Modeling Solution Behavior of Poly(N-isopropylacrylamide): A Comparison between Water Models

Area of Science:

• Computational chemistry
• Polymer science
• Physical chemistry

Background:

• Water significantly influences macromolecular structure and function.
• Accurate in silico modeling of polymer aqueous solutions requires appropriate water models.

Purpose of the Study:

• To investigate the impact of different water models on poly(N-isopropylacrylamide) (PNIPAM) solution behavior.
• To refine computational setups for simulating PNIPAM in aqueous environments.
• To compare TIP4P/2005 and TIP4P/Ice water models for PNIPAM simulations.

Main Methods:

• Atomistic molecular dynamics simulations were employed.
• A comparative study of PNIPAM aqueous solutions using TIP4P/2005 and TIP4P/Ice water models was conducted.
• Conformation and hydration of a PNIPAM 30-mer were analyzed across various temperatures and pressures.

Main Results:

• Both water models reproduced the temperature-induced coil-to-globule transition at atmospheric pressure.
• Both models showed polymer hydration enhancement with increasing pressure.
• The PNIPAM-TIP4P/Ice system demonstrated superior agreement with experimental results.

Conclusions:

• The TIP4P/Ice water model provides a more accurate description of PNIPAM aqueous solutions.
• Stronger interactions between TIP4P/Ice water and PNIPAM (both hydrophilic and hydrophobic groups) contribute to improved accuracy.
• Solvent entropy plays a less favorable role in the coil-to-globule transition with the TIP4P/Ice model.