(659c) Investigations into the Gas Hydrate and Amino Acid Complex System

Gas hydrates and amino acids are key materials when investigating the existence of life since they are a source of water and organic precursors in the universe. In particular, a coexistence of gas hydrates and amino acids is of great interest. Herein, we investigate gas hydrate inhibition and crystal lattice incorporation phenomena occurred in gas hydrate + amino acid system. When amino acids were added to the system with a high concentration, they worked as thermodynamic hydrate inhibitors (THIs). Phase equilibrium conditions of gas hydrates in the presence of amino acids were obtained. By shifting the phase equilibrium conditions to lower temperature and higher pressure regions, it was found that amino acids are available for preventing hydrate blockages in gas transportation pipelines. The mechanism of THIs was interpreted by "hydrogen bond" and "hydrophobic effect" between water and amino acid molecules. More interestingly, with a low concentration of amino acids, they worked as kinetic hydrate inhibitors (KHIs) rather than THIs. Heterogeneous nucleation and growth kinetics of gas hydrates were measured. From the experimental results, it was hypothesized that a perturbation of water structure plays a critical role in the working mechanism of KHIs. In addition, crystal structure of gas hydrate + amino acid system was identified using synchrotron powder X-ray diffraction. From the PXRD patterns, an intriguing feature was found that amino acids were incorporated into the gas hydrate crystal lattice. This unusual phenomenon implies the potential for natural coexistence of gas hydrates and amino acids with sharing their crystal structures. The present investigations on gas hydrate + amino acid system will be crucial for understanding their crystallization behavior.