Noncovalent Guest-Host Interactions Unlock the Potential of MOFs for Anesthetic Xenon Recovery: GCMC and DFT Insights into Real Anesthetic Conditions

In this work, we conducted combined Grand Canonical Monte Carlo (GCMC) and Density Functional Theory (DFT) simulations to determine the anesthetic Xe recovery capacities of 19 MOFs from the exhaled quaternary anesthetic gas mixture, Xe/CO2/O2/N2. Among the considered MOFs, COCMUE, GUHMIH, MAHCOQ, and PADKOK have demonstrated overall larger volumetric and gravimetric Xe uptake. We have achieved 40.18 wt.% gravimetric and 376.16 g/L volumetric Xe uptake with these MOFs. These nanoporous materials also show how ligand types can boost selective Xe uptake. Tetrazole, phenyl, pyridyl, carboxamide, dicarboxylic acid, phenoxazine, and triazole ligands in the MOF structures act as Xe trapping regions.

Using DFT simulations and generating electron density difference maps, we found that Xe-host interactions in the top-performing MOFs are maximized mainly due to noncovalent interactions of Xe, such as charge-induced dipole and aerogen–π interactions. Polarized Xe atoms in the vicinity of cations/anions and π systems indicate stronger guest-host interactions. Our combined GCMC and DFT study indicates that selecting MOFs with the appropriate chemical and structural features can significantly enhance Xe-host interactions, paving the way for practical applications in xenon anesthesia.

This repository includes CIF files with atomic point charges as well as input and output samples for GCMC and DFT simulations of the top-performing MOFs.

GCMC simulations were utilized to compute the quaternary gas adsorption isotherms of a Xe/CO2/O2/N2 mixture containing 65% Xe, 5% CO2, 24% O2, and 6% N2. The open-source RASPA package was used to carry out GCMC runs. Adsorption isotherms were calculated at pressures ranging from 0.1 bar to 1 bar in 0.1 bar increments, as well as at 2, 3, and 5 bars, all at a temperature of 298 K. Various GCMC moves, including translation, reinsertion, rotation, molecule swapping, and identity changes were incorporated. The Peng-Robinson equation of state was used to convert pressure to fugacity. The GCMC simulations consisted of 5.1x10^5 cycles, with the first 10^4 cycles serving as the initialization phase. Interactions between adsorbate molecules and those between the adsorbate and adsorbent were modeled using the Lennard-Jones (LJ) potential, while electrostatic interactions were accounted for using the Coulomb potential. The Density Derived Electrostatic and Chemical Charge Partitioning method (DDEC6) was utilized to determine the partial atomic charges of the MOFs.

DFT simulations were conducted on the top-performing materials to analyze geometry-optimized adsorption sites of Xe and the nature of interactions between the adsorbed xenon atoms and the MOFs. We also examined electron density difference maps, frontier molecular orbital distributions, and the density of states of Xe-adsorbed MOFs to characterize the host-guest interactions further.

Electron density distributions were calculated using a combination of Gaussian and plane wave formalisms at the Kohn-Sham DFT level, implemented in the open-source CP2K package. For DFT calculations, we employed the generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) functional, alongside Grimme-D3 dispersion corrections to account for van der Waals interactions. Goedecker-Teter-Hutter (GTH) pseudopotentials and Double-zeta valence plus polarization (DZVP-MOLOPT) basis sets, optimized for molecular geometries, were applied to all DFT simulations. A 500 Ry cutoff for the auxiliary plane wave basis set was employed to ensure computational accuracy. Periodic boundary conditions and spin polarization were always applied.