Salicylic acid supramolecular complexes, their preparation methods and applications

Abstract

This invention relates to the field of cosmetic technology, specifically to a salicylic acid supramolecular complex, its preparation method, and its applications. The components include salicylic acid, panthenol, and cyclodextrin; the weight ratio of salicylic acid to panthenol is (20-79):(40-59). The salicylic acid supramolecular complex prepared by this invention improves upon the inherent defect of salicylic acid's poor water solubility due to its lipid solubility. Furthermore, the prepared salicylic acid supramolecular complex maintains good solubility in various complex formulation systems containing commonly used cosmetic solvents such as ethanol and polyols.

Description

Technical Field

[0001] This invention relates to the field of cosmetic technology, specifically to a salicylic acid supramolecular complex, its preparation method, and its application. Background Technology

[0002] Salicylic acid, a fat-soluble β-hydroxy acid, is a classic active ingredient in cosmetics for acne treatment, exfoliation, and oil control. It can penetrate pores to dissolve sebum and keratin plugs, and its irritation is lower than that of fruit acids, making it more suitable for oily and acne-prone skin, leading to its widespread application in skincare. However, this ingredient has inherent drawbacks. Its fat solubility results in poor water solubility. In complex cosmetic formulations, it is prone to recrystallization due to molecular interactions with solvents such as ethanol, losing its solubilizing effect. Furthermore, long-term use can easily cause skin sensitivity. Solubility and system stability are the core challenges in developing salicylic acid cosmetic formulations. To improve these issues, supramolecular modification methods are currently widely used, with cyclodextrin host-guest complexation becoming the mainstream technology due to its significant solubilizing effect.

[0003] Chinese invention patent CN106726690B discloses a method for preparing water-soluble microspheres of salicylic acid-cyclodextrin inclusion complex. The method involves ultrasonically dispersing and heating salicylic acid in water at a specific mass ratio to form an inclusion complex, then adding excipients such as maltodextrin and chitosan and spray-drying to obtain microspheres. This achieves the basic effects of improving the water solubility and reducing the irritation of salicylic acid. However, this method only uses the single cyclodextrin inclusion principle and does not introduce deep eutectic solvent technology. In systems containing commonly used cosmetic solvents such as ethanol, the inclusion complex is prone to breakage, and the recrystallization problem of salicylic acid remains unresolved. Furthermore, the preparation requires specialized spray-drying equipment, making large-scale production using existing equipment in cosmetic factories impossible. Additionally, it does not consider compatibility with commonly used thickening systems such as carbomer, which can easily cause pH fluctuations and thickening system collapse. In addition, while existing salicylic acid raw materials modified with a single deep eutectic solvent can improve solubility, they have the drawbacks of high irritation and no improvement in efficacy. Existing supramolecular modification technologies cannot simultaneously solve the multi-dimensional problems of salicylic acid solubility, stability, irritation and compatibility with cosmetic systems. Therefore, it is urgent to develop a new salicylic acid modification technology that takes into account the above properties and adapts to the needs of industrial cosmetic production. Summary of the Invention

[0004] The first aspect of the present invention provides a salicylic acid supramolecular complex comprising salicylic acid, panthenol and cyclodextrin; wherein the weight ratio of salicylic acid to panthenol is (20-79):(40-59).

[0005] This invention improves the inherent defect of salicylic acid's poor solubility in water by compounding salicylic acid, panthenol, and cyclodextrin, with the weight ratio of salicylic acid to panthenol being (20-79):(40-59). At the same time, it solves the industry pain point of traditional supramolecular salicylic acid in complex cosmetic systems, where the supramolecular links are broken and salicylic acid recrystallizes due to the molecular action of solvents such as ethanol. It is possible that salicylic acid and panthenol form a deep eutectic solvent system through hydrogen bonds and van der Waals forces. This interaction disrupts the original tight lattice arrangement of salicylic acid, lowers its melting point, and alters its inherent lipophilic properties, significantly improving the dispersibility of salicylic acid molecules in the system and initially improving its water solubility. Simultaneously, cyclodextrin possesses a unique structure with hydrophobic cavities and hydrophilic outer surfaces. Its hydrophobic cavities can encapsulate salicylic acid molecules, while its hydrophilic ends are exposed in the system, further enhancing the aqueous dispersibility of salicylic acid. Furthermore, there are weak intermolecular interactions between cyclodextrin and the salicylic acid-panthenol system, forming a stable ternary supramolecular network structure. This structure resists the solubilization effects of solvents such as ethanol and polyols in cosmetic formulations, preventing solvent molecules from disrupting supramolecular interactions and causing salicylic acid recrystallization. Ultimately, this allows the complex to maintain good and stable solubility in various complex formulation systems, fundamentally solving the defect of salicylic acid's poor water solubility due to its lipophilic nature.

[0006] Optionally, the weight ratio of salicylic acid to panthenol is (2-5):(4-5).

[0007] Optionally, the weight ratio of salicylic acid to panthenol is 1:(2-2.5).

[0008] The cyclodextrins include gamma-type cyclodextrins.

[0009] The panthenol includes D-panthenol (right panthenol).

[0010] The content of the cyclodextrin in the complex is 0.1-2 wt%.

[0011] Optionally, the content of the cyclodextrin in the complex is 0.5-1 wt%.

[0012] A second aspect of the present invention provides a method for preparing a complex, comprising the following steps: S1, Salicylic acid and panthenol are mixed and heated and stirred to obtain phase D; S2, D phase and cyclodextrin are mixed evenly and heated and stirred to obtain salicylic acid supramolecular complex.

[0013] The heating temperature in S1 is 80-120℃.

[0014] Optionally, the heating temperature in S1 is 100-120℃.

[0015] The heating temperature in S2 is 85-120℃.

[0016] Optionally, the heating temperature in S2 is 100-120℃.

[0017] A third aspect of this invention provides an application of a complex in the preparation of cosmetics.

[0018] The compound is added to cosmetics in an amount of 0.1-20 wt%.

[0019] Optionally, the compound is added to the cosmetic at an amount of 0.5-10 wt%.

[0020] Beneficial effects 1. This invention improves the inherent defect of salicylic acid's poor solubility in water by compounding salicylic acid, panthenol and cyclodextrin, with the weight ratio of salicylic acid to panthenol being (20-79):(40-59). At the same time, the prepared salicylic acid supramolecular complex can maintain good solubility in various complex formulation systems containing ethanol, polyols and other commonly used cosmetic solvents.

[0021] 2. The salicylic acid supramolecular complex prepared by this invention has excellent temperature stability.

[0022] 3. This invention significantly reduces the skin irritation of salicylic acid through supramolecular modification.

[0023] 4. The salicylic acid supramolecular complex prepared by this invention can reduce cytotoxicity and solve the problem that long-term use of traditional salicylic acid can easily cause skin sensitivity.

[0024] 5. The salicylic acid supramolecular complex prepared by this invention exhibits stable pH and viscosity performance in commonly used thickening systems in cosmetics, and has a small viscosity-reducing effect on the thickening system, without causing the thickening system to collapse. It can flexibly prepare high-transparency, low-viscosity essence products or high-viscosity gel products according to the formulation requirements, and is suitable for the diversified formulation development needs of various categories of cosmetics such as acne treatment, exfoliation, whitening, and repair. Attached Figure Description

[0025] Figure 1 The graph shows the compatibility of the complex in Example 1 with the thickening system. From left to right, they correspond to: complex + carbomer 980, complex + carbomer 981, and carbomer 980, respectively.

[0026] Figure 2 The stability test of the complex essence in Example 1 is shown from left to right at -18℃, -7℃, 4℃, 25℃, 37℃, 45℃, and 50℃.

[0027] Figure 3For the stability test of the complex essence in Comparative Example 1, the temperatures from left to right correspond to -18℃, -7℃, 4℃, 25℃, 37℃, 45℃, and 50℃.

[0028] Figure 4 For the stability test of the complex essence in Comparative Example 2, the temperatures from left to right correspond to -18℃, -7℃, 4℃, 25℃, 37℃, 45℃, and 50℃.

[0029] Figure 5 The chart shows the stability test results of the complex essences of Example 1 and Comparative Examples 1 and 2, from left to right. The results correspond to the stability of Example 1 at -7℃, the stability of Comparative Example 1 at -7℃, the stability of Comparative Example 2 at -7℃, the stability of Example 1 at 25℃, the stability of Comparative Example 1 at 25℃, the stability of Comparative Example 2 at 25℃, the stability of Example 1 at 45℃, the stability of Comparative Example 1 at 45℃, and the stability of Comparative Example 2 at 45℃.

[0030] Figure 6 Example 1 illustrates the stability of the complex in Comparative Example 1 when added to a cosmetic essence.

[0031] Figure 7 For the cytotoxicity experiment of the complex in Comparative Example 1, the orange curve corresponds to the complex in Example 1, and the blue curve is the control, corresponding to elemental salicylic acid.

[0032] Figure 8 The results of the experiment on the melanin synthesis inhibition rate of the complex in Example 1 are shown.

[0033] Figure 9 The results are from the cell migration experiment of the complex in Example 1. Detailed Implementation

[0034] Example 1 A salicylic acid supramolecular complex comprising salicylic acid, panthenol (D-panthenol) and cyclodextrin (gamma-type cyclodextrin).

[0035] A method for preparing a complex comprises the following steps: S1, mixing 30g of salicylic acid with 69g of panthenol and heating and stirring at 105°C (30min, 600rpm) to obtain phase D; S2, mixing phase D and 1g of cyclodextrin evenly and heating and stirring at 105°C (30min, 600rpm) to obtain the complex.

[0036] Comparative Example 1 A complex consisting of salicylic acid and panthenol (D-panthenol).

[0037] A method for preparing a complex includes the following steps: mixing 30g of salicylic acid with 69g of panthenol, heating and stirring at 105°C (30min, 600rpm) to obtain the complex.

[0038] Performance testing methods and data 1. Compatibility of the complex with the thickening system: 20g of the complex prepared in Example 1 was added to 150g of 2wt% carbomer 980 and 2wt% 981 aqueous solutions, respectively. The pH was adjusted to 7.0 using arginine aqueous solution, and water was added to a final volume of 300g. The control group consisted of 1wt% 981 aqueous solution. Figure 1 As shown, the viscosity (rotational viscosity, 25°C, 63 T-Bar rotor + 12 rpm) from left to right was 7200 mPa·s, 5000 mPa·s, and 9900 mPa·s, respectively. It can be seen that the complex of the present invention has a limited effect on the thickening system, and can produce both high-transparency, low-viscosity essence products and high-viscosity gel products.

[0039] 2. Physical stability: The complexes prepared in Example 1 and Comparative Example 1, as well as the raw materials in Comparative Example 2, were added at 10 wt% to the simplified cosmetic essence formulation shown in Table 1 (by weight percentage). The mixtures were then placed in environments of -18℃, -7℃, 4℃, 35℃, 45℃, and 50℃ for continuous observation. The test results are as follows: Figures 2-5 As shown. Example 1 showed no precipitation at any temperature. Comparative Example 1 was superior to Comparative Example 2, but precipitation still occurred. Figure 6 The samples are supramolecular raw material samples used in Example 1 and salicylic acid-panthenol binary system samples used in Comparative Example 1. As can be seen from the previous figure, the binary system formed by salicylic acid-panthenol can increase the solubility of salicylic acid, but it is still different from the ternary system of the present invention.

[0040] Table 1

[0041] 3. Structural stability: 1) HPLC test refers to "Cosmetic Safety Technical Specifications (2015 Edition) - Method for Determination of Salicylic Acid Content".

[0042] 1) HPLC testing should refer to the "Cosmetic Safety Technical Specifications (2015 Edition) - Method for Determination of Salicylic Acid Content". a) Preparation of standard series solutions i. Take the salicylic acid standard stock solution and prepare a series of salicylic acid standard solutions with concentrations of 5.0 μg / mL, 50.0 μg / mL, 100.0 μg / mL, 150.0 μg / mL and 200.0 μg / mL respectively.

[0043] b) Sample processing i. Weigh 0.25 g (accurate to 0.0001 g) of the complex from Example 1 into a 25 mL stoppered colorimetric tube, add 20 mL of methanol-water solution, vortex for 60 s to disperse evenly, extract by sonication (power: 400 W) for 15 min, cool to room temperature, and then dilute to the 25 mL mark with methanol-water solution (3.5). After vortexing and shaking, filter through a 0.45 μm organic filter membrane. The filtrate can be diluted with methanol-water solution as needed and stored in a 2 mL brown sample vial as the test solution for later use. Store in the dark and it is stable for 5 days.

[0044] c) Reference chromatographic conditions i. Chromatographic column: acid-resistant C8 column (250mm×4.6mm×5μm), or equivalent column; d) The mobile phase gradient elution program is shown in Table 2: Table 2

[0045] i. Flow rate: 1.2 mL / min; ii. Detection wavelength: 300nm; iii. Column temperature: 25℃; iv. Injection volume: 20 μL.

[0046] e) Measurement i. Under the chromatographic conditions of “c”, inject salicylic acid standard series solutions separately for chromatographic analysis, and plot a standard curve with the concentration of the standard series solutions as the abscissa and the peak area as the ordinate.

[0047] ii. Inject the test solution from section “b)”, perform qualitative analysis based on retention time and UV spectrum, measure peak area, and obtain the concentration of salicylic acid in the test solution according to the standard curve. Calculate the salicylic acid content in the sample according to section “f)”.

[0048] f) Presentation of analysis results i. Calculate according to the following formula

[0049] In the formula: ω — mass fraction of salicylic acid in cosmetics, % D – Sample dilution factor (1 if undiluted); ρ — the mass concentration of salicylic acid obtained from the standard solution, in μg / mL; V—Sample volume at final volume, mL; m — Sample size, in grams.

[0050] g) Conclusion: The test results are shown in Table 3. For the four standard samples, the expected value of the same proportion (30wt%) of the sample dilution solution (named 20251206D & 20260105D respectively) at different time periods was 200 μg / mL, and the calculated values ​​were 196.685 & 195.489 respectively. The retention rate of salicylic acid content (98.342% and 97.774%) was greater than 95%, and the sample content remained basically unchanged after 30 days of storage.

[0051] Table 3

[0052] 4. Cell experiments - cytotoxicity experiments 1) Experimental Procedure a) Cell plating: Take HDF cells in the logarithmic growth phase, discard the culture medium, wash twice with PBS, add 0.25% trypsin, digest at 37°C for 4 min, stop digestion with culture medium, centrifuge at 1000 rpm for 3 min, resuspend cells in complete DMEM culture medium, count cells, and adjust the cell concentration to 8 × 10⁶ cells / mL. 5 Add 100 μL / ml to each well of a 96-well plate. Incubate for 24 h (5% CO2, 37℃).

[0053] b) Drug treatment: After culturing cells for 24 hours, the supernatant was aspirated, and 100 μL of different concentrations of the test substance (complex in Example 1) was added to each well. The cells were then placed in an incubator for 24 hours (5% CO2, 37°C). The control group consisted of only salicylic acid.

[0054] c) Cell viability assay: Cell viability was assessed using CCK-8. CCK-8 working solution was prepared by mixing 1 ml of CCK-8 solution with 9 ml of DMEM culture medium and storing in the dark. After 24 hours of drug treatment, cell growth, morphology, and the integrity of the cell monolayer were observed using an inverted microscope, and changes in cell morphology and growth were recorded. The supernatant was removed, and 100 μL of CCK-8 working solution was added to each well. The cells were incubated for 1 hour, and the absorbance was measured at OD450.

[0055] d) Results as follows Figure 7 As shown, the cytotoxicity of the complex in Example 1 is less than that of elemental salicylic acid.

[0056] 5. Cellular Experiments - Melanocytes, Melanin Inhibition Experiment (Whitening) The test plan is shown in Table 4.

[0057] Table 4

[0058] Preparation of working solution (2X) Sample preparation: Dilute the sample to 0.01% as required.

[0059] α-MSH solution: Dilute the 1 mM α-MSH stock solution to 2 μM before use.

[0060] Arbutin solution: Dilute 10mM arbutin stock solution to 100μM before use.

[0061] Operating steps Cell plating: with a cell concentration of 1.5 × 10⁻⁶ cells / cells. 5 / wells were seeded into 6-well plates, and the seeded cell culture plates were placed in an incubator for 24 hours (5% CO2, 37℃).

[0062] Drug administration: administer drugs according to Table 5. After culturing cells for 24 hours, aspirate the supernatant, add the test substance, negative control and positive control according to the table below, mix well, and place in an incubator for 72h+1h.

[0063] Table 5

[0064] Melanin lysis: Add 350 μL of melanin extraction solution to each well, scrape off the cells with a cell scraper, collect them into a 1.5 ml centrifuge tube, and place in an 80 °C water bath for 2 h until the melanin is completely dissolved.

[0065] Protein assay: Take 50 μL of completely lysed cell lysate, mix it with an equal volume of concentrated hydrochloric acid, and measure the protein content using BCA.

[0066] Melanin measurement: The absorbance of the remaining melanin lysate was measured at OD405.

[0067] Results Analysis: GraphPadPrism was used for plotting, and results are expressed as Mean ± SD. T-tests were used for comparisons between groups, all with two tails. P < 0.05 was considered statistically significant, and P < 0.01 was considered highly significant.

[0068] Table 6 summarizes the results of melanin synthesis inhibition rate, where “ / ” indicates that no test was performed.

[0069] Table 6

[0070] When performing statistical analysis using the t-test method, significance compared to the BC group is represented by #, P-value < 0.05 is represented by #, P-value < 0.01 is represented by ##, and P-value < 0.001 is represented by ###.

[0071] The assay was performed according to TSHRH027-2019, "In vitro test for melanin synthesis inhibition in B16 cells". Based on B16, the melanin synthesis inhibition rate results are as follows: Figure 8 As shown: PC (arbutin 100ppm) has a certain inhibitory effect on melanin synthesis, with an inhibition rate of 54.03%. This indicates that the positive control in this experiment was effective. Sample A: Salicylic acid at a concentration of 0.01% has a certain inhibitory effect on melanin synthesis, with an inhibition rate of 26.46%; Sample B (complex of Example 1) at a concentration of 0.01% (salicylic acid concentration) has a certain inhibitory effect on melanin synthesis, with an inhibition rate of 38.04%. This indicates that the complex of Example 1 achieves its whitening effect by inhibiting melanin synthesis at the above concentrations.

[0072] 6. Cell Experiments - Cell Migration Experiments Target cell selection: P7 generation human fibroblasts in good growth condition were selected, with a cell concentration of 1×10⁻⁶. 6 Seed cells at a density of 3 mL into 60 mm culture dishes, 3 mL per well, and place the seeded cell culture dishes into an incubator to continue culturing for 24 h (5% CO2, 37℃).

[0073] Sample addition: Once the plate spreading rate reaches 90%, samples can be added. Aspirate the original culture medium and add the prepared test samples according to the groups in Table 7. After the sample addition is completed, place the culture dish in the incubator and continue to incubate for 24 hours (5% CO2, 37℃).

[0074] Table 7

[0075] Scratching: When the cell deposition rate reaches approximately 90%, a 200μL pipette tip is used to damage the cells and create scratches. During the scratching process, the pipette tip is slightly tilted to the flat surface, and even pressure is applied across the bottom of the plate.

[0076] Photography: Immediately after scratch repair, take 0-hour photographs to record the original scratch size and the observation point number (numbered from top to bottom). Take 4 or more photographs for each well. Mark the observation points. After photography, remove the PBS, add serum-free culture medium to each well, and return to the incubator for approximately 24 hours of incubation. After incubation, take 24-hour photographs at the same location using the same magnification objective lens, based on the 0-hour observation points, to record the scratch repair progress.

[0077] Scratch area calculation: The scratch area is calculated using ImageJ software. The image is processed according to fixed commands to calculate the scratch area.

[0078] Data Processing: Calculate the migration rate for each observation point, expressed as a percentage. Perform data screening, removing outliers while retaining at least three valid migration rate values. Outliers are defined as data falling outside the mean ± (3 × standard deviation). Calculate the relative migration rates of the positive control group and sample group relative to the average migration rate of the blank control group, expressed as multiples without units. Calculate the mean, standard deviation (SD), and CV value of the relative migration rates for each group, and calculate the p-value of that group's migration rate relative to the blank control group.

[0079] Results Analysis: Cell image analysis showed that the scratch area of ​​cells in the positive control group or test substance group was significantly reduced compared with that in the blank control group. Furthermore, the calculated experimental data showed a statistically significant difference in the relative migration rate of this group compared with the relative migration rate of the blank control group (p<0.05), indicating that this group of samples promoted cell migration. This can be expressed as evidence supporting claims of repair efficacy in cosmetics under the experimental conditions.

[0080] For the positive control group and the sample concentration group with cell migration-promoting ability, the CV value should be ≤30% for the test to be considered valid. At least one concentration in all tests should show a positive result; the test substance is then reported as migration-promoting positive. The test results are shown in Figure 8.

[0081] Table 8

[0082] When performing statistical analysis using the t-test method, significance compared to group BC is represented by #, with P-value < 0.05 represented by #, P-value < 0.01 represented by ##, and P-value < 0.001 represented by ###.

[0083] like Figure 6 As shown, the CV values ​​in this experiment were all ≤30%, indicating the experiment was successful. Compared with the BC group, the migration rate of the PC group was significantly increased, with an average of 74.38% and a relative migration rate of 75.66% (P<0.001), indicating that the positive control was effective. Compared with the BC group, the migration rate of sample A (salicylic acid) at a concentration of 0.03% was 28.64%, which was lower than the blank migration rate, indicating that sample A had no repair effect at a concentration of 0.03%. Compared with the BC group, the migration rate of sample B (ternary complex -0.03% (salicylic acid concentration) was significantly increased, with an average of 45.60% and a relative migration rate of 7.70% (P<0.001).

[0084] Results: According to the judgment criteria of the laboratory method "CMXVESOP-12-02 Cell Scratch Test", under the conditions of this experiment, sample A: salicylic acid at a concentration of 0.03% showed a migration rate of 28.64%, which was lower than the blank migration rate. Therefore, sample A was considered to have no repair effect at a concentration of 0.03%. Sample B: the ternary complex, with a salicylic acid concentration of 0.03%, showed a significantly increased migration rate, with a relative migration rate of 7.70%. Therefore, sample B: the ternary complex was considered to have a repair effect under the above conditions.

Claims

1. A salicylic acid supramolecular complex, characterized in that, The components include salicylic acid, panthenol and cyclodextrin; the weight ratio of salicylic acid to panthenol is (20-79):(40-59).

2. The complex according to claim 1, characterized in that, The weight ratio of salicylic acid to panthenol is (2-5):(4-5).

3. The complex according to claim 2, characterized in that, The cyclodextrins include gamma-type cyclodextrins.

4. The complex according to claim 3, characterized in that, The panthenol includes D-panthenol.

5. The complex according to claim 4, characterized in that, The content of the cyclodextrin in the complex is 0.1-2 wt%.

6. A method for preparing the complex according to any one of claims 1-5, characterized in that, Includes the following steps: S1, mix salicylic acid and panthenol, heat and stir to obtain phase D; S2, mix phase D and cyclodextrin evenly, heat and stir to obtain salicylic acid supramolecular complex.

7. The method for preparing the complex according to claim 6, characterized in that, The heating temperature in S1 is 80-120℃.

8. The method for preparing the complex according to claim 7, characterized in that, The heating temperature in S2 is 85-120℃.

9. An application of the complex according to any one of claims 1-5, characterized in that, It is used in the preparation of cosmetics.

10. The application of the complex according to claim 9, characterized in that, The compound is added to cosmetics in an amount of 0.1-20 wt%.

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