Rigorous pK_a Estimation of Amine Species Using Density-Functional Tight-Binding-Based Metadynamics Simulations

Area of Science:

• Computational Chemistry
• Physical Chemistry
• Chemical Engineering

Background:

• Accurate prediction of acid dissociation constants (pK_a) for amine species is essential for developing efficient and economical solvents for carbon capture and storage (CCS).
• Existing computational methods may not fully capture the complexities of proton transfer in aqueous solutions, impacting predictive accuracy.

Purpose of the Study:

• To evaluate the efficacy of density-functional tight-binding (DFTB)-based metadynamics simulations for predicting amine pK_a values.
• To assess the computational cost and accuracy of this method compared to traditional approaches.

Main Methods:

• Employing DFTB-based metadynamics simulations to calculate the free energy difference between protonated and neutral amine states in aqueous solution.
• Validating simulation results against experimental pK_a values for a diverse set of 34 common CO₂ scrubbing amines.

Main Results:

• The simulations achieved a low mean absolute deviation of 0.09 pK_a units when compared to experimental data.
• DFTB-based metadynamics demonstrated superior reproducibility and correlation compared to static quantum mechanical calculations.
• The study highlighted the significant role of dynamical proton transfer and explicit solvent effects in improving pK_a estimation accuracy.

Conclusions:

• DFTB-based metadynamics is a promising, computationally inexpensive approach for accurately predicting amine pK_a values.
• This method offers significant advantages over static calculations by incorporating dynamic proton transfer and solvent effects.
• The findings support the use of this simulation technique for the rational design of advanced amine solvents for carbon capture applications.