Finite-Size Effects and Optimal System Sizes in Simulations of Surfactant Micelle Self-Assembly

Area of Science:

• Computational chemistry
• Biophysical chemistry
• Materials science

Background:

• Surfactants spontaneously form micelles in aqueous solutions.
• Micelles are crucial as membrane mimics, for protein structure analysis, and in drug delivery.
• Understanding micelle formation is vital for various scientific and industrial applications.

Purpose of the Study:

• To systematically characterize the finite-size effect in dodecylphosphocholine (DPC) micelles using coarse-grained simulations.
• To evaluate different coarse-grained solvent models for accuracy in reproducing experimental data.
• To explore multiscale simulation approaches for accurate micelle modeling.

Main Methods:

• Utilized the coarse-grained MARTINI model with various solvent models for simulating DPC micelles.
• Investigated systems ranging from 40 to 150 DPC molecules at a constant concentration.
• Employed multiscale simulations, including back-mapping to all-atom CHARMM36 systems.

Main Results:

• The nonpolarizable solvent model best reproduced SANS spectra for DPC micelles.
• Finite-size effects manifest as oscillations in aggregation number with increasing system size.
• Oscillations diminished when the system supported three micelles; critical micelle concentration estimations agreed with experiments.
• MARTINI simulations showed larger volume but smaller aggregation numbers compared to all-atom models.

Conclusions:

• The study provides a systematic characterization of finite-size effects in DPC micelle simulations.
• Findings offer guidance for selecting appropriate simulation models and parameters for accurate micelle studies.
• Multiscale modeling approaches show promise but require careful consideration of volume and aggregation number differences.