Molecular Insights into the Concentration-Dependent Antagonistic Effect between Asparagine and NaCl on CO Hydrate Growth.

Gas hydrates are considered to be a promising medium for CO sequestration in marine environments. Additionally, salinity and amino acids in marine environments can significantly affect the growth of hydrates. This study employs molecular dynamics (MD) simulations to investigate the influence of asparagine (Asn) on CO hydrate growth within simulated seawater (NaCl 3.5 wt %) filled nanopores using analyses of cage growth rate, diffusion coefficient, radial distribution function, and electrostatic potential. Though NaCl and Asn can individually suppress hydrate growth, their special mass ratio causes the antagonistic effect to weaken their negative influence. In saline solution, the zwitterionic Asn can interact with Na and Cl ions to disturb their electrostatic attraction, inhibiting their crystallization and inducing their redistribution. The fewer crystals mitigate the CO migration barriers toward the water phase, and the Asn-NaCl interaction alleviates their perturbations on surrounding water and CO molecules to stabilize the hydrate. This proposed mechanism was validated from both frontal and lateral perspectives by increasing the NaCl concentration and varying the type of amino acid, respectively. These findings reveal the molecular mechanisms by which specific amino acids influence hydrate behavior and offer insights into optimizing CO sequestration in saline environments.