A hydroxyl porphyrin-based fluoride ion fluorescent probe and a synthesis method thereof

Abstract

This invention discloses a fluoride ion fluorescent probe based on hydroxyporphyrin and its synthesis method. The probe has the following structural formula: By introducing a phenolic hydroxyl group at the meso position of the porphyrin, deprotonation is induced by the strong electronegativity of fluoride ions, transforming the probe from a phenolic to a quinone structure, initiating macrocyclic isomerization of the porphyrin, resulting in fluorescence quenching and a change in solution color from red to green. The probe emits fluorescence at 664 nm under 420 nm excitation, with a Stokes shift of 244 nm. It exhibits a highly selective fluorescence quenching response to fluoride ions, with no interference from other anions, and the fluorescence intensity is linearly correlated with the fluoride ion concentration. This probe is simple to synthesize, has good water solubility, and can be applied to the visualization and quantitative detection of fluoride ions in environmental monitoring and life sciences.

Description

Technical Field

[0001] This invention belongs to the fields of analytical chemistry and fluorescence sensing technology, specifically relating to a fluoride ion fluorescent probe based on a hydroxyporphyrin structure, its synthesis method, and its application in fluoride ion detection. More specifically, this invention relates to a class of functional fluorescent molecular probes that introduce phenolic hydroxyl groups at the meso site of a porphyrin macrocycle as fluoride ion recognition groups. This probe achieves an "on-off" response of the fluorescence signal by inducing molecular structural isomerization through fluoride ion-induced deprotonation. This invention covers the molecular design principles, organic synthesis route, structural characterization methods, and applications of this fluorescent probe in the qualitative, quantitative, and visual detection of fluoride ions in environmental monitoring and life sciences. Background Technology

[0002] Fluoride ions, as the smallest anion with the highest charge density, play a vital role in daily life, industrial production, environmental ecology, and life activities. In oral health, appropriate amounts of fluoride are widely added to toothpaste and drinking water to prevent tooth decay and strengthen tooth enamel; in clinical medicine, fluoride medications are used to treat osteoporosis and other bone diseases. However, fluoride ions are a double-edged sword; excessive intake or long-term exposure can cause serious health problems. Epidemiological studies have shown that excessively high fluoride levels in drinking water (above 1.5 mg / L)... World Health Organization 2017, 4th ed. 370-373.) can lead to endemic fluorosis, manifested as dental fluorosis and skeletal fluorosis. In severe cases, it can also damage the nervous system, kidneys, and endocrine glands. Exposure Health 2021, 13 , 661−680.). Therefore, environmental protection departments have established strict limits on the fluoride ion content in drinking water, food, and environmental water bodies. Developing efficient, sensitive, and convenient methods for detecting fluoride ions is of significant public health importance and environmental protection value. Anal . Chem. 2022, 94 , 11470−11475.).

[0003] Currently, conventional methods for detecting fluoride ions mainly include fluoride ion selected electrode method, ion chromatography, spectrophotometry, and capillary electrophoresis. Among these, the ion selected electrode method is the most widely used due to its simplicity and low cost, but it has limitations such as long response time, susceptibility to interference from hydroxyl ions in complex matrices, and high detection limits. Ion chromatography offers advantages such as high sensitivity and simultaneous analysis of multiple components, but the instruments are expensive, sample pretreatment is cumbersome, and it is not suitable for rapid on-site detection. Traditional colorimetric methods can achieve visual detection, but their sensitivity is usually low and they are easily affected by sample color and turbidity. These traditional methods generally cannot meet the needs of in-situ, real-time, and rapid detection, especially in resource-limited remote areas or emergency monitoring scenarios of sudden pollution events, where their application is significantly limited.

[0004] In recent years, fluorescent molecular probe technology has shown broad application prospects in the fields of ion recognition and biosensing due to its outstanding advantages such as high sensitivity, good selectivity, fast response speed, non-invasive detection, and real-time imaging. Sens. Actuators. B 2016, 232 , 306−312.). Fluorescent probe methods provide a powerful tool for detecting trace targets in complex systems by converting ion recognition events into measurable changes in fluorescence signals (such as fluorescence enhancement, quenching, ratio changes, or lifetime changes). In the study of fluoride ion fluorescent probes, researchers have developed various recognition strategies based on hydrogen bonding, Lewis acid-base interactions, fluorine-boron specific reactions, and deprotonation mechanisms. Org. Lett. 2007, 9 (3109−3112.). Among them, the strategy of using the strong electronegativity and basicity of fluoride ions to induce deprotonation of the recognition group, thereby triggering changes in the photophysical properties of the fluorophore, has attracted widespread attention due to its clear response mechanism and well-defined design concept.

[0005] Porphyrins and their derivatives are a class of macrocyclic conjugated compounds formed by four pyrrole units bridged by methylene groups. They possess excellent properties such as high molar absorptivity, moderate fluorescence quantum yield, easy structural modification, and good biocompatibility, earning them the title of "pigments of life." They have important applications in photodynamic therapy, optoelectronic devices, catalysis, and sensing. Constructing fluorescent probes using porphyrins as signal reporter units can fully utilize their excellent optical properties and structural tunability. However, existing porphyrin-based fluoride ion probes still have the following drawbacks: cumbersome synthesis steps, typically involving multiple reactions and harsh purification conditions, resulting in low yields; and poor water solubility, limiting their direct application in aquatic biological systems and environmental samples. Phys. Chem. Chem. Phys. 2017, 19(4530−4540.); The Stokes shift is small, and the excitation and emission spectra overlap significantly, easily leading to self-absorption and internal filtration effects, which affect the accuracy of detection. Anal Chem. 2014 , 86 (3616−3624.); Most probes adopt fluorescence-enhanced or ratiometric response modes, which can overcome some environmental interference, but the probe design is complex and signal interpretation requires special equipment; the selectivity for fluoride ions needs to be improved, and common anions such as acetate, phosphate, and hydroxide may cause cross-interference.

[0006] To address the problems existing in the prior art, this invention provides a novel fluorescent probe for fluoride ions based on a hydroxyporphyrin structure and its simple and efficient synthesis method. This probe introduces a phenolic hydroxyl group at the meso site of the porphyrin as a recognition group for fluoride ions. The fluoride ion-induced deprotonation process triggers the isomerization transformation of the porphyrin macrocycle, causing the probe to change from a phenolic structure to a quinone structure, resulting in the quenching of its characteristic red fluorescence at 664 nm. This probe has the following outstanding advantages: (1) a short synthetic route, employing a one-pot reaction and simple column chromatography purification, making it easy to prepare on a large scale; (2) the probe molecule is amphiphilic, with significantly improved water solubility compared to traditional porphyrin probes; (3) a Stokes shift as high as 244 nm, effectively avoiding spectral crosstalk between excitation and emission light; (4) excellent selective recognition ability for fluoride ions, including common anions (such as Cl⁻, Br⁻, I⁻, NO⁻, SO₄²⁻). 2 CO3 2 (5) The fluorescence intensity and fluoride ion concentration show a good linear relationship over a wide range, which can be used for quantitative analysis; (6) With fluorescence quenching, the solution color changes from red to green, realizing naked-eye visual detection, which is particularly suitable for rapid on-site screening. Based on the above characteristics, the fluorescent probe provided by this invention has broad application prospects in environmental water sample monitoring, drinking water safety assessment, food fluoride content detection, and dynamic imaging of fluoride ions in biological systems. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a hydroxyporphyrin-based compound, its preparation method, and its application as a fluorescent probe in fluoride ion detection. This probe aims to address the problems of poor selectivity, low sensitivity, poor water solubility, and small Stokes shift in existing fluoride ion detection methods, providing a novel fluorescent probe with high sensitivity, high selectivity, large Stokes shift, good water solubility, and significant color change response to meet the application needs of analytical chemistry, life sciences, environmental monitoring, and biomedicine.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a hydroxyporphyrin-based compound, characterized in that its structure is shown in formula (TM):

[0009] Furthermore, the compound is characterized by the introduction of a phenolic hydroxyl group as a recognition group at the meso position of the porphyrin. The mechanism of action of this compound utilizes the strong electronegativity of fluoride ions to induce deprotonation of the phenolic hydroxyl group, thereby causing the probe molecule to transform from a phenolic structure to a quinone structure. This structural transformation then triggers electron cloud rearrangement and isomerization of the porphyrin macrocycle, ultimately leading to fluorescence quenching of the probe, accompanied by a significant change in solution color from red to green. Furthermore, as a fluorescent probe, the compound of this invention emits strong fluorescence at 664 nm at an excitation wavelength of 420 nm, with a Stokes shift as high as 244 nm, effectively avoiding interference from excitation and scattered light. This probe exhibits a highly selective fluorescence quenching response to fluoride ions, and other common anions do not interfere with its detection. Under optimized conditions, the fluorescence intensity of the probe shows a good linear relationship with the fluoride ion concentration, and can be used for the quantitative detection of fluoride ions.

[0010] The present invention also provides a method for preparing the compound, comprising the following steps: synthesizing the target fluorescent probe molecule TM

[0011] Methyl 4-(di(1H-pyrrolo-2-yl)methyl)benzoate and methyl 5-formylsalicylate were dissolved in dichloromethane under light-protected and inert gas protection. After degassing, a catalyst amount of trifluoroacetic acid was added, and the reaction was stirred at room temperature. Subsequently, a methanol solution containing the oxidant 2,3-dichloro-5,6-dicyanobenzoquinone was added to the reaction solution, and the reaction was continued to be carried out by stirring in the dark for cyclization and oxidation. After the reaction was completed, the product was purified by silica gel column chromatography, the target component was collected, and then crystallized or recrystallized to obtain a purple-red solid product as shown in formula (TM). Attached Figure Description

[0012] Figure 1 The present invention relates to a proton NMR spectrum of a fluoride ion fluorescent probe based on hydroxyporphyrin.

[0013] Figure 2 The present invention discloses the ultraviolet-visible absorption spectrum of a fluoride ion fluorescent probe based on hydroxyporphyrin, which exhibits a characteristic absorption peak at 420 nm in the ultraviolet-visible absorption spectrum.

[0014] Figure 3 The fluorescence intensity of the fluoride ion fluorescent probe of hydroxyporphyrin described in this invention is compared with the fluoride ion concentration at an excitation wavelength of 420 nm.

[0015] Figure 4 The fluoride ion fluorescent probe of hydroxyporphyrin described in this invention exhibits a characteristic absorption peak at 665 nm in its fluorescence emission spectrum at an excitation wavelength of 420 nm. Its fluorescence emission intensity shows a linear response relationship with the fluoride ion concentration in the range of 0-0.84 μM. This linear standard curve (R² = 0.9979) provides a reliable basis for establishing fluorescence sensing of fluoride ion concentration.

[0016] Figure 5 The present invention provides a schematic diagram of the mechanism of fluoride ion detection by the hydroxyporphyrin fluoride ion fluorescent probe, and a diagram showing the selectivity of the probe for fluoride ions under visible light and 395 nm ultraviolet light illumination. Detailed Implementation

[0017] The invention will be further explained below with reference to the synthetic route. The synthetic route of the fluoride ion fluorescent probe based on hydroxyporphyrin described in this invention is as follows:

[0018] Under a light-protected, inert atmosphere, methyl 4-(bis(1H-pyrrolo-2-yl)methyl)benzoate (0.42 g, 1.5 mmol) and methyl 5-formylsalicylate (0.297 g, 1.65 mmol) were dissolved in 150 ml of dichloromethane. After degassing, 0.1 ml of trifluoroacetic acid was added to the solution using a syringe. The mixture was stirred at room temperature for 1 hour, and then a methanol (2 ml) solution of 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ, 1.02 g, 4.5 mmol) was injected into the reaction solution. The mixture was stirred for another 6 hours in the dark. After the reaction was completed, the mixture was purified by silica gel column chromatography using a 200-300 mesh screen with dichloromethane as the eluent. The red main color band was collected under UV light monitoring and concentrated by rotary evaporation to obtain a purple-red solid. The solid was dissolved in methanol and ultrasonically dispersed. After vacuum filtration and washing with methanol, a high-purity purple-red compound A product (25 mg, yield 4%) was obtained.

[0019] This invention relates to a fluoride ion fluorescent probe based on hydroxyporphyrin and its synthesis method. The probe introduces a phenolic hydroxyl group at the meso position of the porphyrin as a recognition group, utilizing the strong electronegativity of fluoride ions to induce deprotonation and achieve a specific fluorescence response. Its mechanism of action is as follows: fluoride ions selectively induce deprotonation of the phenolic hydroxyl group, transforming the probe from a phenolic structure to a quinone structure, thereby initiating electronic rearrangement and isomerization of the porphyrin macrocycle, leading to fluorescence quenching, accompanied by a significant color change in the solution from red to green. At an excitation wavelength of 420 nm, the probe emits fluorescence at 664 nm, with a Stokes shift of 244 nm, effectively overcoming the signal-to-noise ratio limitations caused by spectral overlap in traditional probes, and exhibiting high selectivity for fluoride ions without interference from other common anions. This probe was synthesized using a one-pot method, involving the condensation of methyl 4-(di(1H-pyrrolo-2-yl)methyl)benzoate and methyl 5-formylsalicylate under trifluoroacetic acid catalysis, followed by oxidation with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) to obtain the target probe TM. Although the invention has been described in detail through the above preferred embodiments, it should be understood that the above description should not be considered as limiting the invention. Various modifications and substitutions to the invention will be apparent to those skilled in the art after reading the above. Therefore, porphyrin compounds with phenolic hydroxyl recognition groups having similar technical features as described herein fall within the protection scope of this patent.

Claims

1. A fluorescent probe based on hydroxyporphyrin fluoride ions and its synthesis method, characterized in that... Its molecular structure is shown in formula (TM): The probe is a hydroxyporphyrin derivative with a phenolic hydroxyl group bonded to the meso site of the porphyrin; the phenolic hydroxyl proton of the probe can be removed by fluoride ions, initiating isomerization of the porphyrin macrocyclic structure, which in turn leads to the quenching of its characteristic red fluorescence at 664 nm.

2. A method for preparing the hydroxyporphyrin fluoride ion fluorescent probe of claim 1, characterized in that, Includes the following steps: Methyl 4-(di(1H-pyrrolo-2-yl)methyl)benzoate and methyl 5-formylsalicylate were dissolved in dichloromethane under light-protected and inert gas protection. After degassing, a catalyst amount of trifluoroacetic acid was added, and the reaction was stirred at room temperature. Subsequently, a methanol solution containing the oxidant 2,3-dichloro-5,6-dicyanobenzoquinone was added to the reaction solution, and the reaction was continued to be carried out by stirring in the dark for cyclization and oxidation. After the reaction was completed, the product was purified by silica gel column chromatography, the target component was collected, and then crystallized or recrystallized to obtain a purple-red solid product as shown in formula (TM).

3. The preparation method according to claim 2, characterized in that, The molar ratio of methyl 4-(bis(1H-pyrrolo-2-yl)methyl)benzoate to methyl 5-formylsalicylate is 1:1.

1.

4. The preparation method according to claim 2, characterized in that, The amount of trifluoroacetic acid used is 50% to 100% of the molar amount of the reactants.

5. The preparation method according to claim 2, characterized in that, The amount of 2,3-dichloro-5,6-dicyanobenzoquinone used is three times the molar amount of methyl 4-(bis(1H-pyrrolo-2-yl)methyl)benzoate.

6. A method for detecting fluoride ions using the hydroxyporphyrin fluoride ion fluorescent probe according to claim 1, characterized in that, Includes the following steps: The fluorescent probe described in claim 1 is added to the sample to be tested, and its fluorescence intensity change at a wavelength of 664 nm is monitored under excitation at a wavelength of 420 nm; based on the degree of quenching of fluorescence intensity, qualitative or quantitative detection of fluoride ions is achieved.

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