Computational studies of structure and dynamics of clathrate inhibitor monomers in solution

Theoretical studies of five monomer constituents of gas clathrate inhibitorsvinylpyrrolidone, vinylvalerolactam, L-proline (LP), 1-formylpyrrolidine, and (dimethylaminoethyl)methacrylate (DMAEMA)are performed in the presence of water, with the solvent treated both explicitly and as a continuum. The binding energy increases as the inhibitor is more polarized, but no clear relationship is found between polarization and free energy of solvation values. Comparison of the binding energies of the inhibitor-water complexes and analysis of the hydration shells around the inhibitor sites indicate that short-range interactions influence the clathrate inhibitor effect more than long-range ones do. The balance of hydrophobic and hydrophilic moieties is found to be a determinant factor in the behavior of the inhibitor. In contrast to the other monomers, analyses of the DMAEMA and LP behaviors show that the N site can be associated with the hydrophilic moiety. Besides, DMAEMA has the best hydrophobic solvation around its methyl groups, resembling clathrate formation around methane. The time evolution of the mean square displacement and the power spectrum calculated from velocity autocorrelation functions reveal slight changes in the dynamic behavior of water that are not strong enough to be considered decisive in the inhibition efficiency.