Solvated ensemble averaging in the calculation of partial atomic charges

Area of Science:

• Computational Chemistry
• Molecular Modeling
• Biophysics

Background:

• Partial atomic charges are crucial for molecular mechanics and dynamics simulations.
• Traditional methods often use a single molecular conformation, which can be inaccurate for flexible molecules.
• Molecules with rotatable bonds require consideration of multiple conformations for precise charge calculation.

Purpose of the Study:

• To develop and validate a protocol for deriving partial atomic charges using ensemble averaging.
• To apply this protocol to methyl glycosides, focusing on carbohydrates with numerous hydroxyl groups.
• To assess the convergence and statistical significance of partial charges derived from molecular dynamics (MD) simulations.

Main Methods:

• Performing explicitly solvated MD simulations under periodic boundary conditions.
• Selecting multiple relevant conformations from the MD trajectories.
• Averaging partial atomic charges computed for each selected conformation.
• Utilizing large ensembles (200 conformations) to ensure statistical relevance.

Main Results:

• Ensemble averaging yields partial charges weighted by realistic conformational populations.
• The protocol demonstrates charge convergence across different monosaccharides and within individual monosaccharides.
• Statistically relevant standard deviations for partial charges were computed, aiding in assessing atom type uniqueness.
• Hydroxyl group configurations significantly influence internal energies and the applicability of ensemble-averaged charges.

Conclusions:

• Ensemble-averaged partial charges derived from MD simulations are suitable for condensed phase simulations.
• The protocol offers a robust method applicable to various molecules and solvation conditions.
• Understanding conformational ensembles is key to accurate charge derivation for flexible molecules like carbohydrates.