CN114235877A - Method for testing natural abundance double-quantum transfer spectrum of isomaltulose based on nuclear magnetic resonance technology - Google Patents
Method for testing natural abundance double-quantum transfer spectrum of isomaltulose based on nuclear magnetic resonance technology Download PDFInfo
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Abstract
The invention discloses a method for testing the natural abundance double-quantum transfer spectrum of isomaltulose based on a nuclear magnetic resonance technology, and belongs to the technical field of chemical analysis. The method comprises the following steps: (1) dissolving isomaltulose in a mixed solvent of deuterated dimethyl sulfoxide and tetramethylsilane, transferring the mixture into a nuclear magnetic tube, and placing the nuclear magnetic tube into a detection magnet of a nuclear magnetic spectrometer; (2) selecting deuterated dimethyl sulfoxide in an instrument workstation, and tuning, shimming and field locking; (3) loading a pulse sequence and setting other detection parameters by adopting a pulse mode of adiabatic 180 degrees and gradient-90-gradient steady state; (4) and executing the program after the setting is finished to obtain the natural abundance double-quantum transfer spectrum of the isomaltulose. According to the invention, a pulse mode of adiabatic 180 degrees and gradient-90-gradient steady state is adopted, and the modified pulse sequence is applied to testing the natural abundance double-quantum transfer spectrum of the isomaltulose, so that the clearer natural abundance double-quantum transfer spectrum of the isomaltulose is obtained.
Description
Technical Field
The invention relates to the technical field of chemical analysis, in particular to a method for testing natural abundance double-quantum transfer spectrum (INADEQUATEAD) of isomaltulose based on a nuclear magnetic resonance technology.
Background
Isomaltulose (Isomaltulose) is derived from sugar beet, is a natural sugar with a unique molecular structure. Like sucrose, it consists of glucose and fructose molecules, but its intermolecular linkage is stronger than sucrose, which means that it is completely digested by the human body, but at a slower rate. Isomaltulose, as a natural ingredient capable of slowly releasing carbohydrates, provides the full carbohydrate energy (glucose) in a more stable, sustained manner while maintaining blood glucose balance, and is able to utilize the carbohydrate energy source in the body for a longer period of time. Meanwhile, it is widely used in various foods and sweeteners because of its excellent taste, low sweetness and property of inhibiting tooth decay.
The formula of isomaltulose is as follows:
chinese patents CN100448884C, CN1324038C, CN1324039C, CN1148377C, CN1030530C report the preparation method of isomaltulose. Patent CN1297217C reports the use of isomaltulose in food. Therefore, how to characterize and detect the structure of the isomaltulose is particularly important, and the isomaltulose is more favorably used. In recent years, two-dimensional nuclear magnetic resonance spectroscopy has been applied to the measurement and analysis of organic molecular structures, and a two-dimensional Natural Abundance DoublE QUAntum Transfer Experiment (inadequalte) spectrum is one of the included Natural Abundance DoublE QUAntum Transfer experiments13C-13C chemical shift correlation spectrum, the spectrum is determined in the compound structure13The C spectral peak identification has important value in NMR research, but the spectrum has low sensitivity, so that the spectrum is difficult to make, and application reports are few. There is no report on the inadequaltean profile test method for isomaltulose.
Disclosure of Invention
The invention aims to provide a method for testing the natural abundance double-quantum transfer spectrum of isomaltulose based on a nuclear magnetic resonance technology. By adopting a mode of insulating 180 degrees and gradient-90-gradient steady state and applying the modified pulse sequence to test the natural abundance double-quantum transfer spectrum of the isomaltulose, the clearer natural abundance double-quantum transfer spectrum of the isomaltulose is obtained.
In order to achieve the purpose, the invention provides the following technical scheme:
a method for testing the natural abundance double-quantum transfer spectrum of isomaltulose based on the nuclear magnetic resonance technology comprises the following steps:
(1) dissolving isomaltulose in a mixed solvent of deuterated dimethyl sulfoxide and Tetramethylsilane (TMS), transferring the mixture into a nuclear magnetic tube, and placing the nuclear magnetic tube into a detection magnet of a nuclear magnetic spectrometer;
(2) selecting deuterated dimethyl sulfoxide in an instrument workstation, and tuning, shimming and field locking;
(3) loading a pulse sequence and setting other detection parameters by adopting a pulse mode of adiabatic 180 degrees and gradient-90-gradient steady state;
(4) after the setting is finished, executing a program to obtain an isomaltulose natural abundance double-quantum transfer spectrum;
the pulse sequence in the step (3) is as follows: carbon is taken as an observation nucleus and sequentially passes through a gradient field (hsgt), a rectangular pi/2 pulse (pw), a gradient field (hsgt), a relaxation delay time (d1), a rectangular pi/2 pulse (pw), an adiabatic pulse (ad), a gradient-90-gradient steady state (compad), an adiabatic pulse (ad), two rectangular pi/2 pulses (pw) and a sampling time (at).
Preferably, the time of the gradient field (hsgt) is 2.0 ms; the pulse time of the rectangular pi/2 pulse (pw) is 10.1 mus; the relaxation delay time (d1) is 1.0 s; the pulse time of the adiabatic pulse (ad) is 3.545 ms; the gradient-90-gradient steady state (compad) time is 1.999 ms; the sampling time (at) is 30-65 ms.
Preferably, the other detection parameters in step (3) include: direct spectrum width (sw),13C-13C coupling constant (J)C-C) Scan times (nt) and acquisition mode.
More preferably, the direct dimensional spectral width (sw) is 37878.8 Hz; the above-mentioned13C-13C coupling constant (J)C-C) 45-65 Hz; the number of scanning times (nt) is 256-512.
Preferably, the volume ratio of the deuterated dimethyl sulfoxide to the tetramethylsilane in the mixed solvent in the step (1) is 100: 3; the concentration of the isomaltulose in the mixed solvent was 50 mg/mL.
The invention has the following beneficial technical effects:
the present invention employs Adiabatic 180 ° Pulses (Adiabatic Pulses) based on carbon nuclei, resulting in higher sensitivity than the usual INADEQUATE spectra, especially when the carbon Pulses are not perfectly calibrated for a given sample, and the Adiabatic 180 ° Pulses provide more uniform inversion over a wider 13C spectral width. Adiabatic pulses are radio frequency pulses under special conditions, which are electromagnetic waves. For a nuclear magnetic resonance sequence, radio frequency pulses are indispensable, and it can be said that magnetic resonance signals cannot be generated without the radio frequency pulses. The propagation of electromagnetic vibrations is an electromagnetic wave, and the nature of resonance is energy propagation, and if a Radio Frequency (RF) pulse is emitted at a frequency equal to the precession frequency of hydrogen protons (i.e., larmor frequency) in the magnetic field environment of electrostatic field B0, the protons can absorb energy and generate energy transitions, a phenomenon known as nuclear magnetic resonance. RF pulses are classified into a number of categories, including adiabatic pulses and non-adiabatic pulses, in terms of field sensitivity. The time required for adiabatic pulse is short, and the time is not sensitive to the radio frequency field B1, so that the accuracy of the reversal angle is ensured. The adiabatic pulse has a longer pulse width ratio and a large B1 amplitude, so that the absorption of the RF energy by the sample can be increased; to ensure that the adiabatic pulses are not sensitive to B1 non-uniformities, the pulse angles can only be chosen to be integral multiples of 90 °, which can improve sensitivity to flow, off-resonance and relaxation effects. Furthermore, the use of gradient-90-gradient (Grad-90-Grad) steady state helps to clear the unrelaxed magnetization, which can result in a clearer spectrum.
The two-dimensional inadequaltevad spectrum has two orders of magnitude lower sensitivity than the conventional carbon spectrum, low signal sensitivity, higher noise, more false peaks, and also because the sensitivity of individual carbon nuclei is too low, the spectral peaks are swamped by noise, and the factor value resolution is not high enough, thus causing the loss of peaks. The invention optimizes relevant parameters (13C-13C coupling constant, sampling time, number of scans) for isomaltulose samples13C-13C chemical shift correlation spectroscopy provides a simple and effective means.
Drawings
FIG. 1 shows the results of example 1 of the present inventionProcess for preparing isomaltulose13A pulse sequence of the C spectrum;
wherein, the time sequence of the pulse sequence is divided into three periods of a preparation period, an evolution period and a detection period, carbon is used as an observation nucleus, and a period of relaxation delay time (d1) passes in the preparation period; adding a rectangular pi excitation pulse (p1) on the x axis of the evolution period, and adding a rectangular pi/2 pulse (pw) after the pulse interval time (d 2); setting sampling time (at) in a detection period, and recording a free decay signal by a receiver;
the relaxation delay time (d1) was 1.0s, the rectangular pi pulse (p1) was 0.0 μ s, the pulse interval time (d2) was 0.0 μ s, the rectangular pi/2 pulse (pw) was 5.05 μ s, and the sampling time (at) after the pulse was 865.075 ms.
FIG. 2 shows isomaltulose measured in example 1 of the present invention13And C, spectrum.
FIG. 3 is a pulse sequence of the INDEQUATEAD spectrum of isomaltulose in example 1 of the present invention;
the method comprises the following steps that a pulse sequence is divided into a preparation period, an evolution period and a detection period, carbon is used as an observation core, a gradient field (hsgt), a rectangular pi/2 pulse (pw), a gradient field (hsgt) and a relaxation delay time (d1) are sequentially passed, so that a magnetization vector is in a thermal equilibrium state, and the rectangular pi/2 pulse (pw) is added and sequentially passed through an adiabatic pulse (ad), a gradient-90-gradient steady state (compad), an adiabatic pulse (ad) and two rectangular pi/2 pulses (pw) respectively; setting sampling time (at) in a detection period, and recording a free decay signal by a receiver;
the gradient field (hsgt) time was 2.0ms, the pulse time for the rectangular pi/2 pulse (pw) was 10.1 μ s, the relaxation delay time (d1) was 1.0s, the pulse time for the adiabatic pulse (ad) was 3.545ms, and the gradient-90-gradient steady state (compad) was 1.999 ms; the sampling time (at) after the pulse is 54.067 ms.
FIG. 4 is an INDEQUATEAD spectrum of isomaltulose measured in example 1 of the present invention.
Detailed Description
Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention. It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
Further, for numerical ranges in this disclosure, it is understood that each intervening value, between the upper and lower limit of that range, is also specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in a stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention.
As used herein, the terms "comprising," "including," "having," "containing," and the like are open-ended terms that mean including, but not limited to.
The sample adopted in the embodiment of the invention is isomaltulose, the experimental test is carried out under an Agilent600MHz NMR spectrometer (Agilent, USA), and the whole experimental process does not carry out any sample pretreatment on the sample and does not change the hardware facilities of the instrument.
Example 1
The specific steps of the isomaltulose inadequaltean profile determination are as follows:
step 1, weighing isomaltulose, loading the isomaltulose into a test tube, adding a small amount of deuterated dimethyl sulfoxide TMS (the volume ratio is 100:3), carrying out ultrasonic dissolution sufficiently, transferring the test tube into a nuclear magnetic tube, and then placing the test tube filled with a sample (the isomaltulose concentration is 50mg/mL) into a detection magnet of a nuclear magnetic spectrometer;
step 2, selecting a corresponding deuterated solvent in an instrument workstation, and tuning, shimming and field locking;
step 3, setting up13C test parameters: opening pulse sequence, setting experiment conditions including direct dimension spectrumWidth, scanning times and acquisition mode;
the pulse sequence in this step is: observing the nuclei with carbon, and after a relaxation delay time (d1), bringing the magnetization vector into thermal equilibrium; adding a rectangular pi excitation pulse (p1), and adding a rectangular pi/2 pulse (pw) after a pulse interval time (d 2); finally, a sampling time (at) follows for acquiring the final signal;
in this step, the experimental parameters are set as follows: the direct dimensional spectral width (sw) is 37878.8Hz, the relaxation delay time (d1) is 1.0s, the pulse time of the rectangular pi/2 pulse (pw) is 5.05 μ s, the sampling time (at) of a single sampling time is 865.075ms, the number of repeated scans (nt) is 512, and the entire sampling period is 24min, as shown in FIG. 1.
Step 4, directly executing data pre-sampling after the experiment parameter setting is finished;
and 5, after the data pre-sampling is completely finished, carrying out data post-processing to obtain isomaltulose13C spectrum, as shown in fig. 2.
Step 6, based on that in step 313C, setting the testing parameters of INADEQUATEAD according to the testing result; opening a pulse sequence, and setting experimental conditions including direct dimensional spectral width,13C-13C coupling constant, scanning times and acquisition mode;
the pulse sequence in this step is: using carbon as an observation nucleus, sequentially passing through a gradient field (hsgt), a rectangular pi/2 pulse (pw), a gradient field (hsgt) and a relaxation delay time (d1) to enable a magnetization vector to be in a thermal equilibrium state, adding a rectangular pi/2 pulse (pw), and sequentially passing through a section of adiabatic pulse (ad), a gradient-90-gradient steady state (compad), a section of adiabatic pulse (ad) and two rectangular pi/2 pulses (pw) respectively; setting sampling time (at) in a detection period, and recording a free decay signal by a receiver;
in this step, the experimental parameters are set as follows: the direct dimensional spectral width (sw) is 37878.8Hz, the time of the gradient field (hsgt) is 2.0ms, the relaxation delay time (d1) is 1.0s, the pulse time of the rectangular pi/2 pulse (pw) is 10.1 mus,13C-13c coupling constant (J)C-C) Is 55Hz, and the pulse time of the adiabatic pulse (ad) is3.545ms, gradient-90-gradient steady state (compad) time of 1.999ms, sampling time (at) after pulse of 54.067ms, number of scans (nt) of 450 times, and total sampling period of 17h, as shown in fig. 3.
Step 7, directly executing data pre-sampling after the experiment parameter setting is finished;
and 8, after the data pre-sampling is completely finished, carrying out data post-processing to obtain an inadequaltend spectrum of the isomaltulose, as shown in fig. 4.
Example 2
As shown in Table 1, this example is different from example 1 in the aspect of the present invention13C-13C coupling constant (J)C-C) Preferably, improper coupling constants will result in loss of peaks. Are respectively provided with13C-13C coupling constant (J)C-C) 45Hz, 55Hz, 65Hz, and preferably 55Hz, since it was found that the maximum value of 55Hz, the number of inadequaltead correlation points measured was the greatest and substantially stable.
TABLE 1 samples in different13C-13C coupling constant (J)C-C) Signal correspondence table of INADEQUATEAD spectrum
Example 3
As shown in table 2, in this embodiment, according to the fact that the detected direct dimensional spectral width (sw) is 37878.8Hz, based on embodiment 1, the sampling time (at) of the sampling time is adjusted and set to 35ms and 75ms from 55ms, it is found that the number of measured inadequaltable correlation points changes greatly, and particularly, when the sampling time is 35ms, "side sway" occurs in the peak, which indicates that the setting is too short when the sampling time is 35 ms. Therefore, the sampling time (at) is preferably 54.067 ms.
TABLE 2 signal correspondence table for INADEQUATEAD spectra of samples at different sampling times (at)
| Serial number | Sampling time (ms) | Number of InADEQUATEAD relevant points |
| 1 | at＝35.012 | 8 |
| 2 | at＝54.067 | 12 |
| 3 | at＝74.352 | 9 |
Example 4
As shown in table 3, in this embodiment, on the basis of embodiments 1 and 2, the number of scans (nt) is preferably set to 256, 450, and 512, respectively, and it is found that the results of the scans 450 and 512 are not changed much and tend to be stable, which means that the optimization of the number of scans is more effective and the number of scans 450 is sufficient, so the number of scans (nt) is 450.
TABLE 3 signal correspondence table for INADEQUATEAD spectra of samples at different scan times (nt)
| Serial number | Number of scans | Number of InADEQUATEAD relevant points |
| 1 | nt＝256 | 10 |
| 2 | nt＝450 | 12 |
| 3 | nt＝512 | 12 |
As can be seen from the above table, the proposed method of the present invention enables determination of the inadequaltean profile of isomaltulose, which facilitates the dissection of structural information of carbon-carbon linkage of isomaltulose. It can be seen that the method of the present invention can determine the inadequaltead spectrum of isomaltulose, and that when the direct dimensional width (sw) is 37878.8Hz,13C-13c coupling constant (J)C-C) 55Hz, gradient-90-gradient steady state (compad) 1.999 ms; the sampling time (at) of a single sampling is 54.067ms, the repeated scanning times (nt) are 450 times, and the effect is best when the whole sampling period is 17 h.
The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.
Claims (5)
1. A method for testing the natural abundance double-quantum transfer spectrum of isomaltulose based on the nuclear magnetic resonance technology is characterized by comprising the following steps:
(1) dissolving isomaltulose in a mixed solvent of deuterated dimethyl sulfoxide and tetramethylsilane, transferring the mixture into a nuclear magnetic tube, and placing the nuclear magnetic tube into a detection magnet of a nuclear magnetic spectrometer;
(2) selecting deuterated dimethyl sulfoxide in an instrument workstation, and tuning, shimming and field locking;
(3) loading a pulse sequence and setting other detection parameters by adopting a pulse mode of adiabatic 180 degrees and gradient-90-gradient steady state;
(4) after the setting is finished, executing a program to obtain an isomaltulose natural abundance double-quantum transfer spectrum;
the pulse sequence in the step (3) is as follows: carbon is taken as an observation nucleus and sequentially passes through a gradient field, a rectangular pi/2 pulse, a gradient field, a relaxation delay time, a rectangular pi/2 pulse, a section of adiabatic pulse, a gradient-90-gradient steady state, a section of adiabatic pulse, two rectangular pi/2 pulses and a sampling time.
2. The method for testing the natural abundance double-quantum transfer spectrum of isomaltulose based on the nuclear magnetic resonance technology according to claim 1, wherein the time of the gradient field is 2.0 ms; the pulse time of the rectangular pi/2 pulse is 10.1 mu s; the relaxation delay time is 1.0 s; the pulse time of the adiabatic pulse is 3.545 ms; the gradient-90-gradient steady state time is 1.999 ms; the sampling time is 30-65 ms.
3. The method for testing the natural abundance double-quantum transfer spectrum of isomaltulose based on the nmr technique of claim 1, wherein the other detection parameters in step (3) comprise: wide direct vitamin spectrum,13C-13C-coupling constant, scan times and acquisition mode.
4. The method for testing the natural abundance double-quantum transfer spectrum of isomaltulose based on the nuclear magnetic resonance technology according to claim 3, wherein the direct dimensional spectrum width is 37878.8Hz; the above-mentioned13C-13The C coupling constant is 45-65 Hz; the scanning times are 256-512 times.
5. The method for testing the natural abundance double-quantum transfer spectrum of isomaltulose based on the nuclear magnetic resonance technology according to claim 1, wherein the volume ratio of the deuterated dimethyl sulfoxide to the tetramethylsilane in the mixed solvent in the step (1) is 100: 3; the concentration of the isomaltulose in the mixed solvent was 50 mg/mL.
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