SMIRNOFF99Frosst

SMIRNOFF99Frosst provides a streamlined force field from the Open Force Field Initiative for calculating binding free energies and modeling host–guest thermodynamics.

Key Features:

• Simplified Force Field Parameters: Contains approximately one-tenth the number of parameters of traditional general small-molecule force fields such as GAFF (General AMBER Force Field).
• Host–Guest System Modeling: Models noncovalent host–guest complexes, emphasizing systems with reduced conformational space and minimized protonation-state ambiguities.
• Experimental Validation: Validated with free energy calculations on 43 α- and β-cyclodextrin host–guest pairs against experimental thermodynamic data.
• Comparative Performance: Uses the attach-pull-release (APR) method via the pAPRika package and exhibits a root-mean-square error of 0.9 kcal/mol versus experiment when compared to GAFF versions 1.7 and 2.1.
• Water Model and Charge Calculation: Simulations employed TIP3P water models and AM1-BCC charge assignments.

Scientific Applications:

• Binding free energy prediction: Predicting binding free energies to aid design of ligands with improved affinity and specificity.
• Force field optimization and benchmarking: Enabling force field optimization and benchmarking using host–guest systems to study binding thermodynamics.

Methodology:

Free energy calculations used the attach-pull-release (APR) method implemented in pAPRika on 43 α- and β-cyclodextrin host–guest pairs, employing TIP3P water models and AM1-BCC charges.