Method for monitoring baicalein-betaine eutectic process based on terahertz spectrum

Abstract

The invention relates to the technical field of pharmaceutical analysis, and discloses a method for monitoring a baicalein-betaine eutectic process based on terahertz spectroscopy, and the method comprises the following steps: mixing and ball-milling baicalein and betaine to obtain powder samples, collecting the powder samples with different ball-milling times, drying, mixing with a dispersing agent, tabletting, and drying to obtain the baicalein-betaine eutectic crystal. The method comprises the following steps: measuring spectral data by using terahertz time-domain spectroscopy equipment, selecting a characteristic peak and tracking intensity change to obtain a curve, carrying out nonlinear fitting on the curve, obtaining a molecular vibration mode through a density functional theory, and analyzing the eutectic process by combining the two modes. The terahertz spectrum technology is combined with theoretical calculation, complete analysis of the baicalein-betaine eutectic process from macrodynamics monitoring to microcosmic molecular action mechanism analysis is achieved, and an effective means is provided for eutectic formation research and process optimization.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pharmaceutical analysis, in particular to a method for monitoring the process of baicalein-betaine co-crystal based on terahertz spectroscopy. BACKGROUND

[0002] Traditional Chinese medicine (TCM) has been widely used for thousands of years, attracting research interest from all over the world1. It is of great significance to extract and purify active pharmaceutical ingredients (APIs) from traditional Chinese medicine raw materials to ensure the consistency of drug efficacy. However, due to the limitations of raw materials in water solubility, stability and bioavailability, etc., only less than 1% of raw materials have successfully realized commercialization. For example, baicalin (BAI) is a flavonoid compound extracted from the roots of Scutellaria baicalensis Georgi, which has anti-obesity, antioxidant and anti-cancer effects. However, the low solubility and bioavailability of flavonoids have severely limited their application as raw materials.

[0003] Co-crystal is a widely recognized method to optimize the physicochemical properties of raw materials without changing the molecular structure of the raw materials. In order to form a co-crystal, the raw materials are combined together by non-covalent interactions with biocompatible co-crystal formers (CCFs). Betaine (BTN) is a natural compound widely present in microorganisms, plants and animals. Its biological safety features are particularly prominent, and studies have shown that it has a natural metabolic pathway, low toxicity in the human body, and good biocompatibility in the prevention and treatment of chronic diseases. BAI and BTN can form co-crystals to enhance the physicochemical properties of BAI. However, how BAI-BTN co-crystals are formed remains a mystery, so studying the process of baicalein-betaine co-crystal formation has practical significance.

[0004] In existing technologies, Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction (XRD) and differential scanning calorimetry (DSC) have been used for co-crystal detection. However, for co-crystals, these methods are sometimes time-consuming and lack sufficient information about weak intermolecular interactions. Therefore, it is of great significance to find a suitable method to comprehensively detect and evaluate the properties and dynamic reaction processes of co-crystals. Not only can it deepen the understanding of intermolecular interactions, but also can strengthen the elucidation of the mechanism of co-crystal formation in the pharmaceutical industry.

[0005] Terahertz (THz) spectroscopy is considered to have major advantages in studying the co-crystallization process, which can provide spectral fingerprints as a sensitive probe to distinguish co-crystals and their component structural differences, and has broad application prospects in drug development, such as distinguishing polymorphic materials, monitoring phase transitions, and preparing and characterizing pharmaceutical co-crystals. This method has good application prospects in the analysis and measurement of solid-phase materials, especially in process monitoring and control in the field of pharmaceutical-related research. Terahertz spectroscopy can further elucidate the information of intermolecular interactions, thereby deepening the understanding of co-crystal formation.

[0006] Therefore, the present application provides a method for monitoring the baicalein-betaine co-crystallization process based on terahertz spectroscopy, which solves the problems of long detection time, lack of weak intermolecular interaction information, limited research on the physicochemical properties of raw materials, and insufficient dynamic monitoring of the co-crystallization process in the prior art. SUMMARY

[0007] Therefore, the present application provides a method for monitoring the baicalein-betaine co-crystallization process based on terahertz spectroscopy, which solves the problems of long detection time, lack of weak intermolecular interaction information, limited research on the physicochemical properties of raw materials, and insufficient dynamic monitoring of the co-crystallization process in the prior art.

[0008] The present application provides a method for monitoring the baicalein-betaine co-crystallization process based on terahertz spectroscopy, which includes:

[0009] The method for monitoring the baicalein-betaine co-crystallization process based on terahertz spectroscopy, characterized in that it comprises:

[0010] Mixing baicalein and betaine, and then ball milling after mixing to obtain a powder sample;

[0011] Collecting powder samples of different ball milling times and performing drying treatment;

[0012] Mixing and grinding the dried powder sample with a dispersing agent, and then compressing to obtain tablets;

[0013] Performing spectral measurement on the tablets using a terahertz time-domain spectroscopy device to obtain spectral data;

[0014] Selecting characteristic peaks in the spectral data, tracking the intensity changes of the characteristic peaks, and obtaining a characteristic peak intensity change curve;

[0015] Nonlinear fitting the relationship between the characteristic peak intensity change curve and the ball milling time, using a function model matching the co-crystallization reaction kinetics to obtain a fitting curve and parameters reflecting the reaction rate;

[0016] Optimizing the crystal structure of the baicalein-betaine co-crystal by density functional theory, calculating the molecular vibration frequency, and obtaining the molecular vibration mode corresponding to the characteristic peak;

[0017] Based on the fitting curve and the molecular vibration mode, the baicalein-betaine co-crystal process is analyzed.

[0018] Further, the baicalein and betaine are mixed at a mass ratio of 1:1, the ball milling time is 20 minutes, and the frequency is 30 Hz.

[0019] Further, the mass ratio of the powder sample and the dispersant is 1:5, the pressing pressure is 10 megapascals, and the pressing time is 5 minutes.

[0020] Further, the terahertz time-domain spectroscopy device is used to perform spectral measurement on the tablets to obtain spectral data, including:

[0021] The terahertz time-domain spectroscopy device is used to scan the tablets;

[0022] Based on the asynchronous sampling principle, the single scanning time is shortened, and multiple scans are accumulated and averaged each time;

[0023] Dry air is blown during scanning, and the temperature is kept constant at a set value;

[0024] Based on the device detecting the terahertz wave signal transmitted through the tablets, the terahertz spectral data of the tablets is obtained.

[0025] Further, the method for monitoring the baicalein-betaine co-crystal process based on terahertz spectroscopy, characterized in that the characteristic peaks in the spectral data are selected, the intensity changes of the characteristic peaks are tracked, and the characteristic peak intensity change curve is obtained, including:

[0026] The co-crystal characteristic peaks and the physical mixture characteristic peaks are screened from the spectral data;

[0027] The intensity values of the two characteristic peaks in the spectral data corresponding to different ball milling times are extracted to obtain the change curves of the intensities of the two characteristic peaks with ball milling time.

[0028] Further, the relationship between the characteristic peak intensity change curve and the ball milling time is nonlinearly fitted, a function model matching the co-crystal reaction kinetics is selected, the fitting curve and the parameters reflecting the reaction rate are obtained, including:

[0029] From the characteristic peak intensity change curve, the intensity data of the co-crystal characteristic peaks and the physical mixture characteristic peaks at different ball milling times are extracted, and the data is normalized;

[0030] A function model matching the co-crystal reaction kinetics is selected, and the relationships between the intensities of the two characteristic peaks and the ball milling time are nonlinearly fitted respectively to generate fitting curves;

[0031] Based on the fitting curve, a parameter reflecting the reaction rate is obtained, and the parameter includes the rate of reactant consumption and product generation in the eutectic formation process;

[0032] A determination coefficient of the fitting curve is calculated, and the fitting effect is evaluated based on the determination coefficient.

[0033] Further, when the data is normalized, the normalization formula is:

[0034]

[0035] Where x represents the original value, x min represents the minimum value, and x max represents the maximum value.

[0036] Further, the crystal structure of the baicalein-betaine eutectic is optimized by the density functional theory, the molecular vibration frequency is calculated, and the molecular vibration mode corresponding to the characteristic peak is obtained, including:

[0037] Obtain the initial crystal structure parameters and configuration of baicalein, betaine and eutectic crystal thereof;

[0038] Using the density functional theory, the initial crystal structure parameters and configuration are simulated and calculated using the CASTEP tool to obtain the simulated terahertz spectrum;

[0039] Select the GGA-PBE method to optimize the structure and calculate the frequency of the initial crystal structure parameters and configuration after simulation calculation;

[0040] After structure optimization, the molecular vibration frequency of the eutectic characteristic peak is obtained by energy simulation calculation;

[0041] Frequency analysis is performed on the molecular vibration frequency to generate a simulated terahertz spectrum of the eutectic characteristic peak;

[0042] The simulated terahertz spectrum is compared with the spectrum data, and the theoretical vibration frequency corresponding to the eutectic characteristic peak is determined according to the comparison result, and the molecular vibration mode of the eutectic characteristic peak is analyzed based on the theoretical vibration frequency.

[0043] Further, the GGA-PBE method is selected to optimize the structure and calculate the frequency of the initial crystal structure parameters and configuration after simulation calculation, including:

[0044] The plane wave cutoff energy of the initial crystal structure is fixed by the DFT-D2 correction method of Grimme;

[0045] The plane wave cutoff energy is sampled by the Monkhorst-Pack grid, and the convergence criteria for total energy and atomic force are set;

[0046] Based on the convergence criterion, the crystal structure of the eutectic is optimized, and the volume of the lattice parameters after optimization is recorded;

[0047] The convergence criterion is that the energy of each atom converges to 5.0*10 -7 eV, and the atomic force threshold is The atomic force maximum displacement threshold is

[0048] Further, the eutectic process of baicalein-betaine is analyzed based on the fitting curve and the molecular vibration mode, including:

[0049] According to the fitting curve, the reaction rate of the physical mixture and the eutectic in the eutectic process of baicalein-betaine is analyzed.

[0050] According to the molecular vibration mode, the corresponding swing relationship of the characteristic peaks of the physical mixture, the eutectic and baicalein and betaine is analyzed.

[0051] Compared with the prior art, the beneficial effects of the present application are:

[0052] The present application realizes the complete analysis of the eutectic process of baicalein-betaine from macroscopic monitoring to microscopic mechanism analysis by combining terahertz spectroscopy technology with theoretical calculation. Through characteristic peak tracking and nonlinear fitting, the reaction rate and stage characteristics of eutectic formation are quantified, which provides a quantitative basis for process optimization. With the help of density functional theory, the molecular vibration mode is obtained, the microscopic action corresponding to the characteristic peak is clear, and the reconstruction rule of intermolecular force in eutectic formation is revealed. The combination of fitting curve and molecular vibration mode verifies the synchronicity of macroscopic dynamics and microscopic mechanism in the eutectic formation process, which provides a cross-scale analysis method for eutectic formation mechanism research, and also provides a reference framework for other eutectic system research.

[0053] The present application shortens the eutectic detection time and can monitor the eutectic dynamic process in real time, breaking the limitation of raw material physical and chemical property research and providing a research basis for weak intermolecular interaction information.

[0054] The general description above and the detailed description below are only exemplary and explanatory, not limiting the present disclosure.

[0055] Other features and aspects of the present disclosure will become more apparent from the following detailed description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF DRAWINGS

[0056] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are for purposes of illustration only and are not considered a limitation of the present application. Moreover, in the attached drawings, the same reference numerals will be used to refer to the same or like components throughout the viewing. In the drawings:

[0057] Figure 1 A flow chart of the method for monitoring the baicalein-betaine co-crystal process based on terahertz spectrum provided by the embodiment of the present application is shown in the figure;

[0058] Figure 2 A terahertz spectrum data graph obtained by experiment of the baicalein-betaine co-crystal prepared under different ball milling time provided by the embodiment of the present application is shown in the figure;

[0059] Figure 3 A terahertz absorption spectrum graph of BAI, BTN and BAI-BTN and the physical mixture of baicalein-betaine in the range of 0.5-2.0 terahertz provided by the embodiment of the present application is shown in the figure;

[0060] Figure 4 A normalized change graph of the relative peak intensity at 1.27 THz and 1.53 THz in the frequency domain spectrum in the different ball milling reaction time line by using liquid phase assisted ball milling method provided by the embodiment of the present application is shown in the figure;

[0061] Figure 5 A theoretical calculation graph of the spherocylindrical model of BAI, BTN and BAI-BTN and the physical mixture of baicalein-betaine and an experimental result graph provided by the embodiment of the present application are shown in the figure;

[0062] Figure 6 A theoretical calculation result graph of the two terahertz characteristic peak vibration modes of BAI-BTN provided by the embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0063] Exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present disclosure can be more thoroughly understood and the scope of the present disclosure can be accurately conveyed to those skilled in the art. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0064] Reference Figure 1 As shown in the figure, the embodiment of the present application proposes a method for monitoring the baicalein-betaine co-crystal process based on terahertz spectrum, which comprises the following steps:

[0065] Step S100: mixing baicalein (BAI) and betaine (BTN), and then ball milling after mixing to obtain a powder sample;

[0066] Step S200: collecting the powder sample of different ball milling time and performing drying treatment;

[0067] Step S300: mixing and grinding the dried powder sample with a dispersant, and pressing to obtain tablets;

[0068] Step S400: performing spectral measurement on the tablets using a terahertz time-domain spectroscopy device to obtain spectral data;

[0069] Step S500: selecting a characteristic peak in the spectral data and tracking changes in the intensity of the characteristic peak to obtain a characteristic peak intensity change curve;

[0070] Step S600: performing nonlinear fitting on the relationship between the characteristic peak intensity change curve and the ball milling time, using a function model matching the kinetics of the eutectic reaction to obtain a fitting curve and parameters reflecting the reaction rate;

[0071] Step S700: optimizing the crystal structure of the baicalein-betaine eutectic by density functional theory, calculating the molecular vibration frequency, and obtaining the molecular vibration mode corresponding to the characteristic peak;

[0072] Step S800: analyzing the baicalein-betaine eutectic process based on the fitting curve and the molecular vibration mode.

[0073] It can be understood that adding liquid-assisted ball milling can promote molecular diffusion, and the mechanical force of the grinding ball can break the original intermolecular forces to provide conditions for eutectic formation.

[0074] Specifically, powder samples are collected at different ball milling times, such as 0, 10, 20, and 30 minutes, and the specific time frequency is determined according to actual needs, and then the residual liquid of the powder sample is removed by drying treatment, which is drying treatment at 40°C.

[0075] It can be understood that when the dried powder sample is mixed and ground with a dispersant, the dispersant can reduce the scattering of terahertz waves by sample particles, ensure the uniformity of the optical path of the tablets, and improve the reliability of the spectral data.

[0076] It can be understood that the tablets include a physical mixture of baicalein-betaine and a eutectic of baicalein-betaine (BAI-BTN).

[0077] It can be understood that when the terahertz waves of the terahertz time-domain spectroscopy device pass through the tablets, waves of a specific frequency are absorbed by the sample, forming a characteristic absorption peak, which can reflect molecular vibration or intermolecular interaction.

[0078] It can be understood that the change in the intensity of the characteristic peak directly reflects the progress of eutectic formation.

[0079] It can be understood that the reaction rate parameters can be obtained by fitting the relationship between the characteristic peak intensity and the ball milling time with a function model matching the eutectic reaction kinetics, such as a pseudo-first-order kinetic equation, so as to quantitatively describe the kinetic process of eutectic formation, such as the reaction rate and the time to reach equilibrium.

[0080] It can be understood that by optimizing the crystal structure of the eutectic through density functional theory (DFT), calculating the molecular vibration frequency, and determining the molecular vibration mode corresponding to the characteristic peak, such as the swing vibration of baicalein or betaine, the origin of the characteristic peak can be explained from the molecular level, and the micro-mechanism of eutectic formation, such as the type of intermolecular interaction, can be revealed.

[0081] It can be understood that the combination of the macro-kinetic trend of the fitting curve, such as the eutectic formation rate, and the theoretically calculated micro-vibration mode, such as the change of intermolecular force, can completely analyze the eutectic formation process; the change of characteristic peak intensity reflects the accumulation of eutectic "quantity"; the vibration mode reveals the structural change of eutectic "quality", and the combination of the two can clarify the complete mechanism of eutectic formation.

[0082] It can be seen that the present application overcomes the defect that the traditional method cannot be continuously monitored by tracking the change of the characteristic peak intensity, and reflects the progress of eutectic formation in real time; terahertz spectroscopy is sensitive to intermolecular hydrogen bonds, van der Waals forces and other weak interactions, providing micro-interaction information that is difficult to obtain by traditional spectroscopy, and assisting in the analysis of the eutectic mechanism; nonlinear fitting realizes the quantitative description of eutectic kinetics, and theoretical calculation clearly defines the molecular vibration mode, comprehensively revealing the eutectic formation rule from macro to micro.

[0083] It can be seen that the present application provides a basis for controlling the ball milling conditions, such as time and frequency, by clearly defining the reaction rate and equilibrium time, thereby improving the efficiency and stability of eutectic preparation. Furthermore, it provides technical support for improving the physicochemical properties of active ingredients of traditional Chinese medicines such as baicalein, and promotes the commercialization of the active ingredients.

[0084] Referring to Figure 1 In some embodiments of the present application, baicalein and betaine are mixed in a mass ratio of 1:1, the ball milling time is 20 minutes, and the frequency is 30 Hz.

[0085] Specifically, baicalein and betaine are mixed in a mass ratio of 1:1, 15 μl of ultrapure water is added, 10 stainless steel balls with a diameter of 3 mm are used, a high-speed vibration ball mill is used to ball mill the sample at a frequency of 30 Hz, the ball milling time is 20 minutes, and powder samples at different ball milling times are collected.

[0086] Specifically, as Figure 2 The terahertz spectroscopy data obtained from the experiment of preparing baicalein-betaine eutectic by liquid-assisted ball milling at different ball milling times is shown, and the data is obtained from terahertz-time-domain spectroscopy (THz-TDS) measurement.

[0087] It can be understood that the BAI and BTN are mixed and then ball-milled at room temperature. During this process, a significant change in the frequency domain spectrum is observed. Figure 2 It is shown that the eutectic absorption spectrum presents a significant enhancement trend as the ball-milling process proceeds. The characteristic absorption peak of the physical mixture appears at 1.53 THz, and the intensity of the characteristic absorption peak of the physical mixture gradually decreases as the ball-milling time prolongs, while the characteristic absorption peak of the eutectic appears at 1.27 THz, and the intensity of the characteristic absorption peak of the eutectic gradually increases as the ball-milling time prolongs.

[0088] Figure 2 The arrows indicate the change of the absorption peak of the physical mixture and the formation process of the eutectic. This observation shows that the initial mixture reactants are consumed as the eutectic formation reaction effectively proceeds. After about 18 minutes of ball-milling, the absorption spectrum only shows a characteristic eutectic peak, indicating that the solid-state eutectic conversion has been completed. After 40 minutes of reaction, the absorption peak no longer changes significantly.

[0089] It can be understood that the change in the spectral characteristics at different ball-milling times can clearly reflect the progress of eutectic formation. Through the dynamic evolution of the characteristic peak, it is proved that terahertz spectroscopy can be used as a reliable means to distinguish physical mixtures from eutectics and track the eutectic formation process, laying an experimental foundation for subsequent mechanism analysis.

[0090] It can be seen that through the correlation of spectral characteristics and ball-milling time, it is shown that the eutectic formation is a dynamic process of gradual consumption of reactants and gradual generation of products, providing direct experimental evidence for understanding the kinetic characteristics of eutectic formation.

[0091] Referring to Figure 1 It is shown that in some embodiments provided by the present application, the mass ratio of the powder sample to the dispersant is 1:5, the pressure of the pressing is 10 MPa, and the pressing time is 5 minutes.

[0092] Specifically, the dried powder sample and the dispersant are uniformly mixed in a mass ratio of 1:5, and then manually ground with a mortar and pestle for 5 minutes to obtain a mixture. Then the mixture is pressed into a tablet with a thickness of 1 mm under a pressure of 10 MPa, and the pressing time is 5 minutes. The dispersant is a cyclic olefin copolymer.

[0093] Referring to Figure 1 It is shown that in some embodiments provided by the present application, the process of obtaining spectral data by using a terahertz time-domain spectroscopy device to perform spectral measurement on the tablet includes:

[0094] The terahertz time-domain spectroscopy device is used to scan the tablet, and the pressed tablet is fixed on the sample stage of the terahertz time-domain spectroscopy device to ensure that the tablet is completely in the transmission light path;

[0095] Based on the principle of asynchronous sampling, the single scan time is shortened, and multiple scans are accumulated and averaged each time;

[0096] Specifically, the frequency range of terahertz waves is set, such as 0.5-5.0 terahertz, the asynchronous sampling mode is enabled to shorten the single scan time, and the number of accumulated scans is set, such as 1024 times, for subsequent averaging to reduce noise;

[0097] Dry air is blown during scanning and the temperature is kept constant at a set value, and the temperature set value is room temperature, to avoid the influence of temperature fluctuation on the stability of the spectral signal;

[0098] Based on the device detecting the terahertz wave signal transmitted through the tablet, the terahertz spectral data of the tablet is obtained.

[0099] It can be understood that the device emits terahertz waves, which are received by the detector after passing through the tablet, and records the time-domain signal of the terahertz waves, such as the change of amplitude with time. Based on the principle of asynchronous sampling, the device quickly completes one scan and repeats the scan for a set number of times to obtain multiple sets of time-domain signals. The time-domain signals of multiple scans are averaged to eliminate random noise and improve the signal-to-noise ratio. Through Fourier transform, the time-domain signal is converted into a frequency-domain spectrum, and the absorption intensity at different frequencies, i.e. spectral data, is obtained, which is used to reflect the absorption characteristics of the terahertz waves in the tablet.

[0100] As shown in Figure 3 , the terahertz absorption spectra of baicalein, betaine, baicalein-betaine co-crystal and baicalein-betaine physical mixture in the range of 0.5-2.0 terahertz (THz) are shown.

[0101] As can be seen from Figure 3 , the absorption peak of baicalein appears at 1.19 terahertz. In contrast, the absorption peak of betaine appears at 1.53 terahertz, the absorption peak of the physical mixture appears at 1.53 terahertz, and the absorption peak of the baicalein-betaine co-crystal appears at 1.27 terahertz. The co-crystal also shows absorption peaks at 0.71, 0.86, 1.73 and 1.96 terahertz.

[0102] It can be understood that the terahertz absorption peak of the co-crystal is not simply a linear combination of the spectra of the raw materials, which indicates that there is a complex intermolecular interaction, and the terahertz spectrum shows obvious differences before and after the co-crystal reaction, which helps to clearly distinguish the co-crystal and non-co-crystal samples. At the same time, the terahertz spectrum of the physical mixture sample is different from that of the co-crystal sample, indicating that the co-crystal reaction cannot occur spontaneously and must be carried out by ball milling, which also lays the foundation for monitoring the co-crystal process by controlling the ball milling time.

[0103] Referring toFigure 1 As shown, in some embodiments of the present application, the process of selecting characteristic peaks in the spectral data, tracking the intensity changes of the characteristic peaks, and obtaining the characteristic peak intensity change curve includes:

[0104] Screening eutectic characteristic peaks and physical mixture characteristic peaks from the spectral data;

[0105] Extracting the intensity values of the two characteristic peaks in the spectral data corresponding to different ball milling times to obtain the change curves of the intensity of the two characteristic peaks with ball milling time.

[0106] It can be understood that by tracking the intensity changes of the two characteristic peaks, the process of the physical mixture converting into the eutectic can be directly reflected: the intensity of the physical mixture characteristic peak decreases with the ball milling time, that is, the reactant decreases, and the intensity of the eutectic characteristic peak increases with the ball milling time, that is, the product increases.

[0107] Specifically, the terahertz spectrum of the tablets at the ball milling time of 0 minutes (initial physical mixture), 10 minutes, 12 minutes, 18 minutes, 40 minutes, etc. is measured to obtain the frequency domain spectral data at the corresponding time points, and each time point corresponds to one spectral curve. The horizontal axis of the spectral curve is the frequency, and the vertical axis is the absorption intensity.

[0108] Specifically, when screening the characteristic peaks, the spectra of the pure eutectic (a sample known to be completely reacted) and the initial physical mixture are compared to identify the difference peaks: the peak unique to the eutectic and not present or with extremely low intensity in the physical mixture is the “eutectic characteristic peak”, such as 1.27 THz; the peak with significant intensity in the physical mixture and disappearing or with extremely low intensity in the eutectic is the “physical mixture characteristic peak”, such as 1.53 THz.

[0109] Specifically, when extracting the intensity values of the characteristic peaks, for the spectral data at each ball milling time, the absorption intensity values (vertical axis values) corresponding to the eutectic characteristic peak (such as 1.27 THz) and the physical mixture characteristic peak (such as 1.53 THz) are read. Taking the ball milling time as the horizontal axis (unit: minutes), and taking the intensity of the eutectic characteristic peak and the intensity of the physical mixture characteristic peak as the vertical axis (unit: arbitrary intensity unit, consistent), respectively; the intensity values at each time point are labeled in the coordinate system, and the points are connected by a curve to obtain two intensity change curves: one reflecting the change of the eutectic characteristic peak intensity with time, and the other reflecting the change of the physical mixture characteristic peak intensity with time.

[0110] It can be understood that the change curves of the intensity of the two characteristic peaks with ball milling time can directly visualize the dynamic process of eutectic formation, and the reaction progress can be judged without complex calculation.

[0111] Referring to Figure 1As shown, in some embodiments of the present application, the relationship between the characteristic peak intensity change curve and the ball milling time is nonlinearly fitted, a function model matching the eutectic reaction kinetics is adopted, a fitting curve and parameters reflecting the reaction rate are obtained, including:

[0112] From the characteristic peak intensity change curve, the intensity data of the eutectic characteristic peak and the physical mixture characteristic peak at different ball milling times are extracted, and the data are normalized;

[0113] A function model matching the eutectic reaction kinetics is selected, and the relationship between the intensity of the two characteristic peaks and the ball milling time is nonlinearly fitted respectively to generate a fitting curve;

[0114] Based on the fitting curve, parameters reflecting the reaction rate are obtained, including the rate of reactant consumption and product generation in the eutectic formation process;

[0115] The determination coefficient of the fitting curve is calculated, and the fitting effect is evaluated based on the determination coefficient.

[0116] Specifically, when the data are normalized, the normalization formula is:

[0117]

[0118] Where x represents the original value, x min represents the minimum value, and x max represents the maximum value.

[0119] It can be understood that the normalization processing unifies the intensity data of different orders of magnitude to the range of 0-1, so that the change trend of the eutectic peak and the mixture peak can be directly compared (such as the curve slope of the two can directly reflect the reaction speed), avoiding analysis deviation caused by absolute value difference.

[0120] Specifically, as Figure 4 shown, the normalized change of the relative peak intensity at 1.27 THz and 1.53 THz in the frequency domain spectrum in the reaction time line using the liquid-assisted ball milling method is shown.

[0121] In the terahertz absorption spectrum, the characteristic peak value of the physical mixture is 1.53 THz, and the characteristic peak value of the eutectic is 1.27 THz. The two characteristic peak values are selected for quantitative analysis in the solid-state conversion process. In order to eliminate the scale difference between the characteristics, the minimum-maximum normalization is applied to the two characteristic peak values, and the evolution of the terahertz spectrum absorption intensity can directly reveal the formation mechanism of the eutectic in the ball milling process by calculating the relative peak intensity normalization change of the two characteristic peak values over the ball milling time.

[0122] It can be understood that the normalization processing facilitates the determination of the eutectic composition in the intermediate reaction mixture at different ball milling time points in the conversion process. The reaction degree can be quantitatively calculated from the normalization formula through the increase of the eutectic strength and the decrease of the substrate strength.

[0123] Figure 4 The 95% confidence interval of the two groups of data is shown in the form of a color block, Figure 5 The data trend in the figure is fitted by a nonlinear fitting method, and the function relationship of the fitting curve at 1.27 THz and 1.53 THz is shown in Table 1:

[0124] Table 1. Function and R of the fitting curve 2 value

[0125]

[0126] R 2 is a determination coefficient, used to evaluate the fitting effect of a linear regression curve on discrete data points. The value of R 2 is closer to 1, the better the fitting effect.

[0127] According to Figure 4 two curve equations and the overall trend, it can be concluded that the curve fitting equation at 1.27 THz is consistent with the pseudo-first-order kinetic equation:

[0128] Q t = Q e ×(1-e -k×t ),

[0129] wherein Q t represents the real-time absorption peak intensity, Q e represents the final absorption peak intensity, and k represents the rate of change of the function. The characteristic peak intensity at 1.53 THz also decreases exponentially with the reaction. This may be due to the high concentration of reactants in the first 10 minutes of the reaction, resulting in an exponential increase in reaction rate. However, as the concentration of reactants decreases, the reaction rate gradually slows down until the reaction no longer proceeds.

[0130] It can be seen that through normalization processing and nonlinear fitting, the eutectic formation process is converted from qualitative observation to quantitative analysis, providing key technical support for in-depth understanding of eutectic kinetic characteristics and optimization of preparation process.

[0131] Referring to Figure 1 , in some embodiments provided by the present application, the crystal structure of the baicalein-betaine eutectic is optimized by density functional theory, the molecular vibration frequency is calculated, and the molecular vibration mode corresponding to the characteristic peak is obtained, including:

[0132] The initial crystal structure parameters and configuration of baicalein, betaine and the eutectic crystal thereof are obtained;

[0133] The initial crystal structure parameters and configurations are simulated by using the CASTEP tool based on the density functional theory to obtain simulated terahertz spectra;

[0134] The initial crystal structure parameters and configurations after simulation are optimized and frequency calculated by selecting the GGA-PBE method;

[0135] After structure optimization, the molecular vibration frequency of the eutectic characteristic peak is obtained through energy simulation calculation;

[0136] The molecular vibration frequency is analyzed by frequency analysis to generate the simulated terahertz spectrum of the eutectic characteristic peak;

[0137] The simulated terahertz spectrum is compared with the spectrum data, and the theoretical vibration frequency corresponding to the eutectic characteristic peak is determined according to the comparison result, and the molecular vibration mode of the eutectic characteristic peak is analyzed based on the theoretical vibration frequency.

[0138] Specifically, the GGA-PBE method is selected to optimize and calculate the frequency of the initial crystal structure parameters and configurations after simulation, including:

[0139] The plane wave cutoff energy of the initial crystal structure is fixed by the DFT-D2 correction method of Grimme;

[0140] The plane wave cutoff energy is sampled by the Monkhorst-Pack grid, and the convergence criteria of total energy and atomic force are set;

[0141] The crystal structure of the eutectic is optimized based on the above convergence criteria, and the volume of the optimized lattice parameters is recorded;

[0142] The convergence criteria are: the energy of each atom converges to 5.0×10 -7 eV, and the atomic force threshold is The atomic force maximum displacement threshold is

[0143] It can be understood that by optimizing the crystal structure of the eutectic through the density functional theory, calculating the molecular vibration frequency, and comparing the simulated vibration frequency with the experimental spectrum, the molecular vibration mode corresponding to the characteristic peak can be determined, such as the swing vibration of baicalein. Among them, the GGA-PBE method is used to describe the electron exchange correlation energy, the Grimme DFT-D2 correction considers the intermolecular dispersion force such as van der Waals force, the Monkhorst-Pack grid is used to improve the sampling accuracy of the Brillouin zone, and the convergence criteria ensure the reliability of the calculation results.

[0144] Specifically, the simulated terahertz spectrum is compared with the experimentally measured eutectic spectrum data, and the characteristic peak positions are matched, such as experiment 1.27 THz corresponding to simulation 1.25 THz, and experiment 1.73 THz corresponding to simulation 1.79 THz; according to the matching result, the theoretical vibration frequency corresponding to the experimental characteristic peak is determined, and the molecular vibration mode corresponding to the frequency is analyzed, such as 1.25 THz corresponding to the swing vibration of baicalein, and 1.79 THz corresponding to the swing vibration of betaine.

[0145] It can be understood that by theoretically calculating the eutectic characteristic peak, the formation mechanism of the experimental spectrum can be explained from the atomic level, and the limitation that only experiments cannot distinguish "which molecular movement causes the absorption peak" is made up.

[0146] Referring to Figure 1 , in some embodiments provided by the present application, based on the fitting curve and the molecular vibration mode, the baicalein-betaine eutectic process is analyzed, including:

[0147] According to the fitting curve, the reaction rate and reactant concentration of the physical mixture and the eutectic body in the baicalein-betaine eutectic process are analyzed;

[0148] According to the molecular vibration mode, the swing relationship of the physical mixture characteristic peak, the eutectic body characteristic peak, baicalein and betaine is analyzed.

[0149] Specifically, the generation rate is extracted from the fitting curve of the eutectic body characteristic peak (1.27 THz), and the consumption rate is extracted from the fitting curve of the physical mixture characteristic peak (1.53 THz), if the two values are close, it indicates that the eutectic generation and reactant consumption rates are synchronized.

[0150] As Figure 5 , the measured and simulated terahertz spectrum data are shown, and the blue vertical bars correspond to different vibration modes, and the height reflects the corresponding vibration intensity. Figure 5 The difference between the theoretical calculation value and the experimental value of the baicalein-betaine eutectic body is mainly analyzed. The simulated spectrum is generated by the Lorentz function on the basis of vibration mode analysis, and the half maximum full width used is 5 cm- 1 . Table 2 summarizes the characteristic vibration frequencies obtained from DFT calculation and experimental terahertz spectrum.

[0151] Table 2: Vibration mode assignment of baicalein-betaine eutectic body at 1.27 THz and 1.53 THz

[0152]

[0153] Wherein, l is the translation; ω is the swing vibration.

[0154] It can be seen that these peaks correspond to the 1.27 THz and 1.73 THz absorption peaks identified in the experimental results.

[0155] It is worth noting that there is a difference between the theoretical results and the experimental results, which is manifested as a blue shift and a red shift. The observed difference can be attributed to the fact that the theoretical calculation is carried out at 0K, while the experimental measurement is carried out at room temperature. Room temperature and humidity conditions have a certain influence on the measurement results.

[0156] Figure 6 The vibration modes of the two terahertz absorption peaks in the theoretical calculation are shown. The characteristic peak of the baicalein-betaine co-crystal at 1.27 THz corresponds to the vibration mode of the theoretical structure at 1.25 THz. This peak is derived from the swing vibration of baicalein. The characteristic peak of the baicalein-betaine co-crystal at 1.73 THz is similar to the peak of the theoretical model at 1.79 THz, which is mainly due to the swing vibration of the betaine co-crystal. The vibration modes of the BAI-BTN theoretical structure are shown in Table 2.

[0157] It can be understood that by combining macroscopic kinetics (fitting curve) and microscopic mechanism (vibration mode), both the reaction speed and the stage characteristics are determined, and the changes of molecular motion and interaction are revealed, avoiding the one-sidedness of single experiment or theoretical analysis.

[0158] The above examples realize the complete analysis of the baicalein-betaine co-crystallization process from macroscopic monitoring to microscopic mechanism analysis by combining terahertz spectroscopy technology and theoretical calculation. Through characteristic peak tracking and nonlinear fitting, the reaction rate and stage characteristics of co-crystallization formation are quantified, providing a quantitative basis for process optimization. With the help of density functional theory, the molecular vibration mode is obtained, the microscopic action corresponding to the characteristic peak is determined, and the reconstruction rule of intermolecular force in co-crystallization formation is revealed. The combination of fitting curve and molecular vibration mode verifies the synchronicity of macroscopic kinetics and microscopic mechanism in the co-crystallization formation process, providing a cross-scale analysis method for co-crystallization formation mechanism research, and also providing a reference framework for other co-crystallization system research.

[0159] The present application shortens the co-crystallization detection time through the above-mentioned scheme, can real-time monitor the co-crystallization dynamic process, breaks the limitation of raw material physical and chemical properties research, and provides a research basis for weak intermolecular interaction information.

[0160] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it, although the present application has been described in detail with reference to the above examples, those skilled in the art should understand that: the specific embodiments of the present application can be modified or replaced by the same, without departing from the spirit and scope of the present application. Any modification or equivalent replacement, which should be covered within the protection scope of the claims of the present application.

Claims

1. A method for monitoring the baicalin-betaine eutectic process based on terahertz spectroscopy, characterized in that, include: Baicalein and betaine were mixed and then ball-milled to obtain a powder sample. Powder samples with different ball milling times were collected and dried. The dried powder sample is mixed with a dispersant, ground, and then pressed to obtain tablets. The spectral data of the tablets were obtained by using a terahertz time-domain spectrometer. Select characteristic peaks from the spectral data, track the intensity changes of the characteristic peaks, and obtain the characteristic peak intensity change curves; The relationship between the characteristic peak intensity variation curve and the ball milling time was nonlinearly fitted, and a function model matching the eutectic reaction kinetics was used to obtain the fitted curve and parameters reflecting the reaction rate. The crystal structure of the baicalin-betaine eutectic was optimized using density functional theory, and the molecular vibrational frequencies were calculated to obtain the molecular vibrational modes corresponding to the characteristic peaks. The baicalein-betaine eutectic process was analyzed based on the fitted curves and molecular vibrational modes.

2. The method for monitoring the baicalin-betaine eutectic process based on terahertz spectroscopy according to claim 1, characterized in that, The baicalein and betaine are mixed at a mass ratio of 1:1, and the ball milling time is 20 minutes at a frequency of 30 Hz.

3. The method for monitoring the baicalin-betaine eutectic process based on terahertz spectroscopy according to claim 1, characterized in that, The mass ratio of the powder sample to the dispersant is 1:5, the pressing pressure is 10 MPa, and the pressing time is 5 minutes.

4. The method for monitoring the baicalin-betaine eutectic process based on terahertz spectroscopy according to claim 1, characterized in that, The method of using a terahertz time-domain spectroscopy device to perform spectral measurements on the tablets to obtain spectral data includes: The tablets were scanned using a terahertz time-domain spectroscopy device; Based on the principle of asynchronous sampling, the time for a single scan is shortened, and multiple scans are accumulated for each measurement and the average value is taken. Dry air is blown in during scanning and the temperature is kept constant at the set value; Terahertz spectral data of the tablet are obtained by detecting the terahertz wave signal transmitted through the tablet using the equipment.

5. The method for monitoring the baicalin-betaine eutectic process based on terahertz spectroscopy according to claim 4, characterized in that, The method for monitoring the baicalein-betaine eutectic process based on terahertz spectroscopy is characterized by the following steps: selecting characteristic peaks from the spectral data, tracking the intensity changes of the characteristic peaks, and obtaining the characteristic peak intensity change curves, including: Characteristic peaks of eutectic and physical mixtures were screened from spectral data; The intensity values ​​of two characteristic peaks in the spectrum corresponding to different ball milling times were extracted to obtain the curves of the intensity of the two characteristic peaks changing with ball milling time.

6. The method for monitoring the baicalin-betaine eutectic process based on terahertz spectroscopy according to claim 5, characterized in that, The nonlinear fitting of the relationship between the characteristic peak intensity variation curve and the ball milling time, using a function model matched to the eutectic reaction kinetics, yields the fitted curve and parameters reflecting the reaction rate, including: From the characteristic peak intensity variation curve, the intensity data of the eutectic characteristic peak and the physical mixture characteristic peak under different ball milling times were extracted, and the data were normalized. A function model matching the eutectic reaction kinetics was selected, and nonlinear fitting was performed on the relationship between the intensity of the two characteristic peaks and the ball milling time to generate fitting curves. Based on the fitted curve, parameters reflecting the reaction rate are obtained, including the rates of reactant consumption and product formation during eutectic formation. Calculate the coefficient of determination of the fitted curve and evaluate the fitting effect based on the coefficient of determination.

7. The method for monitoring the baicalin-betaine eutectic process based on terahertz spectroscopy according to claim 6, characterized in that, When performing data normalization, the normalization formula is: Where x represents the original value, x min Let x represent the minimum value. max This represents the maximum value.

8. The method for monitoring the baicalin-betaine eutectic process based on terahertz spectroscopy according to claim 7, characterized in that, The optimization of the crystal structure of the baicalin-betaine eutectic using density functional theory, the calculation of molecular vibrational frequencies, and the acquisition of molecular vibrational modes corresponding to characteristic peaks include: To obtain the initial crystal structure parameters and configurations of baicalin, betaine, and their eutectic crystals; Density functional theory was used, and the CASTEP tool was employed to simulate and calculate the initial crystal structure parameters and configuration, thereby obtaining the simulated terahertz spectrum. The GGA-PBE method was selected to optimize the structure and calculate the frequency of the initial crystal structure parameters and configuration after simulation. After structural optimization, the molecular vibrational frequencies of the eutectic characteristic peaks were obtained through energy simulation calculations. Frequency analysis was performed on the molecular vibrational frequencies to generate a simulated terahertz spectrum of the eutectic characteristic peaks; The simulated terahertz spectrum is compared with the spectral data. Based on the comparison results, the theoretical vibrational frequency corresponding to the eutectic characteristic peak is determined, and the molecular vibrational mode of the eutectic characteristic peak is analyzed based on the theoretical vibrational frequency.

9. The method for monitoring the baicalin-betaine eutectic process based on terahertz spectroscopy according to claim 8, characterized in that, The selection of the GGA-PBE method for structural optimization and frequency calculation of the initial crystal structure parameters and configuration after simulation includes: The plane wave cutoff energy of the initial crystal structure was fixed using Grimme's DFT-D2 correction method; The plane wave cutoff energy was sampled in the Brillouin zone using a Monkhorst-Pack grid, and convergence criteria for total energy and atomic force were set. Based on the above convergence criteria, the crystal structure of the eutectic is optimized, and the volume of the optimized lattice parameters is recorded. The convergence criterion is: the energy convergence of each atom is 5.0 × 10⁻⁶. -7 eV, atomic force threshold is The following is the maximum displacement threshold of atomic force:

10. The method for monitoring the baicalin-betaine eutectic process based on terahertz spectroscopy according to claim 9, characterized in that, The analysis of the baicalin-betaine eutectic process based on fitted curves and molecular vibrational modes includes: The reaction rate and reactant concentration of the physical mixture and the eutectic during the baicalin-betaine eutectic process were analyzed based on the fitted curves. The relationship between the characteristic peaks of the physical mixture, the characteristic peaks of the eutectic, and the corresponding oscillations of baicalin and betaine was analyzed based on molecular vibrational modes.

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