A coil-to-globule transition capable coarse-grained model for poly(N-isopropylacrylamide)

Area of Science:

• Computational chemistry and materials science.
• Polymer physics and simulations.

Background:

• Poly(N-isopropyl-acrylamide) (pNIPAM) is a thermoresponsive polymer with applications in drug delivery and smart materials.
• Accurate molecular dynamics simulations are crucial for understanding pNIPAM's behavior but can be computationally expensive.
• Existing models may require temperature-dependent parameters, limiting their applicability.

Purpose of the Study:

• To develop and validate a coarse-grained mesoscopic model for simulating pNIPAM.
• To accurately capture the thermal response of pNIPAM without temperature-dependent parameters.
• To assess the model's ability to simulate pNIPAM in different configurations, including membrane structures.

Main Methods:

• A coarse-grained model based on the Martini force field was developed, representing three beads per monomer.
• The model incorporates an electric dipole for amide moieties, similar to Martini water beads.
• Replica-exchange molecular dynamics simulations were employed to test the model's accuracy and equilibrium properties.

Main Results:

• The model accurately captures the thermal response of pNIPAM across various chain lengths without temperature-dependent parameters.
• A critical temperature of (302.1 ± 1.1) K was observed and found to be invariant with increasing chain length.
• Simulations confirmed thermodynamic equilibrium regardless of initial configurations and showed good agreement with atomistic simulations for membrane structures.

Conclusions:

• The developed mesoscopic model provides an efficient and accurate method for simulating pNIPAM.
• The model successfully reproduces pNIPAM's thermoresponsive behavior and critical temperature.
• This model is suitable for large-scale simulations of pNIPAM, including complex structures like membranes.