A lignin@aspartic acid composite nanocrystal, its preparation method and application

Abstract

This invention belongs to the field of skin sun protection technology, and specifically discloses a lignin@aspartic acid composite nanocrystal, its preparation method and application. This invention prepares lignin@aspartic acid composite nanocrystal by loading lignin into aspartic acid nanocrystals through an in-situ embedding method. The lignin@aspartic acid composite nanocrystal can play an effective role in chemical and physical sun protection, and is also a natural sunscreen agent with antioxidant and skin damage prevention effects.

Description

Technical Field

[0001] This invention relates to the field of skin sun protection technology, and in particular to a lignin@aspartic acid composite nanocrystal, its preparation method, and its application. Background Technology

[0002] Solar ultraviolet radiation can be divided into three bands: long-wave ultraviolet (400-320nm), medium-wave ultraviolet (320-280nm), and short-wave ultraviolet (280-200nm). UVA can induce aging, immunosuppression, and skin tumors. UVB can cause DNA damage in cells after UVB irradiation by upregulating cyclobutane pyrimidine dimers (CPDs), thereby inducing non-melanoma skin cancer. Currently, commercially available sunscreens can be divided into two main categories: inorganic and organic sunscreens. Inorganic sunscreens mainly include titanium dioxide and zinc oxide, which can reflect and scatter ultraviolet rays, providing physical protection, but they easily clog pores and affect the normal secretion of sebaceous and sweat glands. Organic sunscreens, such as salicylates and cinnamates, have a good absorption effect on ultraviolet rays and can convert the absorbed ultraviolet energy into heat energy. Organic sunscreens have more safety risks, such as skin irritation and allergies. These organic molecules can penetrate the skin and induce skin complications.

[0003] Lignin possesses UV protection properties in plants. Its abundant benzene rings and ketone conjugated structures contribute to its strong UV resistance, making it suitable for sunscreens. The presence of numerous phenolic hydroxyl groups also endows lignin with antioxidant properties, potentially slowing down skin aging. However, lignin's inherent UV protection as a sunscreen agent is not ideal, necessitating modification. While modification or synergistic effects with organic sunscreens significantly enhance protection, this can lead to potential risks. Photodegradation products of sunscreens can penetrate the skin, potentially causing skin complications. Furthermore, lignin's UV absorption primarily occurs in the UVB band.

[0004] Aspartic acid, as an amino acid, is an important component of the skin's natural moisturizing factor (NMF). It helps the skin retain moisture, enhances the skin's moisturizing ability, makes the skin soft and smooth, and can also regulate nerve cells, thus acting as a skin conditioner.

[0005] If lignin can be in situ embedded in aspartic acid crystals, the skin toxicity problem can be solved to some extent, while the sun protection effect can be improved through a combination of physical and chemical sunscreens. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a lignin@aspartic acid composite nanocrystal, its preparation method, and its application.

[0007] To achieve the above objectives, the present invention is implemented according to the following technical solution:

[0008] One objective of this invention is to provide a method for preparing lignin@aspartic acid composite nanocrystals, comprising the following steps:

[0009] S1. Take 10-600mg of lignin and 25-1500mg of aspartic acid and add them to 4-300mL of solvent. Stir, rapidly heat to 90℃, reflux and keep at a constant temperature for 2h until the lignin and aspartic acid are completely dissolved.

[0010] S2. Cool down to 30℃ and hold for 30 minutes, then rapidly heat up to 90℃, then cool down to 30℃ and hold for 30 minutes. Repeat this cycle 3-5 times. After crystals grow, cool to room temperature, centrifuge to obtain the precipitate, and wash with distilled water multiple times to obtain lignin@aspartic acid composite nanocrystals.

[0011] Furthermore, in step S1, the solvent is prepared by dissolving 1-100 mL of ethanol or methanol in 4-200 mL of distilled water.

[0012] Furthermore, in step S1, the cooling rate is 5°C every 10 minutes.

[0013] The second objective of this invention is to provide a lignin@aspartic acid composite nanocrystal prepared using the above method.

[0014] The third objective of this invention is to provide an application of lignin@aspartic acid composite nanocrystals in the preparation of skin sunscreens.

[0015] Compared with the prior art, the present invention loads lignin into aspartic acid nanocrystals through an in-situ embedding method to prepare lignin@aspartic acid composite nanocrystals. These lignin@aspartic acid composite nanocrystals can play an effective role in chemical and physical sun protection, and are also natural sunscreens with antioxidant and skin damage prevention effects. Attached Figure Description

[0016] Figure 1 X-ray diffraction patterns of Asp-Lignin crystal, Asp crystal, and Ligin powder.

[0017] Figure 2 The image shows the X-ray diffraction pattern of a single Asp-Lignin crystal.

[0018] Figure 3 Fourier transform infrared spectra of Asp-Lignin crystal, Asp crystal, and Lignin.

[0019] Figure 4The ultraviolet absorption spectra of Asp-Lignin crystals, Asp crystals, and Lignin-based sunscreen emulsions.

[0020] Figure 5 The UV-Vis diffuse reflectance spectra of Asp-Lignin crystals, Asp crystals, and Lignin-based sunscreen emulsions.

[0021] Figure 6 The results show the ability of Asp-Lignin crystal, Asp crystal, and Lignin to scavenge superoxide anions using a superoxide anion scavenging assay kit.

[0022] Figure 7 To assess the sun protection effect of different treatment groups on the back skin of mice. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0024] Example 1

[0025] S1. Take 100 mg of lignin and 100 mg of aspartic acid and add them to a solvent prepared by dissolving 10 mL of ethanol in 100 mL of distilled water. Stir, heat rapidly to 90 °C, reflux and keep at a constant temperature for 2 hours until the lignin and aspartic acid are completely dissolved.

[0026] S2. Decrease the temperature by 5°C every 10 minutes, reduce the temperature to 30°C and hold for 30 minutes, then rapidly increase the temperature to 90°C, then reduce the temperature to 30°C and hold for 30 minutes. Repeat this cycle 4 times. After crystals have grown, cool to room temperature, centrifuge to obtain the precipitate, wash with distilled water 3 times to obtain lignin@aspartic acid composite nanocrystals, denoted as Asp-Lignin crystals.

[0027] Example 2

[0028] S1. Take 100 mg of lignin and 100 mg of aspartic acid and add them to a solvent prepared by dissolving 10 mL of methanol in 100 mL of distilled water. Stir, heat rapidly to 90 °C, reflux and keep at a constant temperature for 2 hours until the lignin and aspartic acid are completely dissolved.

[0029] S2. Every 10 minutes, the temperature is reduced by 5°C to 30°C and held for 30 minutes. Then the temperature is rapidly increased to 90°C, and then the temperature is reduced to 30°C and held for 30 minutes. This cycle is repeated 4 times. After crystals grow, the temperature is cooled to room temperature, centrifuged to obtain the precipitate, and washed 3 times with distilled water to obtain lignin@aspartic acid composite nanocrystals.

[0030] Comparative Example 1

[0031] 100 mg of aspartic acid (Asp) was added to a solvent prepared by dissolving 10 mL of ethanol in 100 mL of distilled water. The mixture was stirred, rapidly heated to 90 °C, and refluxed. The mixture was kept at this temperature for 2 hours until completely dissolved. The temperature was lowered by 5 °C every 10 minutes. The temperature was lowered to 30 °C and held for 30 minutes. The temperature was then rapidly raised to 90 °C, and then lowered to 30 °C and held for 30 minutes. This cycle was repeated 4 times. After crystals grew, the mixture was cooled to room temperature, centrifuged to obtain the precipitate, and washed 3 times with distilled water to obtain aspartic acid crystals, which were denoted as Asp crystals.

[0032] The Asp-Lignin crystals prepared in Example 1 were used as samples for structural analysis, while lignin and the Asp crystals prepared in Comparative Example 1 were used as control groups. The following tests were performed:

[0033] 1. Powder X-ray diffraction

[0034] Asp-Lignin crystals, Asp crystals, and lignin were dried separately, and the crystals were qualitatively analyzed by X-ray diffraction. The results are as follows: Figure 1 As shown, by Figure 1 It is known that the synthesized Asp-Lignin crystal has a certain crystal structure and exhibits physical reflection effects.

[0035] 2. Single-crystal X-ray diffraction

[0036] A small, appropriately sized piece of Asp-Lignin crystal was peeled off from the single crystal, and its crystal structure was analyzed by single-crystal X-ray diffraction. The results are as follows: Figure 2 As shown, by Figure 2 As can be seen, the theoretical XRD pattern of the Asp-Lignin crystal obtained through structural analysis (see...) Figure 2 XRD patterns of (a) and Asp-Lignin crystalline powder (see [reference]). Figure 2 The characteristic peaks (b) in the figure correspond to the characteristic peaks in the figure, which proves that the synthesized product has a certain crystal structure.

[0037] 3. Fourier transform infrared spectroscopy

[0038] Asp-Lignin crystals, Asp crystals, and lignin were dried overnight, and the structure of the lignin@aspartic acid composite nanocrystals was analyzed by Fourier transform infrared spectroscopy. The results are as follows: Figure 3 As shown, by Figure 3 It can be known that 1600cm -1 The peaks represent the C=C vibration of the lignin benzene ring skeleton, indicating that lignin is embedded in the aspartic acid crystals.

[0039] Furthermore, to verify whether lignin@aspartic acid composite nanocrystals can be used to prepare skin sunscreens, the Asp-Lignin crystals prepared in Example 1 were used as samples for structural analysis. Meanwhile, lignin and the Asp crystals prepared in Comparative Example 1 were used as control groups, and the following tests were performed:

[0040] 1. Ultraviolet absorption

[0041] Asp-Lignin crystals, Asp crystals, and lignin were dispersed in three parts of glycerin to prepare sunscreen emulsions, and their UV absorption capacity was tested using a UV-Vis spectrophotometer.

[0042] The results are as follows Figure 4 As shown, by Figure 4 It can be seen that Asp crystals have low ultraviolet absorption, while Asp-Lignin crystals have high absorption in the UVB band.

[0043] 2. Ultraviolet reflection

[0044] Asp-Lignin crystals, Asp crystals, and lignin were dried and then subjected to UV-Vis diffuse reflectance spectroscopy analysis using a Lambda 950.

[0045] The results are as follows Figure 5 As shown, by Figure 5 It is evident that Asp crystals exhibit excellent ultraviolet reflection. Asp-Lignin crystals, which are loaded with lignin, also demonstrate high ultraviolet reflection, with stronger reflection in the UVA band than in the UVB band.

[0046] 3. Antioxidant properties

[0047] According to the superoxide anion scavenging capacity assay kit, Asp-Lignin crystals, Asp crystals, and lignin were added to three portions of working solution, respectively. After 1 hour, the absorbance at 530 nm was measured, and the free radical scavenging rate was calculated using the following formula:

[0048] Superoxide anion scavenging rate D% = (A blank - A determination) ÷ A blank × 100%

[0049] The results are as follows Figure 6 As shown, by Figure 6 It is known that lignin, as an antioxidant, loaded into aspartic acid composite nanocrystals has a strong ability to scavenge superoxide anions.

[0050] 4. Mouse skin protection

[0051] Hair was removed from the backs of each male mouse (purchased from Guangdong Yaokang Biotechnology Co., Ltd.), and the back skin was divided into 5 squares (1cm×1cm) with a marker and photographed as normal skin control (referred to as the Normal group). The anti-ultraviolet effect was evaluated. The skin squares were treated with glycerol, lignin, asp crystals, and asp-lignin crystals for 15 minutes at concentrations of 15-25wt%, respectively, and exposed to UVB radiation for 10 minutes. Meanwhile, the skin of mice without any protection treatment served as the radiation control group (referred to as the No protection group). Photographs were taken 3 days later.

[0052] The results are as follows Figure 7 As shown, by Figure 7 It was found that when normal skin was exposed to UVB, obvious erythema, edema, and ulceration appeared. The glycerol group, lignin group, and Asp crystal group showed obvious erythema, while the Asp-Lignin crystal group did not show obvious erythema, indicating that the lignin@aspartic acid composite nanocrystals have a good sun protection effect.

[0053] In summary, the lignin@aspartic acid composite nanocrystals prepared by this invention have good sun protection effects and can be used to prepare skin sunscreens.

[0054] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing lignin@aspartic acid composite nanocrystals, characterized in that, Includes the following steps: S1. Take 10-600mg of lignin and 25-1500mg of aspartic acid and add them to 5-300mL of solvent. Stir, rapidly heat to 90℃, reflux and keep at a constant temperature for 2h until the lignin and aspartic acid are completely dissolved. S2. Every 10 minutes, the temperature is reduced by 5°C to 30°C and held for 30 minutes. Then the temperature is rapidly increased to 90°C, and then the temperature is reduced to 30°C and held for 30 minutes. This cycle is repeated 3-5 times. After crystals grow, the temperature is cooled to room temperature, centrifuged to obtain the precipitate, and washed multiple times with distilled water to obtain lignin@aspartic acid composite nanocrystals.

2. The method for preparing lignin@aspartic acid composite nanocrystals according to claim 1, characterized in that, In step S1, the solvent is prepared by dissolving 1-100 mL of ethanol or methanol in 4-200 mL of distilled water.

3. A lignin@aspartic acid composite nanocrystal prepared by the method as described in claim 1 or 2.

4. The application of the lignin@aspartic acid composite nanocrystals as described in claim 3 in the preparation of skin sunscreens.

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