Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Novel dual-functional fluorescent sensors based on bis(5,6-dimethylbenzimidazole) derivatives for distinguishing of Ag+ and Fe3+ in semi-aqueous medium
Graphical Abstract
Introduction
Along with the wide use of silver ion (Ag+) as one of heavy metal ions in medicine, electronics, photography and other industrial sectors, the hazard of environmental pollution and the accumulate in the human body caused by Ag+ become more and more serious [1]. It is very necessary to develop the fluorescent sensor for Ag+ detection with high sensitivity and fast response [[2], [3], [4], [5], [6], [7]]. At the same time, as the most abundant transition metal in biological systems, iron plays an important role in many cellular and biochemical process. Both deficiency and excess accumulation of iron in the human body can induce various biological disorders [8]. Thus, more and more attention is paid to the design and synthesis of fluorescent sensors for Fe3+ [[9], [10], [11], [12], [13], [14], [15]].
Obviously, the development of novel sensors for distinguishing multiple analytes is of great significance because they are more efficient than the sensors for single target [[16], [17], [18], [19]]. Recently, several fluorescent sensors have been reported for the simultaneous detection of two or more metal ions [[20], [21], [22], [23], [24], [25], [26]], but only a few sensors can exhibit a distinct fluorescence response towards two or more metal ions [[27], [28], [29]]. At the same time, due to the strong complexing ability of N atom in CN of benzimidazole ring with metal ions, benzimidazole fluorophore has been widely used in the design of fluorescent sensors for sensing Ag+ [[30], [31], [32]] or Fe3+ [[33], [34], [35], [36]], and some benzimidazole- based sensors exhibit a distinct spectral response towards two metal ions, such as Fe3+/Cu2+ [37], Fe3+/Zn2+ [38] and Al3+/Cu2+ [39]. However, to the best of our knowledge, there is no report about the sensors for distinguishing of Ag+ and Fe3+.
It is worth noting that multi-heteroatom sites in sensors may better complex with more metal ions to detect multiple metal analytes [[37], [38], [39]]. Herein, in order to develop fluorescent sensors for metal ions, three novel bisbenzimidazole-based fluorescent sensors have been designed and synthesized (Scheme 1). Their photophysical properties, selectivity and sensitivity for metal ions and sensing mechanism have been investigated. To our delight, sensors 4 show high selectivity and sensitivity, and fast-response for the distinct detection of Ag+ and Fe3+ in semi-aqueous medium over a wide pH range.
Section snippets
Chemicals and Apparatus
All reagents were purchased from commercial suppliers and used without purification. Melting points were performed on an X-5 digital melting point apparatus without correcting. 1H and 13C NMR spectra were collected on a BRUKER DRX-400 spectrometer with CDCl3 used as the solvent and tetramethylsilane (TMS) as an internal standard. Mass spectra (MS) were recorded on a Thermo LCQ DECA XP MAX mass spectrometer. Elemental analysis was obtained with Perkin Elmer Series II 2400. UV–vis spectra were
Synthesis and Photophysical Properties of 4
As shown in Scheme 1, using readily available 2,6-naphthalenedicarboxylic acid 1, 4,5- dimethyl-1,2-phenylenediamine 2 and 1-bromoalkane as starting materials, the target molecules 4a–4c were synthesized by a simple condensation reaction and subsequently the N-alkylation reaction. During the preparation, the crude product 3 just was washed three times with ethyl alcohol after the first reaction step. And fairly pure compound 3 could be obtained. Without further purification, compound 3 could be
Conclusions
In summary, three novel bisbenzimidazole-based fluorescent sensors possessing a distinct spectral response towards Ag+ and Fe3+ have been designed and synthesized. These sensors show high selectivity and sensitivity, and fast response towards Ag+ and Fe3+ in semi-aqueous solution over a wide pH range (4–13). The 1H NMR titration experiments reveal that Ag+ and Fe3+ can bind with the N atom in CΝ of benzimidazole ring to form metal complex, resulting in different absorption as well as
Novelty Statement
Benzimidazole-based dual-functional sensors 4 for highly selective distinguishing of Ag+ and Fe3+ with distinct spectral response in multiple visual detection modes are firstly developed. They can rapidly and steadily work in a semi-aqueous solution with a wide range of pH 4–13.
Acknowledgements
We are grateful to Guangzhou Science and Technology Project Scientific Special (General Items, No. 201607010251), Guangdong Provincial Science and Technology Project (No. 2017A010103016) and the NSF of Guangdong Province (No. 2014A030313429) for financial support.
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2022, Science of the Total EnvironmentCitation Excerpt :Fe3+, Cyt C, and phosphate were also discovered in real specimens. For the first time, Wu et al. (2019) produced three innovative bisbenzimidazole derivatives and used them as dual-functional fluorescence sensors to detect Ag+ and Fe3+ ions in a semi-aqueous environment with unique spectrum responses. After the inclusion of Ag+, the absorption intensity was dramatically reduced.