Simulating Bilayers of Nonionic Surfactants with the GROMOS-Compatible 2016H66 Force Field

Area of Science:

• Biophysical chemistry
• Materials science
• Computational chemistry

Background:

• Polyoxyethylene glycol alkyl ether amphiphiles (C_iE_j) are crucial nonionic surfactants for biophysical and membrane protein research.
• Understanding their behavior in lamellar phases is essential for various applications.

Purpose of the Study:

• To extensively test the GROMOS-compatible 2016H66 force field for molecular dynamics simulations of C_iE_j surfactant lamellar phases.
• To evaluate the force field's accuracy in reproducing experimental trends and structural properties.

Main Methods:

• Molecular dynamics simulations using the GROMOS-compatible 2016H66 force field.
• Simulation of lamellar phases for C₁₂E₂, C₁₂E₃, C₁₂E₄, C₁₂E₅, and C₁₄E₄ surfactants.
• Analysis of structural properties, area per surfactant, phase behavior, order parameters, hydration, flip-flop dynamics, water permeability, and bending rigidity.

Main Results:

• Simulations qualitatively reproduced structural properties and experimental trends for the surfactant series.
• Discrepancies were observed in area per surfactant, C₁₂E₅ equilibrium phase, and order parameters for C₁₂E₃, C₁₂E₄, and C₁₂E₅.
• Highly hydrated polar heads, spontaneous surfactant flip-flops, facilitated water permeation, and low bending rigidity were observed, alongside large hydrophilic pores.

Conclusions:

• The 2016H66 force field provides a good starting point for simulating challenging C_iE_j surfactant systems.
• Despite dynamic complexities like pore formation and rapid flip-flops, the force field captures essential characteristics.
• Further refinement may be needed to address quantitative discrepancies in specific structural parameters.