Surfactants promote the transport of hydrophilic compounds through hydrophobic nanopores in leaves: mechanistic insights

Conventional wisdom identifies two pathways for the uptake of active ingredients through the wax layers found on plant leaf surfaces: (1) lipophilic ingredients dissolve into the waxy substrate, and (2) hydrophilic ingredients are transported through hypothetical hydrophilic channels. Using molecular dynamics simulations, we reveal an additional mechanism by which surfactants with specific molecular structures - known as accelerators or penetrators - can enable the uptake of hydrophilic active ingredients. Depending on their structures, accelerator surfactants can penetrate nanometer-scale hydrophobic voids in the topmost wax layer, known as the epicuticular wax, promoting the formation of water nanoclusters that facilitate the uptake of hydrophilic molecules. This mechanism enables the uptake of hydrophilic nutrients such as methylglucose and certain types of electrolytes. The computational findings explain experimentally observed antagonistic effects in hard water (containing Ca$$^{2+}$$), which arise from selective ion binding to the waxy leaf surface. This study establishes a framework for designing next-generation agrichemical delivery systems to optimize active ingredient uptake through plant leaves by spray application.