A method of assessing the relationship between substrate affinity and hyperpolarization performance of a sabre catalyst precursor

Abstract

The application belongs to the technical field of nuclear magnetic resonance hyperpolarization, and specifically discloses a method for evaluating the relationship between the affinity of a substrate and a SABRE catalyst precursor and the hyperpolarization performance, which comprises the following steps: preparing a to-be-tested NMR sample: dissolving an Ir-based catalyst precursor and the Ir-based catalyst precursor and the substrate in deuterated methanol respectively to obtain different to-be-tested NMR samples; collecting a thermal equilibrium 1 HNMR spectrum: placing the to-be-tested NMR sample into a nuclear magnetic instrument, tuning the lock field shimming, and collecting the hydrogen spectrum of the sample in a thermal equilibrium state; polarization transfer: introducing para-hydrogen, and activating the catalyst precursor to form a SABRE catalyst; placing the sample into a nuclear magnetic shielding instrument, setting a polarization transfer field strength, continuing to introduce para-hydrogen to realize polarization transfer, and stopping the aeration; collecting a hyperpolarized 1 HNMR spectrum: quickly transferring the sample treated by polarization transfer into a nuclear magnetic detection instrument, inputting a preset instruction to collect the hydrogen spectrum in a hyperpolarized state; data processing and analysis: processing and analyzing the obtained hydrogen spectrum data, including calculating an equilibrium constant and a signal enhancement multiple.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nuclear magnetic resonance hyperpolarization, and particularly relates to a method for evaluating the relationship between the affinity of a substrate and a SABRE catalyst precursor and the hyperpolarization performance. BACKGROUND

[0002] Nuclear magnetic resonance technology is widely used in the aspects of explaining molecular dynamics, revealing the structures of complex natural products, proteins and macromolecules, etc. However, the detected signals are derived from the small 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 reducing the temperature or increasing the magnetic field strength, there are disadvantages such as limited improvement effect or high cost. According to the literature, hyperpolarization technology can enhance the signal by 3-5 orders of magnitude, and the current method for improving the sensitivity by using para-hydrogen hyperpolarization technology is a low-cost and obvious improvement method.

[0003] Traditional para-hydrogen induced hyperpolarization (PHIP) requires that the substrate has a carbon-carbon double bond or triple bond. After the addition reaction of para-hydrogen molecules and the substrate, the spin order is transferred to the substrate molecule to achieve hyperpolarization, but this will change the structure of the substrate molecule, so that the process is irreversible. In 2009, the Simon team proposed signal amplification by reversible exchange (SABRE). Before the para-hydrogen is introduced, the substrate molecule will replace the Cl atom on the metal center to combine with the catalyst precursor. After the para-hydrogen is introduced, the para-hydrogen is also coordinated to the metal center of the catalyst precursor. At this time, the spin order of the para-hydrogen 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 structure of the substrate molecule, and the combination and dissociation processes of the substrate and para-hydrogen are both dynamic and reversible. The solution continuously enriches the free state of the hyperpolarized substrate molecule, so as to detect the signal enhancement of the substrate.

[0004] It is essential to study the factors affecting the hyperpolarization efficiency of SABRE to improve the hyperpolarization performance. The literature "Hyperpolarisation of weakly binding N-hyterocycles using signalamplification by reversible exchange", "SABRE hyperpolarization of nicotinamide derivatives and their molecular dynamics properties" discusses the relationship between the factors such as the dissociation rate (kd) of the substrate and the catalyst after passing in para-hydrogen, the longitudinal relaxation time (T1) of the substrate and the enhancement effect of the hyperpolarization signal, but no clear relationship has been established. There is no obvious report on whether there is a correlation between the affinity of the substrate to the precursor and the hyperpolarization performance before passing in para-hydrogen. SUMMARY

[0005] The purpose of the present application is to overcome the defects existing in the prior art, and to provide a method for evaluating the relationship between the affinity of the substrate to the SABRE catalyst precursor and the hyperpolarization performance. The present application evaluates the hyperpolarization efficiency based on 1H NMR spectrum, and uses the 1 The equilibrium constant K calculated by 1H NMR spectrum can be used as a new indicator to represent the affinity of the substrate to the catalyst precursor, and the positive correlation between the ability of the substrate to bind the catalyst precursor and the hyperpolarization performance of the substrate is verified.

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

[0007] (1) Preparation of NMR sample to be tested: dissolve Ir-based catalyst precursor and Ir-based catalyst precursor and substrate in deuterated methanol respectively to obtain different NMR samples to be tested;

[0008] (2) Collecting thermal equilibrium 1 HNMR spectrum: place the NMR sample to be tested prepared in step (1) into a nuclear magnetic instrument, tune the field and uniform field to make the magnetic field as uniform as possible; collect the hydrogen spectrum of the sample in thermal equilibrium state to obtain the line width, magnetic field uniformity and other conditions of the spectrum line. The one-dimensional 1 HNMR spectrum is used for peak assignment, calculation of equilibrium constant and comparison of hyperpolarization spectrum at the same time; the one-dimensional hydrogen spectrum is assigned by comparing the spectrum predicted by ChemDraw and the integral proportion; the equilibrium constant is calculated by integration and the enhancement effect of the signal under thermal equilibrium and hyperpolarization is compared;

[0009] (3) Polarization transfer: the NMR sample prepared in step (1) is connected with para-hydrogen, and the catalyst precursor is activated to form SABRE catalyst; then the polarization transfer field is set in the NMR shielding instrument, and para-hydrogen is continuously connected to realize polarization transfer, and then the aeration is stopped;

[0010] (4) Collection of hyperpolarized 1 HNMR spectrum: the sample after polarization transfer in step (3) is quickly transferred to the NMR detection instrument, and the hyperpolarized hydrogen spectrum can be collected by inputting the preset command;

[0011] (5) Data processing and analysis: the hydrogen spectrum data obtained in steps (2) and (4) are processed and analyzed, including calculation of equilibrium constant and signal enhancement multiple.

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

[0013] In a preferred embodiment of the present application, the substrate in step (1) is a compound containing coordination to the catalyst precursor.

[0014] Further preferably, the compound containing coordination to the catalyst precursor includes pyridine and its substituted derivative. Different substituted pyridine derivatives can be combined with the catalyst to achieve hyperpolarization, but the combination ability and hyperpolarization performance are different.

[0015] In a preferred embodiment of the present application, the PROTON sequence of the NMR instrument is called in steps (2) and (4), which is composed of a non-selective π / 2 radio frequency pulse and a sampling period. The thermal equilibrium 1 HNMR spectrum is used for peak assignment, calculation of equilibrium constant and comparison of hyperpolarized spectrum at the same time. The hyperpolarized spectrum is collected for comparison with the thermal equilibrium spectrum to obtain the signal enhancement multiple of the substrate.

[0016] In a preferred embodiment of the present application, the SABRE catalyst used in step (3) can be reused after activation, and the hyperpolarized spectrum can be collected after re-aeration without further activation treatment.

[0017] In a preferred embodiment of the present application, the para-hydrogen and substrate molecules connected in step (3) can be coordinated to the metal center of the catalyst, and the spin state of para-hydrogen in the polarization transfer field can be transferred to the substrate molecules to achieve hyperpolarization of the substrate molecules.

[0018] In a preferred embodiment of the present application, 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 application, the catalyst precursor in step (3) is activated for 1-3 min, and the parahydrogen pressure is 2-4 bar.

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

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

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

[0023] When the substrate is mixed with the catalyst precursor, the substrate has coordination ability and binds with the catalyst precursor to some extent, and there is a coordination equilibrium process, in which the equilibrium constant is related to the coordination ability. 1 The equilibrium constant calculated by HNMR spectrum is used to judge the affinity of the substrate and the catalyst precursor, and it is found that the affinity is positively correlated with the hyperpolarization performance.

[0024] In order to achieve the above purposes, the second technical scheme of the present application is: a method for evaluating the relationship between the affinity of a substrate and a SABRE catalyst precursor and the hyperpolarization performance of the substrate in the application of screening a substrate capable of realizing SABRE hyperpolarization.

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

[0026] 1. The present application introduces the coordination equilibrium constant K to judge the affinity of 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 moving direction of the equilibrium, that is, the proportion of the substrate-catalyst bound product, so as to judge the affinity of the substrate and the catalyst, and further find that the affinity is positively correlated with the hyperpolarization performance of the substrate.

[0027] 2、The application can be used for analyzing and comparing substrates to realize SABRE hyperpolarization capability, analyzing the substrate hyperpolarization performance through the affinity of the substrate and the catalyst precursor, and helping to further intuitively understand the mechanism of SABRE hyperpolarization.

[0028] 3、The application has certain reference significance for further screening some substrates with poor hyperpolarization effect or not suitable for SABRE hyperpolarization experiment. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The process of realizing hyperpolarization of the substrate coordinated Ir catalyst precursor of the application after introducing para-hydrogen;

[0030] Figure 2 Thermal equilibrium of different systems in deuterated methanol in example 1 of the application 1 HNMR spectrum, (a) is the hydrogen spectrum of the Ir-based catalyst precursor, and (b) is the hydrogen spectrum after mixing 3-fluoropyridine (50 mM) and the Ir-based catalyst precursor (5 mM);

[0031] Figure 3 Superpolarization of 3-fluoropyridine (50 mM) and the Ir-based catalyst precursor (5 mM) in deuterated methanol in example 1 of the application 1 HNMR spectrum. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the application clearer and more apparent, the application will be described in more detail below with reference to the drawings and specific examples, but the protection scope of the application is not limited to these examples.

[0033] The Ir-based catalyst precursor used in the following examples is IrCl(COD)(IMes), and 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 the deuterated methanol is: D, 99.8% (0.03% v / v TMS);

[0036] There are four kinds of substrates, which are 3-fluoropyridine, 3-methylpyridine, 3-methoxypyridine and 3-hydroxypyridine, and the purity of each is 98%.

[0037] The above reagents are directly used without any pretreatment.

[0038] Example 1

[0039] This example is suitable for evaluating the relationship between the affinity of substrates and SABRE catalyst precursors and hyperpolarization performance:

[0040] Step 1: Preparation of NMR samples to be tested: prepare a mixed solution of Ir-based catalyst precursor and deuterated methanol, four substrates (3-fluoropyridine, 3-methylpyridine, 3-methoxypyridine and 3-hydroxypyridine) respectively with a mixed solution of deuterated methanol and Ir-based catalyst precursor, and then put each of the above five mixed solutions into a white sample bottle, wherein the substrate concentration is 50 mM, the Ir-based catalyst concentration is 5 mM, and the deuterated methanol is 500 uL. Then, transfer the above mixed solutions to a nuclear magnetic tube and seal it with a valve. The above operation needs to be carried out in a glove box to ensure anhydrous and anaerobic conditions.

[0041] Step 2: Collecting thermal equilibrium 1 HNMR spectrum: After tuning, field locking and shimming, call the conventional one-dimensional single pulse PRONT sequence to collect thermal equilibrium of each prepared NMR sample to be tested in the nuclear magnetic instrument. 1 HNMR spectrum, set the experimental parameters nt = 1, ss = 0, d1 = 1.

[0042] Step 3: Polarization transfer process: first, introduce about 3 bar of parahydrogen into the sample, and this process lasts for 2 min to complete the activation of the catalyst precursor. Then, put the sample into a magnetic shield instrument, and continue to introduce parahydrogen for bubbling for 30 s. Under the action of the polarization transfer field, the spin state of parahydrogen can be transferred to the substrate molecules. Set the polarization transfer field strength to 80 Guass. After bubbling is completed, immediately close the air inlet valve to stop aeration, and then transfer the sample to a nuclear magnetic detection instrument to collect the hyperpolarization signal.

[0043] Step 4: Collecting hyperpolarization signal: after the computer is preset with sampling instructions, send the instructions to collect the hyperpolarization spectrum when the sample is transferred to the 500 MHz spectrometer. Except for changing the sampling array number array = 8, the rest of the experimental parameters are the same as those set when collecting the thermal equilibrium spectrum for easy comparison of subsequent effects. Collecting 8 one-dimensional spectra is to observe the attenuation process of the hyperpolarization signal.

[0044] Step 5: Data processing and analysis: the experimental data obtained above are processed using mestrenova (version 14.0) software, including adjusting the phase, correcting the baseline, scaling, and integrating the selected range.

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

[0046] Figure 1The process of substrate coordination to Ir catalyst precursor and hyperpolarization after parahydrogenation. The process from structure 1 to 2 shows the combination of substrate and catalyst precursor. Without parahydrogenation, the substrate will replace the Cl atom to coordinate to the catalyst. The process after structure 2 shows the activation of catalyst precursor after parahydrogenation. Both parahydrogen and substrate molecules coordinate to the metal center. Under the action of polarization transfer field, the spin state of parahydrogen is transferred to the substrate molecule to achieve the hyperpolarization of the substrate molecule.

[0047] Figure 2 Thermodynamic equilibrium of different systems in deuterated methanol 1 HNMR spectra. (a) is the hydrogen spectrum of Ir-based catalyst precursor, (b) is the hydrogen spectrum of 3-fluoropyridine (50 mM) mixed with Ir-based catalyst precursor (5 mM). In order to distinguish between free and bound states, the prefixes "f" and "b" are added to represent free and bound states. The characteristic peaks of free substrate, free catalyst and bound substrate are selected to calculate the integral area, so as to obtain the equilibrium constant of substrate coordination catalyst precursor, which can be quantitatively analyzed. The equilibrium process is related to the substrate coordination ability.

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

[0049] Through attribution and comparison, it is found that each substrate has different degrees of enhanced hyperpolarized signal. The data of equilibrium constant K and hyperpolarization enhancement factor ε of each substrate system are summarized in Table 1 as follows:

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

[0051]

[0052] The larger the equilibrium constant K of the system, the more the coordination equilibrium moves to the right, and more substrates are combined to the catalyst, which represents the stronger affinity of the substrate to the catalyst precursor. The corresponding substrate hyperpolarization enhancement factor is also larger. In summary, using the equilibrium constant K as a new indicator to represent the affinity of the substrate to the catalyst precursor, the relationship between the affinity of the substrate to the catalyst precursor and the hyperpolarization performance is positively correlated, in order to provide a new judgment method for the subsequent screening of SABRE substrates. More importantly, it expands the design ideas and application range of optimizing the hyperpolarization enhancement effect.

[0053] The above examples are only used to illustrate the technical solutions of the present application, but not to limit the present application; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can be modified, or some or all of the technical features can be replaced by equivalent replacements; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method of assessing the relationship between affinity and hyperpolarizing performance of a substrate to a SABRE catalyst precursor, characterized in that, The method comprises the following steps: (1) preparing a sample to be tested: dissolving an Ir-based catalyst precursor and an Ir-based catalyst precursor and a substrate in deuterated methanol respectively to obtain different samples to be tested; (2) Collecting thermal equilibrium 1 HNMR spectrum: Put the NMR sample to be tested prepared in step (1) into a nuclear magnetic instrument, tune the lock field and uniform field, and collect the hydrogen spectrum of the sample in a thermal equilibrium state; (3) polarization transfer: passing para-hydrogen into the sample to be tested prepared in step (1) to activate the catalyst precursor to form a SABRE catalyst; then placing the sample in a nuclear magnetic shielding instrument and setting a polarization transfer field strength, continuing to pass para-hydrogen to realize polarization transfer, and then stopping the aeration; (4) Collecting hyperpolarization 1 HNMR spectrum: The sample after polarization transfer treatment in step (3) is quickly transferred into a nuclear magnetic detector, and a preset instruction is input to obtain the hydrogen spectrum in a hyperpolarized state. (5) data processing and analysis: processing and analyzing the hydrogen spectrum data obtained in steps (2) and (4), including calculating the equilibrium constant and the signal enhancement multiple; the calculation of the equilibrium constant is that the characteristic peaks of the free substrate, the characteristic peaks of the free catalyst precursor and the characteristic peaks of the combined substrate are integrated, and the corresponding concentrations are calculated from the integral areas, which are named as Sub, Ir and Sub-Ir respectively, and the equilibrium constant K is calculated by the formula Sub-Ir / (Sub*Ir); the calculation of the signal enhancement multiple is to select a characteristic peak to calculate the ratio of the hyperpolarized signal integral area to the thermal equilibrium signal integral area.

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

3. The method of assessing the relationship between the affinity of a substrate for a SABRE catalyst precursor and the hyperpolarization performance of claim 1, wherein, In step (1), the substrate is a compound containing coordination to the catalyst precursor.

4. The method of assessing the relationship between the affinity of a substrate for a SABRE catalyst precursor and the hyperpolarization performance of claim 3, wherein, The compound containing coordination to the catalyst precursor includes pyridine and its substituted derivative.

5. The method of assessing the relationship between the affinity of a substrate for a SABRE catalyst precursor and the hyperpolarization performance of claim 1, wherein, In steps (2) and (4), the PROTON sequence of the nuclear magnetic instrument is called, which is composed of a non-selective π / 2 radio frequency pulse and a sampling period.

6. The method of assessing the relationship between the affinity of a substrate for a SABRE catalyst precursor and the hyperpolarization performance of claim 1, wherein, The SABRE catalyst used in step (3) can be reused after activation, and the hyperpolarized spectrum can be collected after re-aerating para-hydrogen without further activation treatment.

7. The method of assessing the relationship between the affinity of a substrate for a SABRE catalyst precursor and the hyperpolarization performance of claim 1, wherein, In step (3), the para-hydrogen and the substrate molecules can be coordinated to the catalyst metal center, and the spin state of the para-hydrogen in the polarization transfer field can be transferred to the substrate molecules to realize the hyperpolarization of the substrate molecules.

8. The method of assessing the relationship between the affinity of a substrate for a SABRE catalyst precursor and the hyperpolarization performance of claim 1, wherein, In step (3), the polarization transfer field is set to 80 Guass, the catalyst precursor aeration activation time is 1-3 min, the para-hydrogen pressure is 2-4 bar, and the catalyst precursor activation is completed after each aeration for 28-32 s.

9. 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 1-8 in screening a substrate capable of realizing SABRE hyperpolarization.

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