Mechanistic Insights into the Role of Peptide Hydrophobicity in Methane Hydrate Formation

Peptides and amino acids have been proposed as kinetic inhibitors/promoters for gas hydrate formation. Hydrophobicity has been suggested as a key characteristic, but the underlying mechanisms remain unclear, as well as the influence of concentration. Building upon our previous work on the natural peptide TAFDGGS, this work aims at providing deeper insights into the role of peptides on methane hydrate formation. Experiments were conducted on variants of TAFDGGS designed to enhance hydrophobicity (VAFLGGA) or hydrophilicity (TSYDGGS), at both low and high concentrations. Molecular dynamics simulations were independently performed on the three peptides in the nucleation and growth stages. Experimental results revealed that the hydrophobic peptide VAFLGGA enhanced hydrate formation kinetics by both reducing induction time and accelerating hydrate growth, while the hydrophilic peptide TSYDGGS showed a weaker promoting effect with delayed nucleation. Furthermore, it was found that increasing the peptide concentration provided diminishing returns. Molecular simulations unveiled the mechanisms at the nanoscale, where predominantly hydrophobic amino acids played a key role in the peptide adsorption at the hydrate–liquid interface. These mechanisms were linked to an increase in the nucleation rate and, by saturating the hydrate surface, to a slowdown in subsequent growth, with the intensity of these effects being modulated by overall hydrophobicity. By correlating peptide hydrophobicity with interfacial adsorption behavior, this study lays the foundations for a rational approach to the design of peptides intended to influence gas hydrate kinetics.