Paper List

Journal: ArXiv Preprint
Published: Unknown
Physical ChemistryComputational Biophysics

Collective adsorption of pheromones at the water-air interface

Aix Marseille Univ, CNRS, Centrale Med, IRPHE (UMR 7342), Marseille, France | ICSM, CEA, CNRS, ENSCM, Univ. Montpellier, Marcoule, France | Institut de Recherche sur la Biologie de l’Insecte, UMR 7261, CNRS-Université de Tours, Tours, France

Ludovic Jami, Bertrand Siboulet, Thomas Zemb, Jérôme Casas, Jean-François Dufrêche
Figure
Figure
Figure
Figure
Figure

The 30-Second View

IN SHORT: This paper addresses the core challenge of understanding how amphiphilic pheromones, previously assumed to be transported in the gas phase, can be stabilized and concentrated at the water-air interface of atmospheric aerosols through collective adsorption and a 2D phase transition.

Innovation (TL;DR)

  • Methodology Presents state-of-the-art all-atom molecular dynamics simulations to construct a full Langmuir adsorption isotherm for a pheromone monolayer, a comprehensive approach rare in the field.
  • Biology Quantifies the collective adsorption free energy gain (~2kBT per molecule) for bombykol at the water-air interface, providing a mechanistic explanation for pheromone enrichment on atmospheric aerosols.
  • Theory Identifies and characterizes a two-dimensional liquid-gas phase transition within the pheromone monolayer, modeled successfully with a soft-sticky particle equation of state.

Key conclusions

  • Collective interactions within a bombykol monolayer at the water-air interface provide a stabilization free energy of approximately 2kBT per molecule, significantly enhancing adsorption compared to individual molecules.
  • The monolayer exhibits a clear two-dimensional liquid-gas phase transition, accurately described by a soft-sticky particle equation of state, with the transition plateau evident in the surface tension vs. concentration isotherm.
  • The calculated adsorption free energy increases under lower estimates of the condensing surface concentration (ΓC), indicating that pheromone adsorption onto aerosols is more favorable in dilute regimes, relevant for atmospheric conditions.
Background and Gap： The physico-chemical behavior and phase exchange mechanisms of semiochemicals during atmospheric transport are poorly understood, with a lack of molecular-level models explaining how low-volatility, amphiphilic pheromones interact with and partition onto aerosol surfaces.

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 2kBT. 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.