Polymerization mechanism of natural lacquer sap with special phase structure

Lacquer sap is a water-in-oil natural emulsion with high viscosity. In nature, it exudes from the phloem of lacquer tree to repair its wounds in the presence of O₂. So far, it is unclear how rapid and smooth polymerization of urushiol is achieved in such a viscous sap. Here, we find that there is a diffuse interface layer with 2.43 nm of thickness between two phases. The interface layer consists of urushiol, urushiol-laccase complex, urushiol-stellacyanin complex and water-insoluble glycoprotein. Polymerization of urushiol is realized by multicomponent synergistic effect. Radicals are first formed by laccase-catalyzed oxidation of urushiol at the interface layer, then are transferred to the urushiol oil phase via wate-insoluble glycoprotein and initiate the polymerization of urushiol there. Stellacyanin inhibits the formation of certain radicals and controls the concentration of phenoxy radicals at the interface layer. Through the inhibition of radicals by stellacyanin and the electron transfer mediated by water-insoluble glycoprotein, the polymerization of urushiol at the interface layer is inhibited. This ensures that O₂ can continuously penetrate into the aqueous phase to oxidize the reduced laccase so that the urushiol polymerization can continue smoothly. This polymerization mechanism provides an idea for developing new chemical reaction systems.