Calcutta as a Ph.D. student. His research interest intends to focus on the design and synthesis of small molecular fragments and study their simple photophysics in condensed phase using conventional spectral

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    Sasanka Dalapati received his B.Sc. (Hons) in pure chemistry from Ramakrishna Mission Vidyamandira, Belure (C.U.), in 2006 and M.Sc. in physical chemistry from University College of Science and Technology (C.U.) in 2008. Now he is working in the Department of Chemistry, University of Calcutta as a Ph.D. student. His research interest intends to focus on the design and synthesis of small molecular fragments and study their simple photophysics in condensed phase using conventional spectral techniques.

    Md Akhtarul Alam received his Ph.D from Indian Institute of Technology Guwahati, Guwahati. Presently, as a faculty member in the Department of Chemistry, Aliah University he is working in the field of anions sensor by supramolecular assembly. His research interests include (1) supramolecular chemistry of dendritic macromolecules and (2) design and application of self-assembled chiral molecular architectures.

    Sankar Jana received his B.Sc. (Hons) in pure chemistry from Ramakrishna Mission Vivekananda Centenary College, Rahara (C.U.), in 2006 and M.Sc. in physical chemistry from University College of Science and Technology (C.U.) in 2008. Now he is working in the Department of Chemistry, University of Calcutta as a Ph.D. student. His research interest includes laser spectroscopy of simple synthetic small molecules in condensed phase and in jet cooled molecular beam.

    Rajat Saha received his B.Sc. (Hons) and M.Sc. degree from the University of Kaylyani in Physics. Now he is working in the Department of Physics, Jadavpur University as a Ph.D. student. His research interest includes solid-state physics and crystal engineering.

    Nikhil Guchhait received his Ph.D from Jadavpur University, Kolkata. Presently, as a faculty member in the Department of Chemistry, University of Calcutta. He is working in the field of photochemistry of some self designed molecular systems capable of charge transfer and proton transfer reactions. His interest also includes laser spectroscopy of aromatic molecules and solvated clusters in the supersonic jet cooled molecular beam.

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