A method for amplifying the nuclear magnetic resonance signal intensity by changing a chemical exchange system through reducing the indirect dimension chemical shift

Abstract

The present invention relates to the field of nuclear magnetic resonance technology, and particularly relates to a method for amplifying the intensity of nuclear magnetic resonance signals, comprising the following steps: collecting the one-dimensional nuclear magnetic resonance 1 1H spectrum and 13 13C spectrum of a sample; measuring the pulse widths of the 90-degree hard pulses of 13 13C and 1 1H of the sample; setting the intensities and durations of the z-filter gradients G1, G3 and the coherence selection gradients G2, G4; setting the spectral widths of the direct dimension and the indirect dimension; setting the central frequency of the detected hydrogen nuclei in the one-dimensional spectrum as the central frequency of the new pulse; setting the central frequency of the carbon nuclei as the irradiation decoupling central frequency and setting the decoupling power and sampling time; determining the number of sampling points n i in the indirect dimension; setting the value of the chemical shift reduction factor λ in the indirect dimension; using the INEPT pulse module to generate polarization transfer and enhance the 13 13C magnetization vector; adding n echo trains in the indirect dimension; then using the reversed INEPT module to transfer the 13 13C magnetization vector back to 1 1H; starting to collect nuclear magnetic resonance signals; performing two-dimensional Fourier transform on the signals to obtain the result.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear magnetic resonance, and particularly relates to a method for amplifying the nuclear magnetic signal intensity by changing the chemical exchange system by reducing the indirect dimension chemical shift. Background Art

[0002] Nuclear magnetic resonance technology is a non-destructive characterization tool that can detect the chemical composition, structure, and physical and chemical properties of substances at the molecular level. The high magnetic field brings an improvement in resolution and sensitivity, and together with the introduction of two-dimensional and multi-dimensional experiments, the nuclear magnetic resonance technology has a wider range of applications. However, in many chemical and biological systems, there is a chemical exchange phenomenon, which can lead to serious spectral line broadening and even signal disappearance. This line width increase effect often intensifies at high fields. The dual-field nuclear magnetic resonance spectrometer can combine the advantages of high and low fields, and realize the signals that cannot be detected by the high-field spectrometer due to chemical exchange in the dual-field spectrum. However, due to the limitations of experimental conditions, this special instrument has not been widely used. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies in the above-mentioned prior art, and provide a method for amplifying the nuclear magnetic signal intensity by changing the chemical exchange system by reducing the indirect dimension chemical shift.

[0004] To solve the above technical problems, the present invention provides a method for amplifying the nuclear magnetic signal intensity by changing the chemical exchange system by reducing the indirect dimension chemical shift, including the following steps:

[0005] Collect the one-dimensional nuclear magnetic resonance 1 H spectrum and 13 C spectrum of the sample;

[0006] Measure the 13 C, 1 pulse width of the 90-degree hard pulse of H;

[0007] Set the intensities and durations of the z-filtering gradients G1, G3 and the coherence selection gradients G2, G4;

[0008] Set the spectral widths of the direct dimension and the indirect dimension, where the spectral width of the indirect dimension is λ times the spectral width of the carbon spectrum;

[0009] Set the center frequency of the hydrogen nucleus detected in the one-dimensional spectrum as the center frequency of the new pulse;

[0010] Set the center frequency of the carbon nucleus as the irradiation decoupling center frequency and set the decoupling power and sampling time;

[0011] Determine the number of sampling points n i , that is, the increment times of t1;

[0012] Set the value of the reduction multiple λ of the indirect dimension chemical shift;

[0013] Use an INEPT pulse module to generate polarization transfer and enhance 13 the magnetization vector of C;

[0014] Add n echo trains (n = 0, 1, 2,... n i-1 ) in the indirect dimension. During (1 - λ)*t1, the chemical shift does not evolve, and the λt1 / 2 - 180° - λt1 / 2 module plays the role of chemical shift labeling;

[0015] Then use an inverted INEPT module to make 13 the magnetization vector of C transfer back to 1 H;

[0016] Start collecting nuclear magnetic resonance signals;

[0017] Perform two-dimensional Fourier transform on the signals to obtain a two-dimensional spectrum with reduced indirect dimension chemical shift.

[0018] In a better embodiment, the indirect dimension chemical shift of the obtained two-dimensional spectrum is reduced by λ times, and the signal is amplified.

[0019] In a better embodiment, the phase cycle used in the experiment is: Φ1 = y, y, -y, -y; Φ2 = x, -x; Φ3 = x, x, x, x, -x, -x, -x, -x; Φ4 = x, x, x, x, x, x, x, x, -x, -x, -x, -x, -x, -x, -x, -x; Φ5 = y, -y, -y, y; Φ R = x, -x, -x, x, -x, x, x, -x, -x, x, x, -x, x, -x, -x, x.

[0020] In summary, the present application includes at least one of the following beneficial technical effects:

[0021] A method for changing the chemical exchange system by reducing the indirect dimension chemical shift in a two-dimensional nuclear magnetic resonance spectrum to increase the signal intensity provided by the present invention can change the chemical exchange rate system to amplify the signal intensity, so that signals that cannot be detected by a high-field spectrometer due to chemical exchange can be restored in the two-dimensional spectrum.

[0022] Other features and beneficial effects of the present invention will be described in the subsequent specification, and some will be obvious from the specification or understood by implementing the present invention. The objectives and other beneficial effects of the present invention can be achieved and obtained through the structures specifically pointed out in the specification, claims, and drawings. Description of the Drawings

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings; in the following description of the positional relationship of the drawings, unless otherwise specified, the directions shown by the components in the drawings are used as the reference.

[0024] Figure 1 Pulse sequence diagram of a chemical shift reduction method for increasing the signal intensity of nuclear magnetic resonance spectra;

[0025] Figure 2 Structural formula of a dimethyltriazene compound;

[0026] Figure 3(a) shows the conventional one-dimensional nuclear magnetic resonance hydrogen spectrum of the compound;

[0027] Figure 3(b) shows the conventional one-dimensional nuclear magnetic resonance carbon spectrum of the compound;

[0028] Figure 4 HSQC spectrum of the compound;

[0029] Figure 5 HSQC spectrum of the compound with the chemical shift reduced by 0.1 times. Detailed implementation manners

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention; the technical features designed in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other; based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0031] In the description of the present invention, it should be noted that all terms (including technical terms and scientific terms) used in the present invention have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains, and should not be construed as a limitation of the present invention; it should be further understood that the terms used in the present invention should be understood to have a meaning consistent with their meaning in the context of this specification and the relevant art, and should not be understood in an idealized or overly formal sense, unless otherwise clearly defined in the present invention.

[0032] Although the numerical ranges and parameters listing the broad scope of the present invention are approximate values, the numerical values listed in the specific embodiments are recorded as accurately as possible. However, any numerical value inherently has a certain error. This error is an inevitable result of the standard deviation in its corresponding measurement method.

[0033] It should be noted that in a system with chemical exchange, when the exchange rate constant is much smaller than the frequency interval, it is called slow exchange. At this time, two spectral lines can be seen in the nuclear magnetic resonance spectrum; when the rate constant is much larger than the frequency interval, only one line can be seen at a certain position between the original two spectral lines. At this time, it is called fast exchange, and the line width is proportional to the square of the field strength in the fast exchange limit. Between the two exchange rate systems, there is medium exchange, and at this time the peak intensity is greatly weakened or even unobservable. Therefore, a choice must be made between the high sensitivity and resolution at high fields and the narrower line width and lower relaxation rate at low fields. For this reason, the present invention proposes a new sequence, which can proportionally reduce the chemical shift in the indirect dimension, thereby controlling the influence of chemical exchange and scalar coupling on the nuclear magnetic resonance spectrum. It is based on continuously refocusing the chemical shift and scalar coupling in the indirect dimension, whereby the optimal combination of sensitivity, resolution, and spectral information can be achieved during the experiment.

[0034] The technical solution of the present invention will be further described and illustrated through specific embodiments below. However, the protection scope of the present invention is not limited thereto.

[0035] An embodiment of the present invention provides a method for reducing the chemical shift in the indirect dimension to improve the signal intensity of the nuclear magnetic resonance spectrum. The main steps are as follows:

[0036] 1) Collect the one-dimensional nuclear magnetic resonance 1 1H spectrum and 13 13C spectrum of the sample;

[0037] 2) Measure the pulse widths of the 90-degree hard pulses of 13 13C and 1 1H of the sample;

[0038] 3) Set the intensities and durations of the z-filtering gradients G1, G3 and the coherence selection gradients G2, G4;

[0039] 4) Set the spectral widths of the direct dimension (1H) and the indirect dimension (13C), where the spectral width of the indirect dimension is λ times the spectral width of the carbon spectrum;

[0040] 5) Set the center frequency of the hydrogen nuclei detected in the one-dimensional spectrum as the center frequency of the new pulse, set the center frequency of the carbon nuclei measured in the one-dimensional carbon spectrum as the irradiation decoupling center frequency, and set the decoupling power and sampling time.

[0041] 6) Determine the number of sampling points ni in the indirect dimension, that is, the increment times of t1;

[0042] 7) Set the value of λ, which is the chemical shift reduction factor;

[0043] 8) First, use an INEPT pulse module to generate polarization transfer and enhance the magnetization vector of 13C. Subsequently, add n echo trains (n = 0, 1, 2,... ni-1) in the indirect dimension. During the period of (1-λ)*t1, the chemical shift does not evolve, and the t1 / 2-180°-t1 / 2 module plays the role of chemical shift labeling. Then follows an inverted INEPT module, 13 The magnetization vector of 13C is transferred back to 1 1H. Then start to acquire the nuclear magnetic resonance signal;

[0044] 9) After completing the experiment, what we detect is 1 the magnetization vector of 1H, but from the perspective of t1, it is modulated by the 13 chemical shift of 13C. Therefore, the information obtained is related to 13 13C. We perform two-dimensional Fourier transform on the signal to obtain a two-dimensional spectrum with reduced chemical shift. The chemical shift in the indirect dimension of the obtained two-dimensional spectrum is reduced by λ times, and the signal is amplified.

[0045] The phase cycling adopted in the above experiment is: Φ1 = y, y, -y, -y; Φ2 = x, -x; Φ3 = x, x, x, x, -x, -x, -x, -x; Φ4 = x, x, x, x, x, x, x, x, -x, -x, -x, -x, -x, -x, -x, -x; Φ5 = y, -y, -y, y; Φ R = x, -x, -x, x, -x, x, x, -x, -x, x, x, -x, x, -x, -x, x.

[0046] It should be noted that the description of the order of the above partial steps is only for illustration and explanation, and does not limit the scope of application of this specification. For those skilled in the art, under the guidance of this specification, various adjustments and changes can be made to the order of the steps, and these adjustments and changes are still within the scope of this specification.

[0047] The specific operations according to the above method are as follows:

[0048] In this embodiment, a Varian 500MHz nuclear magnetic resonance spectrometer is used, and the sample is a solution of 0.1 mol / L dimethyltriazene compound dissolved in deuterated chloroform (CDCl3), and the pulse sequence shown in Figure 1 is used.

[0049] Step 1: Respectively acquire a nuclear magnetic resonance hydrogen spectrum and a carbon spectrum of the sample, as shown in Figure 3;

[0050] Step 2: Measure the pulse width of the 90-degree hard pulse of the sample. The pulse width is 10.7 μs for the hydrogen spectrum and 9.7 μs for the carbon spectrum;

[0051] Step 3: Set the intensities of the z-filtering gradients G1 and G3 and the coherence selection gradients G2 and G4 to G1 = 11.32 G / cm, G2 = 9.39 G / cm, G3 = 3.26 G / cm, and G4 = 1.58 G / cm. The durations are ts1 = 4.0 ms, ts2 = 1.0 ms, ts3 = 2.4 ms, and ts4 = 0.5 ms;

[0052] Step 4: Set the pulse width of the direct dimension to 10.7 μs and the pulse width of the indirect dimension to 9.7 μs according to the one-dimensional H and C spectra;

[0053] Step 5: Set the central frequency of the detected hydrogen nuclei in the one-dimensional spectrum as the central frequency of the spectrum, set the central frequency of the measured carbon nuclei in the one-dimensional carbon spectrum as the irradiation decoupling central frequency, set the decoupling power to 45 dB, and the sampling time to 0.5 s;

[0054] Step 6: Set the number of points n i = 512 in the indirect dimension, which is the number of increments of t1;

[0055] Step 7: Based on the above parameters, set the value of λ, which is the reduction factor of the indirect chemical shift. In the figure, λ = 0.1;

[0056] Step 8: First, use an INEPT pulse module to generate polarization transfer and enhance 13 the magnetization vector of C; then add n i echo trains in the indirect dimension. During (1 - λ)*t1, the chemical shift does not evolve, and the t1 / 2 - 180° - t1 / 2 module serves as a chemical shift labeling function; next is an inverted INEPT module, 13 and the magnetization vector of C is transferred back to 1 H; then start collecting nuclear magnetic resonance signals;

[0057] Step 9: After completing the experiment, although what we detect is 1 the magnetization vector of H, from the perspective of t1, it is modulated by the 13 chemical shift of C. Therefore, the information related to 13 C is obtained. We perform two-dimensional Fourier transform on the signals to obtain a two-dimensional spectrum with reduced chemical shift.

[0058] Figure 2Shown is the structural diagram of a dimethyltriazene compound. The two methyl groups connected to the top N atom have an exchange effect. Due to this phenomenon, the line width of the conventional spectrum becomes wider, and the high field often exacerbates this line broadening effect. Therefore, it is necessary to balance the high sensitivity and resolution in the high field with the better line width and lower relaxation rate in the low field.

[0059] Figures 3(a) and 3(b) respectively show the one-dimensional hydrogen and carbon spectra of the dimethyltriazene compound. In the carbon spectrum, the peaks of the 13 C atoms in the two methyl groups connected to the N atom become very weak due to the exchange effect.

[0060] Figure 4 Shown is the HSQC spectrum of the compound magnified 2000 times. The exchanged methyl signal is significantly weaker than the methyl signal connected to the O atom, and the projected line width in the indirect dimension is relatively wide. Figure 5 Shown is the spectrum obtained using the new sequence we developed, with the chemical shift in the indirect dimension reduced by 0.1 times and magnified 100 times. Compared with the Figure 4 circled signal, the exchanged methyl signal is significantly enhanced by at least two orders of magnitude. This is because the exchange rate constant k of the methyl group ex is much larger than the frequency difference Δ between the two exchange sites at this time AB , and the molecule changes from a medium exchange system to a fast exchange system, resulting in signal enhancement.

[0061] In summary, a method provided by the present invention for changing the chemical exchange system by reducing the chemical shift in the indirect dimension to amplify the nuclear magnetic signal intensity can change the chemical exchange system, enhance the signal weakened due to exchange, facilitate our determination of the substance structure, and open up a new way for studying the internal dynamics of molecules.

[0062] In addition, those skilled in the art should understand that although there are many problems in the prior art, each embodiment or technical solution of the present invention can be improved in only one or several aspects, and it is not necessary to solve all the technical problems listed in the prior art or the background art at the same time. Those skilled in the art should understand that the content not mentioned in a claim should not be regarded as a limitation to that claim.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for amplifying the nuclear magnetic resonance signal intensity by changing the chemical exchange system through reducing the indirect dimension chemical shift, characterized in that The indirect dimension chemical shift of the obtained two-dimensional spectrum is reduced by a factor of λ, and the signal is amplified. The steps include: One-dimensional nuclear magnetic resonance of the collected samples 1 1H spectrum and 13 13C spectrum; Measuring the 13 C, 1 Pulse width of the 90-degree hard pulse of H; Set the intensities and durations of the z-filtering gradients G1, G3 and the coherence selection gradients G2, G4; Set the spectral widths of the direct dimension and the indirect dimension, where the spectral width of the indirect dimension is λ times the spectral width of the carbon spectrum; Set the central frequency of the detected hydrogen nuclei in the one-dimensional spectrum as the central frequency of the new pulse; Set the central frequency of the carbon nuclei as the irradiation decoupling central frequency and set the decoupling power and sampling time; Determine the number of sampling points n for the indirect dimension i , that is, the increment times of t1 Set the value of the reduction factor λ of the indirect dimension chemical shift; Use an INEPT pulse module to generate polarization transfer and enhance 13 the magnetization vector of C; Add n echo trains in the indirect dimension. During (1 - λ)*t1, the chemical shift does not evolve; The λt1 / 2 - 180° - λt1 / 2 module serves as a chemical shift labeling function; Then use an inverse INEPT module to make 13 the magnetization vector of C transfer back to 1 H; Start collecting nuclear magnetic resonance signals; Perform two-dimensional Fourier transform on the signals to obtain a two-dimensional spectrum with reduced indirect dimension chemical shift.

2. The method for amplifying the nuclear magnetic signal intensity by changing the chemical exchange system through reducing the indirect dimension chemical shift according to claim 1, wherein, The phase cycle used in the experiment is: Φ1 = y, y, -y, -y; Φ2 = x, -x; Φ3 = x, x, x, x, -x, -x, -x, -x; Φ4 = x, x, x, x, x, x, x, x, -x, -x, -x, -x, -x, -x, -x, -x; Φ5 = y, -y, -y, y; Φ R = x, -x, -x, x, -x, x, x, -x, -x, x, x, -x, x, -x, -x, x.

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