Synthesis,properties And Application Of Skin Whitening Agent Diglucosyl Gallic Acid

In today’s society,various cultures have their own definitions of beauty,and an even skin tone is a common factor in defining beauty in all cultures.It is generally believed that a perfect skin complexion should be bright,radiant,even and free of blemishes.Therefore,improving skin texture has become the main focus of people on beauty nowadays.When human skin is exposed to UV light,a series of biological pathways are triggered:oxidation of proteins and lipids,formation of DNA dimers,synthesis and transfer of melanin,induction of inflammation,generation of prostate PGE-2 and so on.The visible result is that the skin begins to darken and redden,and the skin tone becomes uneven eventually.Diglucosyl gallic acid（DGA）has the advantages of high stability,good water solubility and extremely low toxicity,and it is a whitening molecule with powerful whitening function.It can reduce the generation of free radicals,inhibit the activity of tyrosinase,prevent the transfer of melanin and control of skin inflammation.So DGA can be widely used in cosmetic formulations.In this work,by using methyl gallate,pentaacetyl glucose,sodium hydroxide and hydrochloric acid as raw materials,a new safe and efficient multifunctional whitening agent DGA was synthesized in two steps by a new technological means.The conditions for the synthesis of acetylation and substitution reactions were optimized by single factor experiment and orthogonal experiment,and the optimal conditions for the first step of acetylation reaction were that the molar ratio of reactants n（methyl gallate）:n（pentaacetyl glucose）=1:2.9,catalyst dosage was n（methyl gallate）:n（catalyst）=1:0.7,with the reaction time was 6 h and the reaction temperature was 45°C,and the yield could reach 90.25%.The optimal reaction conditions for the second-step substitution reaction were that the molar ratio of reactants n（intermediate）:n（Na OH）=1:10,the volume ratio of the reaction solvent was V（water）:V（methanol）=1:2,the reaction temperature was 75°C,and the yield could reach 55.17%.The purity of the product was tested by high performance liquid chromatography,and the structures of the intermediate and diglucosyl gallic acid were characterized by FT-IR,MS,¹H NMR,and¹³C NMR.The whitening activity and inhibitory mechanism of whitening agent DGA were studied by inhibiting tyrosine monophenolase and tyrosine diphenolase activities in vitro.And compared with VC,EDTA and gallic acid,the antioxidant capacity of DGA was studied,including DPPH free radical scavenging ability,ABTS⁺free radical scavenging ability,reducing ability,ferrous ion chelating ability and hydroxyl radical scavenging ability.The half inhibitory concentrations IC₅₀ of DGA on monophenolase and diphenolase are 1.46 mg/m L and2.68 mg/m L respectively.The types of inhibitory effects of DGA on tyrosine monophenolase and diphenolase are competitive inhibition,and the inhibition constants K_I separately are 1.18mg/m L and 2.43 mg/m L.The scavenging rates of DGA to DPPH free radicals and ABTS⁺free radicals reached 64.1%and 72.1%respectively,which were close to that of VC at the same mass concentration.When A₇₀₀=1,the mass concentrations of DGA,gallic acid and VC are0.173,0.107 and 0.0884 mg/m L,the reducing ability is close to that of VC,the chelating ability to ferrous ions and the scavenging rate of hydroxyl radicals are 65.1%and 70.8%respectively.Therefore,it can be seen that DGA has a good inhibitory effect on tyrosinase activity and excellent antioxidant capacity.Liposomes were prepared by using DGA,egg yolk lecithin and cholesterol as raw materials,and flexible liposomes were prepared by adding nonionic surfactants with different hydrophilic-lipophilic balance values to activate the edges of the liposomes,The effect of nonionic surfactant additions on flexible liposomes was studied,and the transdermal absorption properties of DGA flexible liposomes were determined.When Tween20 was selected as the edge activator to modify the liposomes and the addition amount was 50%of the mass of egg yolk lecithin,the minimum particle size was 131.9 nm,and the encapsulation efficiency could reach 86.5%,which was smaller than the particle size of DGA liposomes,the encapsulation rate was higher.The transdermal absorption results showed that the transdermal absorption performance of DGA flexible liposome is better than that of DGA liposome and DGA aqueous solution,but the temperature required for transdermal absorption should not exceed 52°C,and the required concentration should not exceed 0.3 mg/m L.The storage stability of DGA flexible liposomes within 60 days was investigated by measuring the particle size,polymer dispersity index distribution and retention rate of flexible liposomes.The results showed that adding nonionic surfactant to modify liposomes could improve its storage stability.It is more conducive to its long-term storage.The prepared DGA was applied to the formula of cosmetic emulsion compared with arbutin and niacinamide,a series of physicochemical indexes and safety properties of the formula were determined,and the efficacy evaluation of the formula on changes in skin pigmentation and the analysis of facial complexion analysis were carried out.The prepared whitening cosmetic emulsions were all milky white liquids in appearance,which were dispersed uniformly and free of foreign matter,no irritating odor,p H value of 6.16,viscosity of 920 Pa s,good centrifugation,light,cold and heat resistance and safety performance.The efficacy evaluation of the formula on skin pigmentation changed and the analysis of facial complexion were tested through clinical research,and which were compared with the whitening functional ingredients arbutin and niacinamide.The results showed that the ITA value increased from D7（+1.96%）to D35（+14.61%）,△L*value increased from D7（+0.34%）to D35（+2.20%）,decreased a*parameter（-9.84%）after 21 days,skin melanin increased from D7（-3.17%）to D35（-12.37%）,the number of UV spots decreased significantly at D35（-8.04%）,indicating that the DGA-containing lotion had the effect of skin tone adjustment and skin melanin reduction.