1 research outputs found
Impact of an Ionic Liquid on Amino Acid Side Chains: A Perspective from Molecular Simulation Studies
Ionic liquids (ILs) are known to modify the structural
stability
of proteins. The modification of the protein conformation is associated
with the accumulation of ILs around the amino acid (AA) side chains
and the nature of interactions between them. To understand the microscopic
picture of the structural arrangements of ILs around the AA side chains,
room temperature molecular dynamics (MD) simulations have been carried
out in this work with a series of hydrophobic, polar and charged AAs
in aqueous solutions containing the IL 1-butyl-3-methylimidazolium
tetrafluoroborate ([BMIM][BF4]) at 2 M concentration. The
calculations revealed distinctly nonuniform distribution of the IL
components around different AAs. In particular, it is demonstrated
that the BMIM+ cations preferentially interact with the
aromatic AAs through favorable stacking interactions between the cation
imidazolium head groups and the aromatic AA side chains. This results
in preferential parallel alignments and enhanced population of the
cations around the aromatic AAs. The potential of mean force (PMF)
calculations revealed that such favorable stacking interactions provide
greater stability to the contact pairs (CPs) formed between the aromatic
AAs and the IL cations as compared to the other AAs. It is further
quantified that for most of the AAs (except the cationic ones), a
favorable enthalpy contribution more than compensates for the entropy
cost to form stable CPs with the IL cations. These findings are likely
to provide valuable fundamental information toward understanding the
effects of ILs on protein conformational stability