Room Temperature Ionic Liquids Meet Biomolecules: A Microscopic View of Structure and Dynamics

Room temperature ionic liquids (RTILs) and biomolecules are both paradigmatic classes of organic molecules, each consisting of a prodigious number of distinct chemical species, organized into large families of homologous compounds. Their combination is set to open new avenues for discoveries and for applications in biochemistry, biomedicine and pharmacology, food science, and nanotechnology. We provide a survey of past and current investigations of the chemical physics properties of systems made of RTILs and biomolecules, focusing on the most microscopic scales of their structure and dynamics. The primary goal of our discussion is to identify the basic principles able to organize and rationalize the vast variety of properties and phenomena displayed by these systems. We consider in turn RTILs combinations with phospholipids, with proteins and peptides, with nucleic acids (mainly DNA) and with carbohydrates from simple sugars to large polysaccharides. These basic components have a clear electrostatic signature, and Coulomb interactions represent the first ordering principle. However, because of size and complexity of both RTILs and biomolecules, dispersion interactions, steric effects, and hydrogen bonding play a secondary but certainly non-negligible role that is reflected in the sensitive dependence of RTIL/biomolecule properties on the RTIL choice. Our overview of the available results highlights both the need and the difficulty of devising general approaches able to predict properties of at least extended families of RTIL/biomolecules combinations, without having to consider them one by one in turn.