CO₂ Hydration Shell Structure and Transformation

Abstract

The hydration-shell of CO is characterized using Raman multivariate curve resolution (Raman-MCR) spectroscopy combined with ab initio molecular dynamics (AIMD) vibrational density of states simulations, to validate our assignment of the experimentally observed high-frequency OH band to a weak hydrogen bond between water and CO. Our results reveal that while the hydration-shell of CO is highly tetrahedral, it is also occasionally disrupted by the presence of entropically stabilized defects associated with the CO-water hydrogen bond. Moreover, we find that the hydration-shell of CO undergoes a temperature-dependent structural transformation to a highly disordered (less tetrahedral) structure, reminiscent of the transformation that takes place at higher temperatures around much larger oily molecules. The biological significance of the CO hydration shell structural transformation is suggested by the fact that it takes place near physiological temperatures.

Temperature and polarization dependent Raman spectra of liquid H2O and D2O

“…It is also noteworthy that such Fermi‐resonance coupling has definitively been confirmed to occur at high pressures in isotopically doped ice . Thus, the incorporation of Fermi resonance coupling into theoretical calculations of the Raman spectrum of water remains an outstanding challenge, whose resolution promises to facilitate the more quantitative structural interpretation of solvation‐ and aggregation‐induced hydration‐shell Raman spectra in aqueous solutions of relevance to biological self‐assembly and activity . Recently reported calculations of the Raman spectrum of liquid water have incorporated Fermi resonance, as was previously done for water clusters …”

Space-Resolved OH Vibrational Spectra of the Hydration Shell around CO2

“…As a reference system, we also ran a simulation of pure water. The trajectories from these simulations were used in ref ( 18 ), but here we present additional analyses and conclusions based on these data. We repeat the main details of the simulations here.…”

“…On the theoretical side, we mention statistical simulations with classical force-fields (see, e.g., refs ( 9 − 14 )), MD simulations with many-body force-fields 8 generated from quantum-mechanical cluster calculations, as well as simulations that retain the electrons, such as QM/MM-MD simulations 14 , 15 or ab initio MD (AIMD) simulations. 16 − 18 Many of these simulation studies emphasize structural properties, like radial distribution functions, to discuss the featues of the CO 2 hydration. In addition a number of quantum-mechanical studies of small CO 2 –water clusters, published throughout the years, have added valuable insight concerning CO 2 –water interactions.…”

“…For a different class of solutes, Ben-Amotz and co-workers developed an essentially similar strategy based on Raman measurements and multivariate curve resolution (MCR) analysis to single out the “solute-affected” spectrum 25 from a solution spectrum and characterize the solvation shell around organic molecules in aqueous or organic solvents. In a collaborative experimental–computational effort, 18 this approach was turned into a tool to provide evidence for a phase transition in the water layer surrounding a CO 2 molecule at ambient temperatures, that would otherwise have been very difficult to obtain. Our analyses in the current paper build on the same AIMD simulation trajectories that were used in ref ( 18 ).…”

“…In a collaborative experimental–computational effort, 18 this approach was turned into a tool to provide evidence for a phase transition in the water layer surrounding a CO 2 molecule at ambient temperatures, that would otherwise have been very difficult to obtain. Our analyses in the current paper build on the same AIMD simulation trajectories that were used in ref ( 18 ). Those simulations were performed with the BLYP-D3 density functional, i.e., with dispersion interactions taken into account.…”