Understanding Conformational Entropy in Small Molecules.

Area of Science:

• Computational chemistry
• Molecular modeling
• Statistical mechanics

Background:

• Calculating conformational entropy for flexible molecules is challenging due to the exponential growth of possible conformers.
• Existing methods include full conformer calculations or empirical corrections, each with limitations.

Purpose of the Study:

• To develop accurate models for predicting conformational entropy across a wide range of small molecules.
• To investigate the correlations between torsional degrees of freedom in molecules.

Main Methods:

• Conformer sampling was performed on over 120,000 small molecules, generating approximately 12 million conformers.
• A physically motivated statistical model was developed and cross-validated.
• The model incorporates insights into conformational disorder and torsional correlations.

Main Results:

• The developed statistical model achieved a mean absolute error of ~4.8 J/mol·K (under 0.4 kcal/mol at 300 K).
• The model revealed significant correlations between torsional degrees of freedom in most molecules, contrary to common assumptions of independence.
• The number of low-energy conformations is greatly restricted by these correlations.

Conclusions:

• The developed models accurately predict molecular entropies and free energies.
• The findings advance the understanding of small molecule conformational entropy by highlighting the importance of torsional correlations.
• This work provides a more refined approach to modeling molecular flexibility and its thermodynamic contributions.