Method for evaluating relationship between affinity and hyperpolarization performance of substrate and SABRE catalyst precursor

Abstract

The invention belongs to the technical field of nuclear magnetic resonance hyperpolarization, and particularly discloses a method for evaluating the relationship between affinity and hyperpolarization performance of a substrate and an SABRE catalyst precursor, and the method comprises the following steps: preparing NMR samples to be detected: dissolving an Ir-based catalyst precursor, the Ir-based catalyst precursor and the substrate in deuterated methanol respectively to obtain different NMR samples to be detected; collecting a heat balance 1H NMR spectrum: putting a to-be-detected NMR sample into a nuclear magnetic instrument, tuning field locking and shimming, and collecting a hydrogen spectrum of the sample in a heat balance state; carrying out polarization transfer: introducing parahydrogen, and activating the catalyst precursor to form an SABRE catalyst; putting into a nuclear magnetic shielding instrument, setting polarization transfer field intensity, continuously introducing parahydrogen to realize polarization transfer, and stopping introducing gas; collecting a hyperpolarization 1HNMR spectrum: rapidly transferring the sample subjected to polarization transfer treatment into a nuclear magnetic detector, and inputting a preset instruction to collect a hydrogen spectrum in a hyperpolarization state; and data processing and analysis: carrying out processing analysis on the obtained hydrogen spectrum data, wherein the processing analysis comprises calculation of a balance constant and a signal enhancement multiple.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear magnetic resonance hyperpolarization, and in particular relates to a method for evaluating the relationship between the affinity of a substrate and a SABRE catalyst precursor and hyperpolarization performance. Background Art

[0002] Nuclear magnetic resonance technology is widely used to explain molecular dynamics, reveal complex natural products, proteins and macromolecular structures, etc. However, the detected signal comes from the tiny population difference between nuclear spin states, which leads to the low sensitivity of the technology. Therefore, it is necessary to improve the detection sensitivity of nuclear magnetic resonance. Although the population difference can be increased by lowering the temperature or increasing the magnetic field strength, there are disadvantages such as limited improvement effect or high cost. According to literature reports, hyperpolarization technology can enhance the signal by 3-5 orders of magnitude. At present, using parahydrogen hyperpolarization technology to improve sensitivity is a low-cost method with obvious improvement effect.

[0003] Traditional parahydrogen induced polarization (PHIP) requires that the substrate has a carbon-carbon double bond or triple bond. After the parahydrogen molecule reacts with the substrate, the spin order is transferred to the substrate molecule to achieve hyperpolarization, but this will change the structure of the substrate molecule, making the process irreversible. In 2009, Simon's team proposed signal amplification by reversible exchange (SABRE). Before the introduction of parahydrogen, the substrate molecule will replace the Cl atom on the metal center and bind to the catalyst precursor. After the introduction of parahydrogen, the parahydrogen also coordinates to the metal center of the catalyst precursor. At this time, the spin order of the parahydrogen molecule is transferred to the substrate molecule, and then the hyperpolarized substrate molecule is separated from the metal center. Unlike traditional PHIP, this process does not destroy the molecular structure of the substrate. The binding and dissociation process of the substrate and parahydrogen is dynamically reversible. The free polarization-enhanced substrate molecules are continuously enriched in the solution, so that the substrate signal enhancement is detected.

[0004] Studying the factors that affect the SABRE hyperpolarization efficiency is crucial to improving the hyperpolarization performance. The literature "Hyperpolarisation of weakly binding N-hyterocycles using signal amplification by reversible exchange", "SABRE hyperpolarization of nicotinamide derivatives and their molecular dynamics properties" and other papers have discussed the relationship between the substrate-catalyst dissociation rate (kd) and substrate longitudinal relaxation time (T1) after the introduction of parahydrogen and the enhancement effect of the hyperpolarization signal, but no clear relationship has been drawn. Whether there is a correlation between the replacement of Cl atoms in the substrate before the introduction of parahydrogen and the affinity of the precursor and the hyperpolarization performance has not been reported. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a method for evaluating the relationship between the affinity of substrate and SABRE catalyst precursor and the hyperpolarization performance. The present invention evaluates the hyperpolarization efficiency based on 1HNMR spectrum and utilizes the substrate to coordinate the catalyst precursor. 1 The equilibrium constant K was calculated from the HNMR spectrum, which can be used as a new indicator to characterize the affinity between the substrate and the catalyst precursor, verifying the positive correlation between the ability of the substrate to bind to the catalyst precursor and the hyperpolarization performance of the substrate.

[0006] In order to achieve the above objectives, one of the technical solutions of the present invention is: a method for evaluating the relationship between the affinity between a substrate and a SABRE catalyst precursor and the hyperpolarization performance, comprising the following steps:

[0007] (1) preparing NMR samples to be tested: dissolving an Ir-based catalyst precursor and an Ir-based catalyst precursor and a substrate in deuterated methanol to obtain different NMR samples to be tested;

[0008] (2) Collecting thermal balance 1 HNMR spectrum: Place the NMR sample to be tested obtained in step (1) into a nuclear magnetic spectrometer, tune and lock the field to make the magnetic field as uniform as possible; collect the hydrogen spectrum of the sample under thermal equilibrium to obtain the line width of the spectrum, magnetic field uniformity, etc. 1 HNMR spectra are used for peak assignment, equilibrium constant calculation and hyperpolarization spectrum comparison; peak assignment of the one-dimensional hydrogen spectrum is performed by comparing the spectrum predicted by ChemDraw and the integral ratio; equilibrium constant is calculated by integration and the signal enhancement effect under thermal equilibrium and hyperpolarization is compared;

[0009] (3) Polarization transfer: Parahydrogen is introduced into the NMR sample to be tested prepared in step (1) to activate the catalyst precursor to form a SABRE catalyst; the sample is then placed in a nuclear magnetic shielding instrument to set the polarization transfer field strength, and parahydrogen is continued to be introduced to achieve polarization transfer, and then the ventilation is stopped;

[0010] (4) Collecting Hyperpolarization 1 HNMR spectrum: the sample after polarization transfer treatment in step (3) is quickly transferred to the nuclear magnetic resonance detector, and the hydrogen spectrum in the hyperpolarized state can be obtained by inputting the preset instructions;

[0011] (5) Data processing and analysis: Process and analyze the hydrogen spectrum data obtained in steps (2) and (4), including calculation of equilibrium constants and signal enhancement factors.

[0012] In a preferred embodiment of the present invention, in step (1), the concentration of the Ir-based catalyst precursor in the deuterated methanol is 4-6 mM, and the concentration of the substrate is 40-60 mM.

[0013] In a preferred embodiment of the present invention, the substrate in step (1) is a compound containing a catalyst precursor coordinated thereto.

[0014] Further preferably, the compound containing the catalyst precursor coordinated includes pyridine and its substituted derivatives. Pyridine derivatives with different substituents can combine with the catalyst to achieve hyperpolarization, but the binding ability and hyperpolarization performance are different.

[0015] In a preferred embodiment of the present invention, the steps (2) and (4) call the PROTON sequence of the nuclear magnetic spectrometer, which consists of a non-selective π / 2 radio frequency pulse and a sampling period. 1 HNMR spectra are used for peak attribution, equilibrium constant calculation and comparison of hyperpolarized spectra. Hyperpolarized spectra are collected for comparison with thermal equilibrium spectra to obtain substrate signal enhancement multiples.

[0016] In a preferred embodiment of the present invention, the SABRE catalyst used in step (3) can be reused after activation, and the hyperpolarized spectrum can be collected after the parahydrogen is reintroduced without the need for reactivation treatment.

[0017] In a preferred embodiment of the present invention, the parahydrogen introduced in step (3) can coordinate with the substrate molecule to the catalyst metal center, and the spin state of the parahydrogen can be transferred to the substrate molecule in the polarization transfer field to achieve hyperpolarization of the substrate molecule.

[0018] In a preferred embodiment of the present invention, the optimal polarization transfer field for hydrogen spectrum in step (3) is set to 80 Guass (G).

[0019] In a preferred embodiment of the present invention, in step (3), the catalyst precursor ventilation activation time is 1-3 min, and the parahydrogen pressure is 2-4 bar.

[0020] In a preferred embodiment of the present invention, the spectrum can be collected every 28-32 seconds after the activation of the catalyst precursor in step (3) is completed.

[0021] In a preferred embodiment of the present invention, in step (4), the NMR sample is transferred from the polarization transfer field to the nuclear magnetic spectrometer for detection, and the process takes 3-6 seconds.

[0022] In a preferred embodiment of the present invention, the equilibrium constant is calculated in step (4) by integrating the characteristic peaks of the free substrate, the free catalyst precursor and the bound substrate from the hydrogen spectrum collected in step (2), and then calculating the corresponding concentrations from the integrated areas, which are named Sub, Ir and Sub-Ir respectively, and the equilibrium constant K is calculated by the formula Sub-Ir / (Sub*Ir); the signal enhancement factor is calculated by selecting a characteristic peak and calculating the ratio of the integrated area of ​​the hyperpolarized signal to the integrated area of ​​the thermal equilibrium signal.

[0023] When the substrate is mixed with the catalyst precursor, due to the coordination ability of the substrate, it has a certain combination with the catalyst precursor, and there is a coordination equilibrium process, in which the equilibrium constant is related to the coordination ability. 1 The equilibrium constant calculated from the HNMR spectrum was used to determine the affinity between the substrate and the catalyst precursor, and it was found that the affinity was positively correlated with the hyperpolarization performance.

[0024] In order to achieve the above objectives, the second technical solution of the present invention is: application of a method for evaluating the relationship between the affinity of a substrate and a SABRE catalyst precursor and the hyperpolarization performance in screening substrates that can achieve SABRE hyperpolarization ability.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention introduces the coordination equilibrium constant K to judge the affinity between the substrate and the catalyst precursor. Since the substrate will bind and coordinate with the catalyst, there is a coordination equilibrium process, in which the equilibrium constant can reflect the direction of equilibrium movement, that is, the ratio of the generated substrate-catalyst binding product, thereby judging the affinity between the substrate and the catalyst, and further finding that the affinity is positively correlated with the performance of the substrate being hyperpolarized.

[0027] 2. The present invention can be used to analyze and compare substrates that can achieve SABRE hyperpolarization ability. The hyperpolarization performance of the substrate can be analyzed by the affinity between the substrate and the catalyst precursor, which helps to further intuitively understand the mechanism of SABRE hyperpolarization.

[0028] 3. The present invention has certain reference significance for further screening some substrates with poor hyperpolarization effect or unsuitable for SABRE hyperpolarization experiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the process in which the substrate-coordinated Ir catalyst precursor of the present invention is hyperpolarized after the introduction of parahydrogen;

[0030] Figure 2 The thermal equilibrium of different systems in deuterated methanol in Example 1 of the present invention is 1 HNMR spectra, (a) is the hydrogen spectrum of the Ir-based catalyst precursor, (b) is the hydrogen spectrum of 3-fluoropyridine (50 mM) mixed with the Ir-based catalyst precursor (5 mM);

[0031] Figure 3 The super reaction of 3-fluoropyridine (50 mM) and Ir-based catalyst precursor (5 mM) in deuterated methanol in Example 1 of the present invention is shown in FIG. 1 HNMR spectrum. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is described in more detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0033] The Ir-based catalyst precursor used in the following examples is IrCl(COD)(IMes), Imes=

[0034] 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene,COD=cycloocta-1,5-diene;

[0035] The solvent is deuterated methanol, the molecular formula is CD3OD, and the purity of deuterated methanol is: D, 99.8% (0.03% v / v TMS);

[0036] There are four substrates, namely 3-fluoropyridine, 3-methylpyridine, 3-methoxypyridine and 3-hydroxypyridine, with a purity of 98%.

[0037] All the above reagents were used directly without any pretreatment.

[0038] Example 1

[0039] This example is suitable for evaluating the relationship between substrate affinity and SABRE catalyst precursor and hyperpolarization performance:

[0040] Step 1: Prepare the NMR sample to be tested: prepare a mixed solution of Ir-based catalyst precursor and deuterated methanol, and a mixed solution of four substrates (3-fluoropyridine, 3-methylpyridine, 3-methoxypyridine and 3-hydroxypyridine) with deuterated methanol and Ir-based catalyst precursor, respectively. Put the above five mixed solutions into white sample bottles, where the substrate concentration is 50mM, the Ir-based catalyst concentration is 5mM, and the deuterated methanol is 500uL. Then transfer the above mixed solutions into NMR tubes, cover them with valves and seal them. The above operations need to be carried out in a glove box to ensure anhydrous and oxygen-free conditions.

[0041] Step 2: Acquisition of thermal balance 1 HNMR spectrum: Place the various NMR samples prepared above in the NMR spectrometer, tune, lock and even the field, and then use the conventional one-dimensional single-pulse PRONT sequence to collect the thermal equilibrium 1 HNMR spectrum, set the experimental parameters nt=1, ss=0, d1=1.

[0042] Step 3: Polarization transfer process: First, introduce parahydrogen at about 3 bar into the sample. This process lasts for 2 minutes to complete the activation of the catalyst precursor, so that both parahydrogen and substrate can coordinate to the catalyst metal center. Then put the sample into the magnetic shielding instrument, and continue to introduce parahydrogen bubbling for 30 seconds. Under the action of the polarization transfer field, the spin state of parahydrogen can be transferred to the substrate molecule. The polarization transfer field strength is set to 80 Guass. Immediately after the bubbling is completed, close the air inlet valve to stop ventilation, and transfer the sample to the nuclear magnetic detector to collect hyperpolarized signals.

[0043] Step 4: Collecting hyperpolarized signals: After the computer presets the sampling instructions, when the sample is transferred to the 500MHz spectrometer, the instructions are sent to collect the hyperpolarized spectrum. In addition to changing the sampling array number array=8, the other experimental parameters are consistent with the settings when collecting the thermal equilibrium spectrum to facilitate subsequent effect comparison. The purpose of collecting 8 one-dimensional spectra is to observe the attenuation process of the hyperpolarized signal.

[0044] Step 5: Data processing and analysis: The experimental data obtained above were all processed using mestrenova (version

[0045] 14.0) software for processing, including: adjusting phase, correcting baseline, calibration, and integrating the selected range.

[0046] Figure 1The process of hyperpolarization of the Ir catalyst precursor coordinated to the substrate after the introduction of parahydrogen. The process from structure 1 to 2 shows the combination process of the substrate and the catalyst precursor. Before the introduction of parahydrogen, the substrate and the catalyst are mixed, and the Cl atom is replaced to achieve the coordination of the substrate to the catalyst. The process after structure 2 shows that the catalyst precursor is activated after the introduction of parahydrogen. Both the parahydrogen molecules and the substrate molecules are coordinated to the metal center. Under the action of the polarization transfer field, the spin state of the parahydrogen is transferred to the substrate molecule to achieve the hyperpolarization of the substrate molecule.

[0047] Figure 2 The thermal equilibrium of different systems in deuterated methanol is 1 HNMR spectra. (a) is the hydrogen spectrum of the Ir-based catalyst precursor, and (b) is the hydrogen spectrum of the mixture of 3-fluoropyridine (50mM) and the Ir-based catalyst precursor (5mM). In order to distinguish between the free state and the bound state, the prefixes "f" and "b" are added to represent the free state and the bound state, respectively. The characteristic peaks of the free substrate, free catalyst and bound substrate are selected to calculate the integrated area, thereby obtaining the equilibrium constant of the substrate-coordinated catalyst precursor, which can be quantitatively analyzed to determine whether the equilibrium process is related to the substrate coordination ability.

[0048] Figure 3 The hyperpolarization of 3-fluoropyridine (50 mM) and Ir-based catalyst precursor (5 mM) in deuterated methanol 1 HNMR spectrum. Thermodynamic means the hydrogen spectrum of 3-fluoropyridine collected in the thermal equilibrium state, and SABRE means the hydrogen spectrum of 3-fluoropyridine collected after hyperpolarization. A characteristic peak is selected for integration, and the signal enhancement factor ε of the substrate can be obtained by comparing the integrated areas in the thermal equilibrium and hyperpolarized spectra.

[0049] Through classification and comparison, it was found that each substrate had enhanced hyperpolarization signals to varying degrees. The data of the equilibrium constant K and the hyperpolarization enhancement factor ε of each substrate system are summarized in Table 1, as shown below:

[0050] Table 1 Equilibrium constant K and signal enhancement ε of each system

[0051]

[0052] The larger the equilibrium constant K is, the more the coordination equilibrium is shifted to the right, and more substrates are bound to the catalyst, which means that the affinity between the substrate and the catalyst precursor is stronger, and the substrate hyperpolarization enhancement factor of the corresponding system is also greater. In summary, the equilibrium constant K is used as a new indicator to characterize the affinity between the substrate and the catalyst precursor, and the relationship between the affinity between the substrate and the catalyst precursor and the hyperpolarization performance is evaluated to be positively correlated, in the hope of providing a new judgment method for the subsequent screening of SABRE substrates, and more importantly, expanding the design ideas and application scope for optimizing the hyperpolarization enhancement effect.

[0053] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for evaluating the relationship between substrate affinity and SABRE catalyst precursor and hyperpolarization performance, characterized in that: The following steps are involved: (1) preparing NMR samples to be tested: dissolving an Ir-based catalyst precursor and an Ir-based catalyst precursor and a substrate in deuterated methanol to obtain different NMR samples to be tested; (2) Collecting thermal balance 1 HNMR spectrum: Place the NMR sample to be tested obtained in step (1) into a nuclear magnetic spectrometer, tune and lock the field, and collect the hydrogen spectrum of the sample under thermal equilibrium; (3) Polarization transfer: Parahydrogen is introduced into the NMR sample to be tested prepared in step (1) to activate the catalyst precursor to form a SABRE catalyst; the sample is then placed in a nuclear magnetic shielding instrument to set the polarization transfer field strength, and parahydrogen is continued to be introduced to achieve polarization transfer, and then the ventilation is stopped; (4) Collecting Hyperpolarization 1 HNMR spectrum: the sample after polarization transfer treatment in step (3) is quickly transferred to the nuclear magnetic resonance detector, and the hydrogen spectrum in the hyperpolarized state can be obtained by inputting the preset instructions; (5) Data processing and analysis: Process and analyze the hydrogen spectrum data obtained in steps (2) and (4), including calculation of equilibrium constants and signal enhancement factors.

2. The method for evaluating the relationship between substrate affinity and SABRE catalyst precursor and hyperpolarization performance according to claim 1, characterized in that: In the step (1), the concentration of the Ir-based catalyst precursor in the deuterated methanol is 4-6 mM, and the concentration of the substrate is 40-60 mM.

3. The method for evaluating the relationship between substrate affinity and SABRE catalyst precursor and hyperpolarization performance according to claim 1, characterized in that: In the step (1), the substrate is a compound coordinated to a catalyst precursor.

4. The method for evaluating the relationship between substrate affinity and SABRE catalyst precursor and hyperpolarization performance as claimed in claim 3, characterized in that: The compound containing a catalyst precursor coordinated thereto includes pyridine and its substituted derivatives.

5. The method for evaluating the relationship between substrate affinity and SABRE catalyst precursor and hyperpolarization performance according to claim 1, characterized in that: In the steps (2) and (4), the PROTON sequence provided by the nuclear magnetic resonance instrument is called, which is composed of a non-selective π / 2 radio frequency pulse and a sampling period.

6. The method for evaluating the relationship between substrate affinity and SABRE catalyst precursor and hyperpolarization performance according to claim 1, characterized in that: The SABRE catalyst used in the step (3) can be reused after activation, and the hyperpolarized spectrum can be collected after the parahydrogen is reintroduced without the need for reactivation treatment.

7. The method for evaluating the relationship between substrate affinity and SABRE catalyst precursor and hyperpolarization performance according to claim 1, characterized in that: The parahydrogen introduced in step (3) can coordinate with the substrate molecules to the catalyst metal center, and the spin state of the parahydrogen can be transferred to the substrate molecules in the polarization transfer field, thereby achieving hyperpolarization of the substrate molecules.

8. The method for evaluating the relationship between substrate affinity and SABRE catalyst precursor and hyperpolarization performance according to claim 1, characterized in that: In the step (3), the polarization transfer field is set to 80 Guass (G), the catalyst precursor ventilation activation time is 1-3 min, the parahydrogen pressure is 2-4 bar, and each ventilation is 28-32 s after the catalyst precursor activation is completed.

9. The method for evaluating the relationship between substrate affinity and SABRE catalyst precursor and hyperpolarization performance as claimed in claim 1, characterized in that: The equilibrium constant calculated in the step (4) is to select the characteristic peak of the free substrate, the characteristic peak of the free catalyst precursor and the characteristic peak of the bound substrate from the hydrogen spectrum collected in the step (2), and then calculate the corresponding concentrations from the integrated areas, which are named Sub, Ir and Sub-Ir respectively, and the equilibrium constant K is calculated by the formula Sub-Ir / (Sub*Ir); the signal enhancement factor is calculated by selecting a characteristic peak to calculate the ratio of the integrated area of ​​the hyperpolarized signal to the integrated area of ​​the thermal equilibrium signal.

10. Use of the method for evaluating the relationship between the affinity of a substrate and a SABRE catalyst precursor and the hyperpolarization performance according to any one of claims 1 to 9 in screening substrates capable of achieving SABRE hyperpolarization ability.

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