Melanin is the main cause of pigmentation in human skin, eyes and hair. In order to study the effects of polyoxometalates on the tyrosinase activity and melanin content of B16 mouse melanocytes, five polyoxometalates with Dawson structure with different vanadium substitutions were synthesized. Taking B16 mouse melanoma cells as a model, which was divided into blank group, control group and polyoxometalates experiment group (12.5, 25, 50, 100, 200 μmol/L), the cell viability was detected by thiazolyl blue (MTT) method, and the diphenyl picryl hydrazinyl (DPPH) free radical scavenging ability and the melanin content and tyrosinase activity in B16 melanoma cells were determined by enzyme labeling method. Finally, molecular docking was used to simulate the binding mechanism of polyoxometalate and tyrosinase. The results of the study showed that two phosphomolybdic acids (H7[P2Mo17VO62] and H8[P2Mo16V2O62]) are highly effective melanin production inhibitors, and the best inhibitory rates of melanin synthesis at a concentration of 200 μmol/L are 74.40% and 75.14%, respectively, which have an effect on the cell. The inhibitory rates of tyrosinase activity were 35.71% and 40.00%. With the increase of the number of vanadium atoms substituted, the two inhibitory activities gradually decreased. MTT reduction experiments show that H7[P2Mo17VO62] and H8[P2Mo16V2O62] are not toxic to cells, and the cell viability is greater than 80%. Both polyoxometalates (POMs) have strong DPPH scavenging ability, with IC50 of 1.683 and 2.800 mg/mL, respectively. Molecular docking simulation proved that all five polyoxometalates can form stable complexes with tyrosinase, and the main force of the combination are non-covalent bonds such as van der Waals forces and hydrogen bonds. In addition, the docking score is less than -146 kJ/mol. Based on the above research, H7[P2Mo17VO62] and H8[P2Mo16V2O62] can effectively inhibit the production of melanin in B16 mouse melanoma cells. The mechanism is related to the inhibition of tyrosinase activity. We believe that they are promising candidates for the development of safe cosmetics.

Melanogenesis is a process to synthesize melanin, which is a primary responsibility for the pigmentation of human skin, eye and hair. In order to study the effect of polyoxometalates on tyrosinase activity and melanin content in mouse melanocytes, four polyoxometalates with Dawson structure were synthesized. Intracellular and docking studies have shown that the two transition metal phosphomolybdic acids (H8[P2Mo17Fe(OH2)61] and H8[P2Mo17Ni(OH2)61]) are highly effective melanogenesis inhibitors with 22.4 % and 24.1 % inhibitory activities at a concentration of 200 μM. Among the four POMs synthesized, the three phosphomolybdic acids showed extremely significant inhibitory effects on the tyrosinase activity in B16 cells (p<0.0001), and the inhibitory activities were 77.5 %, 79.3 % and 44.4 % at a concentration of 200 Μm, respectively. MTT reduction experiments show that the three polyacids (H6[P2Mo18O62], H8[P2Mo17Co(OH2)61] and H8[P2Mo17Ni(OH2)61]) have basically no effect on the viability of B16 cells. Molecular dynamics simulation studies also show that H8[P2Mo17Ni(OH2)61] forms a stable complex with tyrosinase, with a docking fraction of −51.54 kcal/mol. Based on intracellular and docking studies, we believe that H8[P2Mo17Ni(OH2)61] is a promising candidate for safe cosmetic development.