A Selective and Reversible Fluorescent Probe for Cu and GSH Detection in Aqueous Environments

Abstract

Cu²⁺ and Biothiols play a critical role in diverse biological processes in organisms. Herein, we reported using a well‐known ESPT molecule 2‐(2’‐Pyridyl)benzimidazol(PBI) as a fluorescent probe to detect Cu²⁺ and GSH in aqueous solution. PBI presented a rapid fluorescence “ON‐OFF” response on Cu²⁺ over other metal cations, with a low detection limit (39.4 nM), and also been applied in real water samples detection. Through mass spectroscopy, single crystal X‐ray diffraction and DFT calculation, we confirmed that two PBI molecules would form a stable complex with one Cu²⁺. After adding GSH, PBI‐Cu²⁺ complex would release the free probe, and the “on‐off‐on” recognition process to achieve continuous detection of Cu²⁺ and GSH.

Full text

A Selective and Reversible Fluorescent Probe for Cu2+and
GSH Detection in Aqueous Environments
Zaiwu Wang+,[a] Zuyao Li+,[a] Junhao Huang,[a] Shu Han,[a] Xueming Li,*[a] and Zizhou Wang*[b]
Cu2+and Biothiols play a critical role in diverse biological
processes in organisms. Herein, we reported using a well-
known ESPT molecule 2-(2’-Pyridyl)benzimidazol(PBI) as a
fluorescent probe to detect Cu2+and GSH in aqueous solution.
PBI presented a rapid fluorescence “ON-OFF” response on Cu2+
over other metal cations, with a low detection limit (39.4 nM),
and also been applied in real water samples detection. Through
mass spectroscopy, single crystal X-ray diffraction and DFT
calculation, we confirmed that two PBI molecules would form a
stable complex with one Cu2+. After adding GSH, PBI-Cu2+
complex would release the free probe, and the “on-off-on”
recognition process to achieve continuous detection of Cu2+
and GSH.
Introduction
Cu2+as an important ion in plants and animals is needed for
various biological functions.[1] Excessive Cu2+intake may cause
neurodegenerative diseases, such as Menkes, Wilson’s and
Alzheimer.[2,3] Hence, accurate determination of Cu2+in living
organisms is critical.[4] Various analytical methods have been
developed, including high-performance liquid chromatography
(HPLC), atomic absorption spectroscopy, inductively coupled
plasma mass spectrometry (ICP-MS), voltammetry.[5] Neverthe-
less, these methods were limited by high costs, laborious
operational methods and inability to response immediately. In
recent years, the use of chemical optical probes as an
alternative to these traditional approaches has garnered a lot
of attention.[6–8] Numerous chemical fluorescence probes have
been reported, however some disadvantages, such as long
response time, poor anti-interference ability and poor solubility
in water limited their applications.[7]
Biothiols are molecules that play a fundamental role in
living systems and a key role in a variety of biological processes
in the body.[9–11] However, some fluorescent thiol probes were
still difficult to distinguish GSH/Cys/Hcy as a result of their
similar structure.[12,13] For now, using Cu2+complexes as a
fluorescent probe may be one of the most promising methods
for detection of biothiols.[14–18]
Reported excited-state intramolecular proton-transfer
(ESIPT) based fluorescent probes were mainly designed based
on the structures of 2-(2’-hydroxyphenyl) benzoxazole (HBO),
2-(2’-hydroxyphenyl)benzimidazole (HBI) and 2-(2’-
hydroxyphenyl)benzothiazole (HBT), in which the weak basic
heterocyclic structures were used as hydrogen-bonded
acceptors.[19] Unlike ESIPT probes, excited-state proton transfer
(ESPT) of PBI assisted by a single water molecule. A water
molecule could connect the pyridine N atom and benzimida-
zole NH group with a hydrogen-bonded network to process
ESPT. When PBI coordinated with Cu2+, the ESPT would be off,
and resulting in fluorescence quenching. In addition, if Cu2+
and GSH were added sequentially, ESPT fluorescence of PBI
would go through an “on-off-on” process for recognition of
Cu2+and GSH in HEPES buffer solution. Consequently, it is of
great significance to develop a new fluorescent probe with
high selectivity and sensitivity that can be used for the
detection of Cu2+and GSH in aqueous environments.
In this paper, a new type of “on-off-on” PBI was used to
detect Cu2+and GSH. The PBI exhibited a highly selective and
sensitive response to Cu2+among the various competing metal
ions and anions with a low detection limit (39.4 nM). Also, the
PBI-Cu2+complex has an excellent potential for GSH detection.
The mechanism of luminescence change was characterized by
Mass Spectra, Titration curve and DFT calculation, indicating a
2 : 1 stoichiometric complexation between PBI and Cu2+. In
addition, we can visualize from the crystal structure that the
coordination ratio of PBI and Cu2+is 2 : 1.
Results and Discussion
Synthesis of PBI
1,2-phenylenediamine (1.08 g, 10 mmol), 2-pyridine
formaldehyde (1.12 g, 10.5 mol) and methanol (40 mL) were
mixed and stirred at room temperature for 4 h under the blue
LED lamp (15 W, 395 nm) (Scheme 1). Then the solvent was
removed in vacuum, the residue was purified by chromatog-
raphy (petroleum ether (PE): ethyl acetate (EA) =3 : 1) to obtain
1.05 g PBI(white powder, yield 45.8 %). Melting point: 217–
217.6 °C. 1H NMR (500 MHz, DMSO) δ=13.12 (s, 1H), 8.74–8.75
[a] Z. Wang,+Z. Li,+J. Huang, S. Han, Dr. X. Li
Guangxi Key Laboratory of Electrochemical and Magneto-chemical
Function Materia, College of Chemistry and Bioengineering, Guilin
University of Technology,
541004 Guilin, China
E-mail: lixueming@glut.edu.cn
[b] Dr. Z. Wang
School of Chemistry and Chemical Engineering, Guangzhou University,
510006 Guangzhou, China
E-mail: wzzh@gzhu.edu.cn
[+]Equal first author.
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/slct.202300012
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