Aroyl hydrazone with large Stokes shift as a fluorescent probe for detection of Cu2+ in pure aqueous medium and in vivo studies

doi:10.1016/j.jphotochem.2020.112501

Journal of Photochemistry and Photobiology A: Chemistry

Volume 395, 15 May 2020, 112501

https://doi.org/10.1016/j.jphotochem.2020.112501 Get rights and content

Highlights

•
Aroyl hydrazone based probe with large Stokes shift for Cu²⁺ sensing is employed.
•
The sensing property is monitored by UV–vis and fluorescence studies.
•
It is operative in pure aqueous medium and has very high binding constant.
•
The binding mode has been explained on the basis of Intramolecular Charge Transfer.
•
The probe has been applied for in vivo sensing of Cu²⁺ in Drosophila.

Abstract

An aroyl hydrazone based fluorescent probe, hpsh, has been developed for the selective detection of Cu²⁺ ions in pure aqueous medium by static fluorescence quenching. The fluorescence quenching of hpsh in the presence of Cu²⁺ takes place as a result of ground state complex formation through intramolecular charge transfer (ICT). Addition of Cu²⁺ ions changes the color of the solution from colorless to yellow-green which is clearly visible by naked eye. Large Stokes shift of hpsh prevents the self-quenching of the probe in absence of metal ions. The observed stoichiometry between Cu²⁺ and probe has been found as 1:2 (M: L). MTT assay of hpsh on fruit flies confirms that the probe is non-toxic and biocompatible. The plausible in vivo bioimaging application of the probe to detect Cu²⁺ in Drosophila gut tissues as well as in adult fruit fly has been investigated with excellent results.

Graphical abstract

Introduction

Significant possibilities in the field of fluorescent imaging tools capable of monitoring specific targets are continuously being explored in recent years [1,2]. In this regard, many attempts have been made to design small size molecular fluorophores with oriented chemical,

photophysical and biological properties that monitor toxic transition metal ions [3,4]. Cu²⁺ sensors have been the subject of intense study owing to its environmental significance, pivotal role in various physiological processes and in a number of neurodegenerative diseases [[5], [6], [7], [8]]. Excess copper is considered as a biohazard as it is prone to produce reactive oxygen species (ROS), activating oxidative damage of protein, nucleic acid and lipids [9]. Although amount of copper can be calculated precisely by modern analytical techniques viz. Atomic absorption spectroscopy, Ion selective electrode and inductively coupled plasma mass spectroscopy [10,11], but these techniques bear some underlying drawbacks as these are relatively complicated, labor-intensive and costly. These techniques hamper the practical applications of the probe in biological field. Owing to high sensitivity, selectivity, easy detection by visual or instrumental methods and fast response, fluorescence is the most promising tool to meet the demand of in-field monitoring [[12], [13], [14]]. Therefore, the development of easily accessible and environment-friendly molecular probes for Cu²⁺ detection is still in pursuit [15,16].

For bio application, a practical imaging agent must be stable, nontoxic, fairly soluble in water and produce complete quenching of fluorophore upon binding the analyte under study. However, in most of the cases self-quenching takes place in fluorophores showing small Stokes shifts viz. BODIPY, coumarin, rhodamine and fluorescein [17]. Though they are known to show strong fluorescence in dilute solutions but turn weakly fluorescent in concentrated solutions or in the solid state due to severe self-absorption among closely located molecules. Thus, a large Stokes shift is a great and significant property of a fluorophore [18]. Sie et al. (2017) [16] have reported a Schiff base sensor for the detection of Cu²⁺, Co²⁺ and Hg²⁺ ions in water/DMSO matrix with real sample analysis, Aderinto et al. (2017) [19] have reported an ICT mechanism based Cu²⁺ sensor in tris-HCl buffer/DMF matrix with its application in real water samples, Bu et al. (2014) [20] have reported an indole base based Schiff base for the detection of Cu²⁺ in DMF, More and Shankarling (2017) [13] have reported a reversible and turn off fluorescence sensor for Cu²⁺ ion in ACN-HEPES buffer media. In all the above reported works there are some drawbacks viz. absence of biological application, mixed matrix solution, reversibility of the probe. Keeping these precedencies in view, in this paper, a highly selective quenching fluorescent probe with large Stokes shift for Cu²⁺ in aqueous media has been reported, which acts by way of static quenching mechanism. Herein, the current study attempts to gain a clear and deeper understanding of this phenomenon by means of in vivo trapping of Cu²⁺ in gut tissue of Drosophila.

Section snippets

Reagents

Analytical reagent grade 2-hydroxypropiophenone (Sigma–Aldrich, USA), salicylic acid hydrazide (TCI Chemicals, India), solvents (Merck Chemicals, India), Chloride salts of Na⁺, K⁺, Mg²⁺, Ca²⁺, Ba²⁺, Al³⁺, Cr³⁺, Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Pb²⁺ (Merck Chemicals, India) were purchased and used without any further purification. Metal salt solutions were prepared in milli Q water.

Synthesis of probe

Synthesis of the probe hpsh was done by the reported method [21] by refluxing a mixture of salicylic

hpsh

Yield (77 %). M.P. 239 ^oC. Anal. Calc. for C₁₆H₁₆N₂O₃ (284.31): C, 67.50; H, 5.56; N, 9.76. Found: C, 67.35; H, 5.46; N, 9.87 %. HR-MS: [M + Na]⁺, m/z, 307.10. IR (cm⁻¹, KBr): ν(O–H) 3415, ν (N–H) 3326, ν (C = O) 1644, ν (C double bond N) 1614, ν (N–N) 926. 180. ¹H NMR data: 1.23 (3H, J =7.2 Hz, CH₃); 2.90 (2H, CH₂), 6.903–8.005 (Ar–H), 11.68 (s, 1H, NH), 13.19 (s, 1H, OH). ¹³C NMR (DMSO-d6): 11.05 (CH₃); 21.22 (CH₂); 113.47–132.84 (aromatic carbons);83 163.01 (CN); 166.76 (C–OH); 185.27 (C = O).

hpsh-Cu²⁺

Green,

Conclusions

In this study, we have reported a fluorescent probe, hpsh having large Stokes shift for selective and distinct quenching of Cu²⁺ ion in pure aqueous medium. The ground state complex formation of hpsh with Cu²⁺ reveals the quenching to be static in nature. The functioning of hpsh is regulated by intramolecular charge transfer (ICT) mechanism. Thus, hpsh could be applied as a highly selective fluorescence probe for Cu²⁺ ion without any interference. Moreover, according to the Jobs plot, a 1: 2

CRediT authorship contribution statement

Romi Dwivedi: Conceptualization, Methodology, Visualization, Investigation, Data curation, Writing - original draft, Software. Saumya Singh: Resources. Brijesh Singh Chauhan: Investigation. S. Srikrishna: Formal analysis. Anoop Kumar Panday: Software. Lokman H. Choudhury: Software. Vinod Prasad Singh: Supervision, Validation.

Declaration of Competing Interest

There are no conflicts to declare.

Acknowledgements

The authors thank the Head, S.A.I.F., Indian Institute of Technology, Patna, India for recording mass spectra and fluorescence data.

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Aroyl hydrazone with large Stokes shift as a fluorescent probe for detection of Cu2+ in pure aqueous medium and in vivo studies

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Reagents

Synthesis of probe

hpsh

hpsh-Cu2+

Conclusions

CRediT authorship contribution statement

Declaration of Competing Interest

Acknowledgements

Sens. Actuators B

Sens. Actuators B Chem.

Talanta

Sens. Actuators B Chem.

J. Lumin.

J. Org. Chem.

Org. Lett.

Polyhedron

Talanta

Eur. J. Med. Chem.

Sens. Actuators B Chem.

Tetrahedron

J. Photochem. Photobiol. A

J. Lumin.

New J. Chem.

Analyst

Analyst

New J. Chem.

Nutr. Rev.

Aroyl hydrazone with large Stokes shift as a fluorescent probe for detection of Cu²⁺ in pure aqueous medium and in vivo studies

hpsh-Cu²⁺