The Hydration Structure of Carbon Monoxide by Ab Initio Methods

TL;DR

This study uses advanced ab initio methods to analyze the hydration structure of carbon monoxide in water, revealing its hydrophobic nature and evaluating the accuracy of molecular models against high-level calculations and experimental data.

Contribution

It provides a detailed ab initio assessment of CO hydration structure and evaluates the accuracy of existing molecular models, highlighting discrepancies and confirming hydration thermodynamics.

Findings

CO is primarily hydrogen-bonded via water donating to the C atom.

The MM model overestimates hydrogen bonding and atomic radius.

Calculated hydration free energy agrees well with experimental data.

Abstract

The solvation of carbon monoxide (CO) in liquid water is important for understanding its toxicological effects and biochemical roles. In this paper, we use ab initio molecular dynamics (AIMD) and CCSD(T)-F12 calculations to assess the accuracy of the Straub and Karplus molecular mechanical (MM) model for CO(aq). The CCSD(T)-F12 CO--H2O potential energy surfaces show that the most stable structure corresponds to water donating a hydrogen bond to the C center. The MM-calculated surface it incorrectly predicts that the O atom is a stronger hydrogen bond acceptor than the C atom. The AIMD simulations indicate that CO is solvated like a hydrophobic solute, with very limited hydrogen bonding with water. The MM model tends to overestimate the degree of hydrogen bonding and overestimates the atomic radius of the C atom. The calculated Gibbs energy of hydration is in good agreement with experiment (9.3 kJ/mol calc. vs 10.7 kJ/mol exptl.). The calculated diffusivity of CO(aq) in TIP3P-model water was 5.19 x 10-5 cm2/s calc., more than double the experimental value of 2.32 x 10-5 cm2/s