A ratiometric fluorescence chemosensor for Mg2+ ion and its live cell imaging

Accepted Manuscript Title: A Ratiometric Fluorescence Chemosensor for Mg2+ Ion and Its Live Cell Imaging Authors: Pitchai Marimuthu, Andy Ramu PII: DOI: Reference:

S0925-4005(18)30656-7 https://doi.org/10.1016/j.snb.2018.03.158 SNB 24443

To appear in:

Sensors and Actuators B

Received date: Revised date: Accepted date:

28-8-2017 22-3-2018 26-3-2018

Please cite this article as: Pitchai Marimuthu, Andy Ramu, A Ratiometric Fluorescence Chemosensor for Mg2+ Ion and Its Live Cell Imaging, Sensors and Actuators B: Chemical https://doi.org/10.1016/j.snb.2018.03.158 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

A Ratiometric Fluorescence Chemosensor for Mg2+ Ion and Its Live Cell Imaging

Pitchai Marimuthua and Andy Ramua* a

Department of Inorganic Chemistry, School of Chemsitry, Madurai Kamaraj University,

*Corresponding

Author: Tel: +91 0452-245 8410, 9442623835.

address: [email protected] (Andy Ramu)

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*E-mail

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*E-mail: [email protected]

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Madurai-625 021, Tamil Nadu, India

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Graphical abstract

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Highlights 

8-HQC-PTH fluorescence sensor has been synthesized in simple procedure.

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8-HQC-PTH is selectively quenched by Mg2+ ion in the presence of other metal ions

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The sensor has both colorimetric and ratiometric fluorescent response for Mg2+

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The charge transfer mechanism was confirmed by using Job’s plot and density functional theory (DFT)

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An imaging application of 8-HQC-PTH for Mg2+ live cells was developed by

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fluorescence microscopy.

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Abstract

The present study deals with the sensitivity of ratiometric fluorescence chemosensor using probe (E) -N'-((8-hydroxyquinolin-2-yl) methylene) -4-methylbenzohydrazide (8-HQC-

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PTH), as a selective chemosensor for Mg2+ in the presence of other alkaline earth metal ions.

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Among the various metal ions screened, this probe shows a significant fluorescence response

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towards Mg2+ ion. Furthermore, the receptor 8-HQC-PTH exhibits a good binding constant

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and lower detection limit for Mg2+ in DMSO. This chemosensor operates via intramolecular

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charge transfer (ICT) mechanism, which is further supported by DFT studies. The confocal laser scanning micrographs of HeLa cells confirm the cell permeability of 8-HQC-PTC and

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its ability to selectively detect Mg2+ ion in living cells.

Keywords: Quinoline derivative, Chemosensor, Mg2+ ion, Ratiometric fluorescence, Live-

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cell bio-imaging

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1. Introduction The chemosensors are capable of recognizing and sensing metal ions and have attracted considerable attention because of their application in biological, environmental, and chemical processes. Synthesis of neoteric sensors and their detection are more important due to their novel applicability [1-2]. Chemosensors are molecules of abiotic origins that bind

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selectively and reversibly with the analyte of interest with a concomitant change in their property. Nowadays, large group of researchers have focused to develop a neoteric probe to

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design chemosensors, which can be used for the detection of different species, including

cations, anions, biomolecules and neutral species [3-7]. Among the several sensors,

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fluorescence sensors are considered as one of the convenient tools for detection of metal ions

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due to their versatile properties such as selectivity, sensitivity and easy separation [8-9].

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Specifically, optical chemosensors are designed in such a way that the detection mechanism

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is mainly based on the interaction between the analytes and a receptor molecule [10-11]. Optical sensors are based on various mechanisms, such as the Intramolecular Charge Transfer

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(ICT) [12], Chelation Enhanced Fluorescence (CHEF) [13], Photo-induced Electron Transfer (PET), Charge Transfer (CT) from chelator to fluorophore and deprotonating mechanisms

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[14-16]. The complexity in the fluorescence emission mechanism for chemosensor leads to the usage of quantum computing in recent years to understand the systems [17-18]. The

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charge transfer mechanism can be determined with a correct estimation by electron-hole theory [19]. Based on this, prediction and designing of PCT and PET processor probe with

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special applications is most important [20]. Mg2+ is one of the most important cations [21], having involved in various biological

functions and environmental applications. The deficiency of Mg2+ in diet plays an etiological role in various diseases [22-24]. Mg2+ plays an essential part in a large number of cellular mechanism such as the biochemical process of cell proliferation and the deoxyribonucleic

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acid (DNA) structure stability [25-26]. It also has a pivotal function in neuronal activity, neuromuscular transmission and cardiac excitabilities [27-28]. Other cellular functions include protein, DNA synthesis, membrane stabilization, the proliferation of cells and also cell death. The reliable and efficient way of detecting the presence of Mg2+ is desirable. However, till now, sensing materials for Mg2+ detection are limited [29-31]. The design and

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synthesis of probes for Mg2+ detection in aprotic solvent with high selectivity is desirable

[32-38]. Hence, the present study aims to explore a quinoline-based sensor probe (8-HQC-

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PTH) which is obtained by the reaction between p-toluic-hydrazide with 8-hydroxyquinoline-

2-carboxaldehyde, as shown in Scheme 1. The probe was characterized by ESI-MS and NMR techniques (Fig.S1-S2). The fluorescence experiments of selected metal ions displayed a

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dramatic fluorescence intensity enhancement for Mg2+ over all other cations. This showed

2.1 Materials and methods

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HQC-PTH +Mg2+ was studied using DFT.

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that 8-HQC-PTH is a suitable probe to sense Mg2+ ion and this binding mechanism of 8-

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All reagents and solvents were used as received from commercial suppliers without further purification. UV-Vis spectra were recorded on a JASCO-500 spectrophotometer with

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a quartz cuvette (cell length 1cm). The fluorescence spectra were recorded with an Agilent Cary Eclipse Fluorescence Spectrofluorimeter. 1H and

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C NMR spectra were recorded on a

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BRUKER 300 MHz spectrometer using CDCl3 and DMSO-d6 as solvent using TMS as the internal standard. ESI-MS analysis was performed on the positive and negative ion modes on

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a liquid chromatography–ion-trap mass spectrometry instrument (LCQ Fleet, Thermo Fisher Instruments Limited, USA). DFT calculations were performed at the B3LYP/LANL2DZ (d) level using the Gaussian 09 program.

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2.2 Preparation of stock solution Stock solution of 8-HQC-PTH was prepared in the concentration of 1x10-3 M in DMSO and metal ion solutions were prepared in the same concentration using double distilled water. This stock solution of 8-HQC-PTH (50 µL) was diluted with 2 ml of DMSO

All the spectroscopic studies were carried out at room temperature.

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2.3 Determination of the limit of detection and binding constant

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to a final concentration of 25 µM which is used for selectivity and sensitivity experiments.

The limit of detection was calculated using the formula, 3σ/s, where σ is the standard deviation of blank solution and slope (s) is derived by calibration curve. The binding constant

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was determined from the fluorescence data employing reformed Benesi-Hildebrand equation,

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1/∆I = 1/∆I max + (1/K [C]) (1/∆I max). Here ∆I = I-Imin and ∆I max = Imax-Imin, where Imin, I, and

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Imax are the emission intensities of the probe in the absence of Mg2+ ion, at an intermediate

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Mg2+ concentration, and at a concentration of complete saturation where K is the binding

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constant and [C] is the Mg2+concentration respectively. The binding constant k calculated from the plot of (Imax-Imin) / (I-Imin) against [C] -1 of Mg2+ ion.

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2.4 Synthesis of 8-HQC-PTH

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p-Toluic hydrazide (0.043g, 1mmol) was added gradually to 8-hydroxyquinoline-2carbaldehyde (0.05 g, 1 mmol) dissolved in ethanol (15 ml). The reaction mixture was refluxed at 85 ºC for 6 h. The progress of the reaction was monitored by thin layer

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chromatography and after completion of the reaction, the mixture was cooled to room temperature. The organic layer was washed twice with 5 ml of distilled water, and then dried over sodium sulfate. It was further purified by column chromatography on silica gel (20% ethyl acetate in petroleum ether). A yellow solid was obtained with 85% yield. The detailed NMR spectrum and ESI-Mass of 8-HQC-PTH were shown in Fig S1, S2.

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Scheme 1 3. Results and discussion 3.1 UV-Vis spectral studies Initially, the probe is characterized by UV-Visible absorption spectrum and the

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abserved results are shown in Fig. 1. This probe exhibits two absorption bands at 299 and 340 nm which are attributed to π- π* and n- π* transitions. These peaks did not show any

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significant changes in the presence of other metal ions, though in the presence of Mg2+ ion, the absorption of 8-HQC-PTH is quantitatively quenched with the formation of a new absorption at 312 nm. In order to check the sensitivity of the 8-HQC-PTH towards Mg2+ ion,

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the sensitivity experiments were performed. Upon addition of various concentrations of

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Mg2+ ions, absorption bands at 299 and 340 nm are gradually decreased due to formation of

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the complexes. The absorption of 8-HQC-PTH is recorded in the range of 0-75 M of

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Mg2+and it is observed that the detection limit is 4.2x10-7 M for Mg2+ ion. Using the

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absorbance titration data, the binding constant of 8-HQC-PTH with Mg2+ ion was found to be 4.5x10-3 M-1. The detected absorption changes are shown in Figs. 1a and b.

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Figure 1

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3.2 Fluorescence studies of 8-HQC-PTH Selectivity is a significant parameter for evaluating performance of any fluorescence

sensing system. There was no significant changes observed in the fluorescence intensity in

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the presence of various metal ions, such as K+, Mg2+, Cr3+, Fe3+, Cu2+, Zn2+, Al3+, Cd2+, and Ba2+. 8-HQC-PTH displayed marked quenching fluorescence intensity at 474 nm and the new band appeared at 590 nm upon addition of Mg2+ ion. The fluorescence intensity was not affected even in the presence of other metal cations. From figure 2a, it can be seen that only Mg2+ ions induced fluorescence changes, while other metal ions led to a very small or no 6

fluorescence change. This result indicates clearly that the 8-HQC-PTH has good selectivity towards Mg2+ ion over the other competing cations. The effect of various co-existing cations on Mg2+ ion sensing was also determined. Figure 2

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To obtain a better insight into the response mechanism of 8-HQC-PTH towards Mg2+ ions, spectroscopic titrations were also carried out under the same working conditions. As

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shown in Fig.2b, when excited at 340 nm, the fluorescence band at 474 nm decreased and a

band at 590 nm increased which gives ratiometric fluorescence spectra, and isosbetic point at

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Figure 3

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560 nm, when increasing the concentration of Mg2+ ion from 0 to 75 M.

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The effect of other co-existing cations on Mg2+ ion sensing was also determined. The

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fluorescence response of the sensing system towards Mg2+ ion in the presence of various metal ions is shown in figure 3a. The blue bars represent the fluorescence intensity of 8-

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HQC-PTH in the presence of Mg2+ ion and the brown bar represents the fluorescence

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intensity of 8-HQC-PTH + Mg2+ and other competing cations. The presence of the selected metal ion does not interfere with Mg2+ binding to the 8-HQC-PTH, indicates that their co-

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exciting ions have negligible interference effects on Mg2+ sensing by the present 8-HQC-PTH

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system. Furthermore, the quenching efficiency is analyzed by following Stern-Volmer Eq.: F0/F = Ksv [Q] + 1

Where F0 and F are the intensities of 8-HQC-PTH before and after addition of Mg2+,

[Q] is the molar concentration of the Mg2+ and Ksv is the quenching constant. The working curve is mapped by (F0−F)/F0 of 8-HQC-PTH with the concentration of Mg2+ and a significant linear correlation (R2 = 0.9891) occurred between the quenching efficiency of 7

(F0−F)/F0 and the Mg2+ concentration in the range of 0–75 M. (Fig. 3b). Detection limits and association constant (ka) can also be obtained from the fluorescence titration. The detection limits were calculated to be 4.7 x 10-8 M for 8- HQC-PTH. The sensor of 8- HQC-PTH is effective to form a 1:1 complex, which was confirmed by Job’s plot analysis (Fig. 4). This binding stoichiometry was further confirmed by ESI-MS (Fig S3 in supporting

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information).

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Figure 4 3.3 NMR Studies

To understand the binding mode of the 8-HQC-PTH with Mg2+ ions, 1H-NMR

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titration was performed with the increasing equivalent of Mg2+ ions (Fig. 5). The 8-HQC-

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PTH gives signals at 12.3 and 10.9 ppm corresponding to –OH proton of quinoline and –NH

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proton of amide in hydrazide respectively. On the other hand, upon addition of Mg2+ ions, the

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intensity of these peaks at 12.3 and 10.9 ppm was suppressed and the signals are deshielded.

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These results indicate that the protons of -OH and –NH groups are deprotonated by the addition of Mg2+ and hence coordination occurred between 8-HQC-PTH and Mg2+ ions.

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Upon further addition of Mg2+ ions, the signals at 12.3 and 10.9 ppm vanished along with the suppression of imine signal intensity by broadening. Finally, these experimental evidences

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conclude that the quinoline –OH and amide -NH are involved in the coordination with Mg2+

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ions.

Figure 5

The proposed sensing of 8-HQC-PTH under the present experimental condtions is

based on ICT mechanism. The ICT from the electron rich quinoline to hydrazide takes place and the whole process is shown in Scheme 2. When Mg2+ is added, it forms a complex involving hydroxyl (-OH) of quinoline ring, nitrogen (-NH) of hydrazide moiety. Due to this 8

complexation, the intramolecular charge transfer is suppressed. This indicates that 8-HQCPTH, strongly binds with Mg2+ ion through the formation of coordination complex. Similarly, the intensity of the band at 474 nm was decreased and the band at 590 nm is increased, due to the formation complex between 8-HQC-PTH. This result indicats that a more efficient coordination of Mg2+ ion occurs with hydroxyl of quinoline ring, the nitrogen of quinoline

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moiety (N), imine nitrogen (C=N) and the nitrogen (-NH) of hydrazide moiety. When Mg2+ ion is added, the charge transfer was arrested due to the strong complexation of Mg2+ with 8-

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HQC-PTH. In addition, it is well known that Mg2+ ion (a Soft acid), preferentially interacts

with the nitrogen, and hydroxyl group according to Pearson's HSAB theory. Thus the changes

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Scheme 2

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in the fluorescence spectrum, are clearly justified.

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3.4 Theoretical Studies.

The geometry of 8-HQC-PTH was optimized using DFT-B3LYP 6-31G level using

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Gaussian 09 package. The sensor 8-HQC-PTH has effective binding sites to form a 1:1 complex with Mg2+ and this supports the experimental finding obtained from Job's plot. DFT-

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calculations, shows that the quinoline unite act as HOMO whereas hydrazide unit act as

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LUMO of 8-HQC-PTH, thus, indicating that the intramolecular charge transfer (ICT) slightly takes place from the quinoline unit to hydrazide unit. Thus, when Mg2+ binds with hydroxyl group of quinoline ring, the nitrogen unit of quinoline moiety, imine nitrogen (C=N) and the

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nitrogen of hydrazide moiety, the ICT is inhibited resulting in remarkable fluorescence quenching. The titration of 8-HQC-PTH with Mg2+ shows that the quenching process is consistent with the coordination of hydroxyl of quinoline ring, the nitrogen unit of quinoline moiety (-N), imine nitrogen (C=N) and the nitrogen unit (-NH) of hydrazide moiety. DFT calculations on 8-HQC-PTH and its HOMO, LUMO form indicates that electron transfer

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takes place from the quinoline unit to hydrazide by Intramolecular Charge Transfer (ICT) process. Figure 6 3.5 Confocal cell imaging:

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The HeLa cells were incubated with 8-HQC-PTH (5.0 μM) in DMSO/PBS buffer (pH 7, 1/49, v/v) [49] at 36°C for about 30 minutes and imaged through confocal

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fluorescence microscopy with 340 nm excitation (Fig. 7b). To remove the excess 8-HQCPTH present in the extracellular medium, the system was washed with HEPES buffer for five

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times. Initially, HeLa cells were incubated with 8-HQC-PTH for 5h and it shows blue

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fluorescence. Then 25 μM of Mg2+ ion was added to it incubated for 1 h and then recorded

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the fluorescence microscopy. It shows excellent red fluorescence images. These studies

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indicates that 8-HQC-PTH has superior sensing property towards Mg2+ ions.

Table 1

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Conclusion

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Figure 7

In conclusion, a highly selective and sensitive fluorescence chemosensor for Mg2+ ion

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is reported using 8-HQC-PTH as a probe molecule in DMSO solution. The probe is characterized by NMR and ESI-MS spectroscopy. The sensing mechanism of this ratiometric chemosensor is explained by using DFT and NMR titration analysis. It shows that the probe expresses clear ICT mechanism and the later addition of the Mg2+ ions indicates the supressesion of ICT and a new band is seen at 590 nm. The sensing ability is also applied to

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the HeLa cell lines. It shows that good cell permeability and less toxicity. Thus, the ability of 8-HQC-PTH sensing behavior of Mg2+ ions is successfully applied to living HeLa cells. Acknowledgements P. M. thanks UGC for the financial support. P. M. and A. R thank Dr. G. Sivaraman

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for cell imaging studies and P. M. thanks to Prof. S. Muthusubramanian and Dr. A.

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Dhakshinamoorthy for help to corrected our manuscript.

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[43] A.A. Taherpour, M. Jamshidi, O. Rezaei, Recognition of Switching On or Off

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fluorescence emission spectrum on the schiff-bases as a Mg2+ chemosensor: a first

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principle DFT and TD-DFT, J. Mol. Struct. 1147 (2017) 815 – 820.

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[44] X. Zhou, P. Li, Z. Shi, X. Tang, C. Chen, W. Liu, A highly selective fluorescent sensor for distinguishing cadmium from Zinc ions based on a quinoline platform,

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[45] B. Zhang, H. Liu, F. Wu, G. Hao, Y. Chen, C. Tan, Y. Tan, Y. Jiang, A dual-

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response quinoline-based fluorescent sensor for the detection of Copper (II) and Iron (III) ions in aqueous medium, Sens. Actuators B 243 (2017) 765–774.

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[46] H. Kim, J. Kang, K.B. Kim, E.J. Song, C. Kim. A highly selective quinoline-based fluorescent sensor for Zn(II), Spectrochim. Acta A 118 (2014) 883–887.

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[47] J. Tian, X. Yan, H. Yang, F. Tian. A novel turn-on Schiff-base fluorescent sensor for aluminum (III) ions in living cells, RSC Adv. 5 (2015) 107012-107019.

[48] A.S. Murugan, N. Vidhyalakshmi, U. Ramesh, J. Annaraj, A Schiff’s base receptor for red fluorescence live cell imaging of Zn2+ ions in zebrafish embryos and naked

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eye detection of Ni2+ ions for bio-analytical application, J. Mater. Chem. B. 5 (2017) 3195-3200. [49] Q. Zhao, M. Yu, L. Shi, S. Liu, C. Li, M. Shi, Z. Zhou, C. Huang, and F. Li, Cationic iridium(III) complexes with tunable emission colour as phosphorescent

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dyes for live cell imaging, Organometallics. 5 (2010) 1085-1091.

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Biographies P.Marimuthu obtained M.Sc. degree in Chemistry from Madurai Kamaraj University, Madurai, Tamil Nadu, India, on 2012. At present, he is doing Ph.D., under the supervision of Dr. A. Ramu, Department of Inorganic Chemistry, School of chemistry, Madurai Kamaraj University, Madurai, Tamil Nadu, and India. His research interest mainly focuses on Fluorescence of chemosensors and living cell images.

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Dr. A. Ramu received his M.Sc degree in Chemistry at Madurai Kamaraj University,

Madurai, India (1983). He joined as an Assistant Professor in the Department of Chemistry,

Chennai, India (1993).

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ANJA College, Sivakasi, India (1984). He earned his Ph.D. at University of Madras, He joined as a Professor, School of Chemistry, Madurai Kamaraj

University, and Madurai, India on 1999. He has published 50 articles in reputed scientific journals and contributed few chapters in books. His main research areas include the

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Coordination Chemistry, Application of DNA binding by using UV, CD Spectroscopy for

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stereo chemical investigations, binding nature of the complexes, Cytotoxic studies, Geo

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hydrology - Water quality assessment and water pollution, Phase transfer catalysis & Phyto

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Chemistry.

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Figure captions Figure 1. a) UV–Vis. Spectra of 8-HQC-PTH (25 µM) in the presence of various metal ions such as K+, Mg2+, Ba2+, Cu2+, Al3+, Fe3+, Zn2+, Cd2+, Hg2+ and Cr3+ (25 µM) in DMSO, b)

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UV-Vis. Spectra of 8-HQC-PTH (25 μM) upon the titration of Mg2+ 0 to 75 M in DMSO. Figure 2. a) Fluorescence spectra of 8-HQC-PTH (25 µM) in the presence of various metal

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ions such as K+, Mg2+, Ba2+, Cu2+, Al3+, Fe3+, Zn2+, Cd2+, Hg2+ and Cr3+ (25 µM) in DMSO,

b) Fluorescence spectra of 8-HQC-PTH (25 μM) upon the titration of Mg2+ 0 to 75 M in

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DMSO.

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Figure 3. a) Competitive experiments of 8- HQC-PTH toward Mg2+: Brown bars represent of

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various metal ions with an added into a 8- HQC-PTH + Mg2+ in DMSO solution and Blue

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bars represent fluorescence intensity of 8- HQC-PTH + Mg2+, λex 340nm. (25 µM). b) Linear relationship plot obtained from fluorescence titration of 8-HQC-PTH (M) with

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concentration of Mg2+ ions (0 to 75 M).

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Figure 4. Job’s plot Fluorescence intensity of diagram between 8- HQC-PTH and Mg2+ ion.

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Figure 5. 1H NMR titration plots of quinoline-base (8-HQC-PTH) sensor with Mg2+ in DMSO-d6.

Figure 6. HOMO and LUMO of 4-((benzo [d] thiazol-2-ylthio) methyl) -5, 7-dihydroxy-2H-

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chrome -2-one (8-HQC-PTH) calculated with DFT/TD-DFT at B3LYP/6-31G (d) level using Gaussian 09. Figure 7. Bright field image of (a) 8-HQC-PTH and (d) 8-HQC-PTH with Mg2+ ions, fluorescence images of (b) 8-HQC-PTH and (e) 8-HQC-PTH with Mg2+ ions (c) Overlay

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image of (c) 8-HQC-PTH and (f) 8-HQC-PTH with Mg2+ ions in DMSO/PBS buffer (pH7,

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1/49, v/v) at 36°C for 30 min.

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Figure 1. a) UV–Vis. Spectra of 8-HQC-PTH (25 µM) in the presence of various metal ions such as K+, Mg2+, Ba2+, Cu2+, Al3+, Fe3+, Zn2+, Cd2+, Hg2+ and Cr3+ (25 µM) in DMSO, b)

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UV-Vis. Spectra of 8-HQC-PTH (25 μM) upon the titration of Mg2+ 0 to 75 M in DMSO.

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Figure 2. a) Fluorescence spectra of 8-HQC-PTH (25 µM) in the presence of various metal

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ions such as K+, Mg2+, Ba2+, Cu2+, Al3+, Fe3+, Zn2+, Cd2+, Hg2+ and Cr3+ (25 µM) in DMSO, b) Fluorescence spectra of 8-HQC-PTH (25 μM) upon the titration of Mg2+ 0 to 75 M. in

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DMSO.

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Figure 3. a) Competitive experiments of 8- HQC-PTH toward Mg2+: Brown bars represent of

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various metal ions with an added into a 8-HQC-PTH + Mg2+ in DMSO solution and Blue bars represent fluorescence intensity of 8-HQC-PTH + Mg2+, λex340nm (25µM).

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b) Linear relationship plot obtained from fluorescence titration of 8-HQC-PTH (M) with

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concentration of Mg2+ ions (0 to 75M.).

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Figure 4. Job’s plot Fluorescence intensity of diagram between 8- HQC-PTH and Mg2+ ion.

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Figure 5. 1H NMR titration plots of quinoline-base (8-HQC-PTH) sensor with Mg2+ in

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DMSO-d6.

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Figure 6. HOMO and LUMO of 4-((benzo [d] thiazol-2-ylthio) methyl)-5,7-dihydroxy-2H-

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chrome-2-one (8-HQC-PTH) calculated with DFT/TD-DFT at B3LYP/6-31G (d) level using

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Gaussian 09.

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Figure 7. Bright field image of (a) 8-HQC-PTH and (d) 8-HQC-PTH with Mg2+ ions, fluorescence images of (b) 8-HQC-PTH and (e) 8-HQC-PTH with Mg2+ ions (c)

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Overlay image of (c) 8-HQC-PTH and (f) 8-HQC-PTH with Mg2+ ions in

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DMSO/PBS buffer (pH7, 1/49, v/v) at 36°C for 30 min.

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Scheme captions Scheme 1: Synthesis of Probe (8-HQC-PTH)

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Scheme 2: Proposed interaction of Mg2+ ions with 8- HQC-PTH

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Scheme 1: Synthesis of Probe (8-HQC-PTH)

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Scheme 2. Proposed interaction of Mg2+ ions with 8- HQC-PTH.

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Tables Table 1. Comparison table for various probes for the detection of Mg2+. S. No

Probe

Metal

Detect limit

Application

Ref

4-hydroxy-5-isopropyl-2 thylisophthalaldehyde

Mg2+

2.70 x10-6 M

Fluorescent “turn-on” sensor

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2

4-hydroxy-3-((2-hydroxy-5methylphenyl)diazenyl)-2Hchromen-2-one (E)-2-((2-(pyridin-2l)hydrazono)methyl)quinolin -8-ol Isatin-3-(7Methoxychromone-3methylidene) hydrazone (Z)-2-hydroxy-N'-(2hydroxybenzylidene)benzohy drazide 8-hydroxyquinoline-5carbaldehyde-(benzotriazol1′-acetyl) N-(quinolin-8-yl)-2(quinolin-8-yloxy) acetamide

Mg2+ & F-

2.4 x 10-8 M & 2.3 x 10-8 M

Fluorescent “turn-on-off” sensor

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Mg2+

1.9 x 10-7 M

Fluorescent “turn-on” sensor

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6

Mg2+

-

Zn2+ & Cd2+

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N-(1H-benzo[d]imidazol-2yl)quinoline-2-carboxamide (QLBM) (bis(2 quinolinylmethyl) benzylamine (E)-4-methoxy-N-(8methylquionline2yl)methylene)aniline (L) 2-Hydroxyquinoline-3carbaldehyde

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8

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11

12

(8-HQC-PTH)

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1.7 × 10−7 M

Fluorescent “turn-on” sensor

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Fluorescent “turn-on” sensor

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Mg2+

Fluorescent “turn-on” sensor

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Fluorescent “turn-on” sensor

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Fluorescent sensor and Live cell imaging

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Zn2+

1.8 × 10-4 M & 9.8 × 10-5 M 1.35× 10−7 M & 1.24 × 10−7 M 1.2 x 10-6 M

Fluorescent “turn-on” sensor

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Al3+

1.2 × 10−7 M

Fluorescent “turn-on” sensor

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Zn2+ & Ni2+

7.2 x 10-8 M & 3.3 x 10-7 M

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Mg2+

4.7 x 10-8 M

Live cell imaging on lung cancer cell line and tracking of Zn(II) ion in Zebra fish embryos Ratiomentric Fluorescent sensor and Live cell imaging

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7

5.16 x 10-7 M

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5

Mg2+

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4

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3

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1

Cu2+, Fe3+

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This work