Proton solvation in protic and aprotic solvents

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Solution Chemistry

Background:

• Protonation significantly influences molecular system properties.
• Accurate determination of proton solvation free energy is crucial for understanding protonation equilibria and solution chemistry.
• Existing methods require precise solvation energy data for various protic and aprotic solvents.

Purpose of the Study:

• To compute proton affinities (PAs), electrostatic solvation energies, and pKA values in protic and aprotic solvents.
• To determine the proton solvation energy in acetonitrile (MeCN), methanol (MeOH), water, and dimethyl sulfoxide (DMSO).
• To validate computational methods against experimental pKA values.

Main Methods:

• Utilized a combination of quantum chemical and electrostatic approaches for high-accuracy pKA computations.
• Performed gas-phase proton affinity (PA) calculations using quantum chemical density functional theory.
• Computed electrostatic solvation contributions by solving the Poisson equation.

Main Results:

• Achieved high accuracy in computed proton solvation free energies for MeCN, MeOH, water, and DMSO.
• Obtained values of -255.1, -265.9, -266.3, and -266.4 kcal/mol for MeCN, MeOH, water, and DMSO, respectively.
• The computed solvation energy for water (-266.3 kcal/mol) closely matches the consensus value (-265.9 kcal/mol).

Conclusions:

• The study successfully computed accurate proton solvation free energies in key solvents.
• Correlations between pKA values and solvation energies in MeCN, MeOH, and DMSO indicate single-solvent molecule attachment for the solvated proton.
• The findings provide valuable data for computational chemistry and molecular system studies.