A SABRE hyperpolarization method for enhancing the signals of labile hydrogens based on dynamic covalent bond exchange
By introducing dynamic covalent bond exchange into SABRE hyperpolarization technology, hyperpolarization of active hydrogen is achieved, and the problems of harsh experimental conditions and high cost in the existing technology are solved, and the application scope of hyperpolarization technology is expanded.
Patent Information
- Application Number
- CN202211729555.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-12-30
- Publication Date
- 2025-07-18
- Estimated Expiration
- 2042-12-30
AI Technical Summary
The existing secondary hydrogen hyperpolarization technology requires strict experimental conditions and complex processes for the hyperpolarization of active hydrogen, which poses safety hazards and is costly, making it difficult to widely use.
By integrating the dynamic exchange of the hemiacetal formed by aldehyde and hydroxyl groups into SABRE and combining it with coordination-based SABRE, the spin state of the secondary hydrogen to the hemiacetal product is achieved, and the hyperpolarization of CD3OH and active hydrogen is obtained by using the dynamic exchange of the hemiacetal.
The enhanced active hydrogen signal is achieved, the application scope of SABRE hyperpolarization is broadened, and a convenient and economical hyperpolarization method is provided, which avoids the harsh conditions of high pressure and high temperature, and reduces the difficulty of equipment and operation.
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Figure CN116026875B_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of nuclear magnetic resonance hyperpolarization, and particularly relates to a SABRE hyperpolarization method for enhancing the signal of labile hydrogen based on dynamic covalent bond exchange. Background Art
[0002] Nuclear magnetic resonance (NMR) technology has been widely used in elucidating the structures of biological macromolecules, magnetic resonance imaging (MRI), geological exploration, drug screening, etc. However, its inherent low sensitivity has limited its application and development to a certain extent. According to the well-known Boltzmann equation, this is mainly due to the fact that the NMR signal originates from a very small population difference between the upper and lower energy levels of atomic nuclei. The problems of low sensitivity can be overcome to a certain extent by increasing the magnetic field strength, increasing the sample concentration, and performing multiple scans. However, the time cost, sample cost, and equipment cost of these methods are very high. Recently, it has been reported in the literature that the use of hyperpolarization technology can be used as a solution to improve the sensitivity of NMR, which can enhance the NMR signal by 3 to 5 orders of magnitude, thus greatly improving the sensitivity of nuclear magnetic resonance.
[0003] Hyperpolarization technology is one of the research hotspots in the field of NMR in recent years. Para-hydrogen induced polarization (PHIP) is a method for enhancing the signal of target molecules through the reaction of para-hydrogen with target molecules. Hydrogen molecules have two nuclear spin isomers, ortho-H2 and para-H2, corresponding to two possible couplings of the nuclear spins of the two hydrogen nuclei in the hydrogen molecule. When the nuclear spin states of the two hydrogen atoms in ortho-hydrogen are parallel, the nuclear spin quantum number I = 1, which is called the triplet state. When the nuclear spin states of the two hydrogen atoms in para-hydrogen are antiparallel, the nuclear spin quantum number I = 0, which is called the singlet state.
[0004] SABRE is a hyperpolarization method in which para-hydrogen and complex molecules undergo a reversible exchange reaction on a coordination compound, and the hyperpolarized state is transferred to the substrate molecule through spin-spin coupling. Its principle of realization is that the target molecule (usually a molecule containing an N atom) and para-hydrogen are jointly bound to a transition metal (usually iridium, Ir) complex, and the spin order of para-hydrogen can be transferred to the target molecule. In this process, para-hydrogen and the substrate continuously bind and dissociate on the catalyst, which is a reversible process. Therefore, a large number of hyperpolarized target molecules are accumulated in the solution, thereby achieving signal enhancement. Compared with technologies such as optical pumping hyperpolarization and dynamic hyperpolarization, para-hydrogen hyperpolarization has the advantages of high signal enhancement multiple, low equipment cost, and simple structure.
[0005] Due to the strict requirements of the parahydrogen hyperpolarization technique for the structure of substrate molecules, the research scope is limited. Through the exchange interaction between labile hydrogen protons, the hyperpolarization of substrate molecules containing labile hydrogen that cannot be directly hyperpolarized is indirectly achieved. Therefore, the use of the exchange interaction of labile hydrogen is of great significance for expanding the application scope of the hyperpolarization technique. Currently, the research on the hyperpolarization of labile hydrogen in the field of parahydrogen hyperpolarization mainly includes: The literature "Hyperpolarizing water with parahydrogen, ChemPhysChem 2017, 18, 2426 - 2429" requires a parahydrogen pressure of 7 bar and heating to 90 °C to achieve, which is relatively demanding and unsafe for experimental conditions. In the literature "Using parahydrogen to hyperpolarize amines, amides, carboxylic acids, alcohols, phosphates, and carbonates, Sci. Adv. 2018, 4, eaao6250", the SABRE - Relay technique is used, and ammonia is used as a relay to transfer hyperpolarization. This process is more complex and difficult to achieve, and high - pressure ammonia is also toxic and dangerous. In the literature "Surface - mediated hyperpolarization of liquid water from parahydrogen, Chem., 2018, 4, 1387 - 1403", complex materials are used as catalysts, and it also requires a parahydrogen pressure of 7 bar and heating to about 100 °C to make the water peak show a hyperpolarized inverted peak signal. In the literature "Hyperpolarized magnetic resonance of exchangeable protons using parahydrogen and aminosilane, J. Phys. Chem. C 2020, 124, 14541 - 14549", the hyperpolarization of labile hydrogen is achieved at room temperature and atmospheric pressure using aminosilane, which is an important breakthrough. Since several previous methods for hyperpolarizing labile hydrogen require relatively complex and demanding experimental conditions, and have the disadvantages of high sample cost, high equipment requirements, and difficulties and insecurity in actual operation.
[0006] Therefore, it is highly necessary to develop a new and easily achievable SABRE hyperpolarization method for enhancing the signal of labile hydrogen. Summary of the Invention
[0007] The object of the present invention is to overcome the defects existing in the prior art and provide a SABRE hyperpolarization method for enhancing the signal of labile hydrogen through dynamic covalent bond exchange. By integrating the dynamic exchange of hemiacetals formed by aldehyde groups and hydroxyl groups into SABRE and combining it with coordination-based SABRE, the transfer of the spin state of para-hydrogen (para-H2) to the hemiacetal product is achieved, and further, the hyperpolarization of CD3OH and labile hydrogen is obtained through the dynamic exchange of hemiacetals.
[0008] The hemiacetal reaction is a common reversible chemical reaction. Aldehydes and alcohols can undergo nucleophilic addition reactions to form hemiacetals. Pyridinecarboxaldehyde and deuterated methanol will undergo a hemiacetal reaction, and the product has the same ability to coordinate to the catalyst as pyridinecarboxaldehyde. Therefore, when the product coordinates, the hyperpolarized product decomposes into deuterated methanol and pyridinecarboxaldehyde, and then the hyperpolarized deuterated methanol accumulates in the solution, thereby enhancing the signal of labile hydrogen.
[0009] To achieve the above object, one of the technical solutions of the present invention is: a SABRE hyperpolarization method for enhancing the signal of labile hydrogen through dynamic covalent bond exchange, comprising the following steps:
[0010] (1) Prepare the NMR sample to be measured: Dissolve pyridinecarboxaldehyde and the Ir-based catalyst precursor in a deuterated methanol solution and mix evenly to obtain the NMR sample to be measured;
[0011] (2) Collect the thermal equilibrium 1 1H NMR spectrum: Put the NMR sample prepared in step (1) into a nuclear magnetic resonance instrument, perform shimming at room temperature to make the magnetic field as uniform as possible; measure the NMR spectrum of the sample in the thermal equilibrium state (room temperature) to obtain the line width, magnetic field uniformity, etc. of the spectrum. This one-dimensional 1 1H NMR spectrum is also used for spectral peak attribution and comparison with the hyperpolarized spectrum;
[0012] (3) Hyperpolarization transfer process: Take out the NMR sample from the nuclear magnetic resonance instrument, introduce para-hydrogen gas to activate the catalyst precursor in the NMR sample to form an active SABRE catalyst; place the NMR sample treated with para-hydrogen gas activation in a magnetic shield for polarization transfer, set the polarization transfer field strength, continue to introduce para-hydrogen gas and then stop ventilation;
[0013] (4) Detect the signal of hyperpolarized labile hydrogen: Transfer the NMR sample treated in step (3) to the nuclear magnetic resonance instrument for detection; input the preset sampling instruction to obtain the 1 1H NMR spectrum of the hyperpolarized state;
[0014] (5) Data post-processing and analysis: Perform data processing and analysis on the 1 1H NMR spectrum collected in step (4).
[0015] In a preferred embodiment of the present invention, in step (1), the concentration of pyridinecarboxaldehyde in the deuterated methanol solution is 40 - 60 mM, and the concentration of the Ir-based catalyst precursor is 4 - 6 mM.
[0016] In a preferred embodiment of the present invention, the pyridinecarboxaldehyde in step (1) includes one of pyridine-2-carboxaldehyde, pyridine-3-carboxaldehyde, and pyridine-4-carboxaldehyde. The aldehyde groups in the above pyridinecarboxaldehydes at different substitution positions can all achieve the hyperpolarization of labile hydrogen, but there are differences in the strength of the hyperpolarization signals.
[0017] In a preferred embodiment of the present invention, the NMR spectrometer in steps (2) and (4) is a 500 MHz Agilent ProPulse NMR spectrometer. The pulse sequence for collecting the NMR spectrum is PROTON, and the parameters of the pulse sequence are nt = 0, ss = 0, d1 = 1 s, pw = 2.838, array = 20; the excitation pulse is a non-selective 30° radio frequency pulse, and signal sampling period follows after this pulse acts; collecting the spectrum of thermal equilibrium is for comparison with the spectrum after hyperpolarization.
[0018] To compare the enhancement effect, the pulse sequence and experimental parameters used for collecting the hyperpolarized spectrum in step (4) are exactly the same as those in step (2). After the sampling is completed, the hyperpolarized NMR spectrum can be obtained. Comparing with the thermal equilibrium spectrum shows that the substrate and the labile hydrogen protons have been hyperpolarization-enhanced.
[0019] In a preferred embodiment of the present invention, the SABRE catalyst formed by activation in step (3) can be reused. Subsequent use does not require re-activation; each time a signal is collected later, only the NMR sample treated by activation needs to be placed in a magnetic shielding instrument and bubbled with parahydrogen for 12 - 18 s.
[0020] In a preferred embodiment of the present invention, under the action of the SABRE catalyst in step (3), both parahydrogen and pyridinecarboxaldehyde in the NMR sample coordinate to the SABRE catalyst; under the action of the polarization transfer field, the spin state of parahydrogen can be transferred to pyridinecarboxaldehyde.
[0021] In a preferred embodiment of the present invention, in step (3), for 1 H (proton NMR, the superscript represents the proton), the applicable range of the polarization transfer field is 10 - 100 Gauss (G), and the best is 80 Gauss (G).
[0022] In a preferred embodiment of the present invention, in step (3), the pressure of the parahydrogen gas for activating the NMR sample is 1 - 5 bar, and the activation time is 1 - 3 min.
[0023] In a preferred embodiment of the present invention, the time for introducing para-hydrogen during polarization transfer in step (3) is 12 - 18 s.
[0024] In a preferred embodiment of the present invention, in step (4), the NMR sample is transferred to a nuclear magnetic resonance instrument for detection, and this process takes 2 - 8 s.
[0025] To achieve the above object, the second technical solution of the present invention is: an application of a SABRE hyperpolarization method in enhancing the signal of labile hydrogen.
[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0027] 1. The present invention firstly introduces dynamic covalent bonds as the reversible exchange of SABRE, realizes the hyperpolarization of labile hydrogen protons, broadens the design idea of SABRE, and expands the scope of the existing research system;
[0028] 2. The present invention integrates the dynamic exchange of hemiacetal formed by aldehyde group and hydroxyl group into SABRE, combines it with coordination-based SABRE, realizes the transfer of the spin state of para-hydrogen (para-H2) to the hemiacetal product, and further obtains the hyperpolarization of CD3OH and labile hydrogen through the dynamic exchange of hemiacetal;
[0029] 3. The catalyst, ligand and solvent used in the present invention can all be purchased from conventional channels, and the para-hydrogen hyperpolarization conditions used are mild, providing a convenient and economical method for hyperpolarizing labile hydrogen, and effectively solving the problem of high requirements for experimental conditions and equipment in the existing methods;
[0030] 4. The present invention provides inspiration for other hyperpolarization methods and promotes the in-depth study of the hyperpolarization mechanism. BRIEF DESCRIPTION OF THE DRAWINGS
[0031] Figure 1 It is a process schematic diagram of a SABRE hyperpolarization method for enhancing the signal of labile hydrogen based on dynamic covalent bond exchange. Among them, (a) is the dynamic reversible hemiacetal reaction of pyridine-4-carbaldehyde and deuterated methanol; (b) is the process of the substrate (pyridine-4-carbaldehyde and hemiacetal product) coordinating to the Ir catalyst precursor to obtain hyperpolarization.
[0032] Figure 2 For pyridine-4-carbaldehyde (50 mM) and IrCl(COD)(IMes) (5 mM) in deuterated methanol solution in Example 1 1 1H NMR spectrum. DETAILED DESCRIPTION OF THE INVENTION
[0033] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention will be described in more detail below with reference to the accompanying drawings and specific embodiments. However, the protection scope of the present invention is not limited to these embodiments.
[0034] The solvent used in the following examples is deuterated methanol, with the molecular formula CD3OD. The purity of deuterated methanol is: D, 99.8% (0.03% v / v TMS). The labile hydrogen comes from the H atoms in the -OH group of deuterated methanol that are not fully deuterated, as well as trace amounts of H2O molecules contained in the reagents used. The iridium-based catalyst precursor used is IrCl(COD)(IMes), where Imes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene and COD = cycloocta-1,5-diene.
[0035] Substrate (pyridinecarboxaldehyde) part: The substrate is pyridine-4-carboxaldehyde with a purity of 97%.
[0036] The above reagents are used directly without any pretreatment.
[0037] Example 1
[0038] A SABRE hyperpolarization method for enhancing labile hydrogen signals based on dynamic covalent bond exchange and the use of this method to enhance labile hydrogen signals:
[0039] Step 1: Prepare the sample to be measured: First, dissolve pyridine-4-carboxaldehyde with the molecular formula C6H5NO and the iridium (Ir)-based catalyst precursor IrCl(COD)(IMes) in a deuterated methanol solution and mix well. Pyridinecarboxaldehyde serves as a ligand for the Ir-based catalyst precursor, with a concentration of 50 mM; the concentration of the Ir-based catalyst precursor IrCl(COD)(IMes) used is 5 mM. Dissolve both in 700 μL of deuterated methanol solution and mix well, then transfer the solution to a sample tube and seal it with a valve. This process needs to be carried out in an anhydrous and oxygen-free glove box.
[0040] Step 2: Collect the thermal equilibrium 1 HNMR spectrum: The instrument used in this experiment is a 500 MHz Agilent ProPulse NMR nuclear magnetic resonance spectrometer. Place the sample tube in the NMR instrument to measure the 1HNMR spectrum, using a conventional one-dimensional pulse sequence to collect 20 array one-dimensional spectra. The conventional one-dimensional pulse sequence is the one-dimensional hydrogen spectrum PROTON pulse sequence that comes with the NMR nuclear magnetic resonance spectrometer. The RF pulse uses a 30° flip angle, and the RF pulse is followed by a signal sampling period. The pulse sequence parameters are set to nt=0, ss=0, d1=1s, pw=2.838, array=20. The sampling temperature is 298K. The 20 array one-dimensional spectra collected are used for comparison with the SABRE hyperpolarized spectrum.
[0041] Step 3: Hyperpolarization transfer process: In order to activate the catalyst, it is necessary to introduce 3 bar of parahydrogen into the sample tube and bubble for 2 minutes. After the catalyst is fully activated, the parahydrogen and the substrate can coordinate to the catalyst. After the activation process is completed, the sample needs to be placed in a magnetic shielding instrument for polarization transfer. Parahydrogen is bubbled in the magnetic shielding instrument for 15 seconds. Under the action of the polarization transfer field, the spin state of the parahydrogen can be transferred to the substrate coordinated at the same time. The field strength of the magnetic shielding instrument can be controlled by controlling the current, and the set field strength is 80 Gauss. After the polarization transfer process is completed, the parahydrogen valve needs to be closed, the gas supply needs to be stopped, and the sample needs to be quickly transferred to the NMR spectrometer cavity for signal acquisition.
[0042] Step 4: Detect the active hydrogen signal after hyperpolarization
[0043] For the detection transferred from the magnetic shielding instrument to the 500MHz nuclear magnetic instrument, the signal data after hyperpolarization can be collected by quickly sending sampling instructions on the computer. In order to compare the effects before and after hyperpolarization, the pulse sequence and experimental parameters used in the hyperpolarization spectrum are exactly the same as those in the above-mentioned thermal equilibrium spectrum. The purpose of collecting 20 array one-dimensional spectra is to obtain the attenuation effect of the hyperpolarized signal.
[0044] Step 5: Data post-processing and analysis
[0045] All experimental data were processed using MestReNova software (version 14.0.0, Mestrelab Research), including baseline adjustment, phase adjustment, calibration, and integration.
[0046] Figure 1(a) is the reversible reaction equation for the formation of hemiacetal from pyridine-4-carbaldehyde and deuterated methanol. Figure (b) shows the process of hyperpolarization obtained by coordinating the substrates (pyridine-4-carbaldehyde and hemiacetal product) to the Ir catalyst precursor. Both the hemiacetal product and pyridine-4-carbaldehyde generated by the reaction exist as substrates in the solution. After introducing parahydrogen, both the hemiacetal product and pyridine-4-carbaldehyde coordinate with parahydrogen to the metal center of the Ir catalyst precursor. During this process, the spin state of parahydrogen is transferred to the two ligands. The hyperpolarized ligands dissociate reversibly and exchange into the solution, and at the same time, the hemiacetal product also dissociates hyperpolarized CD3OH through hemiacetal exchange, that is, hyperpolarization of labile hydrogen is generated.
[0047] Figure 2 is the 1 1H NMR spectrum of pyridine-4-carbaldehyde. Thermodynamic represents the hydrogen spectrum of pyridine-4-carbaldehyde collected under thermal equilibrium, and SABRE represents the hydrogen spectrum of pyridine-4-carbaldehyde collected after hyperpolarization. Among them, the chemical shift of the labile hydrogen is marked as CD3OH / HOD at 4.9 ppm, and the methyl peak of the deuterated methanol solvent is marked as CD2HOD at 3.4 ppm. Through assignment and comparison with the thermal equilibrium spectrum, it can be found that hyperpolarized signals are generated for the pyridine ring protons (chemical shift δ 5-9 ppm) of both substrates, the hemiacetal product and the residual pyridine-4-carbaldehyde. As Figure 2 shown, both the hemiacetal product and the residual pyridine-4-carbaldehyde coordinate to the Ir catalyst precursor and obtain hyperpolarization. In addition, a hyperpolarized inverted peak also appears at 3.4 ppm for the residual methyl peak of the deuterated methanol solvent marked as CD2HOD, indicating that the deuterated methanol is also hyperpolarized, originating from the reversible exchange of the hemiacetal. More importantly, the labile hydrogen at 4.9 ppm obtains a greatly enhanced reverse signal after hyperpolarization, not only canceling the forward signal intensity but also showing a strong reverse inverted peak, proving that this method can achieve hyperpolarization of the labile hydrogen signal and significantly enhance its signal intensity. In summary, using the SABRE hyperpolarization method based on dynamic covalent bond exchange to enhance the labile hydrogen signal provides a simple and feasible method for hyperpolarization of labile hydrogen, expanding the design ideas and application scope of SABRE.
[0048] The examples cited in the present invention aim to further elaborate the specific operation of the SABRE hyperpolarization method for enhancing the labile hydrogen signal by using dynamic covalent bond exchange, to illustratively explain the principle and efficacy of the present invention, rather than to limit the present invention. It should be noted that for any person skilled in the art, without departing from the spirit and scope of the present invention, modifications to the above embodiments should also be regarded as within the protection scope of the present invention.
Claims
1. A SABRE hyperpolarization method for enhancing the signal of labile hydrogen based on dynamic covalent bond exchange, characterized in that, It includes the following steps: (1) Prepare the NMR sample to be measured: Dissolve pyridinecarboxaldehyde and the Ir-based catalyst precursor in a deuterated methanol solution, and mix them evenly to obtain the NMR sample to be measured; (2) Acquisition of thermal equilibrium 1 H NMR spectrum: The NMR sample to be measured prepared in step (1) is placed in a nuclear magnetic resonance instrument, and the NMR spectrum in the thermal equilibrium state is measured after field shimming at room temperature; (3) Hyperpolarization transfer: Take out the NMR sample from the NMR spectrometer, pass parahydrogen gas to activate the catalyst precursor in the NMR sample to form the SABRE catalyst; Place the NMR sample in a magnetic shield for polarization transfer, set the polarization transfer field strength, continue to pass parahydrogen gas and then stop ventilation; The SABRE catalyst formed by activation can be reused. After each signal acquisition, only place the activated NMR sample in the magnetic shield and pass parahydrogen for bubbling for 12 - 18 s; Under the action of the SABRE catalyst, both parahydrogen and pyridinecarboxaldehyde in the NMR sample coordinate to the SABRE catalyst; Under the action of the polarization transfer field, the spin state of parahydrogen is transferred to pyridinecarboxaldehyde; (4) Detect the signal of hyperpolarized labile hydrogen: Transfer the sample processed in step (3) to a nuclear magnetic resonance instrument for detection, and input the preset sampling instruction to obtain the 1 HNMR spectrogram; (5) Data post-processing and analysis: Perform data processing and analysis on the spectrum collected in step (4).
2. The SABRE hyperpolarization method according to claim 1, characterized in that, In step (1), the concentration of pyridinecarboxaldehyde in the deuterated methanol solution is 40 - 60 mM, and the concentration of the Ir-based catalyst precursor is 4 - 6 mM.
3. The SABRE hyperpolarization method according to claim 1, wherein In step (1), the pyridinecarboxaldehyde includes one of pyridine-2-carboxaldehyde, pyridine-3-carboxaldehyde, and pyridine-4-carboxaldehyde.
4. The SABRE hyperpolarization method according to claim 1, characterized in that, The NMR spectrometer in steps (2) and (4) is a 500 MHz Agilent ProPulse NMR spectrometer, and the pulse sequence for collecting the NMR spectrum is PROTON. The parameters of the pulse sequence are nt = 0, ss = 0, d1 = 1 s, pw = 2.838, and array = 20.
5. The SABRE hyperpolarization method according to claim 1, wherein In step (3), the polarization transfer field ranges from 10 - 100 Gauss (G).
6. The SABRE hyperpolarization method according to claim 1, wherein In step (3), the pressure of the parahydrogen gas for activating the NMR sample is 1 - 5 bar, and the activation time is 1 - 3 min.
7. The SABRE hyperpolarization method according to claim 1, wherein, In step (3), the time for passing parahydrogen gas during polarization transfer is 12 - 18 s.