Elsevier

Talanta

Volume 81, Issues 1–2, 15 April 2010, Pages 678-683
Talanta

A stilbene-based fluoroionophore for copper ion sensing in both reduced and oxidized environments

https://doi.org/10.1016/j.talanta.2010.01.002Get rights and content

Abstract

The high sensitivity and abundance of fluorophores makes fluorescence technique among one of the most promising tools to develop chemo- and biosensors. Fluorescent sensors for ions, also called fluoroionophores, are commonly composed of an ion recognition unit (ionophore) and a fluorogenic unit (fluorophore). Here we report the synthesis and characterization of a new stilbene derivative conjugated with the di-2-picolylamine (dpa) group. It is found that the fluorescence of the stilbene derivative using dpa as ionophore is sensitive to copper ions, including Cu2+ (oxidized state) and Cu+ (reduced state). The sensitive and selective stilbene-based fluoroionophore for copper ions are based on the internal charge transfer along with the electron donor-π-acceptor stilbene motif and incorporate a dpa-containing aniline-derivatized ligand framework. By modifying the stilbene with di-2-picolylamine (dpa), the significant fluorescence quenching was observed upon binding with copper ions involving both the reduced and oxidized environments, indicating the great sensitivity and specificity for copper ion sensing. The presence of metal ions such as Ag+, Al3+, Ba2+, Ca2+, Cd2+, Co2+, Cr3+, Fe2+, Fe3+, Hg2+, K+, Mg2+, Mn2+, Na+, Ni2+, Pb2+, Sn2+, and Zn2+ had little influence on the selectivity and sensitivity of Cu2+ and Cu+. The optical sensor design undertakes promising for potential application to multiplex sensing of different analytes through distinct ligand conjugation and functionalization of individual fluorophore.

Introduction

Copper is third in abundance (after Fe3+ and Zn2+) among the essential transition metals in the human body and plays an important role in various physiologic processes. Owing to the possibility of leaking of copper ion into the environment through various routes and causing exposure of human body to high level of copper, recently, much effort have witnessed a large number of reports on exploring fluorescent chemosensors for the detection of copper ions due to their biological and environmental significance [1], [2], [3]. Fluorescent sensors for ions, also called fluoroionophores, are commonly composed of an ion recognition unit (ionophore) and a fluorogenic unit (fluorophore). One strategy employed in the design of fluoroionophores for metal cations is to conjugate a fluorophore unit with ionophore [4], [5], [6], [7]. There is important significance to understand the multiple roles of copper with availability of fluorescent probe systems permitting quantitative determination and detecting of copper fluxes and levels over a broad concentration range, especially at lower concentration of nM level. The high sensitivity and abundance of fluorophores makes fluorescence technique among one of the most promising tools for chemo- and biosensor development [8], [9], [10]. Currently most of the reported Cu2+ fluorescent sensors have been underwent a quenching of the fluorescence emission on the binding of the metal ion [11], [12], [13], [14], owing to its paramagnetic nature. In addition, although a few sensors in which the binding of a Cu2+ ion causes an increase in the fluorescence have also been reported, the fluorescence in most cases has high background with comparatively weak enhancement and usually indicate the sensitivity of μM scale. Therefore, the works related to highly sensitive and selective fluorescent sensor for the determination of Cu2+ are of great challenge and increasing interest. Herein, we report a new fluoroionophore (1) for both Cu2+ and Cu+ ions (in oxidized and reduced states, respectively) based on simple stilbene conjugated with a di-2-picolylamine (dpa) group as not only a fluorophore but also a ionophore, which undergoes a remarkable fluorescent quenching resulting from the binding of Cu2+ and Cu+ down to nM level and a high selectivity toward Cu2+ ion over other tested metal ions in aqueous solution.

Electron donor-π-acceptor (D-π-A) conjugated systems generally exhibit characteristic electronic absorption and emission spectra associated with internal charge transfer (ICT). Electronic or structural perturbations on the amine lone pair electrons influence the ICT properties and thus the electronic spectra, providing a useful signal transduction method for the design of chemosensors [3]. The di-2-picolylamine (dpa) group is known to possess a remarkable binding ability to some transition metal ions, which has been applied in the molecular design of fluoroionophores. Currently, most of copper ion sensors based on these dpa-derived D-π-A systems display the “on-off” type fluorescence sensing mode [4]. We describe here the design of a highly sensitive and selective small molecular stilbene-derived fluorescent sensor suitable for the copper ion (Scheme 1). In this system, the dpa ligand in 1 as an ionophore possess an excellent ability to coordinate transition metal ions and have demonstrated particular utility in the formation of metal ion sensors. Highly fluorescent sensory molecules are favourable in performing the “on-off” type of fluorescence signalling. Stilbene 1 displays fluorescence quenching upon the binding of transition metal ions, where the binding-triggered conformational twisting and in turn the inhibition of ICT play an important role. This modular approach allows for the easy variation of the components, which makes the process of system optimisation very simple compared with previously investigated fluorescent probes for copper ions.

Section snippets

Reagents

The following materials were used: α-bromo-p-tolunitrile and 2-(bromomethyl)pyridine hydrobromide (Sigma Chemical Co.), 4-nitrobenzaldehyde (Yizheng East Chemical Co.). Other chemicals were purchased from local company as analytical reagents and were distilled prior to use. Column chromatography was performed using EM Silica gel 60 (300–400 mesh).

Characterization

Melting points were uncorrected. All IR spectra were recorded at room temperature from 4000 to 450 cm−1. UV–vis spectra were recorded with a UV2300

Synthesis of stilbene fluorophores

Synthesis of the stilbene derivatives 1 and 2 is depicted in Scheme 2. The stilbene derivatives 3, trans-4-(4-nitrostyryl)benzonitrile was obtained through Wittig reaction of α-bromo-p-tolunitrile and 4-nitrobenzaldehyde. Reduction of 3 with SnCl2·2H2O in EtOH gave trans-4-(4-aminostyryl)benzonitrile (4), which were then reacted with 2-(bromomethyl)pyridine in acetonitrile to afford the stilbene derivatives 1 and 2 in 18.4% and 41.5% yield, respectively.

In the absorption spectrum of stilbene,

Conclusion

In conclusion, a copper-sensitive fluorescent fluoroionophores was synthesized by modifying the stilbene with di-2-picolylamine (dpa), in which significant fluorescence quenching was observed upon binding with copper ions, indicating a high sensitivity and specificity of this chemosensor for copper ions. The presence of metal ions such as Ag+, Al3+, Ba2+, Ca2+, Cd2+, Co2+, Cr3+, Fe2+, Fe3+, Hg2+, K+, Mg2+, Mn2+, Na+, Ni2+, Pb2+, Sn2+, and Zn2+ had little influence on the selectivity and

Acknowledgments

This work was financially supported by the NSFC (20874025), the Program for New Century Excellent Talents in Universities (NCET-07-00273), the “973” National Key Basic Research Program of China (2007CB310500), The Project Sponsored by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry, the Doctoral Fund of Ministry of Education of China (20060532022), the 985 fund of HNU.

References (17)

  • S. Bhattacharya et al.

    Tetrahedron Lett.

    (2000)
  • B. Valeur et al.

    Coord. Chem. Rev.

    (2000)
  • A. Torrado et al.

    J. Am. Chem. Soc.

    (1998)
  • Y. Zheng et al.

    Org. Lett.

    (2001)
  • A.P. De Silva et al.

    Chem. Rev.

    (1997)
  • L. Fabbrizzi et al.

    Chem. Eur. J.

    (1996)
  • F. Pina et al.

    Eur. J. Inorg. Chem.

    (2000)
  • Y. Zheng et al.

    J. Am. Chem. Soc.

    (2003)
There are more references available in the full text version of this article.

Cited by (18)

  • Synthesis and characterization of gated photochromic diarylethene functionalized with dipicolylamine

    2020, Dyes and Pigments
    Citation Excerpt :

    We demonstrated the photochromic reactivity could be controlled by the existence of Ag+ ion, where the existence of Ag+ ion can change the electronic state of BTF-AE. Dipicolylamine (DPA) has been widely adopted to develop the metal ions sensors, especially for zinc and copper ions [45–50]. Upon binding with metal ion, the excited state energy level of DPA functionalized fluorophore decreased, which leads to a blue shift in the absorption spectrum.

  • A bis(pyridine-2-ylmethyl)amine-based selective and sensitive colorimetric and fluorescent chemosensor for Cu<sup>2+</sup>

    2016, Sensors and Actuators, B: Chemical
    Citation Excerpt :

    Thus, the calculated electronic structure properties are in excellent agreement with the experimental results. In conclusion we designed and synthesized a novel DPA-based colorimetric and fluorescent chemosensor 1 that can be utilized as an excellent selective and sensitive colorimetric and fluorescent chemosensor to detect Cu2+ ion comparing with previously reported probes [31–34]. Confocal microscopy experiment also showed that the 1 can be used for monitoring Cu2+ within living HepG2 cells.

  • A BODIPY derivative as a colorimetric, near-infrared and turn-on chemosensor for Cu<sup>2+</sup>

    2012, Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy
    Citation Excerpt :

    Thus, the determination of copper is important due to its utility as well as toxicity. Most of the reported Cu2+ ions fluorescent chemosensors work in a turn-off mode due to the quenching effect of paramagnetic nature of Cu2+ [4–20]. For the practical applications, fluoroionphores showing turn-on (fluorescence enhancement) as a result of metal-ion binding are more interesting.

View all citing articles on Scopus
View full text