A method for analyzing and determining the aggregation structure of compounds containing polar bonds in condensed state

Abstract

The invention discloses a method for analyzing and determining the aggregation structure in a condensed state of a compound containing a polar bond. The method comprises the following steps: obtaining the parallel polarization Raman spectrum frequency and the vertical polarization Raman spectrum frequency of the polar bond by using Raman spectroscopy, calculating the difference between the parallel polarization Raman spectrum frequency and the vertical polarization Raman spectrum frequency and plotting the difference with the environmental variable of the sample under test, and inverting the condensed state aggregation structure corresponding to the environmental variable value by using the environmental variable value corresponding to the inflection point of the obtained curve, or obtaining the characteristic point of the curve by using the environmental variable value corresponding to the characteristic point by using the environmental variable value, and then analyzing and judging the condensed state aggregation structure corresponding to other environmental variable values ​​under the same environmental variable; the epitaxial method comprises the following steps: linearly fitting and extending the monotonically increasing and monotonically decreasing data points respectively, and recording the obtained intersection points as characteristic points.

Description

Technical Field

[0001] The invention belongs to the field of analysis and testing technology and structure in condensed state, relates to the determination of aggregation structure in condensed state of polar bond compound by spectroscopy, and specifically relates to a method for analyzing and determining aggregation structure in condensed state of polar bond compound. Background Art

[0002] The patent specification with publication number CN 113376139 A discloses a method for detecting the molecular structure of petroleum, including: determining the rheological parameters of a petroleum sample to be detected with a unit thickness, determining the Raman scattering laser parameters according to the rheological parameters, irradiating multiple petroleum samples to be detected according to the Raman scattering laser parameters, and determining the frequencies of different lights after the Raman effect occurs in each petroleum sample to be detected and determining the timestamp of the occurrence of each frequency light; determining outlier frequency light according to each frequency light corresponding to the multiple petroleum samples to be detected and the corresponding timestamp, taking the average value of each frequency light after removing the outlier frequency light as the target frequency light, and generating a target spectrum according to each target frequency light; inputting the target spectrum into a carbon-hydrogen bond number prediction model to obtain the carbon-hydrogen bond number of the petroleum sample to be detected; and determining the molecular structure of the petroleum sample to be detected according to the carbon-hydrogen bond number and the mass of the petroleum sample to be detected with a unit thickness.

[0003] Intermolecular interactions have important applications in many scientific fields (life sciences, crystal chemistry and supramolecular chemistry). Not only that, the dipole interaction forces in intermolecular interactions may also affect the stable structure, distribution and energy of solute molecules in the solvent; hydrogen bonds also play an indispensable role in the formation of protein secondary structures in living organisms.

[0004] Therefore, in the past few decades, intermolecular interactions have been the research focus of many scientists.

[0005] It is well known that some special vibration modes such as C=O are sensitive to changes in the solution environment. Raman spectroscopy can detect changes in the vibration frequency of each vibration mode, so Raman spectroscopy is widely used to study intermolecular interactions.

[0006] In a mixed solution, the dilution effect weakens the induced dipole-induced dipole (TD-TD) interaction between adjacent C=O vibration modes, so that the parallel polarization Raman vibration frequency of C=O and the vertical polarization Raman vibration frequency do not overlap. We name this difference as the coupling frequency difference.

[0007] In his master's thesis "Study on Raman Inconsistency Effect and Aggregate Structure of C=O", Xu Wenwen disclosed the conversion relationship between the Raman spectral intensity in the vertical and parallel directions of the sample collected by a polarizer and the intensity of the isotropic and anisotropic Raman spectra. This conversion relationship is a first-order linear change relationship. Therefore, the characteristic positions such as the inflection point of the intensity difference between the isotropic and anisotropic Raman spectra are consistent with the corresponding positions of the coupling frequency difference curve.

[0008] The present invention has found that the coupling frequency difference is closely related to the weak molecular interaction and the aggregate structure of the solution phase. Therefore, the present invention uses this as an indicator to analyze and determine the solution phase aggregate structure of a substance. Summary of the invention

[0009] The object of the present invention is to provide a method for determining metastable aggregation structures in condensed matter, especially aggregation structures with intermolecular interactions involving hydrogen bonds.

[0010] The present invention provides a method for analyzing and determining the aggregation structure of polar bond-containing compounds in condensed states. The method of the present invention can directly analyze and determine the number of hydrogen bonds formed and the microscopic structure of polar bond-containing compounds in condensed states, and is expected to be applied to the fields of solution self-assembly, supramolecular material preparation, protein structure determination, etc.

[0011] A method for analyzing and determining the aggregation structure in a condensed state of a compound containing polar bonds, wherein the method is a spectral method, using a laser Raman spectrometer, placing a polarizer at the light output position of a laser light source, adjusting the polarization direction of the polarizer so that the polarization direction of the polarizer is just consistent with the polarization direction of the laser light source, placing an analyzer in front of the slit of the laser Raman spectrometer, adjusting the polarization angle between the analyzer and the polarizer, collecting and obtaining the parallel polarization Raman spectrum frequency and the vertical polarization Raman spectrum frequency of the polar bonds, calculating and obtaining the difference between the parallel polarization Raman spectrum frequency and the vertical polarization Raman spectrum frequency, and plotting it against the environmental variables of the sample under test, using the environmental variable value corresponding to the inflection point of the obtained curve to infer the condensed state aggregation structure corresponding to the environmental variable value, or using the epitaxial method to obtain the characteristic point of the curve and using the environmental variable value corresponding to the characteristic point to infer the condensed state aggregation structure corresponding to the environmental variable value, and then analyzing and determining the condensed state aggregation structure corresponding to other environmental variable values ​​under the same environmental variables;

[0012] The extension method is: linearly fit and extend the monotonically increasing and monotonically decreasing data points respectively, and the obtained intersection points are recorded as the characteristic points. The linear fitting method can be the least square method, etc.

[0013] The parallel polarization Raman spectrum frequency and the vertical polarization Raman spectrum frequency of the polar bond are obtained by utilizing the angle between the polarizer and the analyzer to obtain the polarized Raman spectrum. The polarization directions of the polarizer and the analyzer are parallel to each other, and the obtained Raman spectrum is a parallel polarization Raman spectrum. Conversely, if the polarization directions of the polarizer and the analyzer are perpendicular to each other, the obtained Raman spectrum is a vertical polarization Raman spectrum.

[0014] The difference between the parallel polarization Raman spectrum frequency and the perpendicular polarization Raman spectrum frequency, referred to as the coupling frequency difference, can be positive or negative. In a preferred embodiment, it refers to the value obtained by subtracting the parallel polarization Raman spectrum frequency from the perpendicular polarization Raman spectrum frequency of the polar bond vibration frequency.

[0015] The coupling frequency difference is plotted against the environmental variables of the sample under test to obtain a variation trend diagram of the coupling frequency difference and the environmental variables, namely, a characteristic curve.

[0016] The polar bond-containing compound of the present invention may include a compound containing at least one polar bond of C=O, C=S, S=O, CO, CN, and HO, and specific types may be proteins, fats, and the like.

[0017] The method of the present invention can also be used for determining the molecular aggregation structure of acetone, methanol, pyrrolidone, formic acid, formamide and the like in different solvents.

[0018] In a preferred embodiment, the aggregation structure analysis and determination method of the condensed state of the compound containing polar bonds, the wavelength of the laser light source is 633nm, 532nm, 514nm or 488nm, preferably 532nm or 488nm, or a semiconductor laser is used, the power is 15-75mW, the depolarization ratio is> 100:1, the line width is <0.00001nm, the spectrometer is a monochromator and a CCD liquid nitrogen cooling device connected together, the grating groove is 1200G / mm, the blazing wavelength is 500nm, and the spectral resolution is 0.5cm -1 .

[0019] The environmental variable of the present invention may be temperature, pressure or concentration. Different environmental conditions include the aggregated structure of polar bond-containing compounds under different polar solvents and different concentration conditions, and also include the aggregated structure information between polar bond-containing compounds at different temperatures or pressures. Parallel polarization Raman spectra and vertical polarization Raman spectra at different concentrations, temperatures or pressures are measured, and the difference between the parallel polarization Raman spectrum frequency and the vertical polarization Raman spectrum frequency is plotted against the corresponding temperature or pressure, and the aggregated structure is analyzed according to the characteristic information of the spectrum.

[0020] In a preferred example, in the method for analyzing and determining the aggregation structure in the condensed state of a compound containing polar bonds, the environmental variable is concentration, and the volume fraction obtained according to the inflection point or epitaxial method is converted into a ratio of the amount of substance to obtain a preliminary molecular formula. After molecular modeling energy optimization, the vibration spectrum after modeling structure optimization is calculated using Gaussian software, and the rationality and final conformation of the condensed state aggregation structure are determined by comparing the experimental spectrum corresponding to the volume fraction.

[0021] In a preferred example, in the method for analyzing the aggregation structure of a condensed state of a compound containing polar bonds, the sample to be tested is a mixture of N-methylpyrrolidone and methanol.

[0022] In a preferred example, in the method for analyzing the aggregation structure of a condensed state of a compound containing polar bonds, the sample to be tested is a mixture of N-methylpyrrolidone and water.

[0023] In a preferred example, in the method for analyzing the aggregation structure of polar bond-containing compounds in a condensed state, the sample to be tested is a mixture of formamide and acetonitrile.

[0024] In a preferred example, in the method for analyzing the aggregation structure of polar bond-containing compounds in a condensed state, the sample to be tested is a mixture of ethylene carbonate and acetonitrile.

[0025] The method of the present invention can be used to determine the number of hydrogen bonds formed, the solution phase microstructure of polar bond compounds and other information.

[0026] Compared with the prior art, the present invention has the following main advantages:

[0027] The inflection points and characteristic points described in the present invention can be used to determine the structural ratio formed between the solvent and the solute, and directly obtain the number of hydrogen bonds formed. In conjunction with quantum chemical molecular structure optimization calculations, information such as the solution phase microstructure of polar bond compounds can be inferred. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 In the figure, A and B are the polarized Raman data of N-methylpyrrolidone in methanol tested in Example 1, and CE is Figure 2 Theoretical values ​​obtained from structural modeling;

[0029] Figure 2 For Example 1 Figure 1 The calculated structure of hydrogen bonding between N-methylpyrrolidone and methanol was obtained from the measurement results;

[0030] Figure 3 Polarized Raman data of N-methylpyrrolidone in water tested in Example 2;

[0031] Figure 4 For Example 2 Figure 3Schematic diagram of the hydrogen bond structure between N-methylpyrrolidone and water calculated from the measurement results;

[0032] Figure 5 Polarized Raman data of formamide in acetonitrile tested in Example 3;

[0033] Figure 6 For Example 3 Figure 5 Schematic diagram of the dimer formed by self-polymerization of formamide and the hydrogen bond structure between formamide and acetonitrile calculated from the measurement results;

[0034] Figure 7 Polarized Raman data of ethylene carbonate in acetonitrile tested in Example 4;

[0035] Figure 8 For Example 4 Figure 7 The dimer structure formed by the self-polymerization of ethylene carbonate was calculated from the measurement results. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with the accompanying drawings and specific examples. It should be understood that these examples are only intended to illustrate the present invention and are not intended to limit the scope of the present invention. The operating methods in the following examples without specifying specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturer.

[0037] A method for analyzing and determining the aggregation structure of a compound containing polar bonds in a condensed state, comprising:

[0038] 1) Adjust the polarization direction of the polarizer so that it is exactly consistent with the polarization direction of the laser light source. At this time, the light output energy is the highest.

[0039] 2) Prepare samples containing polar bond compounds under different environmental conditions, place an analyzer in front of the slit of the Raman spectrometer, adjust the angle of the analyzer so that its polarization direction is parallel to that of the polarizer, and collect the parallel polarized Raman spectrum of the sample to be tested. Then adjust the polarization direction of the analyzer so that it is perpendicular to the polarization direction of the polarizer, collect the Raman signal and obtain the vertically polarized Raman spectrum.

[0040] 3) Read the parallel polarization Raman spectrum frequency and the vertical polarization Raman spectrum frequency of the polar bond stretching vibration, calculate their frequency difference, and use their frequency difference to plot the corresponding test environmental variables. Use the epitaxy method, the curve inflection point, etc. to obtain the characteristic value, and use the mole fraction ratio corresponding to the characteristic value to infer the corresponding solution structure. This method can be used to determine the number of hydrogen bonds formed, the solution phase microstructure of polar bond compounds, and other information.

[0041] In step 1), the polarization direction of the polarizer is adjusted so that the polarization direction of the polarizer is just consistent with the polarization direction of the laser light source. An energy meter can be used to adjust the polarization direction of the polarizer while measuring the light energy value. When the energy value is the highest, the polarization direction of the polarizer is consistent with the polarization direction of the laser light source.

[0042] Example 1

[0043] Structure of N-methylpyrrolidone in methanol. Use a pipette to transfer a certain volume of N-methylpyrrolidone and methanol to a volume fraction of (V N-甲基吡咯烷酮 :V 总 )0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 solutions are to be tested. The laser (Coherent, CVI MELLES GRIOT) can generate continuous lasers. We use 532nm as the excitation wavelength, and the laser power can be adjusted between 15 and 75mW. Adjust the angle of the analyzer so that its polarization direction is parallel and perpendicular to the polarizer, respectively, and collect parallel polarized Raman spectra and vertical polarized Raman spectra of each concentration. The monochromator and CCD liquid nitrogen cooling device are connected together (manufacturer, Princeton Instruments Inc; model ID: LN / 2048X512.B / I, UVAR.). Finally, the spectrum is output by the computer through the detection system. In order to maximize the spectral signal-to-noise ratio, we collect each spectrum for about 100-200s, and collect 20-30 spectra for superposition. Figure 1 It can be seen that N-methylpyrrolidone and methanol have a turning point at a concentration of 0.8, forming a 2:1 hydrogen bond complex. Figure 2 shown. Figure 1 C, D, and E in Figure 2 The theoretical value obtained by structural modeling is completely consistent with the experimental value, so the final result is Figure 2 The final structure is a plausible one.

[0044] Example 2

[0045] Similar to Example 1, except that the structure of N-methylpyrrolidone in water is determined. Figure 3 It can be seen that the volume fraction of 0.6 is the jump point in the coupling frequency difference and concentration diagram. It can be calculated that at this time, N-methylpyrrolidone and water form a hydrogen bond complex with a molar ratio of 1:4, such as Figure 4 shown.

[0046] Example 3

[0047] Similar to Example 1, except that the structure of formamide in acetonitrile was determined. Figure 5As shown in Figure 2, the characteristic point appears when the formamide volume fraction is 0.40 through epitaxy. At this time, the formamide dimer begins to dissociate and eventually forms a 1:1 complex structure with acetonitrile molecules. The calculation shows that formamide dissociates from dimers into single molecules and forms a 1:1 complex structure with acetonitrile, as shown in Figure 2. Figure 6 shown.

[0048] The extension method of this embodiment is to perform linear fitting on the monotonically increasing and monotonically decreasing data points and extend them respectively, and the obtained intersection points are recorded as the characteristic points. Specifically, the data points corresponding to concentrations of 0.05, 0.1, 0.2, and 0.3 are linearly fitted by the least squares method, and the data points corresponding to concentrations of 0.6-1.0 are linearly fitted by the least squares method. The intersection of the two fitted straight lines is the characteristic point.

[0049] Example 4

[0050] Similar to Example 1, except that the structure of ethylene carbonate in acetonitrile is determined. Ethylene carbonate plays an important role in lithium-ion batteries and is one of the most common solvents. Determining its structural changes plays an important role in improving performance. Figure 7 As shown in the figure, the concentration effect of ethylene carbonate in acetonitrile dispersant measured by polarized Raman spectroscopy is shown. According to its frequency change and coupling frequency difference, ethylene carbonate gradually depolymerizes from dimer to single molecule structure due to the addition of acetonitrile. Figure 8 shown.

[0051] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A method for analyzing and determining the aggregation structure of a condensed state of a compound containing polar bonds, characterized in that: The method for analyzing and determining the aggregation structure in the condensed state of the compound containing polar bonds is a spectral method, which is used to determine the structural ratio formed between the solvent and the solute. A laser Raman spectrometer is used. A polarizer is placed at the light output position of the laser light source. The polarization direction of the polarizer is adjusted so that the polarization direction of the polarizer is just consistent with the polarization direction of the laser light source. An analyzer is placed in front of the slit of the laser Raman spectrometer, and the polarization angle between the analyzer and the polarizer is adjusted. The parallel polarization Raman spectrum frequency and the vertical polarization Raman spectrum frequency of the polar bonds are collected and obtained. The difference between the parallel polarization Raman spectrum frequency and the vertical polarization Raman spectrum frequency is calculated and plotted against the environmental variables of the sample under test. The environmental variable value corresponding to the inflection point of the obtained curve is used to infer the condensed state aggregation structure corresponding to the environmental variable value. Alternatively, the characteristic point of the curve is obtained by an epitaxial method, and the environmental variable value corresponding to the characteristic point is used to infer the condensed state aggregation structure corresponding to the environmental variable value, and then the condensed state aggregation structure corresponding to other environmental variable values ​​under the same environmental variable is analyzed and determined. The extension method is: linearly fitting and extending the monotonically increasing and monotonically decreasing data points respectively, and the obtained intersection points are recorded as the characteristic points.

2. The method for analyzing and measuring the aggregation structure in the condensed state of a compound containing polar bonds according to claim 1, characterized in that: The polar bond-containing compound includes a compound containing at least one polar bond of C=O, C=S, S=O, CO, CN, and HO.

3. The method for analyzing and measuring the aggregation structure in the condensed state of a compound containing polar bonds according to claim 1, characterized in that: The wavelength of the laser light source is 633nm, 532nm, 514nm or 488nm, or a semiconductor laser is used, with a power of 15-75mW, a depolarization ratio of >100:1, a line width of <0.00001nm, and a spectrometer is a monochromator and a CCD liquid nitrogen cooling device connected together, with a grating groove of 1200G / mm, a blazing wavelength of 500nm, and a spectral resolution of 0.5cm -1 .

4. The method for analyzing and measuring the aggregation structure in the condensed state of a compound containing polar bonds according to claim 1, characterized in that: The environmental variable is temperature, pressure or concentration.

5. The method for analyzing and measuring the aggregation structure in the condensed state of a polar bond-containing compound according to claim 4, characterized in that: The environmental variable is concentration. The volume fraction obtained according to the inflection point or epitaxial method is converted into the ratio of the amount of substance to obtain a preliminary molecular formula. After molecular modeling energy optimization, the vibration spectrum after modeling structure optimization is calculated using Gaussian software. The rationality and final conformation of the condensed state aggregation structure are determined by comparing the experimental spectrum corresponding to the volume fraction.

6. The method for analyzing and measuring the aggregation structure in the condensed state of a compound containing polar bonds according to claim 1, characterized in that: The sample to be tested is a mixture of N-methylpyrrolidone and methanol.

7. The method for analyzing and measuring the aggregation structure in the condensed state of a compound containing polar bonds according to claim 1, characterized in that: The sample to be tested is a mixture of N-methylpyrrolidone and water.

8. The method for analyzing and measuring the aggregation structure in the condensed state of a compound containing polar bonds according to claim 1, characterized in that: The sample to be tested is a mixture of formamide and acetonitrile.

9. The method for analyzing and measuring the aggregation structure in the condensed state of a compound containing polar bonds according to claim 1, characterized in that: The sample to be tested is a mixture of ethylene carbonate and acetonitrile.

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