A bimetallic organic framework capable of recognizing cysteine and a preparation method thereof

Abstract

The present invention relates to the fields of biomedicine and material chemistry, and discloses the synthesis of a bimetallic-organic framework (MOF) ZnCoBTCHx with significant selectivity for sulfur-containing amino acids. ZnCoBTCHx exhibits rapid and visual recognition of cysteine, while methionine shows only minor changes due to the lack of a thiol group. Ultraviolet-visible absorption spectroscopy and X-ray photoelectron spectroscopy show that due to the variable valence nature of cobalt ions in ZnCoBTCHx, significant electron transfer occurs between the host and the guest. Notably, ZnCoBTCHx shows the ability to distinguish between -SH and -S- groups in amino acids. This unique property makes ZnCoBTCHx an effective sensor for thiol enzyme activity and has great application potential in the field of biomedicine.

Description

Technical Field

[0001] The present invention relates to the fields of biomedicine and material chemistry, and particularly to a bimetallic organic framework capable of recognizing cysteine and a preparation method thereof. Background Art

[0002] Amino acids, as the basic components of polypeptides and proteins, play a crucial role in various metabolic processes and serve as biomarkers for predicting disease risks. However, due to the identical functional groups (amino and carboxyl groups) of amino acids, the preparation of highly selective materials for differentiating these compounds remains a challenge. Metal-organic frameworks (MOFs) are a class of porous crystalline materials with periodic channels, typically constructed from inorganic metal ions / clusters and organic ligands. Bimetallic metal-organic frameworks generally refer to MOF structures containing two different metal ions. Since the metal active sites of monometallic MOFs are limited and relatively single, introducing a bimetallic system into MOFs can increase the types of metal sites and make the arrangement more diverse. For example, the bimetallic system of Fe-ZIF and ZIF-8 was the earliest reported bimetallic MOF. Introducing a second ion into single Fe-ZIF exhibited more excellent catalytic performance after pyrolysis. This indicates that bimetallic organic frameworks have certain advantages. Summary of the Invention

[0003] The object of the present invention is to synthesize a three-dimensional bimetallic organic framework (MOF), ZnCoBTCHx, with periodic tubular and DNA groove-like pore structures. In this framework, Co2+ and Co3+ partially replace Zn2+ at the metal sites, enhancing the functionality of the active metal centers. Due to the specific pore shape and size, ZnCoBTCHx exhibits a rapid and significant ability to selectively recognize cysteine (Cys), while the change for methionine lacking a mercapto group is very small. Importantly, ZnCoBTCHx can distinguish between -SH and -S- groups in amino acids. This unique ability makes ZnCoBTCHx an excellent sensor for sulfhydryl enzyme activity, showing great application potential in biomedical research and disease diagnosis.

[0004] To achieve the above object, the present invention provides the following technical solution: A bimetallic organic framework capable of recognizing cysteine, including the synthesis of a bimetallic MOF - ZnCoBTCHx, which is prepared from hypoxanthine, 1,3,5-benzenetricarboxylic acid, metal zinc and cobalt ions. This MOF has two unique pore geometries: similar to DNA grooves and tubular structures. ZnCoBTCHx significantly enhances the detection signal for cysteine, accompanied by an obvious color change in the solution, showing good selectivity. The variable valence state of cobalt in ZnCoBTCHx promotes electron transfer during the recognition process, resulting in a color change of the solution from colorless to yellow and the MOF from dark purple to light purple, thus providing a visual recognition effect.

[0005] Preferably, the bimetallic organic framework capable of recognizing cysteine includes the following steps:

[0006] S1. A mixture of Zn(NO3)2·6H2O (0.08 mmol), Co(NO3)2·6H2O (0.04 mmol), hypoxanthine (0.08 mmol), 1,3,5-benzenetricarboxylic acid (0.04 mmol) and DMF (5 mL) is sealed in a polytetrafluoroethylene autoclave together with 1 M HNO3 (1.1 mL) and heated at 140 °C for 72 hours;

[0007] S2. After cooling to room temperature at a rate of 5 °C / h, dark purple crystals are obtained by filtration, with a yield of approximately 40% (based on hypoxanthine);

[0008] S3. The selected suitable single crystal is immediately mounted on a single crystal X-ray diffractometer for structure determination under the condition of 100 K.

[0009] Preferably, the single crystal X-ray diffraction (SCXRD) analysis shows that ZnCoBTCHx crystallizes in the hexagonal space group P63 / m. Both Zn and Co ions adopt tetrahedral coordination geometries, coordinating with the pyrimidine nitrogen and imidazole nitrogen in hypoxanthine, as well as the carboxylic acid oxygen and bridging oxygen in BTC respectively. This coordination mode forms a three-dimensional MOF along the c-axis, showing two different channel geometries. The first type is a tubular channel with a diameter range of approximately to The second type has alternating large pores and small pores, similar to the size grooves of DNA, with diameters of approximately and The tubular channel has a narrow pore size distribution (about ), while the channel similar to the DNA groove shows a broader distribution (about ).

[0010] Preferably, through the analysis of the powder X-ray diffraction (PXRD) experimental results, it was found that the diffraction peak positions of ZnCoBTCHx hardly changed in different solvents and at pH = 2 - 13.

[0011] Preferably, the thermogravimetric analysis (TGA) showed that heating ZnCoBTCHx above 450 °C would cause structural decomposition.

[0012] Preferably, the full X-ray photoelectron spectroscopy (XPS) spectrum of ZnCoBTCHx confirmed the presence of Co, Zn, N, C, and O in the MOF. High-resolution XPS spectral analysis revealed that the Co 2p 3 / 2 peak was located at 781.9 eV, accompanied by a satellite peak at 785.3 eV, and the Co2p 1 / 2 peak was located at 797.2 eV, and the corresponding satellite peak was at 803.1 eV.

[0013] Preferably, by utilizing the strong oxidation property of Co3+ in the ZnCoBTCHx framework, we proposed that this MOF could be further used to detect sulfur-containing amino acids. In the control experiment, aqueous solutions of 20 common L-amino acids were used as test samples. 5 mg of ZnCoBTCHx was immersed in 5 mL of each 1.0 mM amino acid solution and stored in the dark for 3 days. It is worth noting that ZnCoBTCHx showed a significant color change when exposed to cysteine (Cys), changing from colorless to yellow, and at the same time, the crystal color changed from dark purple to light purple.

[0014] A preparation method of a bimetallic organic framework capable of recognizing cysteine, the preparation method comprising the following steps:

[0015] S1. A mixture of Zn(NO3)2·6H2O (0.08 mmol), Co(NO3)2·6H2O (0.04 mmol), hypoxanthine (0.08 mmol), 1,3,5-benzenetricarboxylic acid (0.04 mmol), and DMF (5 mL) was sealed in a polytetrafluoroethylene autoclave together with 1 M HNO3 (1.1 mL) and heated at 140 °C for 72 hours;

[0016] S2. After cooling to room temperature at a rate of 5 °C / h, dark purple crystals were obtained by filtration, and the yield was approximately 40% (based on hypoxanthine);

[0017] S3. The selected suitable single crystal was immediately mounted on a single crystal X-ray diffractometer for structure determination under the condition of 100 K.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. The present invention synthesized a three-dimensional bimetallic organic framework (MOF), ZnCoBTCHx, with a periodic pore structure of tubular and DNA-groove-like channels.

[0020] 2. In this framework, Co2+ and Co3+ partially replace Zn2+ at the metal sites, enhancing the functionality of the active metal centers.

[0021] 3. Due to the specific pore shape and size, ZnCoBTCHx exhibits a rapid and significant ability to selectively recognize cysteine (Cys), while the change for methionine lacking a thiol group is very small.

[0022] 4. Importantly, ZnCoBTCHx can distinguish between -SH and -S- groups in amino acids. This unique ability makes ZnCoBTCHx an excellent thiol enzyme activity sensor, showing great application potential in biomedical research and disease diagnosis. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Single crystal structure of ZnCoBTCHx (a) Asymmetric unit (b) Coordination mode of metals. (c) Three-dimensional framework formed along the c-axis direction (d) Perspective view of the ZnCoBTCHx framework showing an alternating pattern of large and small pores along the a-axis;

[0024] Figure 2 For the present invention (a) Tubular channels and corresponding diameter distribution diagrams (b) DNA-groove channels and corresponding diameter distribution diagrams;

[0025] Figure 3 PXRD diagrams of ZnCoBTCHx under different solvents and different pH conditions;

[0026] Figure 4 Thermogravimetric analysis diagram of ZnCoBTCHx;

[0027] Figure 5 XPS diagrams of ZnCoBTCHx (a) Full spectrum (b) High-resolution spectrum of Co 2p;

[0028] Figure 6 (a) Time-dependent UV-visible absorption spectral change diagram after adding L-cysteine (0.001 mol / L) to ZnCoBTCHx, (b) UV spectra of ZnCoBTCHx after being soaked in 0.001 mol / L and 0.01 mol / L L-cysteine for 2 days;

[0029] Figure 7(a) Time-dependent UV-Vis absorption spectra of methionine (0.001 mol / L) after adding ZnCoBTCHx, (b) UV spectra of ZnCoBTCHx after soaking in 0.001 mol / L and 0.01 mol / L methionine for 2 days;

[0030] Figure 8 Time-dependent UV-Vis absorption spectra of glutathione (0.001 mol / L) after adding ZnCoBTCHx. Detailed implementation manners

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] Refer to Figures 1-8 , the present invention provides a technical solution: a bimetallic organic framework capable of recognizing cysteine, including synthesizing a bimetallic MOF - ZnCoBTCHx, which is prepared by hypoxanthine, 1,3,5-benzenetricarboxylic acid, metal zinc and cobalt ions. This MOF has two unique pore geometries: similar to DNA grooves and tubular structures. ZnCoBTCHx significantly enhances the detection signal for cysteine and is accompanied by an obvious color change in the solution, showing good selectivity. The variable valence state of cobalt in ZnCoBTCHx promotes electron transfer during the recognition process, resulting in the solution color changing from colorless to yellow and the MOF changing from dark purple to light purple, thus providing a visual recognition effect.

[0033] In this embodiment, a preparation method of a bimetallic organic framework capable of recognizing cysteine is characterized by including the following steps:

[0034] S1. Seal a mixture of Zn(NO3)2·6H2O (0.08 mmol), Co(NO3)2·6H2O (0.04 mmol), hypoxanthine (0.08 mmol), 1,3,5-benzenetricarboxylic acid (0.04 mmol) and DMF (5 mL) together with 1 M HNO3 (1.1 mL) in a polytetrafluoroethylene autoclave and heat at 140 °C for 72 hours;

[0035] S2. After cooling to room temperature at a rate of 5 °C / h, obtain dark purple crystals by filtration, yield: about 40% (based on hypoxanthine);

[0036] S3. Immediately install the selected suitable single crystal on a single crystal X-ray diffractometer and conduct structure determination under the condition of 100K.

[0037] In this example, single crystal X-ray diffraction (SCXRD) analysis shows that ZnCoBTCHx crystallizes in the hexagonal space group P63 / m. Both Zn and Co ions adopt tetrahedral coordination geometries, coordinating with the pyrimidine nitrogen and imidazole nitrogen in hypoxanthine, as well as the carboxylic acid oxygen and bridging oxygen in BTC respectively. This coordination mode forms a three-dimensional MOF along the c-axis, showing two different channel geometries (as Figure 1 ), the first type is a tubular channel with a diameter range of about to The second type has alternating large pores and small pores, similar to the major and minor grooves of DNA, with diameters of about and The tubular channels have a narrow pore size distribution (about ), while the channels similar to DNA grooves show a broader distribution (about ), as Figure 2 shown.

[0038] In this example, through the analysis of the experimental results of powder X-ray diffraction (PXRD), it is found that when ZnCoBTCHx is in different solvents and pH = 2 - 13, the positions of the diffraction peaks hardly change, indicating that ZnCoBTCHx has high water stability and chemical stability (as Figure 3 shown).

[0039] In this example, thermogravimetric analysis (TGA) shows that heating ZnCoBTCHx above 450 degrees will cause structural decomposition, indicating that this MOF has high thermal stability.

[0040] In this example, the full spectrum of X-ray photoelectron spectroscopy (XPS) of ZnCoBTCHx confirms the presence of Co, Zn, N, C, and O in the MOF (see Figure 5 a), and the high-resolution XPS spectrum (see Figure 5 b) analysis reveals that the Co 2p 3 / 2 peak is located at 781.9 eV, accompanied by a satellite peak at 785.3 eV, and the Co 2p 1 / 2 peak is located at 797.2 eV, with the corresponding satellite peak at 803.1 eV. These binding energy characteristics indicate the oxidation states of Co(II) and Co(III), indicating that the cobalt in ZnCoBTCHx exists in a mixed valence state.

[0041] In this example, taking advantage of the strong oxidation property of Co3+ in the ZnCoBTCHx framework, we propose that this MOF can be further used to detect sulfur-containing amino acids. In the control experiment, aqueous solutions of 20 common L-amino acids were used as test samples. 5 mg of ZnCoBTCHx was immersed in 5 mL of each 1.0 mM amino acid solution and stored in the dark for 3 days. Notably, ZnCoBTCHx showed a significant color change when exposed to cysteine (Cys), changing from colorless to yellow, and at the same time, the crystal color changed from dark purple to light purple. In contrast, no significant color change was observed for other amino acids, which could be clearly distinguished by the naked eye. These preliminary results indicate that ZnCoBTCHx has strong selectivity for cysteine.

[0042] Time-dependent ultraviolet-visible spectroscopy (UV-Vis) analysis showed that after introducing ZnCoBTCHx crystals into a 1 mM cysteine (Cys) solution, the absorption peak near 200 nm continuously increased and underwent a red shift. At the same time, a new peak appeared at 350 nm, and a shoulder peak was generated at 445 nm and 600 nm, and the color changed to yellow (as Figure 6 ). In contrast, under the same conditions, another sulfur-containing amino acid, methionine (Met), did not show a new absorption peak, as Figure 7 .

[0043] Figure 6 (a) Time-dependent UV-Vis absorption spectral change diagram after adding L-cysteine (0.001 mol / L) to ZnCoBTCHx, measured every 2 minutes for the first hour and then every 1 hour. (b) UV spectra of ZnCoBTCHx after being immersed in 0.001 mol / L and 0.01 mol / L L-cysteine for 2 days.

[0044] Figure 7 (a) Time-dependent UV-Vis absorption spectral change diagram after adding methionine (0.001 mol / L) to ZnCoBTCHx (b) UV spectra of ZnCoBTCHx after being immersed in 0.001 mol / L and 0.01 mol / L methionine for 2 days.

[0045] This difference prompted us to hypothesize that it is related to the sulfhydryl group in Cys. To further verify our hypothesis, we selected a macromolecule containing a sulfhydryl group, glutathione (GSH). The results showed that ZnCoBTCHx also exhibited a color response to glutathione (as Figure 8 ), but the rate was slower than that of cysteine.

[0046] Figure 8Time-dependent UV-visible absorption spectral changes of glutathione (0.001 mol / L) after the addition of ZnCoBTCHx, measured every 2 minutes for the first hour and then every 1 hour. (b) UV spectra of ZnCoBTCHx after being immersed in 0.001 mol / L and 0.01 mol / L glutathione for 2 days.

[0047] In summary, we designed and synthesized a three-dimensional bimetallic organic framework (MOF), ZnCoBTCHx, with a periodic tubular and DNA groove-like pore structure. In this framework, Co2+ and Co3+ partially replace Zn2+ at the metal sites, enhancing the functionality of the active metal centers. Due to the specific pore shape and size, ZnCoBTCHx exhibits a rapid and significant ability to selectively recognize cysteine (Cys), while the change for methionine lacking a thiol group is very small. Importantly, ZnCoBTCHx can distinguish between -SH and -S- groups in amino acids, and this unique ability makes ZnCoBTCHx an excellent thiol enzyme activity sensor, showing great application potential in biomedical research and disease diagnosis.

[0048] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device.

[0049] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A bimetallic organic framework capable of recognizing cysteine, characterized in that: A bimetallic MOF, ZnCoBTCHx, was synthesized. This material was prepared from hypoxanthine, 1,3,5-benzenetricarboxylic acid, metal zinc, and cobalt ions. The MOF has two unique pore geometries: a DNA groove-like structure and a tubular structure. ZnCoBTCHx significantly enhanced the detection signal for cysteine, accompanied by an obvious color change in the solution, showing good selectivity. The variable valence state of cobalt in ZnCoBTCHx promoted electron transfer during the recognition process, resulting in a color change of the solution from colorless to yellow and the MOF from dark purple to light purple, thus providing a visual recognition effect. The preparation method of a bimetallic organic framework capable of recognizing cysteine includes the following steps: S1. A mixture of 0.08 mmol of Zn(NO3)2·6H2O, 0.04 mmol of Co(NO3)2·6H2O, 0.08 mmol of hypoxanthine, 0.04 mmol of 1,3,5-benzenetricarboxylic acid, and 5 mL of DMF was sealed in a polytetrafluoroethylene autoclave together with 1.1 mL of 1 M HNO3 and heated at 140 °C for 72 hours; S2. After cooling to room temperature at a rate of 5 °C / h, dark purple crystals were obtained by filtration, with a yield of 40% based on hypoxanthine; S3. The selected suitable single crystal was immediately mounted on a single crystal X-ray diffractometer for structure determination under the condition of 100K.

2. The bimetallic organic framework capable of recognizing cysteine according to claim 1, characterized in that: The single-crystal X-ray diffraction (SCXRD) analysis indicates that ZnCoBTCHx crystallizes in the hexagonal space group P63 / m, and both Zn and Co ions adopt tetrahedral coordination geometries, coordinating with the pyrimidine nitrogen and imidazole nitrogen in hypoxanthine, as well as the carboxylic oxygen and bridging oxygen in BTC, respectively. This coordination mode forms a three-dimensional MOF along the c-axis, exhibiting two different channel geometries. The first type is a tubular channel with a diameter ranging from to The second type has alternating large and small pores, similar to the major and minor grooves of DNA, with diameters of and The tubular channels have a narrow pore size distribution while the channels similar to DNA grooves show a broader distribution 3. The bimetallic organic framework capable of recognizing cysteine according to claim 1, characterized in that: Through the analysis of the powder X-ray diffraction (PXRD) experimental results, it was found that the positions of the diffraction peaks of ZnCoBTCHx hardly changed in different solvents and at pH = 2 - 13.

4. A bimetallic organic framework capable of recognizing cysteine according to claim 1, characterized in that: The thermogravimetric analysis (TGA) showed that heating ZnCoBTCHx above 450 degrees would cause structural decomposition.

5. A bimetallic organic framework capable of recognizing cysteine according to claim 1, characterized in that: The full X-ray photoelectron spectroscopy (XPS) spectrum of the ZnCoBTCHx confirmed the presence of Co, Zn, N, C, and O in the MOF. High-resolution XPS spectral analysis revealed that the Co 2p 3 / 2 peak was located at 781.9 eV, accompanied by a satellite peak at 785.3 eV. The Co 2p 1 / 2 peak was located at 797.2 eV, and the corresponding satellite peak was at 803.1 eV.

6. The bimetallic organic framework capable of recognizing cysteine according to claim 1, characterized in that: Utilizing the strong oxidation property of Co3+ in the ZnCoBTCHx framework, this MOF was further used to detect sulfur-containing amino acids. In the control experiment, aqueous solutions of 20 common L-amino acids were used as test samples. 5 mg of ZnCoBTCHx was immersed in 5 mL of each 1.0 mM amino acid solution and stored in the dark for 3 days. Notably, ZnCoBTCHx showed a significant color change when exposed to cysteine (Cys), from colorless to yellow, and at the same time, the crystal color changed from dark purple to light purple.

Images