Collective adsorption of pheromones at the water-air interface

TL;DR

This study uses molecular dynamics simulations to explore how pheromones like bombykol adsorb and organize at water-air interfaces, revealing phase transitions and energetic insights relevant to atmospheric chemistry and biological communication.

Contribution

It provides the first detailed molecular-level understanding of pheromone adsorption behavior and phase transitions at water-air interfaces using all-atom simulations.

Findings

Identification of a two-dimensional liquid-gas phase transition.

Quantification of free energy gain during adsorption (~2 k_B T).

Development of an equation of state describing monolayer behavior.

Abstract

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 behavior 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 soft-sticky particle equation of state accurately describes the monolayer's behavior. The analysis uncovers a two-dimensional liquid-gas phase transition within the monolayer. Collective adsorption stabilises the molecules at the interface and the calculated free energy gain is approximately $2\:k_\mathrm{B}T$. This value increases under lower estimates of the condensing 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.