Quadrupole nuclear two-dimensional high-resolution solid NMR method based on five-quantum excitation enhancement

Abstract

The invention discloses a quadrupole nuclear two-dimensional high-resolution solid NMR method based on five-quantum excitation enhancement, and the method comprises the steps: carrying out the optimization of a frequency offset satellite transition selective flip pulse based on a first change hill climbing algorithm, obtaining an LP-opt pulse, designing an LP-opt 5QMAS pulse sequence, and carrying out the time sequence of the LP-opt 5QMAS pulse sequence, the method sequentially comprises a layout number transfer enhancement pulse, a first center transition selective excitation pulse, a first LP-opt pulse, a second LP-opt pulse, a second center transition selective excitation pulse and a third center transition selective excitation pulse. According to the invention, high-order quantum transition effective excitation which is difficult to excite by a traditional rectangular pulse method is realized. Especially for a nuclear spin system with a large nuclear quadrupole interaction constant (CQ) generated due to asymmetry of a local structure, the five-quantum excitation material shows excellent five-quantum excitation efficiency in a 5QMAS experiment.

Description

Technical Field

[0001] This invention relates to the field of nuclear magnetic resonance spectroscopy, specifically to a two-dimensional high-resolution solid-state NMR method based on five-quantum excitation enhancement of quadrupole nuclei. Background Technology

[0002] Nuclear magnetic resonance (NMR) plays a crucial role in characterizing the local structure of materials. Solid-state NMR (SSNMR) characterization, being non-destructive, is an important tool for studying the microstructure of materials. Through complex pulse sequence design and multidimensional experiments, SSNMR can provide precise structural information such as chemical shifts and coupling constants of relevant samples, further revealing structural characteristics such as coordination states, internuclear distances, and species distribution.

[0003] In solid samples, due to restricted molecular motion, anisotropic interactions such as chemical shift anisotropy, dipole interactions, and quadrupole interactions cause broadening of NMR spectral lines, thus limiting the resolution, sensitivity, and quantitative accuracy of NMR spectra. Especially for atomic nuclei with spin quantum numbers greater than 1 / 2, the presence of their unique quadrupole interactions can lead to NMR signal broadening on the order of MHz in some cases. Magic angle rotation (MAS) technology uses an angle of approximately 54.74° to rotate the sample to average anisotropic interactions, improving spectral resolution to some extent. However, for the second-order quadrupole interaction in quadrupole nuclei (spin quantum number I > 1 / 2), magic angle rotation cannot completely eliminate anisotropic interactions, leaving significant residual effects and resulting in still considerable spectral broadening and overlap.

[0004] With the development of pulse methods in nuclear magnetic resonance spectroscopy, a two-dimensional high-resolution multiple-quantum magic-angle spinning (MQMAS) method for half-integer quadrupole nuclei (spin quantum number I=N / 2, N=3,5,7,9, where N is an integer) was proposed in 1995 by Lucio Frydman et al. This method, based on conventional magic-angle spinning (without requiring extremely strong magnetic fields or complex experimental equipment), utilizes the different scaling properties of multiple quantum coherence to partially separate the second-order quadrupole effect in a two-dimensional correlation spectrum. Compared to single-quantum coherence, by constructing echoes of multiple quantum coherence and single-quantum correlation in a two-dimensional experiment, the second-order quadrupole interaction can be refocused in a specific direction of the two-dimensional spectrum. Further, through shearing transformations, isotropic NMR lines unaffected by quadrupole interaction broadening can be obtained in the indirect dimension of the two-dimensional spectrum, thus achieving high-resolution observation of half-integer quadrupole nuclei and extracting isotropic chemical shifts and quadrupole interaction parameters at different sites. Regarding the selection of excitations in multiple quantum coherence orders, for nuclei with spin quantum number I ≥ 5 / 2 (e.g.: 27Al, 17 O, 95 Mo, 47 / 49 The five-quantum magic angle rotation (5QMAS) experimental pulse method of Ti et al. can be realized by exciting and converting five-quantum coherence. Compared with three-quantum magic angle rotation (3QMAS) in two-dimensional maps, it can further improve the isotropic resolution of certain nuclei (I=5 / 2).

[0005] The existing 5QMAS experimental procedure typically includes: exciting five quantum coherences using a specific pulse sequence under magic angle rotation (MAS) conditions, achieving coherence order selection through pulse phase cycling to obtain a detectable signal, and obtaining the spectrum using a two-dimensional Fourier transform. However, the following technical problems still exist in practical applications: First, the excitation and conversion efficiency of the current hard pulse-based half-integer quadrupole high-resolution five-quantum magic angle rotating solid-state nuclear magnetic resonance pulse method is limited by the power of the radio frequency hardware and the uniformity of the high-power radio frequency field, resulting in limited sensitivity. Secondly, current high-resolution five-quantum magic angle rotating solid-state NMR pulse methods based on hard pulses and half-integer quadrupole nuclei exhibit low robustness to experimental parameters such as radio frequency bias and high-power pulse width, leading to complex experimental parameter optimization and difficulties in experimental setup. These factors are particularly prominent in complex material systems or under conditions of low sample content / short experimental time.

[0006] Therefore, there is an urgent need for a new two-dimensional high-resolution solid-state NMR spectroscopy method based on 5QMAS, which can improve the experimental efficiency of high-resolution five-quantum magic angle rotating solid-state NMR with multi-quantum nuclei, especially half-integer quadrupole nuclei, without changing the existing hardware architecture, simplify the experimental operation process, obtain higher sensitivity from two-dimensional 5QMAS correlation spectra, and facilitate structural characterization and analysis. Summary of the Invention

[0007] The purpose of this invention is to address the problems in the prior art by proposing a two-dimensional high-resolution solid-state NMR method based on five-quantum excitation enhancement of quadrupole nuclei. By improving the 5QMAS pulse sequence, the signal-to-noise ratio of half-integer quadrupole nuclei signals in solid-state 5QMAS experiments is improved.

[0008] To achieve the above objectives, the present invention provides the following technical solution: The four-pole nuclear two-dimensional high-resolution solid-state NMR method based on five-quantum excitation enhancement includes the following steps: Step 1: Adjust the nuclear magnetic resonance spectrometer. Place the rotor containing the X-nucleus standard sample into the probe sample chamber and optimize the 90° pulse width for the X-nucleus center transition selectivity to maximize the peak height or area of ​​the X-nucleus. Then, calibrate the chemical shift value of the peak center of the X-nucleus standard sample. Step 2: Place the rotor containing the sample to be tested into the sample chamber of the probe. Set the X-nucleus center transition selectivity 90° pulse width according to the optimized X-nucleus center transition selectivity 90° pulse width in Step 1, and set the number of accumulations and the cycle delay. Use the onepulse pulse sequence to obtain the one-dimensional X-nucleus direct excitation spectrum of the sample to be tested. Step 3: Based on the first modification hill climbing algorithm, optimize the satellite transition selective flip pulse with frequency offset to obtain the LP-opt pulse, and design the LP-opt 5QMAS pulse sequence. The LP-opt 5QMAS pulse sequence includes the layout number transfer enhancement pulse, the first center transition selective excitation pulse, the first LP-opt pulse, the second LP-opt pulse, the second center transition selective excitation pulse, and the third center transition selective excitation pulse in chronological order. Adjust the pulse width of the LP-opt pulse to maximize the peak height or area; based on the optimized 90° pulse width for X-nucleus center transition selectivity in step 1, calculate the pulse widths of the layout number transfer enhancement pulse and the center transition selectivity excitation pulse; based on the accumulation count and cycle delay in step 2, set the accumulation count and cycle delay of the LP-opt 5QMAS pulse sequence, and set the indirect dimension increment step and indirect dimension increment; apply the LP-opt 5QMAS pulse sequence to the sample to be tested, perform a multi-quantum experiment, and obtain the corresponding two-dimensional X-nucleus multi-quantum spectrum.

[0009] As described above, the LP-opt pulse is generated based on the following steps: Step A1: Record the selective flip pulse of the satellite transition with frequency offset as the initial shape pulse, discretize the initial shape pulse to obtain a series of discrete points, and set an upper limit temperature. initial value Set the maximum number of iterations. ; Using the initial shape pulse as the current shape pulse, the number of iterations... The initial value is set to 1, and the current temperature is... The initial value is ; A nuclear spin system model was constructed using spin dynamics to simulate the five-quantum coherent excitation efficiency and spectral signal-to-noise ratio of an LP-opt 5QMAS pulse sequence constructed from pulses of the current shape as LP-opt pulses. Step A2: Based on the preset perturbation pulse sequence length and the length of the perturbation pulse sequence Maximum disturbance amplitude corresponding to each discrete point covered Add a perturbation to the current shape pulse to obtain candidate pulses; Among them, the length of the perturbation pulse sequence The number of discrete points that are perturbed: , in, The total cumulative reward is a preset value, which must satisfy the requirement that the set perturbation pulse sequence length is met during the first iteration. Less than the total number of discrete points included in the current shape pulse; Maximum disturbance amplitude The following requirements must be met: ; Step A3: Construct a nuclear spin system model using spin dynamics to simulate the five-quantum coherent excitation efficiency and spectral signal-to-noise ratio of the LP-opt 5QMAS pulse sequence constructed from candidate pulses as LP-opt pulses; If the evaluation metric of an LP-opt 5QMAS pulse sequence constructed using candidate pulses as LP-opt pulses is better than that of an LP-opt 5QMAS pulse sequence constructed using pulses of the current shape as LP-opt pulses, then: Use the candidate pulse as the new current shape pulse; Reset upper limit temperature : , in, This is the minimum temperature limit value. The rate of temperature drop is the coefficient. This is the temperature limiting factor, when hour, ; In scope Select a random number as the new current temperature ; When the number of iterations and At that time, the number of iterations Add 1, and return to step A2, where The preset threshold; When the number of iterations or The iteration stops when the current shape pulse is reached, and the corresponding current shape pulse is used as the final LP-opt pulse to construct the corresponding LP-opt 5QMAS pulse sequence; If the evaluation metric of the LP-opt 5QMAS pulse sequence constructed from candidate pulses as LP-opt pulses is lower than or equal to the evaluation metric of the LP-opt 5QMAS pulse sequence constructed from pulses of the current shape as LP-opt pulses: The pulse shape remains unchanged; Reset current temperature : , in, For no improvement in iteration count, The counting starting point is the loop iteration corresponding to the most recent round of updating the current shape pulse; When the number of iterations and At that time, the number of iterations Add 1, and return to step A2, where The preset threshold; When the number of iterations or The iteration stops when the current shape pulse is reached, and the corresponding current shape pulse is used as the final LP-opt pulse to construct the corresponding LP-opt 5QMAS pulse sequence; The evaluation index is either the five-quantum coherent excitation efficiency or the spectral line signal-to-noise ratio, or both. A higher five-quantum coherent excitation efficiency, or a higher spectral line signal-to-noise ratio, or both, indicates that the corresponding LP-opt 5QMAS pulse sequence is superior.

[0010] In step A2.1 as described above, When the number of iterations At that time, the index of the point in the disturbance window is randomly selected; When the number of iterations At that time, the score is evaluated based on the defined perturbation location. Select the disturbance window. Among them, the disturbance location evaluation score for: , in, Indicates the index of the discrete point to which the perturbation is performed. Indicates the first The number of historical perturbations at a discrete point For the first The average reward at each discrete point , It is the first The total reward for each discrete point is denoted as the single-point total reward. Each update of the current shape pulse updates the corresponding total reward for each discrete point. When the magnitude of a discrete point is updated once, the corresponding total reward for that single point is... Increment the value by 1. To balance the hyperparameters of exploration and utilization; When the number of iterations The corresponding perturbation window selection rules are as follows: Based on the length of the perturbation pulse sequence All possible combinations of discrete points to be disturbed are pre-selected as pre-selected disturbance windows. The corresponding disturbance locations within these windows are then evaluated using scores. The largest pre-selected perturbation window is used as the perturbation window; if there are more than one pre-selected perturbation window, the perturbation location is evaluated. If all values ​​are the maximum, then a pre-selected perturbation window is randomly chosen as the perturbation window for perturbation.

[0011] As described above, step A2 specifically includes the following steps: Step A2.1: Based on the currently set perturbation pulse sequence length Select the perturbation window, which represents a set of discrete points in the current shape pulse; Step A2.2: Convert the amplitude of the current shape pulse at each discrete point within the selected perturbation window using the perturbation amplitude. Replacement is performed to obtain preliminary candidate pulses. Among them, the disturbance amplitude corresponding to each discrete point in the current disturbance window For range Random values ​​in; Step A2.3: Normalize the amplitude of each discrete point in the preliminary candidate pulse to between 0 and 1 to obtain the candidate pulse.

[0012] As mentioned above, in step 1, the X-nucleus standard sample is a half-integer quadrupole nucleus sample with a nuclear spin quantum number greater than 1 / 2.

[0013] The cyclic delay set in steps 2-3 as described above allows the corresponding free induction attenuation FID signal to fully relax.

[0014] As described in step 3 above, the number of indirect dimension increment steps is set so that the corresponding free induction attenuation FID signal is completely attenuated, and the indirect dimension increment is set to be an integer multiple of the magic angle rotation period.

[0015] As described above, step 3 is performed under high-speed magic angle rotation conditions of not less than 30kHz, and the LP-opt 5QMAS pulse sequence does not require additional RF bias.

[0016] This invention has the following advantages and positive effects: 1. Compared with the traditional single-pulse direct excitation method, the LP-opt 5QMAS pulse sequence designed based on the optimization algorithm adopted in this invention can effectively excite five-quantum coherent signals under low radio frequency power conditions, realize efficient excitation and conversion of multi-quantum coherence, and significantly improve the overall spectral signal intensity.

[0017] 2. Compared to single-pulse excitation, the multi-quantum excitation efficiency of high-power shaped pulses is only about 1.4%. Traditional hard pulse sequences are almost impossible to excite in systems with large quadrupole coupling constants (C0). Q This invention generates an effective signal in a frequency range of approximately 12.1 MHz, and achieves this through low-power optimized pulse design, thus reducing the coupling constant C of the large quadrupole. Q Seeds (such as) 27 The efficient signal excitation of Al significantly improves the signal-to-noise ratio and resolution in large quadrupole interaction systems.

[0018] 3. Traditional frequency-amplitude modulated (FAM) 5QMAS pulse sequences are challenging to optimize, especially for systems with large quadrupole coupling constants. The LP-opt (Low-Power Optimized Pulse) 5QMAS pulse sequence scheme proposed in this invention requires no additional bias parameters and can stably excite multiple quantum signals within a frequency range of ±2 kHz, exhibiting better versatility, repeatability, and experimental stability. Attached Figure Description

[0019] Figure 1 These are schematic diagrams of the hp-5QMAS pulse sequence, FAM-5QMAS pulse sequence, and LP-opt5QMAS pulse sequence.

[0020] Figure 2 It is an aluminum isopropoxide sample. 27 Al spectrum and second-order quadrupole linear fitting. Experimental conditions: magnetic field strength 18.8T, magic angle rotation speed 38kHz. The solid black line represents the spectrum obtained by a single pulse, and the dashed line represents the spectrum obtained by fitting.

[0021] Figure 3 Aluminum isopropoxide samples acquired using hp-5QMAS pulse sequences, FAM-5QMAS pulse sequences, and LP-opt5QMAS pulse sequences. 27 Al5QMAS spectrum. The bottom black solid line in the figure is the one-dimensional X-nucleus direct excitation spectrum of the sample obtained by the onepulse sequence in step 2, where x0.0025 represents the scaling factor of the longitudinal intensity.

[0022] Figure 4Aluminum isopropoxide samples acquired using LP-opt5QMAS pulse sequences at different frequencies 27 Al5QMAS spectrum.

[0023] Figure 5 The changes in the LP-opt5QMAS pulse sequence with RF power and frequency offset are shown in (a) and (b).

[0024] Figure 6 Two-dimensional high-resolution five-quantum magic angle rotating solid-state NMR based on LP-opt5QMAS pulse sequence designed with optimization algorithm 27 Al spectrum. Detailed Implementation

[0025] To facilitate understanding and implementation of the present invention by those skilled in the art, the present invention will be further described in detail below with reference to embodiments. It should be understood that the embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0026] This invention provides a two-dimensional high-resolution solid-state NMR method based on five-quantum excitation enhancement of quadrupole nuclei. This method, by introducing multi-quantum evolution, improves the peak broadening and overlap problems caused by quadrupole interactions in traditional one-dimensional spectra, thereby obtaining higher resolution two-dimensional spectra. 27 In Al nucleus single-quantum spectroscopy experiments, the spectrum often exhibits a broad peak shape due to the quadrupole interaction, making it difficult to distinguish signals from different chemical environments. This invention addresses this by using a two-dimensional high-resolution five-quantum magic angle rotating solid-state NMR pulse method for half-integer quadrupole nuclei designed with an optimization algorithm. This method achieves five-quantum evolution in the indirect dimension of the two-dimensional spectrum, thereby obtaining isotropic chemical shift information and effectively reducing the broadening effect of the quadrupole interaction.

[0027] This invention combines the advantages of multi-quantum coherence methods, overcoming the problems of weak signal and wide spectral linewidth in traditional hard pulse excitation methods in quadrupole nuclear systems. By introducing the LP-opt 5QMAS pulse sequence, not only can efficient excitation of five-quantum coherence be achieved under low power conditions, but also with a large quadrupole coupling constant (C0). Q Even under conditions of approximately 12 MHz, a strong signal can still be obtained, thereby improving the signal-to-noise ratio and resolution of the experiment.

[0028] High-resolution two-dimensional spectroscopy achieved using a five-quantum excitation-enhanced quadrupole two-dimensional high-resolution solid-state NMR method can be effectively applied to solid materials containing quadrupole nuclei (such as... 27Characterizing the microstructure of Al is particularly suitable for studying multiphase systems, amorphous substances, or materials with complex coordination environments. Especially in fields such as aluminum-based molecular sieves, catalysts, and ceramic materials, this method can efficiently distinguish signals from different chemical environments and obtain more accurate structural information.

[0029] Example 1: The four-pole nuclear two-dimensional high-resolution solid-state NMR method based on five-quantum excitation enhancement includes the following steps: Step 1: Instrument configuration and sample preparation.

[0030] To debug the nuclear magnetic resonance spectrometer, place the rotor containing the X-nucleus standard sample into the probe sample chamber, optimize the 90° pulse width for the X-nucleus center transition selectivity to maximize the peak height or area of ​​the X-nucleus, and calibrate the chemical shift value of the peak center of the X-nucleus standard sample.

[0031] In this embodiment, the X-core standard sample (X-core is a half-integer fourth-order nucleus with a nuclear spin quantum number greater than 1 / 2, such as...) 11 B. 27 A solid-state nuclear magnetic resonance rotor (Bruker accessory, hereinafter referred to as the rotor) containing the X-nuclear standard sample was installed. A 1.9mm probe (Bruker accessory, hereinafter referred to as the probe) was mounted on a Bruker Ascend 800 spectrometer for detection. The spectrometer's circuitry and gas path were connected. Topspin software (Bruker software) was run on the spectrometer's computer operating unit to read probe information and confirm the correct connections of the power amplifier, preamplifier, probe coil, and receiver. The rotor containing the X-nuclear standard sample was placed into the probe's sample chamber. The current of each shimming coil was adjusted in the BSMS control panel to ensure a uniform magnetic field within the probe's sample chamber. By adjusting the probe's tuning and matching levers, the probe's input impedance was minimized. At a suitable power, the 90° pulse width for the X-nuclear center transition selectivity was adjusted until the X-nuclear peak height was maximized, obtaining the optimized 90° pulse width for the X-nuclear center transition selectivity. The chemical shift value of the X-nuclear standard sample's peak center was set as a literature reference value. After the measurement was completed, the X-nuclear standard sample was removed, and the rotor was cleaned.

[0032] The spectral peaks in step 1 are obtained by Fourier transform (FT) of the free induction attenuation (FID) signal received by the coil inside the probe. The method for obtaining the spectral peaks described below is the same.

[0033] Step 2: Based on the optimized X-nucleus center transition selectivity 90° pulse width from Step 1, obtain the one-dimensional X-nucleus direct excitation spectrum of the sample to be tested.

[0034] The sample to be tested is loaded into the rotor, and the rotor loaded with the sample to be tested is placed into the sample cavity of the probe. According to the optimized X nucleus center transition selectivity 90° pulse width obtained in step 1, the X nucleus center transition selectivity 90° pulse width is set, and the number of accumulations and the cycle delay are set. The one-dimensional X nucleus direct excitation spectrum of the sample to be tested is obtained using the onepulse pulse sequence and used as a reference.

[0035] The number of accumulations in step 2 is determined by the signal strength (spectral peak height or area) of the corresponding free induction decay FID signal, and the same applies to the following steps; The cyclic delay in step 2 is set according to the corresponding free induction decay FID signal to ensure that the free induction decay FID signal is fully relaxed, and the same applies to the following steps.

[0036] In this embodiment, the experimental conditions for this step are: Bruker 800 M spectrometer with a 1.9 mm diameter rotor and a rotation frequency of 38 kHz. 27 The Al channel (X core) center transition selectivity 90° pulse width is 0.833 µs, the cycle delay is 12.35 ms, and the number of accumulations is 160.

[0037] Step 3: Optimize the satellite transition selective flip pulse with frequency offset using the first-modification hill-climbing algorithm to obtain the LP-opt pulse. Design the LP-opt 5QMAS pulse sequence based on the LP-opt pulse and the center transition selective excitation pulse. Adjust the pulse width of the LP-opt pulse to maximize the spectral peak height or area. Calculate the pulse width of the layout number transfer enhancement pulse and the center transition selective excitation pulse based on the optimized X-nucleus center transition selective 90° pulse width from Step 1. Set the accumulation count and cycle delay corresponding to the LP-opt 5QMAS pulse sequence based on the accumulation count and cycle delay from Step 2, and set the indirect dimension increment step and indirect dimension increment. Apply the LP-opt 5QMAS pulse sequence to the sample under test and perform a multi-quantum experiment on the sample to obtain the corresponding two-dimensional X-nucleus multi-quantum spectrum.

[0038] The LP-opt 5QMAS pulse sequence, in chronological order, includes a placement number transfer enhancement (PT) pulse, a first center transition selective excitation pulse, a first LP-opt pulse (as a multi-quantum excitation pulse), a second LP-opt pulse (as a multi-quantum conversion pulse), a second center transition selective excitation pulse, and a third center transition selective excitation pulse. First, a placement number transfer enhancement (PT) pulse is applied to increase the signal strength of the experimental results. Then, the first center transition selective excitation pulse is applied to excite the initial single-quantum coherent state of the X nucleus spin. Applying the first LP-opt pulse achieves five-quantum excitation, followed by applying the second LP-opt pulse to convert the excited five-quantum state back to a single-quantum coherent state. Then, applying the second center transition selective excitation pulse transforms the single-quantum coherent state into a zero-quantum state. Finally, after applying the third center transition selective excitation pulse, sampling is performed to obtain the spectrum of the LP-opt 5QMAS pulse sequence. The widths of the three applied center transition selective excitation pulses are calculated based on the optimized 90° center transition selective pulse width of the X nucleus in step 1. In this embodiment, the center transition selective excitation pulses are selected as 90° center transition selective pulses, and the onepulse spectrum in step 2 is used for comparison. In the LP-opt 5QMAS pulse sequence implementation, the shape-optimized pulse (LP-opt) is automatically optimized and generated by an optimization algorithm from the satellite transition selective flip pulse with frequency offset, which can achieve uniform excitation within a frequency range of ±2 kHz.

[0039] The LP-opt pulse designed in this invention differs from traditional pulses by using a time-dependent radio frequency to construct the pulse, and then continuously optimizing it to construct a more efficient pulse. This method can effectively excite higher-order quantum transitions that are difficult to excite using traditional rectangular pulses and fast amplitude modulation (FAM) pulse methods. It is particularly effective for exciting high-order quantum transitions caused by the large nuclear quadrupole interaction constant (C0) resulting from local structural asymmetry. Q For nuclear spin systems, this method exhibits excellent five-quantum excitation efficiency in 5QMAS experiments. The optimized construction idea is introduced as follows: The LP-opt pulse generation optimization algorithm is based on the First-Choice Hill Climbing algorithm. It uses the selective flip pulse of the satellite transition with frequency offset as the initial shape pulse, generates perturbations, and iterates. Spin dynamics simulation is used to evaluate the LP-opt 5QMAS pulse sequence formed by the perturbed shape pulse. If the evaluation of the LP-opt 5QMAS pulse sequence formed by the perturbed shape pulse is better than that of the LP-opt 5QMAS pulse sequence formed by the unperturbed shape pulse, it is immediately accepted. Simultaneously, annealing-style perturbation intensity attenuation is used to accelerate the iteration process. Borrowing the temperature attenuation concept from simulated annealing (SA), an upper temperature limit is set. The current temperature, with the disturbance gradually weakening due to no improvement exploration. ( =0~1.0), thereby controlling the size or amplitude of each perturbation. Based on spin dynamics simulation evaluation, after receiving a new perturbation and shape pulse, the upper limit temperature is immediately reset. The next round of perturbation and simulation calculations will then be performed, specifically including the following steps: Step A1: Record the selective flip pulse of the satellite transition with frequency offset as the initial shape pulse, discretize the initial shape pulse to obtain a series of discrete points, and set an upper limit temperature. initial value Set the maximum number of iterations. ; Using the initial shape pulse as the current shape pulse, the number of iterations... The initial value is set to 1, and the current temperature is... The initial value is ; A nuclear spin system model was constructed using spin dynamics to simulate the five-quantum coherent excitation efficiency and spectral signal-to-noise ratio of an LP-opt 5QMAS pulse sequence constructed from pulses of the current shape as LP-opt pulses. In this embodiment, the above modeling and simulation process was performed using the spin dynamics software Simpson.

[0040] Step A2: Based on the preset perturbation pulse sequence length and the length of the perturbation pulse sequence Maximum disturbance amplitude corresponding to each discrete point covered Add a perturbation to the current shape pulse to obtain candidate pulses; Among them, the length of the perturbation pulse sequence This represents the number of discrete points subjected to perturbation; these discrete points can be discontinuous. , in, The total cumulative reward is a preset value, which must satisfy the requirement that the set perturbation pulse sequence length is met during the first iteration. Less than the total number of discrete points included in the current shape pulse.

[0041] Maximum disturbance amplitude The following requirements must be met: , Step A2 specifically includes the following steps: Step A2.1: Based on the currently set perturbation pulse sequence length Select the perturbation window. The perturbation window represents a set of discrete points in the current shape pulse. Different perturbation windows represent different sets of discrete points. Step A2.2: Convert the amplitude of the current shape pulse at each discrete point within the selected perturbation window using the perturbation amplitude. Replacement is performed to obtain preliminary candidate pulses. Among them, the disturbance amplitude corresponding to each discrete point in the current disturbance window For range Random values ​​in; Step A2.3: Normalize the amplitude of each discrete point in the preliminary candidate pulse to between 0 and 1 to obtain the candidate pulse.

[0042] Step A3: Construct a nuclear spin system model using spin dynamics to simulate the five-quantum coherent excitation efficiency and spectral signal-to-noise ratio of the LP-opt 5QMAS pulse sequence constructed from candidate pulses as LP-opt pulses; If the evaluation metrics of an LP-opt 5QMAS pulse sequence constructed from candidate pulses as LP-opt pulses are superior to those of an LP-opt 5QMAS pulse sequence constructed from pulses of the current shape as LP-opt pulses: 1) Receive optimal solution: Use the candidate pulse as the new current shape pulse; 2) Reset the upper limit temperature To make the upper limit temperature Decrease with iteration count to reduce invalid exploration: , in, This is the minimum temperature limit value. The rate of temperature drop is the coefficient. Temperature limit coefficient, temperature limit coefficient Used to ensure the upper limit temperature during the first iteration. (correspond It still meets the range of the "temperature" parameter, that is... ; 3) After accepting the optimal solution, within the range Select a random number as the new current temperature ; 4) When the number of iterations and At that time, the number of iterations Add 1, and return to step A2, where The preset threshold; When the number of iterations or The iteration stops when the current shape pulse is reached, and the corresponding current shape pulse is used as the final LP-opt pulse to construct the corresponding LP-opt 5QMAS pulse sequence.

[0043] The evaluation index is either the five-quantum coherent excitation efficiency or the spectral signal-to-noise ratio, or both. In this embodiment, the five-quantum coherent excitation efficiency is selected. When the five-quantum coherent excitation efficiency is higher, or the spectral signal-to-noise ratio is higher, or both the five-quantum coherent excitation efficiency and the spectral signal-to-noise ratio are higher, it indicates that the corresponding LP-opt 5QMAS pulse sequence is better, that is, it indicates that the corresponding LP-opt pulse is better.

[0044] If the evaluation metric of the LP-opt 5QMAS pulse sequence constructed from candidate pulses as LP-opt pulses is lower than or equal to the evaluation metric of the LP-opt 5QMAS pulse sequence constructed from pulses of the current shape as LP-opt pulses, it indicates no improvement. 1) Maintain the current pulse shape; 2) Regarding the current temperature To mitigate disturbances, attenuation is employed, with a preference for obtaining optimal solutions with smaller improvements. , in, For no improvement in iteration count, The counting starting point is the most recent iteration corresponding to the current shape pulse update, such as: after the current shape pulse is updated... If the current shape pulse remains unchanged during subsequent iterations, then The value is incremented by 1 accordingly until the current shape pulse is updated again, at which point it is incremented again. .

[0045] As the iteration continues without improvement, the current temperature The length of the perturbation pulse sequence is continuously reduced. and the maximum amplitude of random disturbances It is also constantly weakening; 3) When the number of iterations and At that time, the number of iterations Add 1 and return to step A2; When the number of iterations or The iteration stops when the current shape pulse is reached, and the corresponding current shape pulse is used as the final LP-opt pulse to construct the corresponding LP-opt 5QMAS pulse sequence.

[0046] Furthermore, to improve the probability of generating a superior solution, in step A2.1 of this invention, when the number of iterations... At that time, the index of the discrete point in the perturbation window is randomly selected; when the number of iterations... At that time, the score is evaluated based on the defined perturbation location. The perturbation window is selected to guide the perturbation to the optimal position, so that the perturbation position is not random.

[0047] Among them, the disturbance location evaluation score for: , in, Indicates the index of the discrete point to which the perturbation is performed. Indicates the first The number of historical perturbations at a discrete point For the first The average reward at each discrete point , It is the first The total reward for each discrete point is denoted as the single-point total reward. Each update of the current shape pulse updates the corresponding total reward for each discrete point. When the magnitude of a discrete point is updated once, the corresponding total reward for that single point is... Increment the value by 1. To balance the hyperparameters of exploration and utilization.

[0048] When the number of iterations The corresponding perturbation window selection rules are as follows: Based on the length of the perturbation pulse sequence All possible combinations of discrete points to be disturbed are pre-selected as pre-selected disturbance windows. The corresponding disturbance locations within these windows are then evaluated using scores. The largest pre-selected perturbation window is used as the perturbation window; if there are more than one pre-selected perturbation window, the perturbation location is evaluated. If all values ​​are the maximum, then a pre-selected perturbation window is randomly chosen as the perturbation window for perturbation.

[0049] The first perturbation uses a perturbation window based on the currently set perturbation pulse sequence length. Randomly generated, scores are evaluated based on the location of the disturbance. The definition prioritizes the use of discrete points in historically highly rated regions, while also... The term retains the exploration of perturbations for discrete points in the underperturbed region.

[0050] Step 3 is performed under high-speed magic angle rotation (MAS) conditions of not less than 30kHz, and the LP-opt 5QMAS pulse sequence does not require additional RF bias.

[0051] In this embodiment, the experimental conditions for step 3 are: a 1.9mm diameter rotor on a Bruker 800M spectrometer, with a rotation frequency of 38kHz. For the LP-opt 5QMAS pulse sequence, 27 The Al channel multi-quantum pulse power is 125 kHz. At this power, the multi-quantum pulse width and multi-quantum conversion pulse width are both the rotation period (26.32 μs), requiring no optimization. 27 The Al channel center transition selectivity 90° pulse width 10 µs, cycle delay 12.35 ms, and accumulation count 6400 times. To study the efficiency of LP-opt pulse power in 5-quantum excitation and conversion, maximum RF power was set at 135, 125, and 70 kHz. For the 2D LP-opt 5QMAS experiment, 256 linear sampling points were set in the indirect dimension, with an interval of 13.1625 μs between each sampling point.

[0052] The LP-opt 5QMAS pulse sequence used in this invention is a multi-quantum sequence, which can obtain two-dimensional high-resolution spectra. The principle is as follows: For spin quantum number long-term Hamiltonian for: , Under magic angle rotation, spin quantum number Evolutionary phase ( , (where the spin coherence order is): , in, Represents the spin quantum number The evolution phase, , These represent the first-order and second-order perturbation terms of the quadrupole interaction, respectively; It is the precession frequency; It is the resonance offset (unit: parts per million ppm). Represents the magnetic order number. It is the spin quantum number With another magnetic order number spin quantum number scalar coupling constant between them; It is the dependence of non-quadripolar anisotropic interactions on the orientation of the quadrupole tensor, which can be described by additional Euler angles (i.e. polar angles); , All are polar angles. and The static magnetic field in the EFG tensor principal axis system is determined. direction, Represents the spin angular momentum operator Quantity; , It is the expansion coefficient of the quadrupole interaction; It is the asymmetry factor of the quadrupole interaction; , It is the spin quantum number and spin coherence order Relevant coefficients; It is a fourth-order Legendre polynomial; It is the cosine value at the magic angle; It is the spin quantum number; It's time.

[0053] Two-dimensional experiments will indirectly change time. and direct dimension time When correlated, the various isotropic echoes are: , The ratio in the formula : , It can be seen that for 27 Al core, The echo will Generated at the location.

[0054] The working principle of the LP-opt 5QMAS pulse sequence is as follows: 1) The spin system is excited by a selective excitation pulse of the first central transition, causing the density matrix to change from... Stimulated Stimulate and create coherent states.

[0055] 2) Then, using the first LP-opt pulse, the Hamiltonian of a pulse of arbitrary frequency in the experimental coordinate system at this point. It can be written as: , in, The Larmor frequency of spin precession in a radio frequency magnetic field. It is the frequency of the rotating coordinate system. It is time. Represents the pulse phase. They represent along axis, axis, The spin angular momentum operator along the axis; where the direction of the static magnetic field is... Axial direction, Axial direction and The axial direction is with Two mutually orthogonal directions that are perpendicular to each other along an axis.

[0056] When a spin system is simultaneously subjected to the Zeeman effect and a pulse, consider a frequency of... For a rotating coordinate system, we have: , Indicates Hermitian conjugation; The Hamiltonian representing the Zeeman action has a magnitude of ; The total Hamiltonian in the rotating coordinate system can be obtained as: , Frequency of the rotating coordinate system Larmor precession frequency under static magnetic field The difference. Subsequent derivations all use pulses applied to... direction( For example, ( ).

[0057] In the above equation, the Larmor frequency of the spin precession in the radio frequency magnetic field is... , in, It is the gyromagnetic ratio. It is pulse power. It is a time-dependent function; After the first LP-opt pulse is applied, five quantum state selection is performed simultaneously, and at this point there are four paths: =6, 4, -4, -6 ( (This represents the difference in quantum state order before and after the five-quantum-state selection). A new density matrix is ​​obtained. It meets the following conditions: , , in, It is an indirect dimension time; It satisfies the conditions of the BCH corollary, representing the frequency intensity of the corresponding pulse sequence process, the magnitude of which satisfies ; , These are the coherence orders of: , The density matrix below; 3) Next, the second LP-opt pulse is executed, and single quantum state selection is performed. At this point, there are 4 paths, namely... =6, 4, -4, -6, ( The density matrix of a single quantum state is obtained by representing the difference in quantum state order before and after single quantum state selection. : , 4) Then, a second central transition selective excitation pulse is applied to transform the single quantum coherent state into a zero quantum state, corresponding to the path... = ; This represents the difference in quantum state order before and after the selective excitation pulse of the second central transition; 5) Finally, a third center transition selective excitation pulse is applied to obtain the final detection coherent state with a quantum state of -1, i.e., the path. ; This represents the difference in quantum state order before and after the selective excitation pulse of the third center transition.

[0058] Example 2 Based on the quadrupole two-dimensional high-resolution solid-state NMR method based on five-quantum excitation enhancement described in Example 1, the method further includes: Step 4: Considering the influence of pulse sequences on the spectrum, this step focuses on the different effects of the low-power shaped pulse (LP-opt) of this invention and existing technology pulses on the experiment.

[0059] Based on the type of pulse sequence, the pulse widths of the excitation and conversion in the X-nucleus multi-quantum experiment are adjusted to maximize the peak height or area, at which point the multi-quantum coherent transfer efficiency reaches its optimal state. Next, the pulse width for low-power center transition (CT) selective excitation is calculated based on the optimized 90° pulse width for X-nucleus center transitions from step 1. Finally, using the optimized low-power center transition (CT) selective excitation pulse width, and setting the number of accumulations, cycle delay, indirect dimension increment steps, and indirect dimension increment, the corresponding optimized pulse sequence is applied to the X-nucleus sample to perform a multi-quantum experiment, obtaining a one-dimensional X-nucleus multi-quantum spectrum. For the hard pulse (hp) 5QMAS pulse sequence: First, a first hard pulse (as a multi-quantum excitation pulse) is applied to excite the five-quantum coherence of the X nucleus spin. Then, a second hard pulse (as a multi-quantum conversion pulse) is applied to convert the spin of the X nucleus sample to zero quantum coherence. Finally, a center transition selective excitation pulse is applied and then sampled to obtain the one-dimensional X nucleus multi-quantum spectrum of the hp5QMAS pulse sequence.

[0060] For the fast amplitude modulation (fam) 5QMAS pulse sequence: First, a hard pulse is applied to excite the initial single quantum coherence of the X nucleus spin. Then, the first set of fast amplitude modulation (fam) pulses (as multi-quantum excitation pulses) is applied and repeated N times to excite the five quantum states. Then, the excited five quantum states are converted to the zero quantum state by the second set of fast amplitude modulation (fam) pulses (as multi-quantum conversion pulses). Finally, after applying the center transition selective excitation pulse, sampling is performed to obtain the one-dimensional X nucleus multi-quantum spectrum of the FAM 5QMAS pulse sequence.

[0061] Step 4 is performed under high-speed magic angle rotation (MAS) conditions of not less than 30 kHz; The number of indirect dimension increment steps in steps 3-4 is a set value to ensure that the corresponding free induction attenuation FID signal is completely attenuated; The indirect dimension increment in steps 3-4 is an integer multiple of the magic angle rotation period to improve the side strip folding problem; In step 4, when the free induction attenuation FID signal undergoes a two-dimensional Fourier transform, the indirect dimension is processed using the phase-sensitive spectrum method.

[0062] In this embodiment, the experimental conditions for this step are: Bruker 800 M spectrometer with a 1.9 mm diameter rotor and a rotation frequency of 38 kHz. For the hp 5QMAS pulse sequence, 27 The Al channel multi-quantum pulse frequency is 125 kHz, at which the multi-quantum excitation pulse width and multi-quantum conversion pulse width are 4.5 µs and 1.7 µs, respectively.27 Al channel center transition selectivity 90° pulse width 10 µs; cyclic delay 12.35 ms, accumulation count 6400. For fam 5QMAS pulse sequence, 27 The Al channel multi-quantum pulse frequency is 125 kHz, at which the multi-quantum excitation pulse width and multi-quantum conversion pulse width are 4.5 µs and 0.8 µs, respectively. 27 Al channel center transition selectivity 90° pulse width 10 µs; cyclic delay 12.35 ms, accumulation count 6400 times.

[0063] The LP-opt 5QMAS pulse sequence designed in this invention is as follows: Figure 1 As shown, the X nucleus is excited by a multi-quantum LP-opt 5QMAS pulse sequence, and then the pulse is converted into a single quantum transition for sampling.

[0064] like Figure 2 As shown, this invention uses onepulse spectra as the basis for NMR structure analysis. The NMR parameters of the samples in the embodiments of this invention are obtained through peak fitting, which facilitates subsequent spectrum comparison experiments.

[0065] like Figure 3 As shown, one-pulse spectra are used as the basis for NMR structure analysis. By comparing the three pulse sequences involved in this invention at the maximum frequency RF... max The spectrum at 125 kHz was analyzed. Hard pulses are almost unable to excite species signals with large quadrupole coupling constants, and the amplitude modulation fam is difficult to optimize. The optimized shape pulse can effectively excite large C signals. Q Species 5 quantum coherence.

[0066] like Figure 4 As shown, using onepulse spectra as the basis for NMR result analysis, the performance comparison of LP-opt pulses at different frequencies is presented. With the maximum frequency RF... max With the increase of [value], the signal strength was significantly improved, exhibiting a clear peak shape, indicating that the LP-opt 5QMAS pulse sequence can achieve [performance] at low frequencies. 27 Significant excitation of Al multiple quantum signals.

[0067] like Figure 5As shown, the optimized LP-opt pulse sequence of this invention can effectively excite signals within a ±2kHz range without the need for RF bias settings. This characteristic eliminates the need for RF bias optimization, making the experiment simpler and more efficient. It also ensures that even with slight frequency shifts or resonant frequency changes, the experiment maintains good signal strength and consistency, thereby improving the stability and reliability of the experimental results. Furthermore, it greatly simplifies the experimental setup process, avoiding the tedious operation of frequently adjusting bias values ​​under different samples or experimental conditions, significantly improving experimental efficiency, and maintaining high stability and adaptability to different sample / experimental settings.

[0068] like Figure 6 As shown, the two-dimensional high-resolution solid-state NMR spectrum of the quadrupole nucleus based on five-quantum excitation enhancement of the present invention demonstrates that effective elimination of broadening is achieved in the indirect dimension, thereby improving the resolution of the spectrum.

[0069] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A two-dimensional high-resolution solid-state NMR method based on five-quantum excitation-enhanced quadrupole nuclei, characterized in that, Includes the following steps: Step 1: Adjust the nuclear magnetic resonance spectrometer. Place the rotor containing the X-nucleus standard sample into the probe sample chamber and optimize the 90° pulse width for the X-nucleus center transition selectivity to maximize the peak height or area of ​​the X-nucleus. Then, calibrate the chemical shift value of the peak center of the X-nucleus standard sample. Step 2: Place the rotor containing the sample to be tested into the sample chamber of the probe. Set the X-nucleus center transition selectivity 90° pulse width according to the optimized X-nucleus center transition selectivity 90° pulse width in Step 1, and set the number of accumulations and the cycle delay. Use the onepulse pulse sequence to obtain the one-dimensional X-nucleus direct excitation spectrum of the sample to be tested. Step 3: Based on the first modification hill climbing algorithm, optimize the satellite transition selective flip pulse with frequency offset to obtain the LP-opt pulse, and design the LP-opt 5QMAS pulse sequence. The LP-opt 5QMAS pulse sequence includes the layout number transfer enhancement pulse, the first center transition selective excitation pulse, the first LP-opt pulse, the second LP-opt pulse, the second center transition selective excitation pulse, and the third center transition selective excitation pulse in chronological order. Adjust the pulse width of the LP-opt pulse to maximize the peak height or area; based on the optimized 90° pulse width of the X nucleus center transition selectivity in step 1, calculate the pulse width of the layout number transfer enhancement pulse and the center transition selectivity excitation pulse; based on the accumulation count and cycle delay in step 2, set the accumulation count and cycle delay of the LP-opt 5QMAS pulse sequence, and set the indirect dimension increment step and indirect dimension increment. By applying an LP-opt 5QMAS pulse sequence to the sample under test, a multi-quantum experiment was conducted to obtain the corresponding two-dimensional X-nucleus multi-quantum spectrum.

2. The two-dimensional high-resolution solid-state NMR method based on five-quantum excitation enhancement of quadrupole nuclei according to claim 1, characterized in that, The LP-opt pulse is generated based on the following steps: Step A1: Record the selective flip pulse of the satellite transition with frequency offset as the initial shape pulse, discretize the initial shape pulse to obtain a series of discrete points, and set an upper limit temperature. initial value ; Set the maximum number of iterations. ; Using the initial shape pulse as the current shape pulse, the number of iterations... The initial value is set to 1, and the current temperature is... The initial value is ; A nuclear spin system model was constructed using spin dynamics to simulate the five-quantum coherent excitation efficiency and spectral signal-to-noise ratio of an LP-opt 5QMAS pulse sequence constructed from pulses of the current shape as LP-opt pulses. Step A2: Based on the preset perturbation pulse sequence length and the length of the perturbation pulse sequence Maximum disturbance amplitude corresponding to each discrete point covered Add a perturbation to the current shape pulse to obtain candidate pulses; Among them, the length of the perturbation pulse sequence The number of discrete points that are perturbed: ， in, The total cumulative reward is a preset value, which must satisfy the requirement that the set perturbation pulse sequence length is met during the first iteration. Less than the total number of discrete points included in the current shape pulse; Maximum disturbance amplitude The following requirements must be met: ； Step A3: Construct a nuclear spin system model using spin dynamics to simulate the five-quantum coherent excitation efficiency and spectral signal-to-noise ratio of the LP-opt 5QMAS pulse sequence constructed from candidate pulses as LP-opt pulses; If the evaluation metric of an LP-opt 5QMAS pulse sequence constructed using candidate pulses as LP-opt pulses is better than that of an LP-opt 5QMAS pulse sequence constructed using pulses of the current shape as LP-opt pulses, then: Use the candidate pulse as the new current shape pulse; Reset upper limit temperature : ， in, This is the minimum temperature limit value. The rate of temperature drop is the coefficient. This is the temperature limiting factor, when hour, ; In scope Select a random number as the new current temperature ; When the number of iterations and At that time, the number of iterations Add 1, and return to step A2, where The preset threshold; When the number of iterations or The iteration stops when the current shape pulse is reached, and the corresponding current shape pulse is used as the final LP-opt pulse to construct the corresponding LP-opt 5QMAS pulse sequence; If the evaluation metric of the LP-opt 5QMAS pulse sequence constructed from candidate pulses as LP-opt pulses is lower than or equal to the evaluation metric of the LP-opt 5QMAS pulse sequence constructed from pulses of the current shape as LP-opt pulses: The pulse shape remains unchanged; Reset current temperature : ， in, For no improvement in iteration count, The counting starting point is the loop iteration corresponding to the most recent round of updating the current shape pulse; When the number of iterations and At that time, the number of iterations Add 1, and return to step A2, where The preset threshold; When the number of iterations or The iteration stops when the current shape pulse is reached, and the corresponding current shape pulse is used as the final LP-opt pulse to construct the corresponding LP-opt 5QMAS pulse sequence; The evaluation index is either the five-quantum coherent excitation efficiency or the spectral line signal-to-noise ratio, or both. A higher five-quantum coherent excitation efficiency, or a higher spectral line signal-to-noise ratio, or both, indicates that the corresponding LP-opt 5QMAS pulse sequence is superior.

3. The two-dimensional high-resolution solid-state NMR method based on five-quantum excitation enhancement of quadrupole nuclei according to claim 2, characterized in that, In step A2.1, When the number of iterations At that time, the index of the point in the disturbance window is randomly selected; When the number of iterations At that time, the score is evaluated based on the defined perturbation location. Select the disturbance window. Among them, the disturbance location evaluation score for: ， in, Indicates the index of the discrete point to which the perturbation is performed. Indicates the first The number of historical perturbations at a discrete point For the first The average reward at each discrete point , It is the first The total reward for each discrete point is denoted as the single-point total reward. Each update of the current shape pulse updates the corresponding total reward for each discrete point. When the magnitude of a discrete point is updated once, the corresponding total reward for that single point is... Increment the value by 1. To balance the hyperparameters of exploration and utilization; When the number of iterations The corresponding perturbation window selection rules are as follows: Based on the length of the perturbation pulse sequence All possible combinations of discrete points to be disturbed are pre-selected as pre-selected disturbance windows. The corresponding disturbance locations within these windows are then evaluated using scores. The largest pre-selected perturbation window is used as the perturbation window; if there are more than one pre-selected perturbation window, the perturbation location is evaluated. If all values ​​are the maximum, then a pre-selected perturbation window is randomly chosen as the perturbation window for perturbation.

4. The two-dimensional high-resolution solid-state NMR method based on five-quantum excitation enhancement of quadrupole nuclei according to claim 2, characterized in that, Step A2 specifically includes the following steps: Step A2.1: Based on the currently set perturbation pulse sequence length Select the perturbation window, which represents a set of discrete points in the current shape pulse; Step A2.2: Convert the amplitude of the current shape pulse at each discrete point within the selected perturbation window using the perturbation amplitude. Replacement is performed to obtain preliminary candidate pulses. Among them, the disturbance amplitude corresponding to each discrete point in the current disturbance window For range Random values ​​in; Step A2.3: Normalize the amplitude of each discrete point in the preliminary candidate pulse to between 0 and 1 to obtain the candidate pulse.

5. The two-dimensional high-resolution solid-state NMR method based on five-quantum excitation enhancement of quadrupole nuclei according to claim 1, characterized in that, In step 1, the X-nucleus standard sample is a half-integer quadrupole nucleus sample with a nuclear spin quantum number greater than 1 / 2.

6. The two-dimensional high-resolution solid-state NMR method based on five-quantum excitation enhancement of quadrupole nuclei according to claim 1, characterized in that, The cyclic delay set in steps 2-3 allows the corresponding free induction attenuation FID signal to fully relax.

7. The two-dimensional high-resolution solid-state NMR method based on five-quantum excitation enhancement of quadrupole nuclei according to claim 1, characterized in that, In step 3, the number of indirect dimension increment steps is set so that the corresponding free induction attenuation FID signal is completely attenuated, and the indirect dimension increment is set to be an integer multiple of the magic angle rotation period.

8. The two-dimensional high-resolution solid-state NMR method based on five-quantum excitation enhancement of quadrupole nuclei according to claim 1, characterized in that, Step 3 is performed under high-speed magic angle rotation conditions of not less than 30kHz, and the LP-opt 5QMAS pulse sequence does not require additional RF bias.

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