Characterization of rhodamine B hydroxylamide as a highly selective and sensitive fluorescence probe for copper(II)

doi:10.1016/j.aca.2007.08.025

Analytica Chimica Acta

Volume 632, Issue 1, 19 January 2009, Pages 9-14

https://doi.org/10.1016/j.aca.2007.08.025 Get rights and content

Abstract

Rhodamine B hydroxylamide (1) is characterized as a highly selective and sensitive fluorescence probe for Cu²⁺. Under the optimized conditions, the probe exhibits specific absorbance-on and fluorescence-on responses to Cu²⁺ only. This remarkable property may allow Cu²⁺ to be detected directly in the presence of the other transition metal ions, and such an application has been demonstrated to human serum. The reaction mechanism is also investigated and proposed as that the hydroxylamide group of 1 binds Cu²⁺, and the subsequent complexation of Cu²⁺ displays a high catalytic activity for the hydrolytic cleavage of the amide bond, causing the release of fluorophore (rhodamine B) and thereby the retrievement of absorbance and fluorescence. The recovered fluorescence intensity is proportional to the concentration of Cu²⁺ in the range 1–20 μM. The detection limit for Cu²⁺ is 33 nM (k = 3). The reaction mechanism described here may be useful for developing excellent spectroscopic probes with cleavable active bonds for other analytes.

Introduction

The development of fluorescent probes for determining various analytes with high selectivity and sensitivity is a subject of extensive research. However, design and synthesis of excellent fluorescent probes for selective detection of transition metal ions in biosystems remain a great challenge, because they often coexist and most of them have a similar reactivity with common fluorescent probes [1], [2], [3], [4]. Toward this end, a number of design strategies have been proposed, among which the usage of cleavable active bonds (including cleavable photophysical processes) as well as protecting–deprotecting groups has attracted much attention in the past few years [5]. This design strategy is based on the fact that some metal ions can promote the hydrolytic cleavage of specific chemical bonds (e.g., ester bond, amide bond, etc.) in probes, accompanying the change of spectroscopic properties. Several such spectroscopic probes have been proposed in this laboratory, for instance, for Pb²⁺ and singlet oxygen [6], [7]. Recently, we have reported a fluorescein-based probe with a cleavable bond for Cu²⁺[8]. However, the analytical wavelength of this probe seems less ideal.

In an effort to expand our research on developing Cu²⁺ fluorescent probes, we were interested in studying the properties of rhodamine B hydroxylamide 1 (Fig. 1), which is a rhodamine derivative that usually has a longer fluorescence emission than fluorescein has. On the other hand, the hydroxylamide group possesses a strong chelating ability and can form a 5-membered ring complex with Cu²⁺[9], [10], which might promote the redox hydrolysis of an amide bond [11], and thus cause the fluorescence recovery of rhodamine B. Herein, we report the tested results, which reveal that rhodamine B hydroxylamide indeed exhibits a highly selective fluorescence-on reaction with Cu²⁺, and may find a use in detecting Cu²⁺ in biosystems.

Section snippets

Apparatus

A Hitachi F-2500 spectrofluorimeter was used for fluorescence measurements. The absorption spectra were recorded with a Techcomp UV-8500 spectrophotometer (Shanghai, China). ¹H NMR and ¹³C NMR spectra were measured on a Bruker DMX-300 spectrometer at 300 MHz in CDCl₃ with tetramethylsilane as the internal standard. Mass spectra were measured with LC–MS (liquid chromatograph mass spectrometer) 2010A (Shimadzu). Elemental analyses were carried out with a Flash EA 1112 instrument. A model HI-98128

Absorption properties

The absorption spectra of 1 and its reaction solution with various concentrations of Cu²⁺ are shown in Fig. 2, from which it is seen that 1 has nearly no absorption in the visible region (curve 1). This may be attributed to the closed spirolactam form of 1. Upon reaction with Cu²⁺, however, the pink color indicative of rhodamine B is greatly restored with the increase of Cu²⁺ concentration (curves 2–11). More interestingly, the color-on reaction shows a high selectivity toward Cu²⁺ only, rather

Conclusions

The above results clearly show that probe 1 displays a highly selective and sensitive fluorescence response to Cu²⁺ only, rather than the other commonly coexisting ions. Its preliminary application has been successfully demonstrated to human serum. In addition, the combination of spectroscopic units with cleavable active bonds may serve as an important strategy for designing excellent spectroscopic probes for other analytes.

Acknowledgements

We are grateful to the NSF of China (Nos. 20525517 and 20435030), the Ministry of Science and Technology of China (2006AA02Z149), and the Chinese Academy of Sciences for financial support.

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Analytica Chimica Acta

Abstract

Introduction

Section snippets

Apparatus

Absorption properties

Conclusions

Acknowledgements

References (20)

Anal. Chim. Acta

Coord. Chem. Rev.

Anal. Chim. Acta

Tetrahedron Lett.

Angew. Chem. Int. Ed.

J. Am. Chem. Soc.

New J. Chem.

J. Am. Chem. Soc.

Curr. Org. Chem.

Biopolymers

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