The hydration structure of carbon monoxide by ab initio methods

Area of Science:

• Computational Chemistry
• Physical Chemistry
• Chemical Physics

Background:

• Understanding carbon monoxide (CO) solvation in water is crucial for its toxicological and biochemical implications.
• Accurate molecular models are needed to simulate CO's behavior in aqueous environments.

Purpose of the Study:

• To evaluate the accuracy of the Straub and Karplus molecular mechanical (MM) model for carbon monoxide in water.
• To compare MM simulations with high-level ab initio molecular dynamics (AIMD) and CCSD(T)-F12 calculations.

Main Methods:

• Ab initio molecular dynamics (AIMD) simulations.
• Coupled-cluster with singles and doubles and a ক্রমবর্ধমান-factor of 12 (CCSD(T)-F12) calculations.
• Molecular mechanical (MM) modeling using the Straub and Karplus model.
• Simulations employed TIP3P and TIP4P-FB water models.

Main Results:

• CCSD(T)-F12 potentials show water donating hydrogen bonds to the carbon atom of CO, contrary to the MM model's prediction.
• AIMD simulations indicate CO behaves as a hydrophobic solute with minimal hydrogen bonding.
• The MM model overestimates hydrogen bonding and the carbon atom's radius.
• Gibbs energy of hydration with TIP3P water was accurate, but diffusivity was overestimated; TIP4P-FB showed poorer hydration energy but better diffusivity.

Conclusions:

• The Straub and Karplus MM model exhibits inaccuracies in describing CO-water interactions, particularly hydrogen bonding.
• AIMD simulations provide a more realistic depiction of CO solvation as a hydrophobic solute.
• The choice of water model (TIP3P vs. TIP4P-FB) impacts the accuracy of calculated hydration energy and diffusivity.