A method for preparing a water-soluble nitrogen heterocyclic carbene modified gold nanoparticle

Abstract

The present application relates to the technical field of nanomaterial preparation, and particularly relates to a preparation method of water-soluble azacyclo carbene modified gold nanoparticles. 5-ethynyl-1-methyl-1H imidazole is used as a starting compound, polyethylene glycol modified azacyclo carbene imidazole salt is obtained through alkylation and click reaction, then silver complex is generated through reaction of the imidazole salt and silver oxide, metal conversion of the synthesized silver complex with dimethyl sulfur gold chloride is carried out to obtain gold complex, and finally ligand exchange is carried out in an aqueous solution through the gold complex and citric acid modified gold nanoparticles to obtain azacyclo carbene modified gold nanoparticles. The preparation method is simple and fast, has high yield, does not need to add a reducing agent additionally, has the characteristics of green environmental protection, and the target product prepared has high water solubility, good biocompatibility and uniform morphology.

Description

Technical Field

[0001] This invention relates to the field of nanomaterial preparation technology, and in particular to a method for preparing water-soluble nitrogen heterocyclic carbene-modified gold nanoparticles. Background Technology

[0002] Gold nanoparticles (GNPs) possess high surface area and biocompatibility, along with unique optical properties and good biocompatibility, making them promising candidates for applications in the biomedical field, such as sensing, imaging, and photothermal therapy. However, a major challenge in nanomaterial design in the biomedical field is achieving sufficient stability and dispersibility in aqueous solutions. Currently, thiols are commonly used to modify gold nanoparticles to improve their stability in aqueous solutions. However, the S-Au bond is not completely inert, limiting the long-term stability of these GNPs. Recently, nitrogen-containing heterocyclic carbene (NHC) has attracted increasing attention as a substitute ligand for thiols in the functionalization of GNPs. NHC is a strong σ-electron donor, capable of forming strong covalent bonds with metals. Furthermore, the framework of the NHC ligand and the N atom connected to the C central atom can be modified. By altering the structure of the NHC ligand, its electronic, spatial, and functional properties can be changed to achieve the desired purpose. Although GNPs have great application potential in the biomedical field, the applications of NHC-modified GNPs in the biological field have been rarely explored. To enable their application in the biomedical field, NHC-modified GNPs must possess a certain degree of solubility in aqueous systems. However, to date, most NHC-modified GNPs are hydrophobic, limiting their application in biomedicine. Against this backdrop, providing a method for preparing nitrogen-heterocyclic carbene-modified gold nanoparticles with high water solubility, good biocompatibility, and high yield has become a pressing technical problem to be solved in this field. Summary of the Invention

[0003] To achieve the above objectives, the present invention provides a method for preparing water-soluble nitrogen heterocyclic carbene-modified gold nanoparticles, comprising:

[0004] (1) The first product was prepared by alkylation reaction using 5-ethynyl-1-methyl-1H imidazole as a raw material;

[0005] (2) Using the first product and N3-PEG as raw materials, a PEG-modified nitrogen-containing heterocyclic carbene imidazole salt was prepared by click chemical reaction under an inert atmosphere;

[0006] (3) Using the PEG-modified nitrogen-heterocyclic carbene imidazole salt and silver oxide as raw materials, a silver complex was prepared by reaction; then, the silver complex was reacted with dimethyl thiogold chloride as raw materials to prepare a nitrogen-heterocyclic carbene gold complex.

[0007] (4) Using citric acid-modified gold nanoparticles and the nitrogen heterocyclic carbene gold complex as raw materials, the water-soluble nitrogen heterocyclic carbene-modified gold nanoparticles are prepared by ligand exchange reaction.

[0008] This invention first designs a nitrogen-containing heterocyclic carbene imidazole salt with excellent water solubility. This structure can promote the water solubility and biocompatibility of gold nanoparticles. Then, through simple ligand exchange, nitrogen-containing heterocyclic carbene-modified gold nanoparticles are obtained. The prepared gold nanoparticles have good dispersibility, uniform particle size, and good morphology in aqueous solution, thus solving the problem of poor water solubility of nitrogen-containing heterocyclic carbene-modified gold nanoparticles.

[0009] In the preparation of nitrogen heterocyclic carbene gold complexes, 5-ethynyl-1-methyl-1H imidazole was chosen as the precursor, which is easy to functionalize and modify, has a simple synthetic route, reduces production costs and byproducts, and is easy to purify.

[0010] Furthermore, most studies on the preparation of multi-metal carbene complexes involve harsh reaction conditions. However, using silver carbene complexes to prepare other metal carbene complexes via metal exchange is a highly effective method, and the reaction can be carried out at room temperature. This invention utilizes the Ag(I) complex generated directly from silver oxide (Ag₂O), eliminating the need for separation before the transfer reaction; the AgCl generated during the transfer process can be directly removed by filtration. This method is simple and yields a single product.

[0011] In addition, citric acid-modified gold nanoparticles were selected for ligand exchange. Citric acid was adsorbed onto the surface of gold nanoparticles through electrostatic adsorption, which facilitated the ligand exchange reaction and made it easier for nitrogen heterocyclic carbene ligands to bond with gold nanoparticles, resulting in uniformly sized nitrogen heterocyclic carbene surface-modified gold nanoparticles.

[0012] In this invention, the structure of 5-ethynyl-1-methyl-1H imidazole is as follows:

[0013]

[0014] In some embodiments, step (1) includes: dissolving 5-ethynyl-1-methyl-1H imidazole and an alkylating agent in a solvent and heating the mixture at 40–60 °C to obtain the first product.

[0015] The yield of the first product can be significantly increased at the above reaction temperature.

[0016] In some embodiments, the alkylating agent is at least one selected from iodomethane, iodoethane, and iodopropane;

[0017] And / or, the solvent is toluene.

[0018] In some embodiments, the molar ratio of 5-ethynyl-1-methyl-1H imidazole to the alkylating agent is 1:1 to 1.2.

[0019] In some embodiments, step (2) includes: using the first product and N3-PEG as raw materials, a crude product is obtained by click chemical reaction under an inert atmosphere; and then the crude product is subjected to silica gel column chromatography to obtain PEG-modified nitrogen-containing heterocyclic carbene imidazole salt.

[0020] The molecular weight of the above N3-PEG is 2000.

[0021] In practice, the chemical reaction is carried out in a sealed environment.

[0022] Preferably, the chemical reaction is carried out for more than 24 hours.

[0023] Preferably, the chromatography column is packed with 200-300 mesh silica gel, and the eluent is dichloromethane:methanol = 15:1 (V:V).

[0024] In some embodiments, the first product, N3-PEG, sodium ascorbate and copper sulfate are dissolved in a solvent, and a crude product is obtained by click chemistry under an inert atmosphere; then the crude product is vacuum dried and concentrated, and then subjected to silica gel column chromatography to obtain PEG-modified nitrogen-containing heterocyclic carbeneimidazole salt.

[0025] Preferably, the molar ratio of the first product, N3-PEG, sodium ascorbate and copper sulfate is 2-4:1:0.4-0.8:0.1-0.4.

[0026] Preferably, the solvent in step (2) is methanol.

[0027] In some embodiments, step (3) includes: dissolving the PEG-modified nitrogen-heterocyclic carbene imidazole salt and silver oxide in a solvent and reacting them in the dark to obtain a silver complex solution; then reacting the silver complex solution with dimethyl thiogold chloride (Au(SMe2)Cl) to obtain a nitrogen-heterocyclic carbene gold complex.

[0028] Preferably, the solvent in step (3) is dichloromethane.

[0029] Preferably, the molar ratio of the PEG-modified nitrogen-containing heterocyclic carbeneimidazole salt to silver oxide is 1:2 to 3.

[0030] Preferably, the reaction is carried out in the dark for more than 24 hours.

[0031] In some embodiments, the silver complex solution is mixed with dimethyl thiogold chloride and reacted. The resulting product is then vacuum dried, dissolved in water, and allowed to stand for more than 6 hours to obtain a nitrogen-heterocyclic carbene gold complex.

[0032] The purpose of the above settling is to remove unreacted Au(SMe2)Cl, which is unstable in water and forms elemental gold, which can be removed by filtration.

[0033] In some implementations, step (4) of the method for preparing the citric acid-modified gold nanoparticles includes:

[0034] A gold nanocrystal seed solution was prepared by mixing HAuCl4, AgNO3 and sodium citrate. The gold nanocrystal seed solution was then mixed with boiling water and cooled to room temperature to obtain the final product.

[0035] In some implementations, step (4) includes the ligand exchange reaction comprising:

[0036] Citric acid-modified gold nanoparticles and the nitrogen-heterocyclic carbene gold complex were mixed and reacted at room temperature.

[0037] Preferably, the mass ratio of citric acid-modified gold nanoparticles to the nitrogen-heterocyclic carbene gold complex is 1:10 to 20.

[0038] The ligand exchange method is characterized by its simplicity, mild conditions, short reaction time, and uniform nanoparticle size. The products obtained from different batches exhibit consistency, demonstrating high application value and potential for widespread adoption.

[0039] Those skilled in the art can further combine the above preferred solutions to obtain other preferred embodiments of the preparation method of the present invention.

[0040] Furthermore, the present invention provides water-soluble nitrogen heterocyclic carbene-modified gold nanoparticles prepared according to any of the above embodiments.

[0041] In some embodiments, the water-soluble nitrogen heterocyclic carbene-modified gold nanoparticles have a particle size of 5–7 nm and are spherical.

[0042] The nitrogen-modified gold nanoparticles synthesized in this invention have easily modifiable substituents on the N atom of the nitrogen-heterocyclic carbene, are easy to synthesize, and exhibit stable performance, making them widely applicable in the biomedical field.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] The preparation method of this invention is simple, rapid, low-cost, and has a high yield. Water-soluble nitrogen-heterocyclic carbene-modified gold nanoparticles can be obtained in an aqueous system through simple ligand exchange, without the need for additional reducing agents, making it environmentally friendly. Furthermore, the target product prepared by the method of this invention exhibits high water solubility, good biocompatibility, and uniform morphology. Attached Figure Description

[0045] Figure 1 For product 1a in CDCl3 1 H-NMR spectrum.

[0046] Figure 2 For product 1a in CDCl3 13 C-NMR spectrum.

[0047] Figure 3 Product 1b in CDCl3 1 H-NMR spectrum.

[0048] Figure 4 Product 1b in CDCl3 13 C-NMR spectrum.

[0049] Figure 5 For product 1c in CDCl3 1 H-NMR spectrum.

[0050] Figure 6 For product 1c in CDCl3 13 C-NMR spectrum.

[0051] Figure 7 The images show TEM images of citric acid-modified gold nanoparticles and nitrogen-heterocyclic carbene-modified gold nanoparticles; where a represents citric acid-modified gold nanoparticles and b represents nitrogen-heterocyclic carbene-modified gold nanoparticles.

[0052] Figure 8 The images show DLS diagrams of citric acid-modified gold nanoparticles and nitrogen-heterocyclic carbene-modified gold nanoparticles; where a represents citric acid-modified gold nanoparticles and b represents nitrogen-heterocyclic carbene-modified gold nanoparticles.

[0053] Figure 9 The images show UV spectra of citric acid-modified gold nanoparticles and nitrogen-heterocyclic carbene-modified gold nanoparticles; where a represents citric acid-modified gold nanoparticles and b represents nitrogen-heterocyclic carbene-modified gold nanoparticles.

[0054] Figure 10 The image shows the chromatogram of the product obtained in Comparative Example 1.

[0055] Figure 11 Figure shows the stability test results of gold nanoparticles modified with water-soluble nitrogen heterocyclic carbene. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0057] Unless otherwise specified, all methods used in the examples were conventional or performed according to techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents and instruments used without specified manufacturers were all conventional products that could be purchased from legitimate channels.

[0058] Example 1

[0059] This embodiment provides a method for preparing water-soluble nitrogen heterocyclic carbene-modified gold nanoparticles, the steps of which include:

[0060] (1) Preparation of nitrogen-heterocyclic carbene gold complexes

[0061] (1a) Add 4 mL of toluene solution, 100 mg of 5-ethynyl-1-methyl-1H imidazole, and 66 μL of iodomethane to a pressure flask. Seal the reaction vessel and heat and stir overnight at 60 °C. After the reaction is complete, cool to room temperature. Wash the resulting white solid three times with toluene and centrifuge to remove the toluene. Recrystallize the obtained solid in diethyl ether. Dry under vacuum at 40 °C for 3 h to give product 1a, with a yield of 85%. Figure 1 : 1 H-NMR (500MHz, CDCl3) δ10.17(s,1H),7.75(s,1H),4.15(s,3H),4.02(s,3H),3.79(s,1H). Figure 2 : 13 C-NMR (126MHz, CDCl3) δ138.15,126.78,117.89,89.56,66.99,37.75,35.22.

[0062] The synthesis route is shown in Equation 1:

[0063]

[0064] (1b) Under nitrogen protection, 100 mg of product 1a, 282.50 mg of N3-PEG (Mw = 2000), 60 μL of 1M sodium ascorbate aqueous solution, 30 μL of 1M copper sulfate aqueous solution, and 10 mL of methanol were added to a dry three-necked flask. The flask was sealed and stirred at room temperature for 24 h under nitrogen atmosphere. The crude product was dried under vacuum to remove methanol. The solid was purified by silica gel column chromatography (the column packing was 200-300 mesh silica gel, and the eluent was dichloromethane:methanol = 15:1 (V:V)). The purified product was dried under vacuum at 40 °C for 3 h to obtain product 1b, with a yield of 53%. Figure 3 : 1 H-NMR (500MHz, CDCl3) δ10.01(s,1H),8.85(s,1H),8.19(s,1H),4.70(t,J=5.0Hz, 2H), 4.25 (s, 3H), 4.13 (s, 3H), 3.98 (t, J = 5.0Hz, 2H), 3.66 (s, 202H), 3.39 (s, 3H). Figure 4 : 13 C-NMR (126MHz, CDCl3) δ139.06,133.95,126.58,125.36,121.09,71.90,70.53-70.35,68.97,59.01,50.54,36.73,36.32.

[0065] The synthesis route is shown in Equation 2:

[0066]

[0067] (1c) Wrap a three-necked flask with aluminum foil and, under nitrogen protection, add 100 mg of product 1b, 24.9 mg of Ag₂O, and 5 mL of dichloromethane. Seal the flask. Stir the reaction at room temperature in the dark for 24 h, filter, and add the filtered silver carbene intermediate solution to a three-necked flask containing 31.6 mg of dimethyl gold sulfide (Au(SMe₂)Cl). Continue stirring the reaction under the same conditions for another 24 h. Centrifuge to obtain the supernatant, and remove dichloromethane by vacuum drying. Then dissolve the solid in water and let it stand for 6 h to remove unreacted Au(SMe₂)Cl. Remove water by vacuum drying to obtain product 1c, with a yield of 57%. Figure 5 : 1 H-NMR (500MHz, CDCl3) δ8.11(s,1H),7.30(s,1H),4.66–4.64(m,2H),4.04(s,3H),3.88(s,3H),3.86(d,J=2.1Hz,2H),3.66(s,332H),3.50(s,9H). Figure 6 :13 C-NMR(126MHz, CDCl3)δ:172.74,135.69,128.45,128.10,125.68,124.88,123.78,123.38,123.07,120 .28,87.11,71.91,70.54-70.33,69.13,59.03,53.98,50.55,38.55,38.37,37.98,37.56,37.52,37.02.

[0068] The synthesis route is shown in Equation 3:

[0069]

[0070] (2) Preparation of citric acid-modified gold nanoparticles

[0071] The glassware and rotor used in this experiment need to be soaked in freshly prepared aqua regia (concentrated hydrochloric acid: concentrated nitric acid = 3:1) for at least 3 hours before the experiment. Then rinse 2-3 times with deionized water and dry in a 65℃ oven for later use. All solutions used in the experiment are freshly prepared and used immediately. The specific implementation steps are as follows:

[0072] (2a) Add 500 μL of 1% (w / v) HAuCl4 solution, 42.5 μL of 0.1% (w / v) AgNO3 solution and 2 mL of 2% (w / v) sodium citrate solution to a brown glass bottle, vortex to mix, and let stand at room temperature for 15 min. The gold nanocrystal seed solution is obtained.

[0073] (2b) Add 47.5 mL of fresh deionized water to a 100 mL three-necked flask and heat to boiling with vigorous stirring. Then, rapidly add the gold nanocrystal seed solution obtained in (2a) to the boiling deionized water, continue vigorous stirring for 30 min, remove the heat source, and slowly cool to room temperature. Centrifuge and wash three times at 14000 rpm to obtain a stock solution of citric acid-modified gold nanoparticles with an average particle size of approximately 6 nm. Store at 4 °C for later use. Figure 7 TEM images of a show that the synthesized gold nanoparticles are uniform in size, with a diameter of approximately 6 nm. DLS reveals that the hydrated particle size of the citric acid-modified gold nanoparticles is approximately 15.3 nm (e.g., ...). Figure 8 As shown in a). UV spectrum (e.g.) Figure 9 As shown in Figure a), the citric acid-modified gold nanoparticles exhibit a distinct plasmon resonance absorption peak at 512 nm.

[0074] (3) Preparation of nitrogen-modified carbene nanoparticles

[0075] Take 1 mL (1 mg / mL) of the citric acid-modified gold nanoparticle solution prepared in Example 2 above, and add 1 mL of freshly prepared 1c (15 mg / mL) solution while stirring. Stir at room temperature for 20 min, centrifuge and wash three times at 14000 rpm to remove free nitrogen-heterocyclic carbene gold ligands, thus obtaining water-soluble nitrogen-heterocyclic carbene-modified gold nanoparticles, which are stored at 4℃ for later use. Figure 7 TEM images of b show that the synthesized nitrogen-heterocyclic carbene-modified gold nanoparticles are spherical, with no other shaped byproducts, and a diameter of approximately 6 nm. DLS shows that the hydrated particle size of the nitrogen-heterocyclic carbene-modified gold nanoparticles is approximately 21.1 nm (e.g., ...). Figure 8 (as shown in b). UV spectrum (e.g.) Figure 9 As shown in b), the nitrogen-heterocyclic carbene-modified gold nanoparticles exhibit a distinct plasmon resonance absorption peak at 516 nm.

[0076] Example 2

[0077] This embodiment provides a method for preparing water-soluble nitrogen heterocyclic carbene-modified gold nanoparticles, the only difference from Example 1 being:

[0078] In step (1a), the product was heated and stirred at 80°C overnight to obtain product 1a, with the yield decreasing from 85% to 65%.

[0079] Comparative Example 1

[0080] This comparative example provides a method for preparing water-soluble nitrogen heterocyclic carbene-modified gold nanoparticles. This comparative example does not use metal exchange; the only difference between this method and Example 1 is the following steps:

[0081] (1c) 100 mg (1 eq) of product 1b, 20 mg (3 eq) of K₂CO₃, and 14.2 mg of Au(SMe₂)Cl (1 eq) were added to a single-necked flask containing 10 mL of acetone solution. The flask was sealed and reacted at 60 °C for 6 h, followed by concentration under vacuum. The resulting product contained byproducts and was difficult to purify (e.g., ...). Figure 10 (As shown).

[0082] Comparative Example 2

[0083] This comparative example provides a method for preparing water-soluble nitrogen heterocyclic carbene-modified gold nanoparticles, the only difference from Example 1 being the following steps:

[0084] (3) Preparation of nitrogen-modified carbene nanoparticles

[0085] 100 mg (1c) of the above-mentioned nitrogen-heterocyclic carbene gold complex was dissolved in 10 mL of dichloromethane. 5 mg of sodium borohydride was dissolved in 0.2 mL of anhydrous ethanol and added to the 1c dichloromethane solution under ice bath conditions. The reaction was carried out at room temperature for 4 h to obtain water-soluble nitrogen-heterocyclic carbene-modified gold nanoparticles.

[0086] In this comparative example, water-soluble nitrogen heterocyclic carbene-modified gold nanoparticles were prepared using a strong reducing agent. The resulting nanoparticles had difficult-to-control particle size and a wide size distribution.

[0087] Test case

[0088] The water solubility of the water-soluble nitrogen heterocyclic carbene-modified gold nanoparticles prepared in the above examples was tested.

[0089] The specific testing method is as follows:

[0090] Take 1 mL (5 mg / mL) of an aqueous solution of nitrogen-modified heterocyclic carbene gold nanoparticles and sonicate in an ice bath for 30 min to ensure thorough dispersion of the nanoparticles. Perform DLS measurements using a laser particle size analyzer (Zetasizer Nano ZS90).

[0091] The test results are as follows Figure 11 As shown, the size did not change significantly after being placed in the aqueous solution for 24 hours.

[0092] As can be seen, the water-soluble nitrogen heterocyclic carbene-modified gold nanoparticles prepared in this invention have good stability.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing water-soluble N-heterocyclic carbene-modified gold nanoparticles, characterized by, The preparation method comprises the following steps: (1) taking 5-ethynyl-1-methyl-1H imidazole as raw material, a first product is prepared by alkylation reaction; (2) taking the first product and N3-PEG as raw materials, a PEG-modified azolium carbene imidazole salt is prepared by click chemistry reaction under inert atmosphere; (3) taking the PEG-modified azolium carbene imidazole salt and silver oxide as raw materials, a silver complex is prepared by reaction; then taking the silver complex and dimethylthio gold chloride as raw materials, an azolium carbene gold complex is prepared by reaction; (4) taking citric acid-modified gold nanoparticles and the azolium carbene gold complex as raw materials, the water-soluble azolium carbene-modified gold nanoparticles are prepared by ligand exchange reaction. The step (1) specifically comprises the following steps: 5-ethynyl-1-methyl-1H imidazole and iodomethane are dissolved in toluene solvent, and the first product is prepared by heating reaction at 40-60 DEG C. The step (2) specifically comprises the following steps: the first product, N3-PEG, sodium ascorbate and copper sulfate are dissolved in a solvent, and a crude product is prepared by click chemistry reaction under inert atmosphere; then the crude product is concentrated by vacuum drying and then purified by silica gel column chromatography to obtain the PEG-modified azolium carbene imidazole salt.

2. The production method according to claim 1, characterized by, The step (3) specifically comprises the following steps: the PEG-modified azolium carbene imidazole salt and silver oxide are dissolved in a solvent, and a silver complex solution is prepared by avoiding light reaction; then the silver complex solution is mixed with dimethylthio gold chloride to prepare the azolium carbene gold complex.

3. The preparation method according to claim 2, characterized in that, The product prepared by mixing the silver complex solution with dimethylthio gold chloride is dried by vacuum drying, dissolved in water and placed for more than 6 hours to obtain the azolium carbene gold complex.

4. The production method according to claim 1, characterized by, In the step (4), the preparation method of the citric acid-modified gold nanoparticles comprises the following steps: HAuCl4, AgNO3 and sodium citrate are mixed to prepare a gold nanocrystal seed solution, and then the gold nanocrystal seed solution is mixed with boiling water to prepare the gold nanoparticles.

5. The preparation method according to claim 1, characterized in that, In the step (4), the ligand exchange reaction comprises the following steps: The citric acid-modified gold nanoparticles and the azolium carbene gold complex are mixed and reacted at room temperature.

6. A water-soluble nitrogen heterocyclic carbene-modified gold nanoparticle, characterized by, The water-soluble azolium carbene-modified gold nanoparticles are prepared by the preparation method of any one of claims 1-5.

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