A turn-on fluorescence chemosensor based on a tripodal amine [tris(pyrrolyl-α-methyl)amine]-rhodamine conjugate for the selective detection of zinc ions

Rathinam Balamurugan, Wen I. Chang, Yandison Zhang, Sri Fitriyani, Jui Hsiang Liu

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Abstract

A novel tetradendate ligand derived from a tris(pyrrolyl-α-methyl)amine (H3tpa) and rhodamine-based conjugate (PR) has been designed for use as a sensor, synthesized and characterized spectroscopically. PR {(tris(5-rhodamineiminopyrrol-2-ylmethyl)amine)} serves as a selective colorimetric as well as a fluorescent chemosensor for Zn2+ in acetonitrile/water (1:1, v/v). In the presence of Zn2+, PR exhibited obvious absorption (558 nm) and emission (577 nm) peaks whose intensity increased along with increasing Zn2+ concentrations. Titration experiments revealed that a large excess of Zn2+ was required to saturate the absorption (λmax) and emission intensities. Upon the addition of 1000 equivalents of Zn2+, the fluorescence intensity of the PR underwent an ∼500-fold increase (Φf = 0.34) with the emission maximum at 580 nm. These kinetics studies demonstrated that the absorption and emission changes were proportional to the Zn2+ concentration. The color of the solution changed from colorless to a dark pink color. The fluorescence of the PR-Zn2+ complex can be reversibly restored by using ammonium water or by heating. Competitive ion tests revealed that the intensity of PR-Zn2+ was not suppressed by excess amounts of other metal ions. The counter anions did not exert obvious influences on the absorption and emission profiles. 1H-NMR and FT-IR spectroscopic investigations of PR and PR-Zn2+ revealed that the pyrrole motifs, -CN- groups and spirolactam of rhodamine B are capable of coordinating cation guest species. Because each arm of the tripodal ligand tautomerizes independently, only moderate fluorescence enhancement could be seen until all three -CN- groups were coordinated by zinc, which may be due to the spirolactam ring opening mechanism of the rhodamine unit. Once all three -CN- groups were locked by coordinating with excess of Zn2+, the isomerization was arrested, and PR exhibited highly enhanced fluorescence. In addition, energy optimized structures of PR were found to be cage-like by Gaussian 09, further supporting that it can access a large excess of Zn2+. Intriguingly, imaging of HeLa cells by using a confocal microscope revealed that this PR probe could be used for biological applications.

Original languageEnglish
Pages (from-to)5456-5462
Number of pages7
JournalAnalyst
Volume141
Issue number18
DOIs
Publication statusPublished - 2016 Sep 21

All Science Journal Classification (ASJC) codes

  • Analytical Chemistry
  • Biochemistry
  • Environmental Chemistry
  • Spectroscopy
  • Electrochemistry

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