A method for the preparation of an ultraviolet absorber and sunscreen

Abstract

The application discloses a preparation method of ultraviolet absorber and sunscreen, and belongs to the cosmetic field. The preparation method of the ultraviolet absorber comprises the following steps: dissolving 5,6-dihydroxyindole-2-carboxylic acid in a solvent to obtain a 5,6-dihydroxyindole-2-carboxylic acid solution; adding 2-formylphenylboronic acid and amino-terminated polydimethylsiloxane into the 5,6-dihydroxyindole-2-carboxylic acid solution, and stirring to obtain a mixed solution; and removing the solvent in the mixed solution to obtain the ultraviolet absorber. The preparation method of the sunscreen comprises the following steps: adding the ultraviolet absorber and zinc oxide nanoparticles into an oil phase in a moisturizing cream base, performing colloidal grinding, and performing heating and stirring until emulsification is achieved; and then mixing a water phase in the moisturizing cream base to obtain the sunscreen. The application can solve the problems that 5,6-dihydroxyindole-2-carboxylic acid has the shortcomings of narrow ultraviolet absorption band, easy oxidation polymerization leading to color deepening, and inability to realize molecular-level synergistic regulation of electronic structure to realize directional red shift of the absorption band.

Description

Technical Field

[0001] This application relates to the field of cosmetic technology, and in particular to a method for preparing an ultraviolet absorber and a sunscreen. Background Technology

[0002] With increasing concern about the cumulative damage to human skin caused by ultraviolet radiation, the optimization of the performance of ultraviolet absorbers, a core functional component of sunscreen products, has become an important research direction in the cosmetics field. These substances selectively absorb ultraviolet light energy, reducing the penetration of ultraviolet rays into skin tissue and providing basic photoprotection for the skin.

[0003] Existing UV absorbers mainly fall into two categories: synthetic organic compounds and inorganic nanoparticles. Organic UV absorbers, such as avobenzone and octocrylene, have specific chromophores in their molecular structures and can absorb medium-wave ultraviolet light. Inorganic nanoparticles, represented by zinc oxide and titanium dioxide, block ultraviolet light through scattering. In addition, 5,6-dihydroxyindole-2-carboxylic acid, a melanin analogue, is also being explored for use in UV protection due to its inherent photostability as a bio-derived material.

[0004] However, the existing technology system still has significant limitations: First, the single-component 5,6-dihydroxyindole-2-carboxylic acid has a narrow ultraviolet absorption band in its unmodified state, making it difficult to cover the long-wave ultraviolet region; second, this substance is prone to intermolecular oxidative polymerization during application, resulting in a darker product color and affecting the appearance of the final product; more importantly, conventional physical mixing methods are difficult to achieve molecular-level synergy of different functional components, and cannot achieve directional redshift expansion of the absorption band through electronic structure modulation. Summary of the Invention

[0005] This application provides a method for preparing an ultraviolet absorber and sunscreen, which solves the problems of existing technologies, such as the narrow ultraviolet absorption band of 5,6-dihydroxyindole-2-carboxylic acid, easy oxidation and polymerization leading to color deepening, and the inability to achieve molecular-level synergistic regulation of electronic structure to achieve directional red shift of the absorption band.

[0006] To achieve the above objectives, the technical solution of this invention is as follows: In a first aspect, embodiments of the present invention provide a method for preparing an ultraviolet absorber, comprising: 5,6-Dihydroxyindole-2-carboxylic acid was dissolved in a solvent to obtain a 5,6-dihydroxyindole-2-carboxylic acid solution; 2-Formylphenylboronic acid and amino-terminated polydimethylsiloxane were added to the 5,6-dihydroxyindole-2-carboxylic acid solution and stirred to obtain a mixed solution. The solvent is removed from the mixed solution to obtain the ultraviolet absorber.

[0007] In conjunction with the first aspect, in one possible implementation, the solvent is tetrahydrofuran.

[0008] In conjunction with the first aspect, in one possible implementation, the content of 5,6-dihydroxyindole-2-carboxylic acid in the 5,6-dihydroxyindole-2-carboxylic acid solution is 2-6 mg / mL.

[0009] In conjunction with the first aspect, in one possible implementation, the content of 2-formylphenylboronic acid in the mixed solution is 14-18 mg / mL, and the content of amino-terminated polydimethylsiloxane is 160-200 mg / mL.

[0010] In conjunction with the first aspect, in one possible implementation, removing the solvent from the mixed solution to obtain the ultraviolet absorber includes: The solvent in the mixed solution is removed by rotary evaporation to obtain the ultraviolet absorber.

[0011] Secondly, another embodiment of the present invention provides a method for preparing a sunscreen, characterized in that the ultraviolet absorber prepared based on the method for preparing an ultraviolet absorber according to any one of claims 1 to 5 comprises: The ultraviolet absorber and zinc oxide nanoparticles are added to the oil phase of the moisturizing cream matrix, and after colloidal grinding and heating and stirring until emulsified, they are mixed and homogenized with the aqueous phase of the moisturizing cream matrix to obtain a sunscreen.

[0012] In conjunction with the second aspect, in one possible implementation, the mass concentration of the ultraviolet absorber is 6wt%-10wt%, and the mass concentration of the zinc oxide nanoparticles is 5wt%-10wt%.

[0013] In conjunction with the second aspect, in one possible implementation, the temperature at which the heating and stirring are carried out until emulsification is 80~90℃, and the rotation speed is 1350~1450r / min.

[0014] In conjunction with the second aspect, in one possible implementation, the method of mixing and homogenizing is selected from at least one of oil bath heating and stirring, mechanical stirring, or magnetic stirring.

[0015] Thirdly, another embodiment of the present invention provides the application of the ultraviolet absorber prepared by the above-described method of preparing ultraviolet absorber or the sunscreen prepared by the above-described method of preparing sunscreen in cosmetics and skin care sunscreen products.

[0016] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages: The method for preparing the ultraviolet absorber provided in this invention uses the artificial melanin 5,6-dihydroxyindole-2-carboxylic acid (DHICA) as the base material. By introducing amino-terminated polydimethylsiloxane (NH2-PDMS) and 2-formylphenylboronic acid (PBS), a dynamic imine-boronic acid ester interaction is constructed in the reaction system. This molecular-level interaction directly regulates the electronic structure of 5,6-dihydroxyindole-2-carboxylic acid, effectively extending its ultraviolet absorption band from the original narrow range of ultraviolet B (UVB) to the long-wave ultraviolet (UVA) region. The ultraviolet absorption characteristics undergo a controllable redshift, significantly broadening the ultraviolet absorption coverage range. Meanwhile, this interaction effectively inhibits the oxidative polymerization of 5,6-dihydroxyindole-2-carboxylic acid, avoiding the problem of product color deepening and maintaining the light-colored appearance of the final product. This achieves a synergistic effect of optimizing UV absorption performance and improving stability at the molecular level, while strictly limiting light absorption to the ultraviolet region and avoiding interference from the visible light band. Ultimately, a highly efficient UV absorber based on the melanin biomimetic principle is obtained.

[0017] The sunscreen preparation method provided in this invention utilizes an ultraviolet absorber prepared by the above method as a core functional component, which synergistically constructs a composite protective system with zinc oxide nanoparticles, achieving multiple technological breakthroughs. Based on the dynamic imine-boronate ester interaction-regulated ultraviolet absorber, the 5,6-dihydroxyindole-2-carboxylic acid in its molecular structure, after directional electronic structure modification, effectively overcomes the narrow ultraviolet absorption band defect of traditional melanin precursors, enabling the sunscreen to achieve broad-spectrum absorption capacity extending to the UVA band while maintaining a light-colored appearance. The synergistic combination of this ultraviolet absorber and zinc oxide nanoparticles in an oil-phase matrix, through colloidal grinding and emulsification processes, forms a stable dispersion system. This retains the physical reflective properties of zinc oxide while utilizing the chemical chelation effect of the ultraviolet absorber to inhibit the photocatalytic activity of zinc oxide, thereby significantly improving the photostability and safety of the product while avoiding the risk of penetration by organic sunscreen agents. Furthermore, this preparation method ensures the uniform distribution of active ingredients in the matrix by pre-dispersing functional components in the oil phase and employing a specific emulsification process, laying a structural foundation for subsequent homogenization treatment. The resulting sunscreen has the dual advantages of molecular-level UV protection and physical shielding. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments of the present invention or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1Mid-infrared emissivity curves of the sunscreen prepared in Example 2 of this application and commercial sunscreen; Figure 2 The solar reflectance diagrams are for the sunscreen prepared in Example 2 of this application and commercial sunscreens. Figure 3 The sunscreen prepared in Example 2 of this application, the sunscreen prepared in Comparative Examples 1 to 3, and the UV absorption rate curves of commercial sunscreens; Figure 4 The SPF values ​​of the sunscreen prepared in Example 2 of this application, the sunscreens prepared in Comparative Examples 1 to 3, and commercial sunscreens are also provided. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that all raw materials in the embodiments of this invention can be purchased commercially or prepared using conventional methods well known to those skilled in the art; the terms "first" and "second" in the embodiments of this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance; the groups in the embodiments of this invention should be understood in the general sense of the chemical field, for example: a group usually refers to a radical, encompassing all "functional groups" in the structure of an organic compound, specifically including hydrogen groups, fluorine groups, chlorine groups, bromine groups, iodo groups, alkyl groups, alkenyl groups, alkynyl groups, methoxy groups, phenyl groups, acyl groups, carboxyl groups, carbonyl groups, nitro groups, hydroxyl groups, sulfonic acid groups, etc. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this invention according to the specific circumstances.

[0022] This application provides a method for preparing an ultraviolet absorber, comprising: Step 1: Dissolve 5,6-dihydroxyindole-2-carboxylic acid in a solvent to obtain a 5,6-dihydroxyindole-2-carboxylic acid solution. Specifically, dissolve 5,6-dihydroxyindole-2-carboxylic acid in a solvent, perform ultrasonic dispersion for 2-3 minutes, and then stir thoroughly at room temperature for about 2 minutes. 5,6-dihydroxyindole-2-carboxylic acid is a synthetic melanin, abbreviated as DHICA, and serves as a melanin precursor in this step.

[0023] Step 2: Add 2-formylphenylboronic acid (PBS) and amino-terminated polydimethylsiloxane (NH2-PDMS) to a solution of 5,6-dihydroxyindole-2-carboxylic acid, and stir to obtain a mixed solution. The mixed solution is pale yellow.

[0024] Specifically, 2-formylphenylboronic acid and amino-terminated polydimethylsiloxane were added to a solution of 5,6-dihydroxyindole-2-carboxylic acid. The mixture was stirred at a uniform speed at room temperature for about 5 minutes to obtain a pale yellow mixed solution.

[0025] Step 3: Remove the solvent from the mixed solution to obtain the ultraviolet absorber.

[0026] The method for preparing the ultraviolet absorber provided in this invention uses the artificial melanin 5,6-dihydroxyindole-2-carboxylic acid (DHICA) as the base material. By introducing amino-terminated polydimethylsiloxane (NH2-PDMS) and 2-formylphenylboronic acid (PBS), a dynamic imine-boronic acid ester interaction is constructed in the reaction system. This molecular-level interaction directly regulates the electronic structure of 5,6-dihydroxyindole-2-carboxylic acid, effectively extending its ultraviolet absorption band from the original narrow range of ultraviolet B (UVB) to the long-wave ultraviolet (UVA) region. The ultraviolet absorption characteristics undergo a controllable redshift, significantly broadening the ultraviolet absorption coverage range. Meanwhile, this interaction effectively inhibits the oxidative polymerization of 5,6-dihydroxyindole-2-carboxylic acid, avoiding the problem of product color deepening and maintaining the light-colored appearance of the final product. This achieves a synergistic effect of optimizing UV absorption performance and improving stability at the molecular level, while strictly limiting light absorption to the ultraviolet region and avoiding interference from the visible light band. Ultimately, a highly efficient UV absorber based on the melanin biomimetic principle is obtained.

[0027] Optionally, tetrahydrofuran is used as the solvent. The choice of a specific solvent significantly optimizes the solubility and stability of the reaction system. As a polar aprotic solvent, tetrahydrofuran efficiently dissolves 5,6-dihydroxyindole-2-carboxylic acid while avoiding side reactions that may be initiated by protic solvents (such as protonation or oxidation of the indole ring). Furthermore, the boiling point of tetrahydrofuran (66°C) is suitable for the subsequent rotary evaporation step, facilitating rapid solvent removal without residue, thus ensuring the purity and yield of the UV absorber. Compared to other solvents (such as methanol or acetone), tetrahydrofuran also promotes the uniform dispersion of 2-formylphenylboronic acid and amino-terminated polydimethylsiloxane, providing an ideal medium for the formation of dynamic imine-boronic ester interactions.

[0028] Furthermore, the concentration of 5,6-dihydroxyindole-2-carboxylic acid in the solution was 2-6 mg / mL (typical but not limiting concentrations could be 2 mg / mL, 3 mg / mL, 4 mg / mL, 5 mg / mL, and 6 mg / mL). Precise control of the reactant concentration balanced the reaction efficiency and product performance. This concentration range ensured that 5,6-dihydroxyindole-2-carboxylic acid was fully dissolved and participated in the reaction, while avoiding intermolecular aggregation or oxidative polymerization (such as the formation of dark polymers) caused by excessively high concentrations. Experimental data showed that the UV absorber prepared at this concentration had optimal absorbance in the 280-400 nm wavelength range. Figure 3 It is light yellow in color. Furthermore, this range, in synergy with the subsequently added 2-formylphenylboronic acid and polydimethylsiloxane, enables precise modulation of the electronic structure and a redshift extension of the absorption band.

[0029] Furthermore, the content of 2-formylphenylboronic acid in the mixed solution is 14-18 mg / mL (typical but not limiting contents such as 14 mg / mL, 15 mg / mL, 16 mg / mL, 17 mg / mL, and 18 mg / mL), and the content of amino-terminated polydimethylsiloxane is 160-200 mg / mL (typical but not limiting contents such as 160 mg / mL, 170 mg / mL, 180 mg / mL, 190 mg / mL, and 200 mg / mL). Through ratio optimization, the dynamic imine-boronic ester interaction was maximized. At this concentration, 2-formylphenylboronic acid can form a stable boronic ester bond with the hydroxyl group of 5,6-dihydroxyindole-2-carboxylic acid, while its aldehyde group forms a dynamic imine bond with the amino group of polydimethylsiloxane. This dual effect synergistically broadens the UV absorption band to 400 nm. Figure 3 The low addition level of polydimethylsiloxane (160-200 mg / mL) is sufficient to build a cross-linking network to inhibit oxidative polymerization, while avoiding excessive hydrophobicity or greasy feel due to overdosing. Compared to mechanical mixtures, the chemical interactions at this ratio increase the SPF value by more than 40%. Figure 4 This demonstrates that its synergistic effect is not obvious.

[0030] Optionally, the solvent in the mixed solution is removed to obtain the UV absorber, including: removing the solvent in the mixed solution by rotary evaporation. Specifically, a rotary evaporator is used to extract the solvent to form a film, and then the neck is cooled. The solvent evaporated at low temperature is condensed to optimize the uniformity and density of the film. Rotary evaporation can efficiently remove tetrahydrofuran at low temperatures (≤40°C), avoiding thermal degradation or oxidation of 5,6-dihydroxyindole-2-carboxylic acid caused by high temperatures. At the same time, the film structure formed during rotary evaporation (as in Example 2) enhances the uniformity and density of the UV absorber, making it more stable in the sunscreen matrix. Compared with conventional vacuum distillation or natural evaporation, rotary evaporation significantly shortens the process time (from several hours to within 30 minutes), and the residual solvent content is less than 0.1%, meeting cosmetic safety standards.

[0031] Another embodiment of the present invention provides a method for preparing a sunscreen, wherein the ultraviolet absorber prepared based on the above-described method for preparing an ultraviolet absorber comprises: UV absorbers and zinc oxide nanoparticles are added to the oil phase of a moisturizing cream base, then emulsified by colloidal grinding and heating with stirring. This emulsified mixture is then homogenized with the aqueous phase of the moisturizing cream base to obtain a sunscreen. Alternatively, the UV absorbers and zinc oxide nanoparticles can replace organic UV filters and be uniformly mixed with the moisturizing cream base according to a pre-defined process to produce a radiation-cooling sunscreen.

[0032] The sunscreen preparation method provided in this invention utilizes an ultraviolet absorber prepared by the above method as a core functional component, which synergistically constructs a composite protective system with zinc oxide nanoparticles, achieving multiple technological breakthroughs. Based on the dynamic imine-boronate ester interaction-regulated ultraviolet absorber, the 5,6-dihydroxyindole-2-carboxylic acid in its molecular structure, after directional electronic structure modification, effectively overcomes the narrow ultraviolet absorption band defect of traditional melanin precursors, enabling the sunscreen to achieve broad-spectrum absorption capacity extending to the UVA band while maintaining a light-colored appearance. The synergistic combination of this ultraviolet absorber and zinc oxide nanoparticles in an oil-phase matrix, through colloidal grinding and emulsification processes, forms a stable dispersion system. This retains the physical reflective properties of zinc oxide while utilizing the chemical chelation effect of the ultraviolet absorber to inhibit the photocatalytic activity of zinc oxide, thereby significantly improving the photostability and safety of the product while avoiding the risk of penetration by organic sunscreen agents. Furthermore, this preparation method ensures the uniform distribution of active ingredients in the matrix by pre-dispersing functional components in the oil phase and employing a specific emulsification process, laying a structural foundation for subsequent homogenization treatment. The resulting sunscreen has the dual advantages of molecular-level UV protection and physical shielding.

[0033] The sunscreen preparation method of this application introduces a synergistic combination of zinc oxide nanoparticles and the aforementioned ultraviolet absorber to construct a multifunctional integrated sunscreen system. Zinc oxide nanoparticles, with their specific optical properties, achieve efficient solar reflection and radiative cooling effects, introducing radiative cooling technology into the field of sunscreen. While providing ultraviolet protection, they effectively control body surface temperature, solving the problems of traditional sunscreen products having limited functionality and neglecting thermal comfort in high-temperature environments. Specifically, the carboxyl group of 5,6-dihydroxyindole-2-carboxylic acid in the ultraviolet absorber forms a chelate with the zinc oxide surface. This molecular-level interaction not only inhibits the aggregation tendency and photocatalytic activity of zinc oxide nanoparticles, improving the product's particle texture and stability, but also significantly enhances the system's safety by scavenging ultraviolet-induced reactive oxygen species (ROS). This design, while maintaining the advantages of zinc oxide's physical sun protection, overcomes the penetration risk and oxidative stress defects of traditional inorganic sunscreens, ultimately achieving synergistic optimization of ultraviolet protection, anti-oxidation, and radiative cooling functions. This provides an innovative solution for developing a new generation of photoprotective materials that combine high safety, thermal comfort, and aesthetic appeal.

[0034] Furthermore, the mass concentration of the UV absorber is 6wt%-10wt% (typical but not limited to 6wt%, 7wt%, 8wt%, 9wt%, and 10wt%), and the mass concentration of the zinc oxide nanoparticles is 5wt%-10wt% (typical but not limited to 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, and 10wt%). This ratio range, through precise control of the synergistic effect of the UV absorber and zinc oxide nanoparticles, not only ensures efficient coverage of the sunscreen in the UV absorption band (UVA+UVB), but also overcomes the technical defects of traditional sunscreen systems, such as the easy aggregation of inorganic particles and rough skin feel. The optimized content of the UV absorber enables it to form a molecular-level interaction with zinc oxide, inhibiting the photocatalytic activity of zinc oxide through dynamic imine-boronate bonds, and reducing the risk of transdermal penetration of nanoparticles through carboxyl chelation. Thus, while ensuring an SPF value ≥40, it significantly improves the safety and comfort of the product, achieving a dual breakthrough in protective efficacy and skin compatibility.

[0035] Furthermore, the heating and stirring temperature for emulsification is 80-90℃ (typical but not limiting temperatures such as 80℃, 85℃, and 90℃), and the rotation speed is 1350-1450 r / min (typical but not limiting rotation speeds such as 1350 r / min, 1400 r / min, and 1450 r / min). Preferably, the heating and stirring temperature for emulsification is 85℃, and the rotation speed is 1400 r / min. These process parameters, through precise control of the emulsification kinetics, enable the UV absorber and zinc oxide nanoparticles to achieve molecular-level dispersion in the oil phase, forming a stable Pickering emulsion structure. The high temperature promotes the interfacial self-assembly of amino-terminated polydimethylsiloxane, while the shear force generated at the specific rotation speed effectively prevents the sedimentation and aggregation of zinc oxide nanoparticles. The resulting sunscreen emulsion has a uniform particle size distribution and stability far exceeding that of conventional mechanically mixed products, solving the problems of whitening and fluctuations in protective performance caused by uneven dispersion of inorganic particles in traditional sunscreens.

[0036] Optionally, the mixing and homogenization method is selected from at least one of oil bath heating and stirring, mechanical stirring, or magnetic stirring. By adapting to the needs of different production scales, a deep coupling of process and material properties is achieved at the molecular interaction level. In particular, oil bath heating and stirring can simultaneously complete solvent removal and interfacial reactions, allowing dynamic imine-boronate bonds to form in situ during emulsification. Magnetic stirring, by controlling the fluid shear rate, avoids the concentration gradient of high-concentration zinc oxide nanoparticles (5wt%-10wt%) in local areas, ensuring that the final product has a consistent ultraviolet absorption network and radiative cooling channels at the microscale. The synergistic effect of its solar reflectance (>50%) and mid-infrared emissivity (>85%) is more than 30% higher than that of traditional stirring methods.

[0037] The mixing method of the ultraviolet absorber, zinc oxide nanoparticles and moisturizing cream matrix and the preparation method of the moisturizing cream matrix are not limited to the above methods, and can be achieved by other suitable mixing and preparation processes in the art.

[0038] The application of ultraviolet absorbers prepared by the above-mentioned method or sunscreens prepared by the above-mentioned method in cosmetics and skin care sunscreen products.

[0039] To ensure that the above-described implementation details and operations of this application can be clearly understood by those skilled in the art, and to highlight the significant advancements in the preparation methods of the ultraviolet absorbers and sunscreens in the embodiments of this application, the following examples illustrate the above technical solutions.

[0040] Example 1 5,6-Dihydroxyindole-2-carboxylic acid was dissolved in tetrahydrofuran to obtain a solution of 5,6-dihydroxyindole-2-carboxylic acid. The concentration of 5,6-dihydroxyindole-2-carboxylic acid in the solution was 2 mg / mL.

[0041] 2-Formylphenylboronic acid and amino-terminated polydimethylsiloxane were added to a solution of 5,6-dihydroxyindole-2-carboxylic acid and stirred to obtain a mixed solution. The content of 2-formylphenylboronic acid in the mixed solution was 14 mg / mL, and the content of amino-terminated polydimethylsiloxane was 160 mg / mL.

[0042] The tetrahydrofuran in the mixed solution was removed by rotary evaporation to obtain the ultraviolet absorber.

[0043] UV absorbers and zinc oxide nanoparticles were added to the oil phase of a moisturizing cream base. After colloid milling and heating with stirring until emulsified, the emulsified oil was mixed and homogenized with the aqueous phase of the moisturizing cream base to obtain a sunscreen. The mass concentration of the UV absorber was 6 wt%, and the mass concentration of the zinc oxide nanoparticles was 5 wt%. The heating and stirring temperature for emulsification was 80℃, and the rotation speed was 1350 r / min. Homogenization was achieved using an oil bath with heating and stirring.

[0044] Example 2 5,6-Dihydroxyindole-2-carboxylic acid was dissolved in tetrahydrofuran to obtain a solution of 5,6-dihydroxyindole-2-carboxylic acid. The concentration of 5,6-dihydroxyindole-2-carboxylic acid in the solution was 4 mg / mL.

[0045] 2-Formylphenylboronic acid and amino-terminated polydimethylsiloxane were added to a solution of 5,6-dihydroxyindole-2-carboxylic acid and stirred to obtain a mixed solution. The content of 2-formylphenylboronic acid in the mixed solution was 16 mg / mL, and the content of amino-terminated polydimethylsiloxane was 180 mg / mL.

[0046] The tetrahydrofuran in the mixed solution was removed by rotary evaporation to obtain the ultraviolet absorber.

[0047] UV absorbers and zinc oxide nanoparticles were added to the oil phase of a moisturizing cream base, followed by colloid milling, heating and stirring until emulsified, and then mixed and homogenized with the aqueous phase of the moisturizing cream base to obtain a sunscreen. The mass concentration of the UV absorber was 8 wt%, and the mass concentration of the zinc oxide nanoparticles was 7.5 wt%. The heating and stirring temperature for emulsification was 85℃, and the rotation speed was 1400 r / min. The mixing and homogenization method was mechanical stirring.

[0048] Example 3 5,6-Dihydroxyindole-2-carboxylic acid was dissolved in tetrahydrofuran to obtain a solution of 5,6-dihydroxyindole-2-carboxylic acid. The concentration of 5,6-dihydroxyindole-2-carboxylic acid in the solution was 6 mg / mL.

[0049] 2-Formylphenylboronic acid and amino-terminated polydimethylsiloxane were added to a solution of 5,6-dihydroxyindole-2-carboxylic acid and stirred to obtain a mixed solution. The content of 2-formylphenylboronic acid in the mixed solution was 18 mg / mL, and the content of amino-terminated polydimethylsiloxane was 200 mg / mL.

[0050] The tetrahydrofuran in the mixed solution was removed by rotary evaporation to obtain the ultraviolet absorber.

[0051] UV absorbers and zinc oxide nanoparticles were added to the oil phase of a moisturizing cream base, followed by colloid milling, heating and stirring until emulsified. This emulsified mixture was then mixed and homogenized with the aqueous phase of the moisturizing cream base to obtain a sunscreen. The mass concentration of both the UV absorber and zinc oxide nanoparticles was 10 wt%. The heating and stirring temperature for emulsification was 90℃, and the stirring speed was 1450 r / min. The homogenization was achieved using magnetic stirring.

[0052] Comparative Example 1 Preparation of 5,6-dihydroxyindole-2-carboxylic acid (DHICA) sunscreen.

[0053] The difference from Example 2 is that no UV absorber was added, and 8 wt% of 5,6-dihydroxyindole-2-carboxylic acid was used to replace the benzophenone component in the moisturizing cream base used in commercial sunscreens.

[0054] Comparative Example 2 Preparation of 2-formylphenylboronic acid (PBS) sunscreen.

[0055] The difference from Example 2 is that no UV absorber was added, and 8 wt% 2-formyl-p-phenylboronic acid was used to replace the benzophenone component in the commercial sunscreen.

[0056] Comparative Example 3 Preparation of amino-terminated polydimethylsiloxane (NH2-PDMS) sunscreen.

[0057] The difference from Example 2 is that no UV absorber was added, and 8 wt% polydimethylsiloxane was used to replace the benzophenone component in commercial sunscreens.

[0058] The following uses the sunscreen prepared in Example 2 as an example, and compares it with commercial sunscreens, Comparative Example 1, Comparative Example 2 and Comparative Example 3 as references, to characterize its various properties as follows.

[0059] Figure 1This is a mid-infrared emissivity curve comparing the sunscreen prepared in Example 2 of this application with a commercially available sunscreen. Figure 1 It is known that the sunscreen prepared in the embodiments of this application has an emissivity of more than 85% in the mid- and far-infrared bands, which is higher than that of commercial sunscreens.

[0060] Figure 2 This is a solar reflectance graph comparing the sunscreen prepared in Example 2 of this application with a commercially available sunscreen. Figure 2 It is known that the sunscreen prepared in the embodiments of this application has the characteristic of high reflectivity in the solar radiation band, with the highest reflectivity being greater than 50%, which is far higher than that of commercial sunscreens.

[0061] Figure 3 The UV absorption rate curves are for the sunscreen prepared in Example 2 of this application, the sunscreens prepared in Comparative Examples 1-3, and commercial sunscreens. The horizontal axis (wavelength range) reflects the coverage of the absorption band; a redshift indicates that the curve broadens to the right (in the long-wave direction). The vertical axis (absorbance) represents the intensity of UV absorption by the material; a higher value indicates stronger protection.

[0062] Figure 4 The SPF values ​​of the sunscreen prepared in Example 2 of this application, the sunscreens prepared in Comparative Examples 1 to 3, and commercial sunscreens are also provided.

[0063] Depend on Figure 3 and Figure 4 It is known that 5,6-dihydroxyindole-2-carboxylic acid (DHICA) sunscreen is a precursor material (artificial melanin) for the UV absorber in this application. When used alone, it does not regulate the electronic structure through dynamic imine-boronic acid ester interactions, and therefore cannot achieve a red shift in UV absorption wavelength and a lighter appearance. Thus, it cannot achieve the synergistic effect of the UV absorber used in the sunscreen of this application. 2-Formylphenylboronic acid (PBS) is a key component for constructing dynamic interactions in this application. When used alone, it lacks synergy with 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and amino-terminated polydimethylsiloxane (NH2-PDMS), and cannot broaden the UV absorption band. NH2-PDMS is used to establish dynamic imine bonds, but when used alone, it cannot form borate ester interactions and cannot inhibit oxidative polymerization or improve skin feel. Comparing the curves of single components (DHICA, PBS, PDMS): the absorption range is narrow and the intensity is low, proving that no effective red shift has occurred. Single components do not form dynamic interactions, and the absorption curve is limited to the short-wave region. Figure 3 This proves that redshift requires the synergistic effect of multiple components.

[0064] The sunscreen prepared in Example 2 of this application exhibits superior absorbance and SPA value compared to Comparative Examples 1-3, demonstrating that the single-ingredient 5,6-dihydroxyindole-2-carboxylic acid (DHICA), 2-formylphenylboronic acid (PBS), and amino-terminated polydimethylsiloxane (NH2-PDMS) are less effective than the sunscreen prepared in Example 2. This application modulates the electronic structure of DHICA through dynamic imine-boronate interactions, achieving a redshift of the absorption wavelength from 280 nm to 400 nm. The sunscreen of this application shows significantly higher absorbance and SPA values ​​in the 300-400 nm range compared to Comparative Examples 1-3 and commercial products. Figure 3 This indicates a wider absorption band coverage (redshift effect). This interaction inhibits the oxidative polymerization of DHICA, preventing the formation of dark colors (compared to traditional melanin materials), maintaining a light appearance while achieving a redshift. The redshift enables the absorption band to cover UVA / UVB, with an SPF value of 40+. Figure 4 The SPF was significantly higher than that of commercial products (SPF≈30) and the comparative ratio.

[0065] The various embodiments in this specification are described in a progressive manner. For the same or similar parts between the various embodiments, please refer to each other. Each embodiment focuses on describing the differences from other embodiments.

[0066] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A method for preparing an ultraviolet absorber, characterized in that, include: 5,6-Dihydroxyindole-2-carboxylic acid was dissolved in a solvent to obtain a 5,6-dihydroxyindole-2-carboxylic acid solution; 2-Formylphenylboronic acid and amino-terminated polydimethylsiloxane were added to the 5,6-dihydroxyindole-2-carboxylic acid solution and stirred to obtain a mixed solution. The solvent is removed from the mixed solution to obtain the ultraviolet absorber.

2. The method for preparing the ultraviolet absorber according to claim 1, characterized in that, The solvent is tetrahydrofuran.

3. The method for preparing the ultraviolet absorber according to claim 1, characterized in that, The content of 5,6-dihydroxyindole-2-carboxylic acid in the 5,6-dihydroxyindole-2-carboxylic acid solution is 2-6 mg / mL.

4. The method for preparing the ultraviolet absorber according to claim 1, characterized in that, The content of 2-formylphenylboronic acid in the mixed solution is 14-18 mg / mL, and the content of amino-terminated polydimethylsiloxane is 160-200 mg / mL.

5. The method for preparing the ultraviolet absorber according to claim 1, characterized in that, The step of removing the solvent from the mixed solution to obtain the ultraviolet absorber includes: The solvent in the mixed solution is removed by rotary evaporation to obtain the ultraviolet absorber.

6. A method for preparing a sunscreen, characterized in that, The ultraviolet absorber prepared according to the preparation method of the ultraviolet absorber according to any one of claims 1 to 5 comprises: The ultraviolet absorber and zinc oxide nanoparticles are added to the oil phase of the moisturizing cream matrix, and after colloidal grinding and heating and stirring until emulsified, they are mixed and homogenized with the aqueous phase of the moisturizing cream matrix to obtain a sunscreen.

7. The method for preparing sunscreen according to claim 6, characterized in that, The mass concentration of the ultraviolet absorber is 6wt%-10wt%, and the mass concentration of the zinc oxide nanoparticles is 5wt%-10wt%.

8. The method for preparing sunscreen according to claim 6, characterized in that, The temperature for heating and stirring to emulsify is 80~90℃, and the rotation speed is 1350~1450r / min.

9. The method for preparing sunscreen according to claim 6, characterized in that, The mixing and homogenization method is selected from at least one of oil bath heating and stirring, mechanical stirring, or magnetic stirring.

10. The use of the ultraviolet absorber prepared by the method of any one of claims 1 to 5 or the sunscreen prepared by the method of any one of claims 6 to 9 in cosmetics and skin care sunscreen products.

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