Adding explicit solvent molecules to continuum solvent calculations for the calculation of aqueous acid dissociation...

Area of Science:

• Computational Chemistry
• Physical Chemistry
• Solution Chemistry

Background:

• Accurate calculation of acid dissociation free energies is crucial for understanding chemical reactions.
• Continuum solvation models provide a computationally efficient way to model solvent effects.
• Short-range interactions, like hydrogen bonding, can be challenging for implicit solvation models.

Purpose of the Study:

• To calculate aqueous acid dissociation free energies for 57 monoprotic acids.
• To evaluate the performance of the SM6 continuum solvation model.
• To investigate the impact of explicit water molecules on solvation free energy calculations for anions.

Main Methods:

• Combined experimental and calculated gas/liquid-phase free energies.
• Utilized the SM6 continuum solvation model for aqueous solvation free energies.
• Incorporated explicit water molecules with the SM6 model for select anions.

Main Results:

• Calculated pK(a) values showed improved agreement with experimental data when a single explicit water molecule was included for certain anions.
• The study highlights the importance of short-range hydrogen bonding for anions concentrating charge on a single heteroatom.
• Calculations for bicarbonate demonstrated the effect of multiple explicit water molecules on pK(a).

Conclusions:

• Augmenting implicit solvation models with a single explicit water molecule is effective for accurately describing strong anion-solvent interactions.
• This hybrid approach offers a more refined method for predicting acid dissociation constants.
• The findings provide valuable insights for computational chemistry and physical chemistry research.