Method and device for generating long-life solvent-free DNP polarized free radicals

Abstract

The invention discloses a method and device for generating long-life DNP polarized free radicals without solvent addition, and the method comprises the following steps: carrying out UV irradiation on a powdery photosensitive DNP polarized reagent to generate the long-life DNP polarized free radicals. The device comprises a thermostat for placing DNP polarization reagent powder and a UV irradiation assembly for irradiating the DNP polarization reagent powder, wherein the UV irradiation assembly is mounted on the thermostat. According to the method, a solvent does not need to be added when the DNP polarized free radicals are generated, various problems, such as a complex optimization process of a solvent ratio, solvent removal and the like, caused by the fact that the solvent needs to be added when conventional UV photosensitive free radicals are generated can be avoided, and the generated DNP polarized free radicals have relatively long service life and can relatively stably exist in the whole temperature changing process of 123-298K.

Description

Technical Field

[0001] The present invention belongs to the technical field of nuclear magnetic resonance and electron paramagnetic resonance, and particularly relates to a method and a device for generating long-lived DNP polarized free radicals without solvent addition. Background Art

[0002] Dynamic Nuclear Polarization (DNP) technology utilizes the double resonance of electrons and nuclei to transfer the high polarization on electrons to nuclei, achieving high polarization of the nuclei to be observed. This method can significantly improve the NMR detection sensitivity of the nuclei to be detected, especially those with low gyromagnetic ratios. Free radicals, as an essential reagent in DNP technology, are responsible for providing free electrons during the polarization transfer process.

[0003] Currently, the sources of free radicals are mainly chemical synthesis and irradiation. UV irradiation to generate free radicals is a way to develop DNP polarization reagents. Generally speaking, this method dissolves photosensitive small molecules in organic solvents (ethanol, glycerol, DMSO, water, etc.), drops them into microbeads, and then places them in a liquid nitrogen dewar for UV light irradiation. However, the free radicals generated by this method can only stably exist in liquid nitrogen and rapidly decrease until quenching when the temperature rises. Although this characteristic is an advantage for molten DNP (experimental temperature < 2K) (in molten DNP technology, low temperature requires free radicals to provide a polarized free radical electron source, and it needs to be removed after high-temperature melting), since the photosensitive small molecules are dissolved in solvents, in order to obtain rigorous physiological metabolic flux data, the hyperpolarized molecular probes prepared by molten DNP still face very complex solvent removal problems before entering the organism. On the other hand, since these free radicals are unstable above liquid nitrogen temperature, it also limits their use in other DNP technology fields (such as (Magic-Angle Spinning) MAS-DNP technology).

[0004] Theoretically speaking, directly irradiating solid small molecules of polarization reagents with UV can also generate free radicals, and it also avoids the selection of organic solvents and the subsequent removal problems. However, the realization of this technology requires certain experimental conditions, and the conditions for the stability of the generated free radicals also need to be studied. So far, there has been no report on the application of generating free radicals by UV irradiating solid small molecules of polarization reagents in dynamic nuclear polarization. Summary of the Invention

[0005] Based on the above-mentioned prior art, the present invention provides a method and a device for generating long-lived DNP polarized free radicals without solvent addition. The method of the present invention can generate relatively stable long-lived free radicals, and these free radicals can be widely applied to various DNP technologies.

[0006] The technical solution adopted to achieve the above object of the present invention is as follows:

[0007] A method for generating long - lived DNP - polarized free radicals without solvent addition, comprising the following steps:

[0008] UV irradiate the powdered photosensitive DNP - polarization reagent to generate long - lived DNP - polarized free radicals. Further, the UV irradiation conditions for generating stable and sufficient concentration of free radicals for DNP enhancement are: the temperature is lower than 223K, and the light source wavelength range is 280 - 450nm.

[0009] Regarding the irradiation temperature, for some photosensitive molecules such as phenylglyoxylic acid, a certain amount of free radicals can generally be generated at temperatures above zero. However, the vast majority of free radicals are relatively stable at temperatures not higher than zero, and the lower the temperature, the more stable they are. Therefore, the recommended reaction conditions for generating a sufficient concentration of free radicals are below 223K, generally 77 - 223K.

[0010] Regarding the light power and irradiation time, they can be adjusted according to the sensitivity of the DNP - polarization reagent to UV irradiation. For DNP - polarization reagents that are more sensitive to UV irradiation, relatively low light power can be used for a shorter irradiation time. For DNP - polarization reagents that are less sensitive to UV irradiation, relatively high light power can be used for a longer irradiation time.

[0011] Further, the storage environment temperature of the generated DNP - polarized free radicals is lower than the temperature during their UV irradiation.

[0012] If you want to store the DNP - polarized free radicals generated by this method for a long time, the storage temperature is lower than the temperature at which the free radicals are generated, and they are stored in an environment without oxygen, water, and light.

[0013] Further, the photosensitive DNP - polarization reagent includes but is not limited to solid photosensitive small molecules such as phenylglyoxylic acid, α - ketoglutaric acid, or oxalic acid.

[0014] Further, while the DNP - polarization reagent powder is being UV - irradiated, the DNP - polarization reagent powder is stirred.

[0015] Further, when the DNP - polarization reagent is unstable under oxygen conditions or prone to water absorption, UV irradiation needs to be carried out in a vacuum and inert gas environment.

[0016] Further, the vacuum degree of the vacuum environment is less than 0.1Pa.

[0017] A device for generating long - lived DNP - polarized free radicals without solvent addition, comprising a thermostat for placing the DNP - polarization reagent powder and a UV irradiation assembly for irradiating the DNP - polarization reagent powder, and the UV irradiation assembly is installed on the thermostat.

[0018] It also includes a stirring assembly, which is installed on the thermostat.

[0019] It also includes a vacuum pumping assembly for evacuating the accommodation chamber of the thermostat, and the thermostat is provided with a vent for introducing inert gas into the accommodation chamber of the thermostat.

[0020] The described thermostat includes a heat preservation box. The stirring assembly includes a stirring motor and a stirring rod. The stirring rod movably penetrates through the center of the top of the heat preservation box. The upper end of the stirring rod is fixedly connected to the output shaft of the stirring motor. The UV irradiation assembly includes a UV light source and a UV optical waveguide. The UV optical waveguide penetrates through the center of the top of the heat preservation box. One end of the UV optical waveguide is connected to the UV light source, and the other end of the UV optical waveguide is located at the middle position inside the heat preservation box. The vacuum pumping assembly includes a vacuum pump and a vacuum tube, and the vacuum tube is respectively connected to the heat preservation box and the vacuum pump.

[0021] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0022] 1. When generating DNP polarized free radicals, the present invention does not need to add solvents, which can avoid various problems generated when solvents need to be added during the generation of conventional UV photosensitive free radicals, such as the complex optimization process of solvent ratio, solvent removal and other problems.

[0023] 2. The method of the present invention for generating DNP polarized free radicals is relatively stable. Experiments show that the method of the present application can generate DNP polarized free radicals that relatively stably exist throughout the temperature change process from 123K to 298K.

[0024] 3. The present invention can greatly expand the application field of the UV photosensitive free radical technology to a wider range of DNP application fields, including but not limited to the molten DNP technology and the solid DNP technology, etc.

[0025] 4. The method of the present invention has a wide application range and can be applied to any solid photosensitive polarized small molecule. Brief Description of the Drawings

[0026] Figure 1 It is a schematic structural diagram of a device for generating long-lived DNP polarized free radicals without solvent addition.

[0027] Among them, 1 - low-temperature heat preservation box, 2 - holding dish, 3 - UV light source, 4 - UV optical waveguide, 5 - stirring motor, 6 - stirring rod, 7 - vacuum pump, 8 - vacuum tube, 9 - vent, 10 - glove, 11 - support column.

[0028] Figure 2 It is an ESR spectrogram of free radicals generated by UV irradiation of different solid DNP polarization reagents in a low-temperature environment provided by dry ice.

[0029] Figure 3ESR spectra of free radicals generated by different solid-state DNP polarization reagents under UV irradiation in the low-temperature environment provided by liquid nitrogen.

[0030] Figure 4 The stability of free radicals generated by different solid-state DNP polarization reagents under UV irradiation in a low-temperature (dry ice) environment at a low temperature (-80 °C). Among them, Figure 4 A1 is the ESR spectrum of free radicals generated by α-KG powder at the same temperature (-80 °C) at different time points, Figure 4 A2 is the normalized ESR signal intensity of free radicals generated by α-KG powder at different time points; Figure 4 B1 is the ESR spectrum of free radicals generated by PHGA solid powder at the same temperature (-80 °C) at different time points, Figure 4 B2 is the normalized ESR signal intensity of free radicals generated by PHGA powder at the same temperature (-80 °C) at different time points; Figure 4 C1 is the ESR spectrum of free radicals generated by Oxa powder at the same temperature (-80 °C) at different time points, Figure 4 C2 is the normalized ESR signal intensity of free radicals generated by Oxa powder at the same temperature (-80 °C) at different time points.

[0031] Figure 5 The stability of free radicals generated by the solid-state DNP polarization reagent Oxa under UV irradiation in a low-temperature (liquid nitrogen) environment at different temperatures. Among them, Figure 5 A is the ESR spectrum of free radicals generated by Oxa powder at different temperatures, Figure 5 B is the temperature-calibrated normalized ESR signal intensity of free radicals generated by Oxa powder at different temperatures; Figure 5 C is the ESR spectrum of free radicals generated by Oxa powder at the same temperature (-50 °C) at different times, Figure 5 D is the normalized ESR signal intensity of free radicals generated by Oxa powder at the same temperature (-50 °C); Figure 5 E is the ESR spectrum of free radicals generated by Oxa powder at the same temperature (25 °C) at different times, Figure 5 F is the normalized ESR signal intensity of free radicals generated by Oxa powder at the same temperature (25 °C).

[0032] Figure 6 Graph of the change in the concentration of free radicals generated by different solid-state polarization reagents under UV irradiation in a low-temperature (dry ice) environment and different dissolved-state polarization reagents under UV irradiation in a low-temperature (liquid nitrogen) environment with temperature.

[0033] Figure 7Solids of free radicals generated by UV irradiation of different solid DNP polarization reagents in a low-temperature (liquid nitrogen) environment 1 H MAS-DNP enhanced spectra.

[0034] Figure 8 Solids of free radicals generated by light irradiation of the solid DNP polarization reagent Oxa in a low-temperature (dry ice) environment 13 CMAS-DNP enhanced spectra. Detailed implementation manners

[0035] For the convenience of those of ordinary skill in the art to understand and implement the present invention, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0036] The device for generating long-lived DNP polarization free radicals without solvent addition of the present invention will be described in detail below with reference to the accompanying drawings.

[0037] Embodiment 1

[0038] The structure for generating long-lived DNP polarization free radicals without solvent addition provided in this embodiment is as Figure 1 shown, including a cryostat, a UV irradiation assembly, a stirring assembly, and a vacuum pumping assembly.

[0039] The cryostat includes a low-temperature insulation box 1, which is a square insulation box body for placing DNP polarization reagent powder and providing the low-temperature environment required for UV irradiation. Generally speaking, the temperature required for UV irradiation is generally below 0 °C, but for special samples, it may also be higher than 0 °C. The temperature realization method in the low-temperature insulation box 1 adopts different temperature realization forms according to different experimental temperature requirements. For example, ice cubes are placed in the low-temperature insulation box 1 to achieve a low-temperature (about 0.5 °C) light environment on ice, and dry ice is placed to achieve a dry ice low-temperature (about -50 °C) light environment. For a lower-temperature (below 77K) light environment, the device disclosed in the Chinese invention patent "A Device and Method for Variable-Temperature Broad-Spectrum Light-Induced Free Radical Generation for dDNP" (Patent No. 202211551352.7) is adopted. The only difference is that the sample spoon in the device disclosed in this invention patent is removed and the corresponding channel for the sample spoon to pass through is removed.

[0040] The low-temperature insulation box 1 is provided with a switchable door for putting in or taking out the holding dish 2 for holding DNP polarization reagent powder. In addition, the polarized free radicals generated after irradiation are taken out through the door and put into the MAS-DNP rotor. These operations can be carried out in the thermostat 1 while wearing gloves 10.

[0041] In the center of the top of the low-temperature incubator 1, there is a support column 11. The support column 11 penetrates through the center of the top of the low-temperature incubator 1 and is fixed to the center of the top of the low-temperature incubator 1. A low-temperature-resistant O-ring seal is used between the support column 11 and the top of the incubator 1 for sealing.

[0042] The UV irradiation component includes a UV light source 3 and a UV optical waveguide 4. The UV optical waveguide 4 penetrates through the support column 11, and a low-temperature-resistant O-ring seal is used between the UV optical waveguide 4 and the support column 11 for sealing. One end of the UV optical waveguide 4 is connected to the UV light source 3, and the other end of the UV optical waveguide 4 is located at the middle position inside the low-temperature incubator 1. UV is propagated through the UV optical waveguide 4 to perform UV irradiation on the DNP polarization reagent powder.

[0043] The stirring component includes a stirring motor 5 and a stirring rod 6. The stirring rod 6 penetrates through the support column 11, and there is a clearance fit between the stirring rod 6 and the support column 11. A low-temperature-resistant O-ring seal is used between the stirring rod 6 and the support column 11 for sealing. The upper end of the stirring rod 6 is fixedly connected to the output shaft of the stirring motor 5, and the lower end of the stirring rod 6 can stir the DNP polarization reagent powder. The stirring rod 6 is controlled by the stirring motor 5 through a program. According to specific experimental needs, different stirring frequencies and stirring intensities can be set. The material of the stirring rod 6 is quartz glass, which has a very good transmittance to ultraviolet light, avoiding attenuation of ultraviolet light during the stirring process, thus affecting UV irradiation.

[0044] The vacuum pumping component includes a vacuum pump 7 and a vacuum tube 8. The vacuum tube 8 is connected to the side wall of the low-temperature incubator 1 and the vacuum pump 7 respectively. By starting the vacuum pump, the inside of the low-temperature incubator 1 can be evacuated.

[0045] At the lower part of the side wall of the low-temperature incubator, there is an air vent 9 for introducing an inert gas. When some DNP polarization reagents are unstable or prone to water absorption in the presence of oxygen, an inert gas (such as nitrogen or argon) is introduced into the low-temperature incubator 1 through the air vent 9 to achieve the anaerobic and anhydrous conditions required for the reaction or storage of these DNP polarization reagents. When it is necessary to achieve anaerobic and anhydrous conditions, the following operations are carried out: First, start the vacuum pump 7 for a certain period of time. When the vacuum degree is less than 0.1 Pa, turn off the vacuum pump 7, introduce a certain amount of nitrogen or argon into the low-temperature incubator through the air vent 9, and finally close the air vent 9.

[0046] The method for generating long-life solvent-free DNP polarized free radicals of the present invention will be described in detail below in combination with the above-mentioned device.

[0047] Example 2

[0048] 1. Add dry ice to the low-temperature incubator 1.

[0049] 2. Open the door of the low-temperature incubator 1, place the holding dish on dry ice, then evenly spread the solid powder of phenylglyoxylic acid (PHGA) on the holding dish, close the door of the low-temperature incubator 1, and wait for 10 minutes to allow the sample temperature to stabilize at around 223 K (the measured surface temperature of dry ice).

[0050] 3. Turn on the UV light source and the stirring motor, and irradiate the solid powder of PHGA with a UV light source with a power of 40 W / cm 2 and a wide wavelength range of 280 - 450 nm for 30 minutes. During the irradiation process, to ensure uniform irradiation, stir the solid powder every 5 minutes.

[0051] 4. After the irradiation of the solid powder of PHGA is completed, place the MAS-DNP rotor and the bracket in the low-temperature incubator 1 to cool down, then load the irradiated solid powder of PHGA into the MAS-DNP rotor and cover the rotor lid.

[0052] 5. Transfer the MAS-DNP rotor loaded with the solid powder of PHGA from the low-temperature incubator 1 to a quartz sample tube dedicated to the ESR spectrometer, lower the temperature of the ESR spectrometer to 123 K, pre-tune and set the relevant experimental parameters, and collect the corresponding ESR spectrum.

[0053] 6. Treat and test the solid powders of α-ketoglutaric acid (α-KG) and oxalic acid (Oxa) respectively according to the methods in steps 1 - 5.

[0054] 7. The ESR spectra of the free radicals generated by irradiating the solid powders of PHGA, α-KG, and Oxa with UV light in a dry ice (223 K) environment are as Figure 2 shown. As Figure 2 can be seen, in a low-temperature environment (223 K), directly irradiating the solid powders of PHGA, α-KG, and Oxa with UV light can generate a certain amount of free radicals for PHGA, α-KG, and Oxa solid powders.

[0055] Example 3

[0056] 1. Set the temperature in the heat preservation container to 77 K through the thermostat, and introduce liquid nitrogen into the heat preservation container to make the temperature in the heat preservation container 77 K. It should be noted here that the device for generating free radicals used in this example is the device disclosed in the Chinese invention patent "A Variable Temperature Broadband Light-Induced Free Radical Generation Device and Method for dDNP" (Patent No. 202211551352.7). The only difference is that the sample spoon in the device disclosed in this invention patent is removed and the corresponding channel for the sample spoon to pass through is removed.

[0057] 2. Load the PHGA solid powder into a DNP-MAS rotor with good ultraviolet transmittance, and then place the DNP-MAS rotor into the quartz tube of the heat preservation container.

[0058] 3. Turn on the variable light source, and irradiate the PHGA solid powder with a UV light source with a power of 40 W / cm 2 and a wide wavelength range of 280 - 450 nm for 30 min. During the light irradiation process, to ensure uniform irradiation, rotate the rotating shaft and rotate the double-layer vacuum Dewar flask in the heat preservation container by 90 degrees every 5 minutes.

[0059] 4. After the irradiation of the PHGA solid powder is completed, transfer the MAS-DNP rotor loaded with the PHGA solid powder to the quartz sample tube dedicated to the ESR spectrometer, lower the temperature of the ESR spectrometer to 123 K, pre-tune and set the relevant experimental parameters, and collect the corresponding ESR spectrum.

[0060] 5. Treat and test the solid powders of α-ketoglutaric acid (α-KG) and oxalic acid (Oxa) respectively according to the methods in steps 1 - 4.

[0061] 6. The ESR spectra of the free radicals generated by irradiating the solid powders of PHGA, α-KG, and Oxa with UV light at low temperature (77 K) of liquid nitrogen are as Figure 3 shown. As can be seen from Figure 3 , when directly irradiating the solid powders of PHGA, α-KG, and Oxa with UV light at low temperature (77 K), the solid powders of PHGA, α-KG, and Oxa can generate a certain amount of free radicals. In addition, by comparing Figure 2 and Figure 3 , it is found that the types of free radicals generated after irradiating the same polarization reagent sample in the dry ice and liquid nitrogen environments are the same.

[0062] Example 4

[0063] 1. Treat the PHGA solid powder according to the methods in steps 1 - 4 of Example 2.

[0064] 2. Transfer the MAS-DNP rotor loaded with the PHGA solid powder to the quartz sample tube dedicated to the ESR spectrometer, lower the temperature of the ESR spectrometer to -80 °C (193 K), pre-tune and set the relevant experimental parameters, and collect the corresponding ESR spectrum. When collecting the ESR spectrum, collect the spectrum once every 5 min, and the collection time is 30 min.

[0065] 3. Treat and test the solid powders of α-ketoglutaric acid (α-KG) and oxalic acid (Oxa) respectively according to the methods in steps 1-2. Among them, the UV irradiation time of oxalic acid (Oxa) is 60 minutes, and the UV irradiation time of α-ketoglutaric acid (α-KG) is 75 minutes.

[0066] 4. The stability of the free radicals generated by UV irradiation of PHGA, α-KG, and Oxa solid powders in a dry ice environment (223K) at -80°C is as Figure 4 shown. It can be seen from Figure 4 that irradiating PHGA, α-KG, and Oxa solid powders in the low-temperature environment provided by dry ice can generate a certain amount of free radicals, and the generated free radicals can remain stable at -80°C. This indicates that directly irradiating solid photosensitive polarization reagents with UV in a low-temperature environment can generate relatively stable free radicals. The free radicals generated by this method can stably exist in the low-temperature environment of -80°C.

[0067] Example 5

[0068] 1. Treat the solid powder of oxalic acid (Oxa) according to the methods in steps 1-3 of Example 3.

[0069] 2. After irradiating the Oxa solid powder, transfer the MAS-DNP rotor loaded with the Oxa solid powder to a quartz sample tube dedicated to the ESR spectrometer. Lower the temperature of the ESR spectrometer to 123K, pre-tune and set the relevant experimental parameters. Then, adjust the temperature of the ESR spectrometer to four temperature points of 173K, 223K, 273K, and 298K in sequence. After stabilizing for 5 minutes at each temperature point, tune and collect the corresponding ESR spectra.

[0070] 3. Treat the solid powder of oxalic acid (Oxa) according to the methods in steps 1-3 of Example 3;

[0071] 4. After irradiating the Oxa solid powder, transfer the MAS-DNP rotor loaded with the Oxa solid powder to a quartz sample tube dedicated to the ESR spectrometer. Lower the temperature of the ESR spectrometer to 223K, pre-tune and set the relevant experimental parameters. Collect an ESR spectrum every 5 minutes, and the total collection duration is 40 minutes.

[0072] 5. Raise the temperature of the ESR spectrometer to 298K, pre-tune and set the relevant experimental parameters. Collect an ESR spectrum every 5 minutes, and the total collection duration is 35 minutes.

[0073] 6. The stability of the free radicals generated by UV irradiation of oxalic acid solid powder in a low-temperature liquid nitrogen (77K) environment with temperature change is as Figure 5 shown. From Figure 5 A andFigure 5 As can be seen from Figure B, when the temperature rises from 123 K to 298 K, the ESR peak shape of oxalic acid radicals changes, and their radical concentration first increases and then decreases to near the initial concentration; when the temperature is stabilized at 223 K, from Figure 5 C and Figure 5 As can be seen from Figure D, the peak shape of oxalic acid radicals remains basically unchanged, and with the increase of time, the radical concentration remains basically unchanged; when the temperature is stabilized at 298 K, from Figure 5 E and Figure 5 As can be seen from Figure F, the peak shape of oxalic acid radicals basically does not change, and the radical concentration gradually decreases with the increase of time.

[0074] Example 6

[0075] 1. Treat the PHGA solid powder according to the method of steps 1-4 in Example 2.

[0076] 2. Transfer the MAS-DNP rotor loaded with the PHGA solid powder to the special quartz sample tube of the ESR spectrometer, lower the temperature of the ESR spectrometer to 123 K, pre-tune and set the relevant experimental parameters, and then adjust the temperature of the ESR spectrometer to four temperature points of 173 K, 223 K, 273 K and 298 K in turn. After stabilizing for 5 minutes at each temperature point, tune and collect the corresponding ESR spectra.

[0077] 3. Mix water and ethanol evenly at a volume ratio of 1:1 to prepare a mixed solvent. Dissolve the PHGA solid powder in the mixed solvent to obtain a PHGA solution with a PHGA concentration of 1 M.

[0078] 4. Use a pipette to aspirate 5 μL of the PHGA solution, slowly drop it into liquid nitrogen to freeze it into microbead samples, and repeat this process until the number of microbead samples prepared meets the requirements of the experiment. Transfer four microbead samples to a quartz Dewar, and use an ultraviolet light source with a light power of 40 W and a wavelength range of 280 nm - 420 nm wide band to irradiate the microbead samples for 50 s. Lower the temperature of the ESR spectrometer to 123 K, pre-tune and set the relevant experimental parameters, and then transfer the 4 microbead samples treated by UV irradiation to the special quartz sample tube of the ESR spectrometer. Adjust the temperature of the ESR spectrometer to three temperature points of 143 K, 158 K and 173 K in turn. After stabilizing for 5 minutes at each temperature point, tune and collect the corresponding ESR spectra.

[0079] 5. Treat and test the solid powders of α-ketoglutaric acid (α-KG) and oxalic acid (Oxa) according to the method of steps 1-4. Among them, the UV irradiation time of the oxalic acid (Oxa) powder is 60 minutes, and the UV irradiation time of the α-ketoglutaric acid powder (α-KG) is 75 minutes.

[0080] 6. The variation of the concentration of free radicals generated by UV irradiation of solid powder α-KG, dissolved α-KG, solid powder PHGA, dissolved PHGA, solid powder Oxa, and dissolved Oxa with temperature is as follows Figure 6 shown. From Figure 6 it can be seen that for dissolved α-KG, PHGA, and Oxa, when the temperature rises to 173 K, the free radicals are basically completely quenched. For solid powder of oxalic acid (Oxa) and solid powder of α-KG, the concentration of free radicals generated by UV irradiation does not decrease during the entire temperature change process from 123 K to 298 K. For solid powder of PHGA, when the temperature rises to 273 K, the content of free radicals begins to decrease, and when the temperature rises to 298 K, about 80% of the free radicals still exist. Therefore, compared with its solution state, the lifetime of its solid free radicals is still extended by a large margin.

[0081] Example 7

[0082] 1. Treat the solid powder of PHGA according to the method of steps 1-3 in Example 3.

[0083] 2. After the irradiation of the solid powder of PHGA is completed, put the MAS-DNP rotor loaded with the solid powder of PHGA into liquid nitrogen for storage.

[0084] 3. Put the MAS-DNP rotor into the MAS-DNP spectrometer for DNP enhancement experiment. The specific experimental conditions are: the magic angle rotation speed for the whole experiment is 0. For the α-KG sample, the microwave irradiation time is 300 seconds. For the PHGA sample, the microwave irradiation time is 60 seconds. For the Oxa sample, the microwave irradiation time is 400 seconds.

[0085] 4. Treat and test the solid powders of α-ketoglutaric acid (α-KG) and oxalic acid (Oxa) according to the method of steps 1-3.

[0086] 5. The signal enhancement effect of free radicals generated by UV irradiation of solid powders of PHGA, α-KG, and Oxa on 1 the signal of Figure 7 H is as follows Figure 7 shown. From 1 it can be seen that for α-KG free radicals, after microwave irradiation for 300 s, the detection signal of 1 H can be enhanced by 1.5 times; for PHGA free radicals, after microwave irradiation for 60 s, the detection signal of 1 H can be enhanced by 2.4 times; for Oxa free radicals, after microwave irradiation for 400 s, the detection signal of

[0087] Example 8

[0088] 1. Prepare two portions of Oxa solid powder separately, and process each portion of the Oxa solid powder according to the method of steps 1-4 in Example 2. Among them, the irradiation time of one portion of the Oxa solid powder is 15 minutes, and the irradiation time of the other portion of the Oxa solid powder is 30 minutes.

[0089] 2. After each portion of the Oxa solid powder is irradiated, place the MAS-DNP rotor loaded with the Oxa solid powder in dry ice for storage.

[0090] 3. Place the MAS-DNP rotor in the MAS-DNP spectrometer for DNP enhancement experiments. The specific experimental conditions are: the magic angle rotation speed for the whole experiment is 8K, and the microwave irradiation time is 400 seconds.

[0091] 4. The free radical pairs generated by UV irradiation of the Oxa solid powder in a dry ice environment 13 The signal enhancement effect of Figure 8 C is as Figure 8 shown. It can be seen from 13 that for the oxalic acid free radicals generated by irradiation for 15 minutes, after microwave irradiation for 400 s, the detection signal of 13 C can be enhanced by 5.5 times; for the oxalic acid free radicals irradiated for 30 minutes, after microwave irradiation for 400 s, the detection signal of

Claims

1. A method for generating long-lived DNP polarized free radicals without solvent addition, characterized in that It includes the following steps: UV irradiate the powdered photosensitive DNP polarization reagent to generate long-lived DNP polarization free radicals.

2. The method for generating long-lived solvent-free DNP polarized free radicals according to claim 1, characterized in that The UV irradiation conditions for generating stable free radicals with a sufficient concentration for DNP enhancement are: the temperature is lower than 223K, and the light source wavelength range is 280 - 450nm.

3. The method for generating long-lived solvent-free DNP-polarized free radicals according to claim 2, wherein: The storage environment temperature of the generated DNP polarization free radicals is lower than the temperature during their UV illumination.

4. The method for generating long-lived solvent-free DNP polarized free radicals according to claim 3, characterized in that: The photosensitive DNP polarization reagent includes but is not limited to phenylglyoxylic acid, α-ketoglutaric acid, and oxalic acid.

5. The method for generating long-lived solvent-free DNP polarized free radicals according to claim 1, characterized in that: While the photosensitive DNP polarization reagent is being UV irradiated, the DNP polarization reagent powder is stirred.

6. The method for generating long-lived solvent-free DNP polarized free radicals according to claim 1, characterized in that: When the photosensitive DNP polarization reagent is unstable or prone to water absorption in the presence of oxygen, UV irradiation needs to be carried out in a vacuum and inert gas environment.

7. The method for generating long-lived solvent-free DNP polarized free radicals according to claim 6, characterized in that: The degree of vacuum in the vacuum environment is less than 0.1 Pa.

8. An apparatus for generating long-lived DNP polarized free radicals without adding solvents, characterized in that: It includes a thermostat for placing the DNP polarization reagent powder and a UV irradiation component for irradiating the DNP polarization reagent powder, and the UV irradiation component is installed on the thermostat.

9. The apparatus for generating long-lived solvent-free DNP polarized free radicals according to claim 8, wherein: It also includes a stirring component, and the stirring component is installed on the thermostat.

10. The apparatus for generating long-life solvent-free DNP polarized free radicals according to claim 8 or 9, characterized in that: It also includes a vacuum pumping component for evacuating the accommodation chamber of the thermostat, and an air vent for introducing inert gas into the accommodation chamber of the thermostat is provided on the thermostat.

11. The apparatus for generating long-lived solvent-free DNP polarized free radicals according to claim 10, characterized in that: The thermostat includes a heat preservation box, the stirring component includes a stirring motor and a stirring rod, the stirring rod movably penetrates through the center of the top of the heat preservation box, the upper end of the stirring rod is fixedly connected to the output shaft of the stirring motor, the UV irradiation component includes a UV light source and a UV optical waveguide, the UV optical waveguide penetrates through the center of the top of the heat preservation box, one end of the UV optical waveguide is connected to the UV light source, the other end of the UV optical waveguide is located at the middle position inside the heat preservation box, and the vacuum pumping component includes a vacuum pump and a vacuum tube, and the vacuum tube is respectively connected to the heat preservation box and the vacuum pump.

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