Preparation method of naphthalimide fluorescent probe and application thereof in mercury ion detection

Abstract

This invention discloses a method for preparing a naphthimide-based fluorescent probe and its application in mercury ion detection. Using 1,8-naphthimide as the starting material, this invention designs and synthesizes a novel Schiff base-based fluorescent probe (probe QA) with naphthimide as the fluorophore, for use in detecting Hg in aqueous solution. 2+ The detection of Hg was performed using probe QA in a MeOH / H2O (v / v = 4:1, pH = 7.0) solution. 2+ It has high sensitivity and selectivity for Hg 2+ The fluorescence quenching of Hg is preferential over that of other competing metal ions, and Hg 2+ The quenching rate of the probe QA can reach 99%. In addition, the raw materials for the synthesis of this probe are inexpensive and readily available, the preparation process of the probe QA is simple, the product yield is high, and it meets the requirements of green environmental protection, showing great application prospects.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fluorescent probe preparation, and relates to cation selective fluorescence detection, in particular to a preparation method of a naphthalimide probe and an application method of the naphthalimide probe in detecting mercury ions. BACKGROUND

[0002] Mercury is the third largest element that is most harmful to human health, and it has various forms such as metallic mercury, inorganic mercury and organic mercury. The toxicity of different forms of mercury and its effects on the nervous, digestive and immune systems, as well as the lungs, kidneys, skin and eyes are different. It is generally believed that organic mercury is the most dangerous and most common form of mercury exposure, especially methylmercury, which is a strong neurotoxin and can be enriched in organisms along the food chain, and has certain effects on the nervous, digestive and immune systems. In addition, mercury exposure not only affects the immune status of organisms, but also causes cardiovascular diseases such as myocardial infarction, heart rate variability and hypertension. In summary, it is of great significance to study a Hg 2+ detection method with high selectivity and high sensitivity.

[0003] It is known that, compared with traditional Hg 2+ detection methods, the fluorescence spectrum method has excellent performances such as simple operation, low cost, short response time, high sensitivity and high selectivity, and has been widely applied in the field of heavy metal ion detection. In addition, the naphthalimide fluorophore has optical properties such as large Stokes shift, good light stability, high quantum yield and structure convenient for modification, and has been widely applied in the fluorescence detection of Hg 2+ . SUMMARY

[0004] The purpose of the present application is to provide a naphthalimide fluorescent probe capable of detecting metal ions Hg 2+ and a preparation method thereof.

[0005] Another purpose of the present application is to provide the application of the above-mentioned naphthalimide probe in the fluorescence detection of Hg 2+ .

[0006] I. Naphthalimide fluorescent probe

[0007] The present application is a naphthalimide fluorescent probe, and the molecular formula is C 20 H 16 N4O3, which is named as QA.

[0008] II. Preparation method of naphthalimide fluorescent probe

[0009] (1) Anhydrous ethanol is used as a solvent, 4-bromo-1,8-naphthal anhydride and ethanolamine are used as substrates with a feeding ratio of 1:1.2, reflux is carried out at 80 DEG C for 4 hours, TLC is monitored, after the reaction is completed, filtration is carried out, and anhydrous ethanol is recrystallized to synthesize an intermediate 3.

[0010] (2) With ethylene glycol methyl ether as solvent, intermediate 3, hydrazine hydrate as substrate, the feeding ratio is 1:4, reflux reaction for 5 hours, TLC monitoring reaction process, after the reaction is finished, distilled water wash 3-4 times, synthesis of intermediate 2.

[0011] (3) With anhydrous ethanol as solvent, intermediate 2, 2-formaldehyde pyridine as substrate, glacial acetic acid as catalyst, the feeding ratio is 1:1.2:1.2, 60℃ reaction for 1.5 hours, TLC monitoring reaction, after the reaction is finished, naphthalimide probe QA is obtained. The synthesis route of QA is shown in Figure 1 . The infrared spectrum and hydrogen spectrum of naphthalimide sensor molecule QA prepared by the above method are shown in Figure 2 and Figure 3 .

[0012] III. Selectivity study of naphthalimide fluorescent probe for Hg 2+ application

[0013] In the solution of probe QA (MeOH / H2O (v:v=4:1)), 10 eq of 1.0×10 -2 mol / L aqueous solution of metal ions (Al 3+ , Ca 2+ , Cu 2+ , Co 2+ , Cr 3+ , Cd 2+ , Fe 3+ , K + , Na + , Mg 2+ , Zn 2+ , Ni 2+ and Hg 2+ ) were added respectively, and the ultraviolet absorption spectrum and fluorescence spectrum were measured. It was found that only Hg 2+ caused obvious ultraviolet absorption spectrum changes, resulting in the disappearance of the absorption peak at 458 nm, while the remaining metal ions did not cause obvious changes in the absorption spectrum (see Figure 4 ). From the fluorescence spectrum (see Figure 5 ), it can be seen that except Fe 3+ and Hg 2+ , the remaining metal ions did not cause obvious fluorescence spectrum changes at 545 nm. Fe 3+ can cause the fluorescence intensity of probe QA to weaken to some extent, but it does not reach quenching. However, when the same amount of Hg 2+ is added, the fluorescence emission intensity of the mixed solution is obviously quenched, with a quenching rate of 99%. Therefore, these results show that in MeOH / H2O (v:v=4:1)) solution, probe QA can be used as a Hg2+ Highly selective fluorescent probes.

[0014] IV. Naphthalimide probes for Hg 2+ Application of interference research

[0015] To further verify the probe's effect on Hg 2+ Compared to other metal ions, Hg exhibits higher selectivity. The study of Hg in MeOH / H₂O (v:v = 4:1) solution was conducted. 2+ With other metal cations (Al) 3+ Ca 2+ Cu 2+ Co 2+ Cr 3+ Cd 2+ Fe 3+ K + Na + Mg 2+ Zn 2+ and Ni 2+ A competitive experiment was conducted on probe QA, and a bar chart of the probe QA detection process was plotted based on the experimental results (see...). Figure 6 This allows for a more intuitive view of the effect of probe QA on Hg. 2+ It has a high degree of specific detection capability.

[0016] V. Naphthalimide probes QA for metal ions Hg 2+ Determination of the lowest limit of detection (LOD)

[0017] The effect of the MeOH / H2O solution of probe QA on Hg was determined by ultraviolet titration. 2+ The lowest limit of detection (LOD) for aqueous solutions was determined, and the data were linearly fitted (see UV titration plot). Figure 7 The LOD linear fitting plot is shown below. Figure 8 Using the formula LOD = 3σ / k, the probe QA for Hg can be calculated. 2+ The LOD is 8.87 × 10 -6 mol / L.

[0018] VI. Naphthalimide probes QA for metal ions Hg 2+ Determination of the complexation constant (Ka)

[0019] probe QA and different concentrations of Hg 2+ Fluorescence titration spectrum in the presence of ( Figure 9 The analysis was performed using the Benesi-Hildebrand equation:

[0020]

[0021] Further explore the complexation constant of probe QA and Hg 2+ Figure 10 , and calculate the Ka as 1.71*10 4 M -1 .

[0022] Seven, naphthalimide probe QA stoichiometry determination of the binding of metal ions Hg 2+

[0023] In order to further determine the stoichiometry of the binding of probe QA and Hg 2+ , Job's plot method is also used. In MeO H / H2O (v:v = 4:1) solution, the total concentration of probe QA and Hg 2+ system is kept constant at 100 μM, and the concentration ratio of probe QA and Hg 2+ is constantly adjusted. The change of fluorescence emission intensity with [QA] / ([Hg 2+ ]+[QA]) ratio concentration is measured, and the fluorescence emission intensity at 545 nm is taken to draw Job'plot graph Figure 11 ). The fluorescence intensity reaches the maximum when [QA] / ([Hg 2+ ]+[QA]) is 0.326, indicating that probe QA is combined with Hg 2+ in a ratio of 1:2, which is consistent with the above fluorescence titration experiment results.

[0024] In summary, the present application has the following advantages:

[0025] 1. The design route of the present application is simple, and a new type of Schiff base fluorescent probe is successfully synthesized by selecting 4-bromo-1,8-naphthal anhydride as the main starting material, realizing sensitive and specific detection of specific metal ion Hg 2+ .

[0026] 2. The fluorescent probe of the present application is based on naphthalimide fluorophore, has stable performance and excellent fluorescence characteristics; and the method for detecting metal ion Hg 2+ of the fluorescent probe has high sensitivity, high specificity, simple operation and low cost. Therefore, the naphthalimide probe QA has good application prospect in heavy metal ion detection. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The present application is a synthesis route diagram of naphthalimide fluorescent probe QA;

[0028] Figure 2 The present application is an infrared spectrum of naphthalimide fluorescent probe QA;

[0029] Figure 3 The present application is a hydrogen spectrum of naphthalimide fluorescent probe QA; ​​

[0030] Figure 4 The UV absorption spectra of the naphthalimide fluorescent probe QA (MeOH / H2O (v:v=4:1)) solution with various metal ions added are shown below.

[0031] Figure 5 The present invention provides a naphthalimide-based fluorescent probe QA(MeOH / H2O (v:v = 4:1), λ ex =460nm, slit: 5nm / 5nm) Fluorescence spectra of various metal ions added to the solution;

[0032] Figure 6 Hg was added to the naphthalimide fluorescent probe QA of this invention along with other interfering ions. 2+ Fluorescence values ​​before and after (λ) ex =460nm, λ em =545nm, slit: 5nm / 5nm). The orange bars represent the fluorescence intensity of probe QA after the addition of interfering ions, and the green bars represent the fluorescence intensity of probe QA after the addition of interfering ions and then Hg. 2+ fluorescence intensity;

[0033] Figure 7 Different concentrations of Hg were added to the solution of the naphthalimide fluorescent probe QA (MeOH / H2O (v:v = 4:1)) of this invention. 2+ The UV titration diagram after the titration;

[0034] Figure 8 This is a fitting curve of the QA UV titration of the naphthalimide fluorescent probe of this invention;

[0035] Figure 9 Different concentrations of Hg were added to the solution of the naphthalimide fluorescent probe QA (MeOH / H2O (v:v = 4:1)) of this invention. 2+ The subsequent fluorescence titration diagram;

[0036] Figure 10 This is the Benesi-Hildebrand diagram of the naphthalimide fluorescent probe QA of the present invention, plotted based on the fluorescence titration results;

[0037] Figure 11 For in [Hg 2+ Under the condition of [QA] = 100 μM, the probe QA and Hg were plotted. 2+ The Job's plot; Detailed Implementation

[0038] Example 1: Preparation of probe QA

[0039] (1) Compound 3 was prepared by dissolving 4-bromo-1,8-naphthalic anhydride (15 mmol, 4.1565 g) in 150 ml of absolute ethanol, adding 2-aminoethanol (18 mmol, 1.099 ml) dissolved in 15 ml of absolute ethanol, and heating the suspension to reflux for 4 hours, monitoring the reaction by TLC (PE:EA = 1:2). After the reaction was completed, it was cooled to room temperature, filtered under reduced pressure, the filter cake was washed with distilled water 3-4 times, recrystallized with ethanol, and dried in an oven to obtain compound 3 as a white solid (3.8219 g, 79.88%). IR (KBr; v, cm –1 ): 3396, 1697, 1661, 1366, 1051, 778.

[0040] (2) Compound 2 was prepared by dissolving compound 3 (7.5 mmol, 2.3917 g) and hydrazine hydrate (30 mmol, 1.876 ml) in 45 ml of 2-methoxyethanol, heating to reflux at 125°C for 5 hours, monitoring the reaction by TLC (DCM:MeOH = 5:1). The reaction was cooled to room temperature and filtered, the filter cake was washed with distilled water, and dried under vacuum at 105°C to obtain compound 2 as a yellow solid (1.8787, 92.40%). IR (KBr; v, cm –1 ): 3462, 3374, 1635, 1587, 1390, 1069, 777.

[0041] (3) Compound 2 (3 mmol, 0.8133 g) was weighed and dissolved in 65 ml of absolute ethanol, 3.6 mmol of acetic acid and 3.6 mmol of 2-pyridinecarboxaldehyde were added in sequence, and the reaction was completed after heating on a water bath at 60°C for 1.5 hours, monitoring the reaction by TLC (DCM:MeOH = 7:1). It was cooled and filtered, the filter cake was washed with ethanol 3-4 times, and dried under vacuum at 60°C to obtain probe 1 as an orange-red solid (1.075 g, 99.5%). IR (KBr; v, cm –1 ): 3422, 3292, 1685, 1637, 1277, 1046, 769. 1 H NMR (300 MHz, DMSO) δ 11.63 (s, 1H), 8.79 (d, J = 8.5 Hz, 1H), 8.62 (dt, J = 4.7, 1.3 Hz, 1H), 8.53 - 8.44 (m, 2H), 8.39 (d, J = 8.5 Hz, 1H), 8.10 (d, J = 8.0 Hz, 1H), 7.88 (td, J = 7.8, 1.8 Hz, 1H), 7.84 - 7.75 (m, 2H), 7.39 (ddd, J = 7.4, 4.8, 1.2 Hz, 1H), 4.80 (t, J = 5.9 Hz, 1H), 4.14 (t, J = 6.7 Hz, 2H), 3.61 (q, J = 6.5 Hz, 2H).

[0042] Example 2: Probe QA detection of Hg 2+

[0043] (1) Weigh an appropriate amount of probe QA and dissolve it in the MeOH / H2O system to prepare a probe stock solution with a concentration of 0.1mM.

[0044] (2) Weigh an appropriate amount of solid metal nitrate and dissolve it in H2O to prepare a 10mM metal ion mother liquor.

[0045] (3) Transfer 3 mL of the probe stock solution from step (1) into a small reagent bottle, and add 300 μL of each metal ion (Al) with a concentration of 10 mM. 3+ Ca 2+ Cu 2+ Co 2+ Cr 3+ Cd 2+ Fe 3+ K + Na + Mg 2+ Zn 2+ Ni 2+ and Hg 2+ The aqueous solution of QA was tested, and the ultraviolet absorption and fluorescence spectra of the system were observed. In the fluorescence spectroscopy test, the excitation wavelength of QA was 460 nm and the emission wavelength was 545 nm. Figure 4 and 5 As shown, QA exhibits a broad absorption band at 460 nm in its absorption spectrum, and the typical emission peak of the probe is around 545 nm in its emission spectrum. Adding Hg... 2+ Subsequently, upon irradiation with a UV lamp, the fluorescence of the probe solution changed from yellow to colorless, indicating fluorescence quenching, which suggests the presence of Hg in the system. 2+ Furthermore, the broad absorption peak and main emission peak of the probe showed a significant decrease, indicating that the probe QA can effectively detect Hg through fluorescence quenching. 2+ .

Claims

1. Use of a naphthalimide probe of the following structure in detecting mercury ions, which is not a diagnostic and therapeutic purpose of a disease.

2. Use of the naphthalimide probe according to claim 1 for detecting mercury ions, characterized in that: After adding mercury ions into the methanol / water solution of the naphthalimide probe, the fluorescence of the probe is quenched.

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