CN103472420A - Method for obtaining high resolution nuclear magnetic resonance heteronuclear spectrogram in unknown spatial distribution magnetic field - Google Patents

Abstract

The invention relates to a method for obtaining a high-resolution nuclear magnetic resonance heteronuclear spectrum under an unknown spatially distributed magnetic field, involving nuclear magnetic resonance. According to the experimental requirements, it is judged whether the signal-to-noise ratio is the priority or the sampling efficiency is the priority. If the signal-to-noise ratio is the priority, use the three-dimensional sampling mode; if the sampling efficiency is the priority, use the spatial codec sampling mode; Store the experimental data after the end; process the stored experimental data, if the experimental data used is obtained by the three-dimensional sampling mode, then construct the experimental data into a three-dimensional time-domain matrix, and only need to perform a three-dimensional Fourier transform on the matrix. Obtain the experimental spectrogram; if the data used is obtained by the spatial codec sampling mode, first divide each data string with a length of np points into np1×N _D , and then form a three-dimensional matrix with the indirect F3 dimension, only for three-dimensional The F2 and F3 dimensions of the matrix are Fourier transformed to obtain a high-resolution NMR heteronuclear spectrum.

Description

A Method for Acquiring High-Resolution NMR Heteronuclear Spectra with Unknown Spatial Magnetic Field Distribution

technical field

The invention relates to nuclear magnetic resonance (NMR, Nuclear Magnetic Resonance), in particular to a method for obtaining a high-resolution nuclear magnetic resonance heteronuclear spectrum under an unknown spatially distributed magnetic field.

Background technique

NMR has become one of the most effective and widely used detection methods. Today, structural elucidation of complex organic molecules relies heavily on proton-detecting heteronuclear NMR techniques. Among these technologies, heteronuclear single quantum coherence HSQC (Heteronuclear Singular Quantum Correlation), heteronuclear multiple quantum coherence HMQC (Heteronuclear Multiple Quantum Correlation), and heteronuclear multiple bond correlation HMBC (Heteronuclear Multiple Bond Correlation) are the most important 2D NMR methods. HSQC and HMQC are related spectra connected directly by chemical bonds, while HMBC is related spectra connected by chemical bonds separated by more than one bond. The early two-dimensional heteronuclear correlation experiments were to directly observe insensitive nuclei such as ¹³ C and ¹⁵ N, and obtain information about their coupling with ¹ H. However, because the natural abundance of ¹³ C and ¹⁵ N is extremely low, and the NMR signal is very weak, it is very difficult to measure the one-dimensional spectrum. It needs to be accumulated many times, and it takes longer to obtain a two-dimensional spectrum, which seriously affects the heteronuclear spectrum. Wide application of two-dimensional spectroscopy. The proposal of trans-detection heteronuclear two-dimensional correlation spectroscopy experiments, such as the heteronuclear multiple quantum coherence HMQC experiment, replaced the earlier heteronuclear correlation spectroscopy (HETCOR) experiment. The HMQC experiment observes the ¹ H free induction decay FID (FreeInduction Decay) signal, and indirectly observes the chemical shift of the insensitive nucleus through internuclear coupling. Compared to HETCOR experiments recording insensitive nuclear FID, the signal-to-noise ratio is greatly improved. The maximum sensitivity of NMR trans detection is (γ _H ) ^5/2 , the magnetic gyro ratio γ _H of ¹ H is about 4 times that of ¹³ C γ _C , (γ _H ) ^5/2 : (γ _C ) ^{5 /2} = 32, so the HMQC experiment detects that the correlation signal is enhanced by 32 times. Nowadays, the most commonly used heteronuclear two-dimensional spectra are HSQC, HMQC and HMBC, usually ¹³ C- ¹ H coupling systems, and ¹⁵ N- ¹ H, ²⁹ Si- ¹ H systems are also widely used.

In recent years, Magnetic Resonance Imaging (MRI, Magnetic Resonance Imaging) has made amazing developments in aspects such as morphology, function and metabolism. Whether it is an inanimate solid, liquid, or organic life, most applications rely on a highly uniform static magnetic field B ₀ with a spatial variation rate of less than 10 ^-9 . Therefore, slight differences in the surrounding environment of different nuclei can lead to significantly different chemical shifts and coupling information. However, a highly uniform field under ideal conditions is usually unattainable. For example, in ex-situ NMR experiments, the research object is placed outside the magnet ^[1,2] ; in impedance high-field or using a hybrid magnet ^{[3, 4]} ; samples (including animals and humans) have motions such as pulsation or breathing, not to mention magnetic field inhomogeneities introduced by air gaps and surgical implants ^[5,6] . Many methods have been proposed for obtaining high-resolution spectra. The spin echo method ^[7,8] can refocus inhomogeneous fields to obtain coupling information to generate echo modulation ^[9-11] . If the spatial distribution of the field pattern is known, a designed matching RF field can be used to cancel the inhomogeneous field. There are two ways to achieve this: the first method is to design the RF field B ₁ (r) to match B ₀ (r) ^[12-14] , and the phase shift of the RF field can be corrected by the B ₀ field; the second method refers to The single-scan experiment method ^[15,16] uses the known gradient field to compensate the phase of the magnetization vector of different voxels to achieve the purpose of eliminating the inhomogeneous field. In both approaches the inhomogeneous field has to be time-independent and its spatial distribution must be known, which becomes a big hurdle. Pelupessy et al. ^[17] proposed to obtain a high-resolution spectrum under an inhomogeneous field by tracking the precession frequency difference between two different spins in a single scan ^[18,19] .

Based on the dipole field modulation technique, the effect of the inhomogeneous field is eliminated by tracking the precession frequency of the spins through the long-range dipole interaction between different molecular spins. In general, the dipole correlation distance (usually 10-100 μm) is much smaller than the size of the sample, and the magnetic field within the dipole correlation distance is relatively uniform, which has little influence on the signal line width. Therefore, iMQC has the advantages of inhomogeneous field high resolution spectrum Attractive application prospects.

references:

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[4]Boaz Shapira, Kiran Shetty, William W Brey, et al.Single-scan2D NMR spectroscopy ona25T bitter magnet[J].Chemical Physics Letters,2007,442(4):478-482.

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[6]Carolyn E Mountford, Sinead Doran, Cynthia L Lean, et al.Proton MRS can determine the pathology of human cancers with a high level of accuracy[J].Chemical Reviews,2004,104(8):3677-3704.

[7]Erwin L Hahn.Spin echoes[J].Physical Review,1950,80(4):580.

[8]Herman Y Carr and Edward M Purcell.Effects of diffusion on free precipitation in nuclear magnetic resonance experiments[J].Physical Review,1954,94(3):630.

[9] EL Hahn and DE Maxwell.Spin echo measurements of nuclear spin coupling in molecules[J].Physical Review,1952,88(5):1070.

[10]RL Vold and SO Chan.Modulated spin echo trains from liquid crystals[J].The Journal of Chemical Physics,1970,53(1):449-451.

[11]Ray Freeman and HDW Hill.High-resolution study of NMR spin echoes: "J spectrum"[J].The Journal of Chemical Physics,1971,54:301-313.

[12] Carlos A Meriles, Dimitris Sakellariou, Henrike Heise, et al. Approach to high-resolution ex situ NMR spectroscopy [J]. Science, 2001, 293(5527): 82-85.

[13] Juan Perlo, Vasiliki Demas, Federico Casanova, et al. High-resolution NMRspectroscopy with a portable single-sided sensor [J]. Science, 2005, 308(5726): 1279-1279.

[14] Vasiliki Demas, Carlos Meriles, Dimitris Sakellariou, et al. Toward ex situation-encoded spectroscopic imaging [J]. Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering, 2006,29(3):137-144.

[15]Boaz Shapira and Lucio Frydman.Spatial encoding and the acquisition of high-resolution NMR Spectra in inhomogeneous magnetic fields[J].Journal of The American Chemical Society,2004,126(23):7184-7185.

[16]B.Shapira and L.Frydman.Spatially encoded pulse sequences for the acquisition of high resolution NMR spectrum in inhomogeneous fields[J].Journal of Magnetic Resonance,2006,182(1):12-21.

[17]P.Pelupessy,E.Rennella and G.Bodenhausen.High-resolution NMR in magneticfields with unknown spatialtemporal variations[J].Science,2009,324(5935):1693-7.

[18]A Wokaun and Richard R Ernst.Selective detection of multiple quantum transitions inNMR by two-dimensional spectroscopy[J].Chemical Physics Letters,1977,52(3):407-412.

[19] K Nagayama, K Wüthrich and RR Ernst. Two-dimensional spin echo correlated spectroscopy (SECSY) for ¹ H NMR studies of biological macromolecules [J]. Biochemical and Biophysical Research Communications, 1979, 90(1): 305-311.

Contents of the invention

The purpose of the present invention is to provide a method for obtaining high-resolution nuclear magnetic resonance heteronuclear spectra under an unknown spatially distributed magnetic field that can eliminate the influence of magnetic field inhomogeneity in magnetic resonance detection, thereby improving the resolution of the spectra.

The present invention comprises the following steps:

1) Determine whether the signal-to-noise ratio or the sampling efficiency is prioritized according to the experimental requirements. If the signal-to-noise ratio is prioritized, use the three-dimensional sampling mode; if the sampling efficiency is prioritized, use the spatial codec sampling mode;

2) Set sequence parameters;

3) Sample the sample after completing the sequence parameter setting, and store the experimental data after sampling;

4) Process the stored experimental data. If the experimental data used is obtained by the three-dimensional sampling mode, the experimental data is constructed into a three-dimensional time-domain matrix, and the experimental spectrum can be obtained by performing a three-dimensional Fourier transform on the matrix ; If the data used is obtained by the spatial encoding and decoding sampling mode, it is necessary to first divide each data string with a length of np points into np1×N _D (wherein np1 corresponds to the spatial encoding F1 dimension, and N _D corresponds to the direct sampling F2 dimension), and then form a three-dimensional matrix with the indirect F3 dimension, and only need to perform Fourier transform on the F2 and F3 dimensions of this three-dimensional matrix to obtain a high-resolution nuclear magnetic resonance heteronuclear spectrum under an unknown spatially distributed magnetic field.

In step 2), the specific method for setting the sequence parameters can be: if the three-dimensional sampling mode is adopted, it is only necessary to set the width and power of all pulses in the sequence, and the setting method is the same as that of the conventional nuclear magnetic resonance experiment; if the spatial In the codec sampling mode, you need to use the pulse generation toolbox of the nuclear magnetic resonance spectrometer to generate a chirp pulse, and set the pulse to the spatial codec module, and set the codec gradient size and time to In the spatial codec module based on J-coupled modulation sampling.

Based on the dipole field modulation method, the present invention proposes a method for obtaining two-dimensional high-resolution heteronucleus spectra under a magnetic field with unknown spatial distribution. The pulse sequence of this technology contains two sampling methods, and the three-dimensional sampling method can obtain two-dimensional high-resolution heteronuclei. Relevant information; the spatial encoding and decoding sampling method can obtain three-dimensional high-score information, of which two-dimensional is the information related to peak heteronucleus, and the other one is the coupling splitting information. The method utilizes the property that the heteronuclear correlation spectrum modulated by the dipole field is not sensitive to the spatial distribution, so as to eliminate the influence of the inhomogeneous magnetic field in the magnetic resonance detection, thereby improving the resolution of the spectrum. The present invention adopts two kinds of modules for exciting dipole field modulation, namely a selective pulse excitation module and a non-selective pulse excitation module. The selective pulse excitation module consists of a Gaussian selective π/2 pulse, a BIRD pulse unit and two gradient fields. The Gaussian selection π/2 pulse is used to select the solvent peak that excites the dipole field, and the addition of two gradient fields to the BIRD pulse unit is used to strengthen the selection of the solvent peak. The non-selective pulse excitation module consists of a TANGO pulse unit, a BIRD pulse unit and two gradient fields. The TANGO pulse unit is used to select the remote coupling signal, and the subsequent BIRD pulse unit plus two gradient fields are used to filter out the impurity signal. These two excitation methods finally ensure that the front unit only stimulates the evolution of the solvent signal, and prepares for the subsequent excitation to become a dipole field.

The present invention adopts two sampling modes, one is a three-dimensional sampling mode, which is composed of two indirect dimensions (F1, F3) and a direct sampling dimension (F2). The indirect dimension F1 is composed of two evolution times of γ _X t ₁ /γ _H and t ₁ to obtain the chemical shift evolution of heteronuclei (X nuclei) not affected by the inhomogeneous field; the indirect dimension F3 is composed of t in front of the sequence ₃ and t ₊₃ before sampling are used to obtain the chemical shift evolution of hydrogen nuclei (H nuclei) which are not affected by the inhomogeneous field. The three-dimensional sampling mode can obtain two-dimensional high-resolution heteronuclear related information in an inhomogeneous field. This mode features a high signal-to-noise ratio, but takes a long time. The other is the spatial codec sampling mode, which consists of a regular indirect dimension (F2) and spatial codec dimensions (F1, F3). This mode uses a spatial encoding module composed of an odd number of linear frequency-modulated adiabatic pulses and a gradient field with alternating positive and negative polarities to replace the two evolution times t ₃ of the indirect dimension (F3); and uses a series of unipolar gradient fields sandwiched by Sampling of the spatial decoding module for π pulses (J-coupled modulation). The main feature of the spatial codec sampling mode is that the sampling time is short, but the signal-to-noise ratio is low. In addition, this mode can obtain three-dimensional high-resolution information, in which two-dimensional is the peak heteronuclear related information, and the other one is the coupled splitting information.

Description of drawings

Figure 1 is a three-dimensional spectrum obtained by three-dimensional sampling of ¹³ C fully-labeled sodium butyrate aqueous solution under an inhomogeneous field with a hydrogen spectrum linewidth of 2500 Hz (the shimming power is turned off). Among them, the high-resolution HSQC spectrum can be obtained by projecting to the F1F3 plane. The resolution of the carbon dimension reaches 19Hz, and the resolution of the hydrogen dimension reaches 28Hz. However, the F2 dimension is still affected by the inhomogeneous field, and the line width is broadened by 2500Hz, that is, the three-dimensional sampling obtained The information is (F3,F1,F2)=(Ω _H ,Ω _C ,Ω _H + _γH ΔB), where Ω _H and Ω _C are the chemical shifts of ¹ H and ¹³ C, respectively.

Fig. 2 is a spectrum obtained by a conventional gHSQC sequence in an aqueous solution of naturally abundant γ-aminobutyric acid (GABA) in a non-uniform field.

Fig. 3 is the HSQC spectrogram that the present invention obtains.

Fig. 4 is a spectrogram obtained by the decoding module using only the 180-degree pulse of the H channel in the spatial codec sampling mode. Project to F1F3 plane to get HSQC information, and project to F2F3 plane to get homonuclear J-decomposition spectrum, that is, three-dimensional high-resolution information is: (F3,F1,F2)=(Ω _H ,Ω _C ,J _HH ), where the hydrogen dimension resolution 28Hz, carbon dimension resolution 20Hz, J _HH is equal to 5Hz.

Fig. 5 is a spectrogram obtained by using 180-degree pulses in both the H channel and the C channel of the decoding module in the spatial codec sampling mode. Project to the F1F3 plane to get the HSQC information, and project to the F1F3 plane to get the heteronuclear J decomposition spectrum, that is, the three-dimensional high-resolution information is: (F3,F1,F2)=(Ω _H ,Ω _C ,J _CH +J _HH ), where hydrogen Dimension resolution 28Hz, carbon dimension resolution 20Hz, J _CH + J _HH is equal to 7Hz.

Among them, Fig. 2 and Fig. 3 show the heteronuclear correlation spectra obtained by the three-dimensional sampling mode of the present invention under the uneven field with a line width of about 1000 Hz for different samples, and Fig. 2 and Fig. 3 show that the present invention is for samples with natural abundance Applicable, it can very well restore the 1000Hz broadened HSQC spectrum to the level of high resolution of hydrogen dimension 34Hz carbon dimension 20Hz. Fig. 4 and Fig. 5 depict the spatial codec sampling mode of the present invention to obtain a three-dimensional high-resolution spectrogram in an uneven field with a line width of about 1000 Hz.

Detailed ways

The invention provides a method for obtaining high-resolution heteronuclear correlation spectra under an unknown spatially distributed magnetic field based on dipole field modulation. The method includes an excited dipole field modulation module, a conventional heteronuclear coherent transfer module, and an indirect dimensional evolution time module. , an odd number of chirp adiabatic pulse spatial encoding modules, and a spatial decoding module based on J-coupled modulation sampling.

For the convenience of description, the carbon-hydrogen heteronuclear system is used as an example, assuming that I ₁ is the spin of the proton in water, and I ₂ and S are a pair of CH coupling pairs in the organic matter in the solution, where I ₂ is the spin of the proton, and S is carbon spin.

The purpose of the excitation dipole field modulation module is to only excite the proton signal in the solvent (water), so that the first evolution time t ₃ is only the evolution of the solvent. When the signal strength of the solvent and the solute is comparable, selective excitation is usually used, and the excitation efficiency decreases with the increase of the inhomogeneous field; when the signal of the solvent is much stronger than that of the solute, or ¹³ C-labeled samples, use the TANGO module, Solvent spins can be excited selectively, using a large inhomogeneous field. In addition, the addition of the BIRD module suppresses the solute ¹³ C-linked proton signal when excitation is not ideal.

Three-dimensional sampling method: the sampling sequence is a three-dimensional sampling mode, and the evolution time t ₁ and evolution time t ₂ correspond to the indirect dimension F1 and direct dimension F2 of the conventional two-dimensional heterokaryon correlation spectrum sequence. Since the directly sampled dimension F2 is always affected by the inhomogeneous field, resulting in linewidth broadening, it usually needs to be discarded. Therefore, in order to obtain a high-resolution two-dimensional spectrum, another evolution time _t3 is needed to form another indirect dimension F3.

Taking HSQC as an example, only the solvent spin I ₁ undergoes the evolution time t ₃ +γ _C t ₁ /γ _H after passing through the previous dipole field excitation module. The INEPT unit in the conventional heteronuclear coherent transfer module flips these spins to the longitudinal direction. According to the dipole field modulation theory, the dipole field generated by the I ₁ spin is:

${\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; [</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&Omega;</span>}}_{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}\mathrm{<span\; class="notranslate">\; \&Delta;B</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}}{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}\mathrm{<span\; class="notranslate">\; \&delta;</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

为I₁自旋偶极退磁时间，μ₀是真空导磁率，

为平衡态的单位体积的I₁自旋磁化。

为溶剂自旋I₁的固有频率位移，r为空间位置，ΔB为不均匀场，Δ_s=(3cos²θ-1)/2，其中θ为梯度场G₁与静磁场的夹角，δ为梯度场G₁的持续时间。in

is the I ₁ spin dipole demagnetization time, μ ₀ is the vacuum permeability,

I ₁ spin magnetization per unit volume for the equilibrium state.

is the natural frequency displacement of the solvent spin I ₁ , r is the spatial position, ΔB is the inhomogeneous field, Δ _s =(3cos ² θ-1)/2, where θ is the angle between the gradient field G ₁ and the static magnetic field, δ is the duration of the gradient field _G1 .

。紧接着S自旋将转移回I₂自旋。B_d无法在后面的演化抵消，对¹³C通道去偶，忽略J_HH偶合作用，可以得到随时间和空间变化的相位：The resulting dipole field B _d will be superimposed on the original magnetic field environment. Now consider the modulation of the solute signal by the dipole field. The spin _I2 is coherently transferred to the S spin by the INEPT cell. The S spin undergoes an evolution time t ₁ to obtain the chemical shift and the evolution phase of the inhomogeneous field, and only the phase of the coherence order p=-1 can be selected through coherent path selection

. Immediately afterwards the S spin will be transferred back to the _I2 spin. B _d cannot be counteracted in the later evolution, decoupling the ¹³ C channel, ignoring the J _HH coupling, the phase that varies with time and space can be obtained:

It is worth noting here that 2/3 is the dipole field factor felt by the _I2 spin from the _I1 spin. Expansion by Bessel function $e^{\mathrm{iz}\cos \mathrm{\&theta;}}=\underset{m=-\&infin;}{\overset{\&infin;}{\mathrm{\&Sigma;}}}{i}^m{J}_m\left(z\right)e^{\mathrm{im\&theta;}}$ . Formula (2) can be expanded as:

Where J _m (ξ ₁ ) is an amplitude modulation factor. From formula (3), it can be obtained that the phase has nothing to do with the spatial variation caused by the coherent path ladder only when m=-1, so finally the phase information of the final signal can be obtained:

，可以得到所得到的信号所在位置为(F₁,F₂,F₃)＝(Ω_C,Ω_H+γ_HΔB,Ω_H)，可以看到F1和F3维将不受到不均匀场的影响。将三维谱图投影至F1-F3平面可以得到高分辨的HSQC谱图。同理HMQC与HMBC适用同样的原理。When the reference frequency of the spectrometer is set to the resonant frequency of the _I spin, i.e.

, the position of the obtained signal can be obtained as (F ₁ , F ₂ , F ₃ )=(Ω _C ,Ω _H +γ _H ΔB,Ω _H ), it can be seen that the F1 and F3 dimensions will not be affected by the inhomogeneous field Influence. High-resolution HSQC spectra can be obtained by projecting the three-dimensional spectra onto the F1-F3 plane. Similarly, HMQC and HMBC apply the same principle.

Based on the spatial codec sampling mode: When the spatial encoding and decoding modules are used to replace the three-dimensional sampling mode evolution time _t3 and sampling time _t2 , the spatial codec sampling mode is obtained, that is, the F2 and F3 dimensions are formed by the spatial codec sampling data. The F1 dimension still uses regular evolution time. Assuming that all encoding and decoding gradient directions are in the z direction, the constant-time spatial encoding method can obtain the evolution time that changes with the position. The preceding (2N _E + 1) linear sweep pulses express the spin-phase encoding as a function of spatial position:

Among them, α=τ _ad /Δ _ad is the ratio of the delay τ _ad to the sweep width Δ _ad of the frequency sweep pulse. G _E is the encoding gradient strength. The 180° ¹³ C pulse in the middle of the spatial codec sampling mode is used to eliminate the J _CH coupling of the I ₂ spin, which is not necessary for the I ₁ spin (water solvent). To deeply explore the difference of the precession frequency of the two spins (I ₁ , I ₂ ) modulated by the remote dipole field, the phase difference can be obtained after (2N _E +1) constant-time phase encodings, which can be expressed as follows:

The spatial encoding composed of an odd number of adiabatic pulses is essentially that the phase is not only modulated by the encoding gradient _GE , but also modulated by the inhomogeneous field ΔB. The amplitude of the decoding gradient G _D is (2N _E +1) times of the encoding gradient, that is, G _D =G _E . Its phase is

处会形成一个回波。当谱仪参考频率设定到I₁自旋（水峰）共振频率，即

，不均匀场对空间编码维(F3)的影响可以被消除掉，进而给出精确的¹H化学位移。这和自旋回波相关谱(SECSY)类似。对于常规直接维(F1)，用同样的方式消除不均匀场影响来给出精确的¹³C化学位移。The phase is independent of the spatial variation, in the time

An echo will be formed. When the spectrometer reference frequency is set to the I ₁ spin (water peak) resonance frequency, i.e.

, the influence of the inhomogeneous field on the spatial encoding dimension (F3) can be eliminated, and then the precise ¹ H chemical shift can be given. This is similar to spin echo correlation spectroscopy (SECSY). For the conventional direct dimension (F1), the inhomogeneous field effects are eliminated in the same way to give ^accurate13C chemical shifts.

J modulation detection scheme such as spatial codec sampling mode, ¹³ C channel 180° pulse optional or not. If 180° pulses are applied to both ¹ H and ¹³ C channels, the information of J _CH +J _HH is obtained from the F2 dimension, that is, the three-dimensional high-resolution spectrum is (F ₁ , F ₂ , F ₃ )=(Ω _C ,±J _CH ± J _HH , Ω _H ) respectively. But if only 180° pulse is applied to the ¹ H channel, the accurate JHH information is obtained in the F2 dimension corresponding to the I ₂ spin, and the corresponding three-dimensional high-resolution spectrum is (F ₁ , F ₂ , F ₃ )=(Ω _C , ±J _HH ,Ω _H ).

The solution involved in the present invention is not only applicable to the detection of the fine structure of chemical samples under an uneven magnetic field, but also applicable to the rapid analysis and measurement of biological metabolites under an uneven magnetic field. All experiments were performed under Varian 500 MHz NMR spectroscopy (Varian, Palo Alto, CA). The steps of using the present invention include:

1) Determine whether the signal-to-noise ratio or the sampling efficiency is prioritized according to the experimental requirements. When the signal-to-noise ratio is prioritized, the 3D sampling mode is used, and when the sampling efficiency is prioritized, the spatial codec sampling mode is used.

2) Set the sequence parameters, the specific method is as follows: in the three-dimensional sampling mode, you only need to set the width and power of all the pulses in the sequence, the setting method is the same as that of the conventional nuclear magnetic resonance experiment; in the spatial codec sampling mode, you need to use the nuclear magnetic resonance spectrometer The pulse generation toolbox of the pulse generation toolbox generates chirp pulses, and sets the pulses to the spatial codec module, and sets the codec gradient size and time to the spatial codec module based on J-coupled modulation sampling according to the spectral width information of the experimental samples.

3) Sample the sample after completing the sequence parameter setting. Store the experimental data after sampling.

4) Process the stored experimental data. If the experimental data used is obtained by three-dimensional sampling mode, construct the experimental data into a three-dimensional time-domain matrix, and only need to perform three-dimensional Fourier transform on the matrix to obtain the experimental spectrum; If the data used is obtained by the spatial encoding and decoding sampling mode, it is necessary to first divide each data string with a length of np points into np1×N _D (where np1 corresponds to the spatial encoding F1 dimension, and N _D corresponds to the direct sampling F2 dimension) , and then form a three-dimensional matrix with the indirect F3 dimension, and only need to perform Fourier transform on the F2 and F3 dimensions of this three-dimensional matrix to obtain a high-resolution nuclear magnetic resonance heteronuclear spectrum under an unknown spatially distributed magnetic field.

Provide specific examples below to verify the method provided by the present invention:

First, ¹³ C-labeled sodium butyrate was used to examine the performance of the sequence in the three-dimensional sampling mode under the natural inhomogeneous field. By artificially not applying shimming coils to generate an inhomogeneous magnetic field with a line width of 2500 Hz, the three-dimensional sampling spectrum shown in Figure 1 is obtained, and projected to the F1F3 plane, a high-resolution HSQC spectrum can be obtained, and the carbon dimension resolution reaches 19Hz , the resolution of the hydrogen dimension reaches 28Hz, the F2 dimension is still affected by the inhomogeneous field, and the line width is broadened by 2500Hz, that is, the three-dimensional information obtained by three-dimensional sampling is (F3,F1,F2)=(Ω _H ,Ω _C ,Ω _H +γΔB ), thus obtaining high-resolution carbon-dimensional and hydrogen-dimensional chemical shift information.

Secondly, in order to more comprehensively test the performance of this method in obtaining high-resolution spectra under inhomogeneous fields, the current of the shimming coil is artificially adjusted to generate an inhomogeneous magnetic field with a linewidth of 1000 Hz. Acquire heteronuclear correlation spectra for downsampling of inhomogeneous fields around 1000 Hz. Fig. 2 and Fig. 3 depict the heteronuclear correlation spectra acquired by the three-dimensional sampling mode of the new method under the inhomogeneous field with a line width of about 1000 Hz for different samples. Figure 2 is the spectrum obtained by the conventional gHSQC sequence under the non-uniform field of the aqueous solution of natural abundance γ-aminobutyric acid (GABA), and Figure 3 is the HSQC spectrum obtained by this method. High-resolution two-dimensional HSQC spectra can be obtained from the cumulative projection of the F1-F3 plane without rotation processing. From the comparison of the pictures, it can be seen that the problem of spectral line broadening caused by the inhomogeneity of the magnetic field can be solved by this method. These two figures show that this method is suitable for samples with natural abundance, and can very well restore the 1000Hz broadened HSQC spectrum to the level of high resolution of hydrogen dimension 34Hz carbon dimension 20Hz.

Finally, the effect of spatial codec sampling mode on sample sampling under inhomogeneous field is detected. The experiment was carried out under an inhomogeneous magnetic field with a line width of 1000 Hz generated by artificially adjusting the current of the shim coil. The sample was a mixed aqueous solution of carbon-labeled methanol and the second carbon-labeled ethanol. Figures 4 and 5 depict the experimental conditions. The obtained high-resolution three-dimensional spectrum. Figure 4 is the spectrogram obtained by the decoding module in the spatial codec sampling mode using only the 180-degree pulse of the H channel, projected to the F1F3 plane to obtain HSQC information, and projected to the F2F3 plane to obtain the homonuclear J-decomposition spectrum, that is, the three-dimensional high-resolution information is: (F3,F1,F2)=(Ω _H ,Ω _C ,J _HH ), where the resolution of the hydrogen dimension is 28Hz, the resolution of the carbon dimension is 20Hz, and J _HH is equal to 5Hz. Figure 5 is the spectrogram obtained by the 180-degree pulse used by both the H channel and the C channel of the decoding module in the spatial codec sampling mode, projected to the F1F3 plane to obtain HSQC information, and projected to the F1F3 plane to obtain the heteronuclear J decomposition spectrum, that is, three-dimensional high-resolution The information is: (F3, F1, F2)=(Ω _H ,Ω _C , J _CH +J _HH ), where the resolution of the hydrogen dimension is 28Hz, the resolution of the carbon dimension is 20Hz, and J _CH +J _HH is equal to 7Hz. The new sequence sampling time of this spatial codec sampling mode is only 34min. It can be seen that compared with the conventional HSQC method, the new sequence can not only recover good high-resolution information in an inhomogeneous magnetic field, but also its simplified spectral peak splitting mode and J-coupling information are more conducive to spectral analysis. Two different sampling modes It can be selected according to the actual measurement situation.

Table 1: Chinese-English comparison table of professional vocabulary

English abbreviations English full name Chinese noun NMR Nuclear Magnetic Resonance nuclear magnetic resonance HSQC Heteronuclear Singular Quantum Correlation heteronuclear single quantum correlation HMQC Heteronuclear Multiple Quantum Correlation heteronuclear multiple quantum correlations HMBC Heteronuclear Multiple Bond Correlation heteronuclear multiple bond correlation HETCOR Heteronuclear Correlation Heterokaryotic correlation FID Free Induction Decay free induction decay MRI Magnetic Resonance Imaging Magnetic resonance imaging iMQC Intermolecular Multiple-Quantum Coherence Intermolecular multiple quantum coherence wxya Gradient Selected HSQC Gradient-selected heteronuclear single-quantum correlations wxya Gradient Selected HMQC Gradient-selected heteronuclear multiple quantum correlations BIRD Bilinear Rotation Decoupling bilinear rotational decoupling TANGO Testing for Adjacent Nuclei with a Gyration Operator The rotation operation detects neighboring nuclei INEPT Insensitive Nuclei Enhanced by Polarization Transfer Polarization transfer strengthens insensitive nuclei SECSY Spin Echo Correlated Spectroscopy spin echo correlation spectrum

Table 2: Character comparison table

See Table 1 for the Chinese-English comparison table of professional vocabulary, and Table 2 for the character comparison table.

Claims (2)

1. The method for obtaining a high-resolution nuclear magnetic resonance heteronuclear spectrogram under an unknown spatially distributed magnetic field is characterized in that it comprises the following steps: 1) Determine whether the signal-to-noise ratio or the sampling efficiency is prioritized according to the experimental requirements. If the signal-to-noise ratio is prioritized, use the three-dimensional sampling mode; if the sampling efficiency is prioritized, use the spatial codec sampling mode; 2) Set sequence parameters; 3) Sample the sample after completing the sequence parameter setting, and store the experimental data after sampling; 4) Process the stored experimental data. If the experimental data used is obtained by the three-dimensional sampling mode, the experimental data is constructed into a three-dimensional time-domain matrix, and the experimental spectrum can be obtained by performing a three-dimensional Fourier transform on the matrix ; If the data used is obtained by the spatial encoding and decoding sampling mode, it is necessary to first divide each data string with a length of np points into np1×N _D (wherein np1 corresponds to the spatial encoding F1 dimension, and N _D corresponds to the direct sampling F2 dimension), and then form a three-dimensional matrix with the indirect F3 dimension, and only need to perform Fourier transform on the F2 and F3 dimensions of this three-dimensional matrix to obtain a high-resolution nuclear magnetic resonance heteronuclear spectrum under an unknown spatially distributed magnetic field. 2. The method for obtaining high-resolution nuclear magnetic resonance heteronuclear spectra under an unknown spatially distributed magnetic field as claimed in claim 1, characterized in that in step 2), the specific method for setting the sequence parameters is: if the three-dimensional sampling mode is adopted , you only need to set the width and power of all pulses in the sequence, the setting method is the same as that of the conventional NMR experiment; if the spatial codec sampling mode is used, you need to use the pulse generation toolbox of the NMR spectrometer to generate chirp pulses, And set the pulse to the spatial codec module, and set the codec gradient size and time to the spatial codec module based on J-coupled modulation sampling according to the spectral width information of the experimental sample.

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