J-coupling constant extraction method based on high precision selective filtering
By employing gradient-enhanced multiple-selective targeted NMR observation experiments and specific radio frequency pulse sequence design, the selectivity and sensitivity issues of J coupling constant extraction in complex compounds were resolved, achieving high-precision J coupling constant extraction, which is suitable for structural analysis of complex chemical and biological samples.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JIMEI UNIV
- Filing Date
- 2026-05-26
- Publication Date
- 2026-07-24
Smart Images
Figure CN122448895A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of nuclear magnetic resonance spectroscopy detection, specifically to a method for extracting the J coupling constant based on high-precision selective filtering. Background Technology
[0002] Nuclear magnetic resonance (NMR) spectroscopy is a non-invasive detection technique commonly used for the compositional analysis and structural determination of complex compounds. NMR spectroscopy allows for the precise measurement of the J-coupling constant between atomic nuclei, thereby determining the coupling topology and spatial configuration of these nuclei. In NMR spectroscopy, the atomic nucleus is the most sensitive and frequently studied nucleus. 1 H. However, due to the numerous spectral peaks and J-coupling splitting in complex substances, the J-coupling information of specific atomic nuclei can be masked, and the extraction of the J-coupling constant faces the challenge of spectral overlap.
[0003] To address this issue, various selective coupling constant NMR methods have been proposed to achieve high-resolution detection of J-coupling in specific atomic nuclei, such as SERF, DQ-SERF, and G-SERF. However, these techniques suffer from insufficient selectivity and are generally unsuitable for complex samples with severe signal overlap. Most of these J-coupling constant extraction methods also suffer from poor selectivity, insufficient filtering efficiency, and low sensitivity. Summary of the Invention
[0004] The purpose of this application is to propose a method for extracting the J-coupling constant based on high-precision selective filtering to address the aforementioned technical problems.
[0005] In a first aspect, the present invention provides a method for extracting the J coupling constant based on high-precision selective filtering, comprising the following steps:
[0006] The first and second protons with J coupling were selected as the target signals. The width of the first 90° hard pulse required to excite the target signal was measured. The one-dimensional proton spectrum of the sample was obtained and the chemical shift information of the first and second protons was determined.
[0007] Based on the chemical shift information of the first and second protons, as well as the width and power of the first 90° hard pulse, a 180° bicolor pulse to flip the target signal is generated, and a J-coupled two-dimensional evolution pulse sequence is constructed based on the 180° bicolor pulse.
[0008] Based on the chemical shift information of the first proton, the radio frequency pulse sequence used in the gradient-enhanced multiple-selective targeted NMR observation experiment is applied to the sample to be tested to obtain a single signal of the first proton;
[0009] The J-coupling two-dimensional evolution pulse sequence is applied to the sample to be tested. Based on the chemical shift information of the first and second protons, the frequency point of the 180° dual-color pulse is aligned with the chemical shift of the first and second protons. J-coupling evolution is performed based on the single signal of the first proton to obtain the J-coupling information of the target signal. The J-coupling information of the target signal is then subjected to two-dimensional sampling and two-dimensional Fourier transform to generate the two-dimensional nuclear magnetic resonance J spectrum of the target signal. The J-coupling constant of the target signal is extracted based on the two-dimensional nuclear magnetic resonance J spectrum.
[0010] As a preferred embodiment, the radio frequency pulse sequence used in the gradient-enhanced multiple-selective targeted NMR observation experiment includes a second 90° hard pulse spaced apart, a 180° monochromatic pulse, a first sweep pulse and a second sweep pulse located on the front and rear sides of the 180° monochromatic pulse respectively, as well as a first gradient field and a second gradient field. The center frequency points of the 180° monochromatic pulse, the first sweep pulse, and the second sweep pulse are aligned with the chemical shift of the first proton based on the chemical shift information of the first proton.
[0011] Preferably, the NMR signals of all protons in the sample are excited by a second 90° hard pulse, phase encoding is performed by a first sweep pulse and a first gradient field, decoupling is performed by a 180° monochromatic pulse, and phase refocusing is performed by a second sweep pulse and a second gradient field. Specifically, the combined effect of the first sweep pulse and the first gradient field, and the second sweep pulse and the second gradient field, layers the NMR signals of the protons in the sample along the vertical direction, and at different positions along the vertical direction, the phase of the NMR signals of protons at different chemical shifts is determined. for:
[0012] ;
[0013] in, The gyrometry of a proton is represented by its magnetic gyrometry. This represents the intensity of the first gradient field and the second gradient field. This refers to one of the locations perpendicular to the ground. This indicates the sweep rate of the first and second sweep pulses. This represents the relative chemical shift of the first proton to the set frequency point of the pulse sequence; when the frequency point of the radio frequency pulse sequence is aligned with the chemical shift of the first proton... When the phase is 0, the phase of the NMR signal is 0, thus filtering out the single signal of the first proton from the NMR signals of all protons.
[0014] Preferably, the first sweep pulse and the second sweep pulse have opposite directions and the same intensity, the first gradient field and the second gradient field have opposite directions and the same intensity, and the widths of the action times of the first sweep pulse, the second sweep pulse, the first gradient field and the second gradient field are the same.
[0015] Preferably, the first and second sweep pulses are 180° sweep pulses, using WURST0 as the pulse waveform.
[0016] Preferably, the J-coupled two-dimensional evolution pulse sequence includes a 180° two-color pulse and two identical evolution times before and after it, as well as two third gradient fields. In the evolution time before the 180° two-color pulse, chemical shift evolution and J-coupled evolution are performed based on the single signal of the first proton. The 180° two-color pulse causes the directions of the magnetization vectors of the first and second protons to be reversed. In the evolution time after the 180° two-color pulse, reverse chemical shift evolution and J-coupled evolution are performed.
[0017] Preferably, both evolution times are t1 / 2, where t1 represents the J evolution time.
[0018] Preferably, the interaction times of the two third gradient fields are located within two evolution times and are adjacent to the interaction time of the 180° two-color pulse.
[0019] Preferably, a 180° bicolor pulse for flipping the target signal is generated based on the chemical shift information of the first and second protons, as well as the width and power of the duration of the first 90° hard pulse. Specifically, this includes:
[0020] The chemical shift information of the first and second protons is used to determine the two corresponding frequency points. The width and power of the first 90° hard pulse are used to generate two single-frequency excitation pulses corresponding to the two frequency points. The parameters of the two single-frequency excitation pulses include amplitude and phase. The amplitude and phase are used to form a vector in the polar coordinate system. The vectors formed by the parameters of the two single-frequency excitation pulses are vector-added to obtain a 180° two-color pulse.
[0021] As a preferred method, obtaining the one-dimensional proton spectrum of the sample to be tested specifically includes:
[0022] A one-dimensional proton spectrum of the sample is obtained by applying a single pulse consisting of a first 90° hard pulse and a signal sampling period to the sample.
[0023] Compared with the prior art, the present invention has the following beneficial effects:
[0024] (1) The J coupling constant extraction method based on high-precision selective filtering mentioned in this invention excites the nuclear magnetic signals of all protons and filters out the single signal of the first proton through the radio frequency pulse sequence used in the gradient-enhanced multiselective targeted NMR observation experiment, which has the advantages of high selectivity and high sensitivity.
[0025] (2) The J-coupling constant extraction method based on high-precision selective filtering mentioned in this invention uses a pulse sequence structure that is simple, has a high signal-to-noise ratio, a wide range of applications, strong robustness, and excellent selectivity. It can extract the J-coupling constant of a specific signal in a system with complex composition without damaging the sample. It can be used on various commercial nuclear magnetic resonance spectrometers to extract the J-coupling constant of a specific target signal in complex chemical and biological samples. Compared with traditional J-coupling constant extraction methods, it has stronger selectivity, better suppression ratio, and a wider range of applications.
[0026] (3) The J coupling constant extraction method based on high-precision selective filtering mentioned in this invention has the advantages of high experimental efficiency, accuracy and universality. It can accurately extract the J coupling constant of a specific target signal in a system with complex composition (when the spectral peaks are crowded), suppress other interference signals, and finally obtain the two-dimensional nuclear magnetic resonance J spectrum of the target signal. It has important application significance for the structural analysis of chemical and biological complex samples in the field of nuclear magnetic resonance spectroscopy detection. Attached Figure Description
[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0028] Figure 1 This is a flowchart illustrating the J-coupling constant extraction method based on high-precision selective filtering, as an embodiment of this application.
[0029] Figure 2 This is a schematic diagram of the pulse sequence used in the J-coupling constant extraction method based on high-precision selective filtering, as described in an embodiment of this application.
[0030] Figure 3 This is an experimental result diagram of the J-coupling constant extraction method based on high-precision selective filtering used in Example 1 of this application for testing estradiol samples; wherein... Figure 3 (a) is the one-dimensional proton NMR spectrum of the estradiol sample; Figure 3 (b)-3(d) are the extraction results of all J coupling constants of the three signals obtained by sampling using the method proposed in this invention. Detailed Implementation
[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.
[0032] Figure 1 The present application illustrates an embodiment of a method for extracting the J-coupling constant based on high-precision selective filtering, comprising the following steps:
[0033] S1, select the first and second protons with J coupling relationship as target signals, measure the width of the first 90° hard pulse required to excite the target signal; obtain the one-dimensional proton spectrum of the sample to be tested and determine the chemical shift information of the first and second protons.
[0034] In a specific embodiment, obtaining the one-dimensional proton spectrum of the sample to be tested specifically includes:
[0035] A one-dimensional proton spectrum of the sample is obtained by applying a single pulse consisting of a first 90° hard pulse and a signal sampling period to the sample.
[0036] Specifically, in the embodiments of this application, the width of the first 90° hard pulse required to excite the target signal is first measured. A single pulse, consisting of the first 90° hard pulse and the signal sampling period, is applied to the sample to obtain a one-dimensional proton spectrum. The chemical shift information of the first and second protons is then determined on this one-dimensional proton spectrum. This one-dimensional proton spectrum contains the chemical shift information of all protons, from which the chemical shift information of the first proton to be observed and the chemical shift information of the second proton coupled with it are selected. Due to the high selectivity of the method of this invention, selection can be made from overlapping regions.
[0037] S2, based on the chemical shift information of the first and second protons and the width and power of the first 90° hard pulse, generate a 180° bicolor pulse to flip the target signal, and construct a J-coupled two-dimensional evolution pulse sequence based on the 180° bicolor pulse.
[0038] In a specific embodiment, a 180° bicolor pulse for flipping the target signal is generated based on the chemical shift information of the first and second protons, as well as the width and power of the first 90° hard pulse duration. Specifically, this includes:
[0039] The chemical shift information of the first and second protons is used to determine the two corresponding frequency points. The width and power of the first 90° hard pulse are used to generate two single-frequency excitation pulses corresponding to the two frequency points. The parameters of the two single-frequency excitation pulses include amplitude and phase. The amplitude and phase are used to form a vector in the polar coordinate system. The vectors formed by the parameters of the two single-frequency excitation pulses are vector-added to obtain a 180° two-color pulse.
[0040] Specifically, the frequency point of the 180° two-color pulse is determined based on the chemical shift information of the first and second protons, and the magnetic field strength of the instrument is used as the basis for this determination. Chemical shift can be calculated Corresponding frequency point As shown in the following formula:
[0041] ;
[0042] in, is the gyrometry of the proton.
[0043] After obtaining the frequency points f1 and f2 corresponding to the chemical shift information of the first and second protons, a 180° two-color pulse capable of simultaneously and effectively exciting the first and second protons is designed, based on the width and power of the first 90° hard pulse's duration. First, two single-frequency excitation pulses are constructed for the f1 and f2 frequencies, respectively. The parameters of each single-frequency excitation pulse include amplitude and phase. Based on these parameters, each single-frequency excitation pulse is represented as a vector in polar coordinates, with its magnitude as amplitude and its angle as phase. Then, the vectors corresponding to these two single-frequency excitation pulses are superimposed to synthesize a composite vector. The amplitude and phase of this composite vector are the equivalent parameters of the desired 180° two-color pulse. The resulting 180° two-color pulse can simultaneously excite both f1 and f2 frequencies in a single excitation, achieving efficient and selective excitation of a specified J-coupled proton pair. Specifically, this 180° two-color pulse can be generated using specialized NMR pulse generation software.
[0044] Furthermore, based on the 180° two-color pulse, a J-coupled two-dimensional evolution pulse sequence was obtained by combining the J-coupled evolution time and gradient field design.
[0045] S3, based on the chemical shift information of the first proton, applies the radio frequency pulse sequence used in the gradient-enhanced multiple-selective targeted NMR observation experiment to the sample to be tested, and obtains a single signal of the first proton.
[0046] In a specific embodiment, the radio frequency pulse sequence used in the gradient-enhanced multiple-selective targeted NMR observation experiment includes a second 90° hard pulse spaced apart, a 180° monochromatic pulse, a first sweep pulse and a second sweep pulse located on the front and rear sides of the 180° monochromatic pulse respectively, as well as a first gradient field and a second gradient field. The center frequency points of the 180° monochromatic pulse, the first sweep pulse, and the second sweep pulse are aligned with the chemical shift of the first proton according to the chemical shift information of the first proton.
[0047] In a specific embodiment, the NMR signals of all protons in the sample are excited by a second 90° hard pulse. Phase encoding is performed using a first sweep pulse and a first gradient field. Decoupling is performed using a 180° monochromatic pulse. Phase refocusing is then performed using a second sweep pulse and a second gradient field. The combined effect of the first sweep pulse and the first gradient field, as well as the second sweep pulse and the second gradient field, layers the NMR signals of the protons in the sample along the vertical direction. At different positions along the vertical direction, the phase of the NMR signals of protons at different chemical shifts is determined. for:
[0048] ;
[0049] in, The gyrometry of a proton is represented by its magnetic gyrometry. This represents the intensity of the first gradient field and the second gradient field. This refers to one of the locations perpendicular to the ground. This indicates the sweep rate of the first and second sweep pulses. This represents the relative chemical shift of the first proton to the set frequency point of the pulse sequence; when the frequency point of the radio frequency pulse sequence is aligned with the chemical shift of the first proton... When the phase is 0, the phase of the NMR signal is 0, thus filtering out the single signal of the first proton from the NMR signals of all protons.
[0050] In a specific embodiment, the first sweep pulse and the second sweep pulse have opposite directions and the same intensity, the first gradient field and the second gradient field have opposite directions and the same intensity, and the widths of the action times of the first sweep pulse, the second sweep pulse, the first gradient field and the second gradient field are the same.
[0051] In a specific embodiment, the first and second sweep pulses are 180° sweep pulses, and WURST0 is used as the waveform of the pulse.
[0052] Specifically, such as Figure 2As shown, in the embodiments of this application, the radio frequency pulse sequence used in the gradient-enhanced multiplet-selective targeted-experiment (GEMSTONE) is first applied to the sample to be tested. The radio frequency pulse sequence used in this gradient-enhanced multiplet-selective targeted-experiment consists of a second 90° hard pulse, a 180° monochromatic pulse, a first sweep pulse and a second sweep pulse located on the front and rear sides of the 180° monochromatic pulse, respectively, as well as a first gradient field and a second gradient field. The first sweep pulse and the first gradient field (denoted as G1) have the same duration of action and are located on the front side of the 180° monochromatic pulse; the second sweep pulse and the second gradient field (denoted as -G1) have the same duration of action and are located on the rear side of the 180° monochromatic pulse. The widths of the durations of the first sweep pulse, the second sweep pulse, the first gradient field, and the second gradient field are the same. The directions of the first sweep pulse and the second sweep pulse are opposite. The sweep pulse is denoted as TE, and the direction within the orange rectangle indicates the direction. The directions of the first gradient field and the second gradient field are opposite. First, the NMR signals of all protons in the sample are excited by a second 90° hard pulse. Phase encoding is then performed using a first sweep pulse and a first gradient field to obtain the phase of the NMR signals of protons at different chemical shifts. Next, the center frequency of a 180° monochromatic pulse is aligned with the chemical shift of the first proton. When the value is 0, there is no relative chemical shift in the entire spatial position of the NMR signal at that location, and the NMR signal is refocused. The remaining NMR signals all have relative chemical shifts and are dispersed. After processing by the combination of the second sweep pulse and the second gradient field, the single signal of the first proton can be filtered out from the NMR signals of all protons. Therefore, GEMSTONE can achieve high-precision extraction of the single signal of the first proton, with a resolution of up to 10 Hz.
[0053] S4. Apply the J-coupling two-dimensional evolution pulse sequence to the sample to be tested. Based on the chemical shift information of the first and second protons, align the frequency point of the 180° dual-color pulse with the chemical shifts of the first and second protons. Perform J-coupling evolution based on the single signal of the first proton to obtain the J-coupling information of the target signal. The J-coupling information of the target signal is then processed by two-dimensional sampling and two-dimensional Fourier transform to generate the two-dimensional nuclear magnetic resonance J spectrum of the target signal. The J-coupling constant of the target signal is extracted based on the two-dimensional nuclear magnetic resonance J spectrum.
[0054] In a specific embodiment, the J-coupling two-dimensional evolution pulse sequence includes a 180° two-color pulse and two identical evolution times before and after it, as well as two third gradient fields. In the evolution time before the 180° two-color pulse, chemical shift evolution and J-coupling evolution are performed based on the single signal of the first proton. The 180° two-color pulse causes the directions of the magnetization vectors of the first and second protons to be reversed. In the evolution time after the 180° two-color pulse, reverse chemical shift evolution and J-coupling evolution are performed.
[0055] In a specific embodiment, both evolution times are t1 / 2, where t1 represents the J evolution time.
[0056] In a specific embodiment, the action times of the two third gradient fields are located within two evolution times, and are adjacent to the action time of the 180° two-color pulse.
[0057] Specifically, the J-coupling two-dimensional evolution pulse sequence in the embodiments of this application consists of a 180° two-color pulse, two evolution times on both sides before and after it, and two third gradient fields (denoted as G2). An evolution time of t1 / 2 is added on both sides before and after the 180° two-color pulse, so that the coupling of the first proton and the second proton evolves therein. After the single signal of the first proton is extracted, chemical shift evolution and J-coupling evolution are performed based on the single signal of the first proton in the first t1 / 2 evolution time. Then, the 180° two-color pulse is applied at the two frequency points corresponding to the chemical shifts of the first proton and the second proton, and the directions of the magnetization vectors of the first proton and the second proton are reversed. In the second t1 / 2 evolution time, the reverse chemical shift evolution is performed, so the previous chemical shift evolution can be canceled out, but the J-coupling evolution remains unchanged. The subsequent evolution continues in the second t1 / 2 evolution time, thereby realizing the complete J-coupling evolution process. The single signal of the first proton is modulated by the J-coupling of the first and second protons, thus obtaining the J-coupling information of the first and second protons. Therefore, in the F1 dimension (J-coupling evolution time t1), the chemical shifts of the NMR signals of the first and second protons are re-converged, and the J-coupling information is preserved. The two third gradient fields on both sides of the 180° two-color pulse are used to filter the signal and prevent interference signals caused by the imperfection of the 180° two-color pulse. Finally, the J coupling information of the target signal is obtained. After the previous step is completed, the sampling period begins. Two-dimensional sampling is performed after the detection time t2 during the sampling period, and then a two-dimensional Fourier transform is performed to obtain the two-dimensional nuclear magnetic resonance J spectrum of the first proton. The horizontal axis of the two-dimensional nuclear magnetic resonance J spectrum is F2 dimension and the vertical axis is F1 dimension. The J coupling information of the first proton and the second proton can be accurately displayed in the F1 dimension of the two-dimensional nuclear magnetic resonance J spectrum. The J coupling constants of the first proton and the second proton can be read on the F1 dimension of the two-dimensional nuclear magnetic resonance J spectrum. The values of the J coupling constants of the first proton and the second proton are the positions of the peaks of the two-dimensional nuclear magnetic resonance J spectrum on the vertical axis (F1 dimension).
[0058] The technical effects of the present invention will be illustrated below through specific embodiments.
[0059] Example 1
[0060] Estradiol is widely present in the human body and is frequently used as a drug. Its molecular structure is complex and contains a large number of hydrogen atoms with similar chemical environments. Under these unfavorable conditions, the spectra of estradiol samples are dominated by complex and crowded peaks. Taking the crowded peaks between 1.7 ppm and 2.0 ppm as an example, traditional J coupling constant extraction methods are almost unable to separate the accurate J coupling constant, which limits the widespread application of nuclear magnetic resonance spectroscopy in complex samples. Therefore, this method extracts three typical signals from estradiol samples and derives their accurate coupling constants with other signals, which is of great significance for the structural analysis of complex molecules. The instrument used in the embodiments of this application is a Varian 500MHz nuclear magnetic resonance spectrometer.
[0061] The J-coupling constant extraction method based on high-precision selective filtering proposed in the embodiments of this application is used for estradiol samples. The specific process is as follows:
[0062] Step 1: Dissolve the estradiol sample in 600 μL of dimethyl sulfoxide (DMSO) and place it in a 5 mm NMR tube as the test sample. Place the test sample into the NMR cavity. After performing tuning, field locking, and shimming operations in the NMR spectrometer software interface, apply the first 90° hard pulse to obtain the results. Figure 3 The one-dimensional proton spectrum shown in (a) clearly reveals the complex structure of the estradiol sample, with signal congestion and overlap occurring in the chemical shift region of 1.7–2.0 ppm (red circle). The first and second protons were selected from the one-dimensional proton spectrum, and their corresponding chemical shift information was recorded.
[0063] Step 2: Using the method proposed in the embodiments of this application, the chemical shifts of the first and second protons, the spectral width of the two-dimensional nuclear magnetic resonance J spectrum, and the number of sampling points were set before the experiment was conducted. The specific parameters of the pulse sequence used in Embodiment 1 of this application are as follows: the power of the second 90° hard pulse is 58dB, and the duration is 13.5μs; the F1 dimension spectral width of the two-dimensional nuclear magnetic resonance J spectrum is 40Hz, and the number of sampling points is 32; the shape of the 180° two-color pulse is R-snob; the duration of the first and second sweep pulses is 100ms, and the intensity is 27dB. First, the three signals in this region—7β, 12β, and 16α—were extracted using GEMSTONE. Figure 3 In (b)-3(d), the blue spectral lines represent the extraction results when GEMSTONE is used alone, yielding the 7β, 12β, and 16α peaks. Figure 3 In (a), the molecular structure is marked in orange, purple, and blue. The 7β, 12β, and 16α signals are used as single signals of the first proton. Further, the J-coupling information of the target signal is extracted using the J-coupling two-dimensional evolution pulse sequence. A two-dimensional Fourier transform is then performed on the final sampling result to obtain... Figure 3 The two-dimensional nuclear magnetic resonance J-spectrum in (b)-3(d) is used to extract the J-coupling constant of the target signal. It can be seen that the 16α signal is coupled with the four signals 15α, 15β, 16β and 17, with J-coupling constants of 9.6Hz, 6.5Hz, 13.2Hz and 9.0Hz, respectively; the 12β signal is coupled with the three signals 11α, 11β and 12α, with J-coupling constants of 3.3Hz, 3.8Hz and 12.9Hz, respectively; the 7β signal is coupled with the two signals 6 and 8, with J-coupling constants of 4.4Hz and 9.8Hz, respectively.
[0064] In summary, the sample used in Example 1 is a representative sample selected by this invention. Two-dimensional nuclear magnetic resonance J spectra can also be obtained using other samples and the method proposed in the embodiments of this application. This invention can obtain accurate J coupling constants for specific signals, which is of great significance for the analysis and identification of molecular structures in complex chemical and biological environments, and can further broaden the application scope of nuclear magnetic resonance technology.
[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for extracting the J-coupling constant based on high-precision selective filtering, characterized in that, Includes the following steps: Select the first and second protons with J coupling as the target signal, and measure the width of the first 90° hard pulse duration required to excite the target signal; Obtain the one-dimensional proton spectrum of the sample to be tested and determine the chemical shift information of the first and second protons; Based on the chemical shift information of the first and second protons, as well as the width and power of the first 90° hard pulse, a 180° bicolor pulse to flip the target signal is generated, and a J-coupled two-dimensional evolution pulse sequence is constructed based on the 180° bicolor pulse. Based on the chemical shift information of the first proton, the radio frequency pulse sequence used in the gradient-enhanced multiple-selective targeted NMR observation experiment is applied to the sample to be tested to obtain a single signal of the first proton; The J-coupling two-dimensional evolution pulse sequence is applied to the sample to be tested. Based on the chemical shift information of the first and second protons, the frequency point of the 180° two-color pulse is aligned with the chemical shifts of the first and second protons. J-coupling evolution is performed based on the single signal of the first proton to obtain the J-coupling information of the target signal. The J-coupling information of the target signal is then subjected to two-dimensional sampling and two-dimensional Fourier transform to generate a two-dimensional nuclear magnetic resonance J spectrum of the target signal. The J-coupling constant of the target signal is extracted based on the two-dimensional nuclear magnetic resonance J spectrum.
2. The J-coupling constant extraction method based on high-precision selective filtering according to claim 1, characterized in that, The radio frequency pulse sequence used in the gradient-enhanced multiple-selective targeted NMR observation experiment includes a second 90° hard pulse spaced apart, a 180° monochromatic pulse, a first sweep pulse and a second sweep pulse located on the front and rear sides of the 180° monochromatic pulse, respectively, as well as a first gradient field and a second gradient field. The center frequency points of the 180° monochromatic pulse, the first sweep pulse, and the second sweep pulse are aligned with the chemical shift of the first proton based on the chemical shift information of the first proton.
3. The J-coupling constant extraction method based on high-precision selective filtering according to claim 2, characterized in that, The NMR signals of all protons in the sample are excited by the second 90° hard pulse. Phase encoding is performed using the first sweep pulse and the first gradient field. Decoupling is performed using the 180° monochromatic pulse. Phase refocusing is performed using the second sweep pulse and the second gradient field. The combined effect of the first sweep pulse and the first gradient field, as well as the second sweep pulse and the second gradient field, layers the NMR signals of the protons in the sample along the vertical direction. At different positions along the vertical direction, the phase of the NMR signals of protons at different chemical shifts is... for: ； in, The gyrometry of a proton is represented by its magnetic gyrometry. This represents the intensity of the first gradient field and the second gradient field. This refers to one of the locations perpendicular to the ground. This indicates the sweep rate of the first and second sweep pulses. This represents the relative chemical shift of the first proton to a predetermined frequency point in the pulse sequence; when the frequency point of the radio frequency pulse sequence is aligned with the chemical shift of the first proton... When the phase is 0, the phase of the NMR signal is 0, thus filtering out the single signal of the first proton from the NMR signals of all protons.
4. The J-coupling constant extraction method based on high-precision selective filtering according to claim 2, characterized in that, The first and second sweep pulses have opposite directions and the same intensity, the first and second gradient fields have opposite directions and the same intensity, and the widths of the action times of the first sweep pulse, the second sweep pulse, the first gradient field, and the second gradient field are the same.
5. The J-coupling constant extraction method based on high-precision selective filtering according to claim 2, characterized in that, The first and second sweep pulses are 180° sweep pulses, using WURST0 as the pulse waveform.
6. The J-coupling constant extraction method based on high-precision selective filtering according to claim 1, characterized in that, The J-coupled two-dimensional evolution pulse sequence includes a 180° two-color pulse and two identical evolution times before and after it, as well as two third gradient fields. In the evolution time before the 180° two-color pulse, chemical shift evolution and J-coupled evolution are performed based on the single signal of the first proton. The 180° two-color pulse causes the directions of the magnetization vectors of the first and second protons to be reversed. In the evolution time after the 180° two-color pulse, reverse chemical shift evolution and J-coupled evolution are performed.
7. The J-coupling constant extraction method based on high-precision selective filtering according to claim 6, characterized in that, Both evolution times are t1 / 2, where t1 represents the J evolution time.
8. The J-coupling constant extraction method based on high-precision selective filtering according to claim 6, characterized in that, The two third gradient fields are applied within two evolution periods, respectively, and are adjacent to the application time of the 180° two-color pulse.
9. The method for extracting the J-coupling constant based on high-precision selective filtering according to claim 1, characterized in that, Based on the chemical shift information of the first and second protons, as well as the width and power of the first 90° hard pulse, a 180° bicolor pulse to flip the target signal is generated, specifically including: Two corresponding frequency points are determined using the chemical shift information of the first and second protons. Two single-frequency excitation pulses corresponding to the two frequency points are generated with reference to the width and power of the action time of the first 90° hard pulse. The parameters of the two single-frequency excitation pulses include amplitude and phase. A vector is formed on the polar coordinate system based on the amplitude and phase. The vectors formed by the parameters of the two single-frequency excitation pulses are vector-added to obtain a 180° bicolor pulse.
10. The method for extracting the J-coupling constant based on high-precision selective filtering according to claim 1, characterized in that, Obtaining the one-dimensional proton spectrum of the sample to be tested specifically includes: A one-dimensional hydrogen spectrum of the sample is obtained by applying a single pulse consisting of the first 90° hard pulse and the signal sampling period to the sample.