Collective adsorption of pheromones at the water-air interface.

Understanding the phase behaviour of pheromones and other messaging molecules remains a significant and largely unexplored challenge, even though it plays a central role in chemical communication. Here, we present all-atom molecular dynamics simulations to investigate the behaviour of bombykol, a model insect pheromone, adsorbed at the water-air interface. This system serves as a proxy for studying the amphiphilic nature of pheromones and their interactions with aerosol particles in the atmosphere. Our simulations reveal the molecular organization of the bombykol monolayer and its adsorption isotherm. A new soft-sticky particle equation of state accurately describes the monolayer's behaviour. The analysis uncovers a two-dimensional liquid-gas phase transition within the monolayer. Collective adsorption stabilizes the molecules at the interface and the calculated free energy gain is approximately 2kBT. This value increases under lower estimates of the dew surface concentration, thereby enhancing pheromone adsorption onto aerosols. Overall, our findings hold broad relevance for molecular interface science, atmospheric chemistry and organismal chemical communication, particularly in highlighting the critical role of phase transition phenomena.