A Schiff base iridium complex useful for photodynamic therapy, and its preparation method and use

Abstract

The present invention discloses a Schiff-base iridium complex useful for photodynamic therapy, as well as its preparation method and use. The structural formula of the Schiff-base iridium complex is shown below: #imgabs0# The Schiff-base iridium complex BQ of the present invention possesses significant advantages in cancer PDT treatment due to its high photostability, large Stokes shift, and strong singlet-to-triplet intersystem crossing rate (ISC), making it a promising alternative to traditional photosensitizers. Furthermore, the Schiff-base iridium complex BQ, with its advantages such as high reactive oxygen species production, high phototoxicity, low dark toxicity, and excellent anticancer efficacy, provides insights into the design of photosensitizers with higher therapeutic efficacy.

Description

Technical Field

[0001] The present invention relates to a Schiff base iridium complex material that can be used for photodynamic therapy and a preparation method thereof, specifically to a Schiff base iridium complex material that has a high active oxygen yield under light irradiation, promotes cancer cell apoptosis, and can be used for tumor photodynamic therapy and a preparation method thereof. Background Art

[0002] Cancer is a malignant disease that seriously threatens human health and has high morbidity and mortality. Common methods for cancer treatment include chemotherapy, radiotherapy, immunotherapy and photodynamic therapy (PDT). PDT has received widespread attention in recent years due to its many advantages such as non-invasiveness, high specificity, strong controllability and few side effects. PDT is based on a photochemotherapy strategy and is mainly composed of three elements: light, photosensitizers (PSs) and oxygen (O2). Among these three basic elements, PSs has the largest research space. PSs, when activated by light, can photocatalytically produce harmful reactive oxygen species (ROS), including superoxide radicals (O2) produced by electron transfer (type I). ·- ), hydroxyl radicals (·OH) and hydrogen peroxide (H2O2), as well as singlet oxygen ( 1 O2), causing oxidative damage to surrounding tissues, presenting a local tumor treatment. Currently, developed PSs have many problems, such as complex material synthesis routes, difficulty in purification, poor stability, and easy self-aggregation under physiological conditions, which reduces fluorescence intensity. Compared with organic PSs, transition metal iridium (III) complexes have the characteristics of strong orbital spin coupling (SOC), high luminescence efficiency, simple synthesis, and higher physical and chemical stability. They have obvious advantages in cancer PDT treatment and are expected to become new anticancer drugs after platinum drugs. At the same time, the structure and electronic properties of iridium complexes are usually determined by the ligand. The diverse structures, redox properties and modifiability of the ligands provide a wide range of space for the design of candidate anticancer complexes. Schiff bases are organic compounds with imine (-C=N-) and hydroxyl (-OH) groups in their molecular structure. The lone pairs of electrons in the N and O atoms easily coordinate with the central metal iridium to form Schiff base iridium complexes. Schiff bases are frequently used as ligands. Schiff bases are highly modifiable ligands and have a wide range of applications in the biological field, including antioxidant, anticancer, and antibacterial properties.

[0003] Based on the above considerations, this study designed a Schiff base iridium complex with photodynamic therapy (PDT) activity, using a benzothiazole derivative as the primary ligand and a Schiff base as the auxiliary ligand. The photophysical properties of the ligand and complex were investigated using UV-visible absorption and phosphorescence emission spectroscopy. The ability and type of ROS generated by the complex were explored through theoretical calculations and ESR spectroscopy. Furthermore, the PDT activity of the complex against cancer cells under illumination was investigated using confocal microscopy. This study aims to pave the way for the design of photosensitizers with higher therapeutic efficacy. Summary of the Invention

[0004] The present invention aims to provide a Schiff base iridium complex material useful for photodynamic therapy, as well as its preparation method and use. Specifically, it provides a Schiff base iridium complex material with high phototoxicity and low dark toxicity, and can be used as an effective photosensitizer for PDT in tumor cells. To achieve this objective, the present invention provides the following technical solutions:

[0005] The present invention provides a Schiff base iridium complex that can be used for photodynamic therapy. The structural formula of the Schiff base iridium complex is as follows:

[0006]

[0007] The present invention also provides a method for preparing a Schiff base iridium complex that can be used for photodynamic therapy, comprising the following steps:

[0008] Step S1, synthesis of the main ligand benzothiazole derivative: 3,4-diethoxybenzaldehyde and o-aminothiophenol were dissolved in ethanol, heated under reflux to react, and a white filamentous product was obtained. The product was filtered under reduced pressure and dried to obtain the main ligand;

[0009] Step S2, synthesis of the intermediate iridium chloride bridge: under nitrogen and light-proof environment, the above-mentioned primary ligand and iridium trichloride trihydrate were added to a three-necked flask, and then a mixed solvent of ethylene glycol monoethyl ether and distilled water was added. After heating and reflux reaction, the mixture was cooled to room temperature to precipitate an orange solid, and the iridium chloride bridge was obtained by vacuum filtration;

[0010] Step S3, synthesis of auxiliary ligand LQ: N,N-diethylaminosalicylaldehyde was dissolved in ethanol, and then glacial acetic acid was added dropwise. After stirring and mixing at room temperature, N,N-ethylhydroxyethyl-p-phenylenediamine was added. After heating and reflux, water was added after cooling to precipitate an orange-red solid, and the solid was filtered under reduced pressure to obtain auxiliary ligand LQ;

[0011] Step S4: Under N2 and light-proof atmosphere, add iridium chloride bridge, auxiliary ligand LQ and ammonium hexafluorophosphate to a Shrek flask respectively, and use a mixed solution of methanol and dichloromethane as solvent. After heating and reflux reaction, stop the reaction and cool to precipitate a yellow solid, and filter under reduced pressure to obtain the target product, Schiff base iridium complex BQ.

[0012] Furthermore, in step S1, the molar ratio of 3,4-diethoxybenzaldehyde to o-aminothiophenol is 1:1.

[0013] Furthermore, in step S2, the molar ratio of the primary ligand to iridium trichloride trihydrate is 2-2.5:1; and the volume ratio of ethylene glycol monoethyl ether to distilled water in the mixed solvent is 3:1.

[0014] Furthermore, in step S3, the molar ratio of N,N-diethylaminosalicylaldehyde to N,N-ethylhydroxyethyl-p-phenylenediamine is 1 to 1.5:1.

[0015] Furthermore, in step S4, the molar ratio of the iridium-chloro bridge, the auxiliary ligand LQ and ammonium hexafluorophosphate is 1:2-2.5:2-4; and the volume ratio of methanol to dichloromethane in the mixed solvent is 1:1.

[0016] Furthermore, in steps S1-S4, the conditions for the heating reflux reaction are:

[0017] Step S1: temperature is 75-80°C, time is 6-8h;

[0018] Step S2: temperature is 110-120°C, time is 24-30h;

[0019] Step S3: temperature is 75-80°C, time is 6-8h;

[0020] Step S4: the temperature is 75-80° C. and the time is 12-15 hours.

[0021] The present invention also provides a use of a Schiff base iridium complex that can be used for photodynamic therapy. The Schiff base iridium complex is used to prepare a photosensitizer; and the photosensitizer is used in a living body.

[0022] Furthermore, the Schiff base iridium complex is used to prepare a photosensitizer for photodynamic therapy; and the photosensitizer is used in phototherapy of cancer cells.

[0023] The technical effects and advantages of the present invention are as follows:

[0024] 1. Schiff base is an important class of compounds in organic chemistry, which has anti-tumor, antiviral, antifungal and antibacterial activities. ^ N ligands utilize the lone pair of electrons on their nitrogen atoms to coordinate with metal Ir(III) to form complexes with excellent biological properties.

[0025] 2. Benzothiazole derivatives have good chemical and physical properties, and can form Ir-C bonds with metal Ir(III). They have strong coordination ability, large dd orbital splitting energy, improved stability of the formed complexes, and low probability of non-radiative transitions, which helps to improve the optical activity of the complexes.

[0026] 3. Schiff base iridium complex BQ has obvious advantages in cancer PDT treatment due to its high photostability, large Stokes shift and strong singlet to triplet intersystem crossing rate (ISC), and has gradually become a compound that can replace traditional photosensitizers.

[0027] 4. Schiff base iridium complex BQ provides ideas for designing photosensitizers with higher therapeutic efficiency due to its advantages such as efficient reactive oxygen production, high phototoxicity, low dark toxicity and excellent anticancer efficacy. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1a is a time-of-flight mass spectrum of the Schiff base iridium complex BQ of the present invention;

[0030] Figure 1b is the hydrogen nuclear magnetic resonance spectrum of the Schiff base iridium complex BQ of the present invention;

[0031] Figure 2 a is a UV-visible absorption spectrum of the Schiff base iridium complex BQ of the present invention in different solvents;

[0032] Figure 2 b is the phosphorescence emission spectra of the Schiff base iridium complex BQ of the present invention in different solvents;

[0033] Figure 3 a is a schematic diagram of the absorbance of a 9,10-anthryl-bis(methylene)dimalonic acid (ABDA) solution containing the Schiff base iridium complex BQ of the present invention under different illumination times;

[0034] Figure 3 b is an electron spin resonance spectrum (ESR) diagram of the Schiff base iridium complex BQ of the present invention under light and dark conditions;

[0035] Figure 4 a is a schematic diagram of the cytotoxicity test of the Schiff base iridium complex BQ of the present invention under light and darkness;

[0036] Figure 4 b is a confocal imaging image of cells under light and darkness using the Schiff base iridium complex BQ of the present invention;

[0037] Figure 5a is a confocal imaging image of the Schiff base iridium complex BQ of the present invention inducing the production of singlet oxygen in cancer cells under light;

[0038] Figure 5 b is a confocal imaging image of the Schiff base iridium complex BQ of the present invention generating singlet oxygen under light to induce cancer cell death;

[0039] Figure 6 This is a confocal imaging diagram of the cell death mechanism induced by the Schiff base iridium complex BQ of the present invention under light irradiation. DETAILED DESCRIPTION

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0041] The flowcharts shown in the accompanying drawings are merely illustrative and do not necessarily include all steps. For example, some steps may be decomposed, while some steps may be combined or partially combined, so the actual execution order may change according to actual circumstances.

[0042] The terms "first," "second," and the like in the specification and claims of this application and in the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a particular order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, such that the embodiments of the application described herein can be practiced in orders other than those illustrated or described herein.

[0043] To address the deficiencies of the prior art, the present invention discloses a Schiff base iridium complex for PDT, the structural formula of the complex is shown below:

[0044]

[0045] The present invention also discloses a method for preparing a Schiff base iridium complex for PDT, comprising the following steps:

[0046] Step S1, Synthesis of the Primary Ligand Benzothiazole Derivative: Dissolve 3,4-diethoxybenzaldehyde and o-aminothiophenol in an appropriate amount of ethanol, heat to 75-80°C, and reflux for 6-8 hours to obtain a large amount of white filamentous product. Filter under reduced pressure and dry to obtain the primary ligand. The synthesis route is as follows:

[0047]

[0048] Step S2, Synthesis of the Intermediate Iridium-Chloro Bridge: Under nitrogen and in the dark, add the primary ligand, iridium trichloride trihydrate, and a mixed solvent of ethylene glycol monoethyl ether and distilled water to a three-necked flask. Heat to 110-120°C and reflux for 24-30 hours. Cool to room temperature to precipitate an orange-yellow solid, which is then filtered under reduced pressure to obtain the iridium-chloro bridge. The synthetic route is as follows:

[0049]

[0050] Step S3, Synthesis of Auxiliary Ligand LQ: Dissolve N,N-diethylaminosalicylaldehyde in ethanol, then add glacial acetic acid dropwise. Stir at room temperature for a period of time, add N,N-ethylhydroxyethyl-p-phenylenediamine, heat to 75-80°C, and reflux for 6-8 hours. After cooling, add water to precipitate an orange-red solid, which is filtered under reduced pressure to obtain auxiliary ligand LQ. The synthesis route is as follows:

[0051]

[0052] Step S4: Under an N2, light-proof atmosphere, add the iridium chloride bridge, auxiliary ligand LQ, and ammonium hexafluorophosphate to a Shrek flask, respectively. A mixed solution of methanol and dichloromethane is used as the solvent. The mixture is heated to 75-80°C and refluxed for 12-15 hours. The reaction is stopped, cooled, and a yellow solid precipitated. The solid is then filtered under reduced pressure to obtain the target product, Schiff base iridium complex BQ. The synthesis route is as follows:

[0053]

[0054] Furthermore, in step S1, the molar ratio of 3,4-diethoxybenzaldehyde to o-aminothiophenol is 1:1.

[0055] Furthermore, in step S2, the molar ratio of the primary ligand to iridium trichloride trihydrate is 2 to 2.5:1, preferably 2.2:1; and the volume ratio of ethylene glycol monoethyl ether to distilled water in the mixed solvent is 3:1.

[0056] Furthermore, in step S3, the molar ratio of N,N-diethylaminosalicylaldehyde to N,N-ethylhydroxyethyl-p-phenylenediamine is 1 to 1.5:1, preferably 1.5:1.

[0057] Furthermore, in step S4, the molar ratio of the iridium-chloro bridge, the auxiliary ligand LQ and ammonium hexafluorophosphate (NH4PF6) is 1:2-2.5:2-4, preferably 1:2.2:4; the volume ratio of methanol to dichloromethane in the mixed solvent is 1:1.

[0058] Furthermore, in steps S1-S4, the conditions for the heating reflux reaction are preferably:

[0059] Step S1: temperature 75°C, time 6h;

[0060] Step S2: temperature is 110°C, time is 24h;

[0061] Step S3: temperature 78°C, time 6h;

[0062] Step S4: temperature is 75° C., time is 12 h.

[0063] The present invention also discloses a use of a two-photon half-sandwich iridium complex that can be used for photodynamic therapy. The Schiff base iridium complex is used to prepare a photosensitizer; and the photosensitizer is used in a living body.

[0064] Furthermore, the Schiff base iridium complex is used to prepare a photosensitizer for photodynamic therapy; and the photosensitizer is used in phototherapy of cancer cells.

[0065] Example 1: Preparation of Schiff base iridium complex BQ:

[0066] Step S1, synthesis of the main ligand benzothiazole derivative:

[0067] To a 100 mL round-bottom flask, 1.94 g (10.0 mmol) of 3,4-diethoxybenzaldehyde and 1.25 g (10.0 mmol) of o-aminothiophenol were added, followed by dissolution in an appropriate amount of ethanol. The mixture was heated under reflux at 75°C for 6 h. After quenching the reaction and cooling, 2.10 g of a white filamentous product was obtained. The product was filtered under reduced pressure and dried to obtain the primary ligand with a yield of 70.2%. ESI-MS = [M+H + ] + : cal: 300.10g / mol, found: 300.13g / mol. 1 H-NMR (400MHz, CD3COCD3, ppm) δ7.97 (dd, J=8.2, 1.3Hz, 2H), 7.67 (t, J=7.3Hz, 1H), 7.58 (dd, J=8.2, 2.0Hz, 1H), 7.44 ( dd, J=7.1, 1.1Hz, 1H), 7.35 (dd, J=7.0, 1.3Hz, 1H), 7.11 (dd, J=8.5, 4.6Hz, 1H), 4.19-4.01 (m, 4H), 1.45-1.35 (m, 6H).

[0068] Step S2, synthesis of intermediate iridium chloride bridge:

[0069] To a 50 mL three-necked flask, under nitrogen and protected from light, were added 0.65 g (2.2 mmol) of the primary ligand and 0.35 g (1 mmol) of iridium trichloride trihydrate. A mixed solvent of 15 mL of ethylene glycol monoethyl ether and 5 mL of distilled water was added. The mixture was heated under reflux at 110°C for 24 hours. After cooling to room temperature, an orange solid precipitated. Filter under reduced pressure to obtain 0.56 g of the iridium-chloro bridge, yielding 66.7%.

[0070] Step S3, synthesis of auxiliary ligand LQ:

[0071] 5.22 g (27 mmol) of N,N-diethylaminosalicylaldehyde was weighed into a 250 mL round-bottom flask and dissolved in 100 mL of ethanol. Two drops of glacial acetic acid were then added dropwise. The mixture was stirred at room temperature for 20 min. 3.24 g (18 mmol) of N,N-ethylhydroxyethyl-p-phenylenediamine was added and the mixture was heated under reflux at 78°C for 6 h. After cooling, water was added to precipitate an orange-red solid. The solid was filtered under reduced pressure to obtain 3.89 g of auxiliary ligand LQ, with a yield of 61%. TOF-MS = [M+H + ] + : cal: 356.48g / mol, found: 356.2322g / mol. 1 H-NMR (600MHz, DMSO, ppm) δ13.99 (s, 1H), 8.61 (s, 1H), 7.25 (d, 1H, J=8.8Hz), 7.19 (d, 2H, J=9.0Hz), 6.69 (d, 2H, J=9.1Hz), 6.27 (dd, 1H , J=8.8Hz, 2.4Hz), 6.04 (d, 1H, J=2.4Hz), 4.71 (t, 1H, J=5.4Hz), 3.54 (dd, 2H, J=11.9Hz, 6.3Hz), 3.41-3.34 (m, 8H), 1.14-1.05 (m, 9H).

[0072] Step S4, synthesis of Schiff base iridium complex BQ:

[0073] Under N2 atmosphere, 1.651 g (1 mmol) of iridium chloride bridge, 0.781 g (2.2 mmol) of auxiliary ligand LQ, and 0.66 g (4 mmol) of ammonium hexafluorophosphate were added to a Shrek bottle wrapped in tinfoil. 50 mL of a 1:1 mixture of methanol and dichloromethane was used as the solvent. The mixture was heated under reflux at 75°C for 12 h. The reaction was stopped and cooled to precipitate a yellow solid. The solid was filtered under reduced pressure to obtain 1.13 g of Schiff base iridium complex BQ with a yield of 44%. TOF-MS = [M-PF6 - ] + : cal: 1143.45g / mol, found: 1144.3678g / mol. 1H-NMR (400MHz, DMSO, ppm) δ8.40 (d, 1H, J=7.6Hz), 8.25 (d, 1H, J=7.9Hz), 8.15 (d, 1H, J=7.3Hz), 8.04 (d, 1H, J=7.5Hz), 7. 73 (s, 1H), 7.44-7.27 (m, 4H), 6.89 (d, 1H, J=9.0Hz), 6.60 (s, 1H), 5.94 (d, 2H, J=8.9Hz), 5.88 (d, 2H, J=8.8Hz), 5.80-5.72 (m, 1H), 5.60 (d, 2H, J=3.3Hz), 5.41 (s, 1H), 4.51 (t, 1H, J=5.4Hz), 3.92 (dd, 2H, J=6.9Hz, 1.7Hz), 3.75-3.64 (m, 2H), 3.4 5-3.33 (m, 8H), 3.20-3.09 (m, 6H), 1.23 (t, 3H, J=6.9Hz), 1.17 (t, 3H, J=6.9Hz), 1.00 (t, 6H, J=6.9Hz), 0.92-0.84 (m, 9H).

[0074] Figure 1a and Figure 1b They are respectively the time-of-flight mass spectrum and the nuclear magnetic resonance hydrogen spectrum of the Schiff base iridium complex BQ of the present invention. The experimental data are consistent with the theoretical data, indicating that the iridium complex BQ is successfully prepared.

[0075] Figure 2 a and Figure 2 b) are the UV-visible absorption and phosphorescence emission spectra of the Schiff base iridium complex BQ in solvents of varying polarity. The experimental results show that the positions of the absorption and emission peaks of the iridium complex BQ remain essentially unchanged in solvents of varying polarity. This is primarily due to the weak dipole-dipole interaction between the iridium complex BQ molecules and the solvent molecules, resulting in minimal influence from solvent polarity. Furthermore, the iridium complex BQ exhibits a large Stokes shift, which effectively reduces background interference in bioimaging applications.

[0076] Figure 3a) An iridium complex BQ was added to a 9,10-anthryl-bis(methylene)dimalonic acid (ABDA) solution, with ABDA used as a singlet oxygen indicator. As the illumination time (400-700 nm) increased, the absorbance of the ABDA solution gradually decreased, indicating that the iridium complex BQ could rapidly generate singlet oxygen under illumination, thereby promoting the oxidation of ABDA. Table 1 shows the singlet oxygen yields of the Schiff base iridium complex BQ of the present invention, the ligand LQ, and the reference Rose Bengal (RB). As shown in Table 1, using RB as the reference, the singlet oxygen yields of the ligand LQ and the iridium complex BQ were 0.4% and 57%, respectively, indicating that the introduction of metallic iridium facilitates the generation of intersystem crossing (ISC) and increases the yield of reactive oxygen species.

[0077] Table 1 Singlet oxygen yields of Schiff base iridium complex BQ and ligand LQ, and reference Rose Bengal

[0078]

[0079] Figure 3 b Using 2,2,6,6-tetramethylpiperidine (TEMP) as a singlet oxygen scavenger, electron spin resonance spectroscopy (ESR) was used to further verify that the reactive oxygen species generated by the iridium complex BQ under light conditions was singlet oxygen, indicating that the iridium complex BQ can be used as a photosensitizer for PDT exploration at the tumor cell level.

[0080] Example 2: Biological studies of target molecules:

[0081] Figure 4 Figure a shows the evaluation of the cytotoxicity of the iridium complex BQ under light and dark conditions using the MTT assay. The specific process is as follows: First, HepG2 cells were seeded in a 96-well plate and incubated for 24 hours. When the cells reached approximately 75% growth, 0 μM, 5 μM, 10 μM, 15 μM, and 20 μM of the complex BQ were added and incubated for a further 12 hours. At this point, half of the 95-well plate was exposed to light and the other half was protected from light with tin foil. Second, the culture medium in the wells was aspirated, and 100 μL of 5 mg / L MTT was added to each well and incubated for a further 4 hours. Finally, the MTT in the wells was aspirated, and 100 μL of DMSO was added to all wells except the blank group. After shaking on a shaker for 10 minutes, the absorbance of each well was measured using a microplate reader (detection wavelength 570 nm), and the results were recorded and calculated. The results showed that the iridium complex BQ exhibited high phototoxicity and low dark toxicity. In the absence of light, it still had a high cell survival rate (>70%) even in a high concentration range (20 μM), while white light (400-700 nm, 10 mW·cm 2 ) irradiation, the cell survival rate decreased significantly.

[0082] Figure 4 b is the use of laser confocal microscopy to further monitor the changes in the cell state of cancer cells under light and dark conditions. HepG2 cells were used as the monitoring object. HepG2 cells were seeded in two small dishes. When the cells in the small dish grew to about 70%, 10μL of 10mM complex BQ solution was added and incubated for 30min. At this time, one dish was placed in the dark and the other dish was placed in the light (400-700nm, 10mW·cm 2 In the dark, the cells appear to be clearly outlined and in good condition. However, when exposed to light, the cells swell, their outlines blur, and blistering forms around the cell membrane. This phenomenon suggests that the iridium complex BQ, when exposed to light, rapidly generates singlet oxygen, killing cancer cells and exhibiting high phototoxicity.

[0083] Figure 5 a Using SOSG as a singlet oxygen detector, the ability of the iridium complex BQ to produce singlet oxygen in cells under light was detected. HepG2 cells were seeded into four groups of small dishes. When the cells in the small dishes grew to about 70%, the culture medium was aspirated and four groups of controls were set up: PBS+Dark, PBS+Light, BQ+Drak and BQ+Light. After incubation for 30 minutes, 4μL of 5mM SOSG storage solution was added to each of the four groups of small dishes and incubated for 15 minutes. Under dark conditions, no fluorescence signal was found in the cells of the PBS+Dark and BQ+Drak groups. Under white light irradiation (400-700nm, 10mW·cm 2 ), there was no fluorescence signal in the PBS+Light group, while a green fluorescence signal appeared in the BQ+Light group, and blebbing appeared around the cell membrane. This result indicates that the iridium complex BQ can effectively produce endogenous singlet oxygen in HepG2 cells under white light irradiation, leading to cancer cell apoptosis.

[0084] Figure 5 b) Live / dead cell staining assay using the iridium complex BQ. Calcein-acetoxymethyl ester (Calcein-AM) is a green fluorescent dye that fluorescently labels live cells, while propidium iodide (PI) is a red fluorescent dye that fluorescently labels dead cells. Their combined use allows for the staining of both live and dead cells. When HepG2 cells were incubated with the iridium complex BQ, Calcein-AM, and PI, a large area of ​​the cells emitted strong green fluorescence in the dark, indicating that BQ is non-toxic in the absence of light and that cell survival is high. After a period of illumination, the red fluorescent area increased, indicating that the cells gradually underwent apoptosis under illumination. The dye PI can only penetrate the membranes of dead cells and localize to the nucleus. It interacts with the DNA in the nucleus, emitting a red fluorescent signal in the nuclear region, revealing the PDT therapeutic effect of BQ on cancer cells under illumination.

[0085] Figure 6 To investigate the mechanism by which the Schiff base iridium complex BQ induces cell death under light, an Annexin V-FITC / PI assay was performed. During early apoptosis, phosphatidylserine primarily attaches to the outer surface of the cell membrane. Annexin V-FITC specifically binds to phosphatidylserine on the membrane surface, staining the cell membrane and emitting a green fluorescence signal. Simultaneously, PI binds to nuclear DNA in late apoptotic stages, emitting a red fluorescence signal. Incubation of HepG2 cells with the iridium complex BQ, Annexin V-FITC, and PI revealed healthy cell health in the absence of light, with no fluorescence observed in either the Annexin V-FITC or PI channels. However, after illumination for a period of time, significant green fluorescence was observed in the cell membrane and red fluorescence was observed in the PI channel in the cell nucleus, suggesting that the iridium complex BQ may induce cancer cell death through apoptosis.

[0086] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A Schiff base iridium complex useful for photodynamic therapy, characterized in that: The structural formula of the Schiff base iridium complex is as follows: 。 2. A method for preparing a Schiff base iridium complex useful for photodynamic therapy according to claim 1, characterized in that: The steps include: Step S1, synthesis of the main ligand benzothiazole derivative: 3,4-diethoxybenzaldehyde and o-aminothiophenol were dissolved in ethanol, heated under reflux to react, and a white filamentous product was obtained. The product was filtered under reduced pressure and dried to obtain the main ligand; Step S2, synthesis of the intermediate iridium chloride bridge: under nitrogen and light-proof environment, the above-mentioned primary ligand and iridium trichloride trihydrate were added to a three-necked flask, and then a mixed solvent of ethylene glycol monoethyl ether and distilled water was added. After heating and reflux reaction, the mixture was cooled to room temperature to precipitate an orange solid, and the iridium chloride bridge was obtained by vacuum filtration; Step S3, synthesis of auxiliary ligand LQ: N,N-diethylaminosalicylaldehyde was dissolved in ethanol, and then glacial acetic acid was added dropwise. After stirring and mixing at room temperature, N,N-ethylhydroxyethyl-p-phenylenediamine was added. After heating and reflux, water was added after cooling to precipitate an orange-red solid, and the solid was filtered under reduced pressure to obtain auxiliary ligand LQ; Step S4: Under nitrogen and light-proof atmosphere, add iridium chloride bridge, auxiliary ligand LQ and ammonium hexafluorophosphate to a Shrek flask respectively, and use a mixed solution of methanol and dichloromethane as solvent. After heating and reflux reaction, stop the reaction and cool to precipitate a yellow solid, and filter under reduced pressure to obtain the target product, Schiff base iridium complex BQ.

3. The method for preparing a Schiff base iridium complex useful for photodynamic therapy according to claim 2, characterized in that: In step S1, the molar ratio of 3,4-diethoxybenzaldehyde to o-aminothiophenol is 1:

1.

4. The method for preparing a Schiff base iridium complex useful for photodynamic therapy according to claim 2, wherein: In step S2, the molar ratio of the primary ligand to iridium trichloride trihydrate is 2-2.5:1; and the volume ratio of ethylene glycol monoethyl ether to distilled water in the mixed solvent is 3:

1.

5. The method for preparing a Schiff base iridium complex useful for photodynamic therapy according to claim 2, wherein: In step S3, the molar ratio of N,N-diethylamino salicylaldehyde to N,N-ethylhydroxyethyl-p-phenylenediamine is 1 to 1.5:

1.

6. The method for preparing a Schiff base iridium complex useful for photodynamic therapy according to claim 2, wherein: In step S4, the molar ratio of the iridium-chloride bridge, the auxiliary ligand LQ, and ammonium hexafluorophosphate is 1:2-2.5:2-4; and the volume ratio of methanol to dichloromethane in the mixed solvent is 1:

1.

7. The method for preparing a Schiff base iridium complex useful for photodynamic therapy according to claim 2, wherein: In steps S1-S4, the conditions for heating under reflux reaction are: Step S1: temperature is 75-80°C, time is 6-8 hours; Step S2: temperature is 110-120°C, time is 24-30 hours; Step S3: temperature is 75-80°C, time is 6-8 hours; Step S4: the temperature is 75-80°C and the time is 12-15 hours.

8. A use of the Schiff base iridium complex for photodynamic therapy according to claim 1, characterized in that: The Schiff base iridium complex is used to prepare a photosensitizer; and the photosensitizer is applied in a living body.

9. The use of the Schiff base iridium complex for photodynamic therapy according to claim 8, characterized in that: The Schiff base iridium complex is used to prepare a photosensitizer for photodynamic therapy; the photosensitizer is applied to cancer cell phototherapy.

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