Effects of 1-butyl-3-methyl-imidazolium acetate on the solution behavior of melittin: A molecular dynamics study

Ionic liquids posses efficiency as solvents, co-solvents or agents for applications involving biomolecules. Due to the increasing interest in systems containing proteins and ionic liquids, we hereby present results from molecular dynamics simulations on solutions containing the polypeptide melittin in pure water, in the neat ionic liquid 1-butyl-3-methyl-imidazolium acetate ([BMI][OAc]) and in the equimolar [BMI][OAc]/H₂O mixture. When compared to the solutions containing the ionic liquid, melittin displays higher mobility and flexibility, lower stability and poorer secondary structure preservation in water. The intramolecular hydrogen bonds in melittin do not play a major role in the structural preservation, but intermolecular hydrogen bonds between melittin and the solvent are important. The micro-solvation of melittin demonstrates that anions and water molecules are in closer contact to melittin, whereas the cations maintain larger distances to the polypeptide. The presence of [BMI][OAc] reduces fluctuation in melittin's structure. Only small differences have been found in the structural arrangement of melittin in the neat ionic liquid and the ionic liquid/water mixture.