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DOI: 10.1002/cplu.201402126
A Ratiometric Tetrazolylpyridine-Based “Turn-On”
Fluorescent Chemosensor for Zinc(II) Ion in Aqueous
Media
Palanichamy Kaleeswaran,[a] Ismail Abulkalam Azath,[a] Vairaperumal Tharmaraj,[a] and
Kasi Pitchumani*[a, b]
The highly selective ratiometric “turn-on” fluorescent sensing
of Zn2+ ion involving 2-(1H-tetrazole-5-yl)pyridine (2PT) in
aqueous medium is reported, which is not observed when
other metal ions are present. Upon 2PT binding selectively
with Zn2+ ion, a fluorescence enhancement is observed that is
attributed to an enhancement of localized emission and sup-
pression of excited-state intramolecular proton transfer. The
described sensing system involving 2PT is also successfully ap-
plied to the detection of Zn2+ ion in real samples with a detec-
tion limit of 7.5ꢀ10À7 m.
Introduction
Zinc, an essential trace element, is the second most abundant
metal in the human body[1] that plays a vital role in numerous
biological processes, such as peptide synthesis, DNA synthesis,
RNA transcription,[2] metabolism of cells, metalloenzyme regu-
lation, and neurophysiology, and it also induces the formation
of b-amyloid, which is related to neurological function. More
than 100 enzymes, such as peptidases,[3] carbonic anhydrases,[4]
and alcohol dehydrogenases,[5] require zinc for their catalytic
activity.[6] Labile zinc is found in the cells of mammalian brain,
pancreas, and prostate. Zinc and its compounds are widely
used in various industries, such as electroplating, rubber, dye,
wood preservatives, ointments, batteries, paint, and pharma-
ceuticals.[7]
moiety,[15] cyclam,[16] Znpyr,[17] Schiff base,[18] thiophene-based
moieties,[19] pyrazoline and pyrazole moieties,[20] and rhoda-
mine-based moieties.[21] However, construction of selective and
ratiometric sensors for Zn2+ remains in high demand. Thus
considerable attention has been focused on developing
simple, inexpensive, ratiometric, “turn-on” sensors for Zn2+ se-
lective determination. Also, understanding the biological and
environmental roles of Zn2+ requires robust and versatile
methods for quantification. The goal has been to devise “turn-
on” fluorescent sensors for Zn2+. However, these turn-on sig-
nals are insufficient for quantification.[22] An alternative ap-
proach involves developing sensors that display a change in
the ratio of multiple emission bands, thus providing quantifica-
tion as a significant advantage, and only a few ratiometric fluo-
rescent sensors for zinc were available recently.[23]
Uncontrolled release of zinc from mossy fiber terminals
causes brain injury, stroke, or neuronal death.[8] Studies show
that a lack of zinc in the body causes prostate cancer, diabetes,
Alzheimer’s disease,[9] night blindness,[10] growth retardation,
and skin lesions, and affects gene expression and enzyme ac-
tivity.[11] Thus, in view of its biological relevance and impor-
tance, a selective sensor for the monitoring of zinc is essential.
Although there are several analyses available to detect zinc
ion, such as atomic absorption spectrometry (AAS),[12] induc-
tively coupled plasma mass spectrometry,[13] and voltamme-
try,[14] they are all expensive and time-consuming. Recently,
many zinc sensors have been developed using the quinolone
Our interest in developing chemosensors for biologically im-
portant cations,[24] anions,[25] and neutral molecules[26] prompt-
ed us to develop a simple ratiometric fluorescence chemosen-
sor involving 2-(1H-tetrazole-5-yl)pyridine (2PT) for the selec-
tive sensing of Zn2+, which involves excited-state intramolecu-
lar proton transfer (ESIPT). Though several ESIPT sensors for
Zn2+ have been reported,[27] the present system is very simple
and is employed in aqueous medium.
Results and Discussion
Synthesis and characterization of the probe
[a] P. Kaleeswaran, Dr. I. A. Azath, Dr. V. Tharmaraj, Prof. K. Pitchumani
School of Chemistry, Madurai Kamaraj University
Madurai 625021 (India)
Compounds 2PT and 4-(1H-tetrazole-5-yl)pyridine (4PT) were
prepared by following the literature procedure[28] using picoli-
nonitrile and sodium azide in the presence of ZnCl2 as a cata-
lyst (Scheme 1), and the products were characterized by NMR
spectroscopy (Figures S1–S4 in the Supporting Information)
and ESI-MS (Figures S5 and S6). As ZnCl2 is used as a catalyst
during the synthesis of the probe, care is taken to remove it
completely from the reaction mixture and the synthesized 2PT
Fax: (+91)452 2459181
[b] Prof. K. Pitchumani
Centre for Green Chemistry Processes
School of Chemistry, Madurai Kamaraj University
Madurai 625021 (India)
Supporting information for this article is available on the WWW under
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemPlusChem 2014, 79, 1361 – 1366 1361