CHARMM force field for protonated polyethyleneimine

Area of Science:

• Computational chemistry
• Polymer science
• Materials science

Background:

• Polyethyleneimine (PEI) is a versatile polymer with applications in gene delivery and catalysis.
• Accurate atomistic simulations require reliable force fields.
• Previous CHARMM force fields for PEI had limitations.

Purpose of the Study:

• To develop and validate a revised CHARMM force field for polyethyleneimine (PEI).
• To accurately model the size and protonation-dependent behavior of PEI chains.
• To provide a foundation for deriving coarse-grained PEI force fields.

Main Methods:

• Development of new residue types for PEI with symmetric C-N-C backbone.
• Derivation of integer charges and bonded parameters from ab initio calculations.
• Validation through extensive molecular dynamics simulations of solvated PEI chains.

Main Results:

• The revised CHARMM force field accurately reproduces experimental diffusion coefficients for PEI.
• Simulations show improved profiles for gyration radius, end-to-end distance, and diffusion.
• The force field is suitable for atomistic simulations of individual PEI chains and polyplexes.

Conclusions:

• The developed CHARMM force field enables realistic atomistic simulations of PEI.
• This model is crucial for understanding PEI behavior in various applications.
• The force field serves as a basis for developing coarse-grained models of PEI.