Room temperature ionic liquids interacting with bio-molecules: an overview of experimental and computational studies

Abstract

We briefly review experimental and computational studies of room temperature ionic liquids (RTILs) interacting with important classes of biomolecules, including phospholipids, peptides and proteins, nucleic acids and carbohydrates. Most of these studies have been driven by the interest for RTILs applications as solvents. Thus, available experimental data cover primarily thermodynamic properties such as the reciprocal solubility of RTILs and bio-molecules, as well as phase boundaries. Less extensive data are also available on transport properties such as diffusion and viscosity of homogeneous binary (RTILs/biomolecules) and ternary (RTIL/biomolecules/water) solutions. Most of the structural information at the atomistic level, of interest especially for biochemical, pharmaceutical and nanotechnology applications, has been made available by molecular dynamics simulations. Major exceptions to this statement are represented by the results from NMR and circular dichroism spectroscopy, by selected neutron and X-ray scattering data, and by recent neutron reflectometry measurements on lipid bilayers on surfaces, hydrated by water-RTIL solutions. A final section of our paper summarizes new developments in the field of RTILs based on amino acids, that combine in themselves the two main aspects of our discussion, i.e. ionic liquids and bio-molecules.

Keywords:

• ionic liquids
• biomolecules
• phospholipids
• proteins
• nucleic acids
• carbohydrates

Notes

No potential conflict of interest was reported by the authors.

1 Most of the studies of AA, peptides and protein solubility take the water-biomolecule as the basic system and study the variation of solubility due to the RTIL addition. Ref. [52] takes the opposite point of view: the basic system is water-RTIL ([CCIm][C(CN)]) solutions at the critical point of solubility gap (cloud point). This reversal of the most popular point of view might be confusing at first.

2 Ionic compounds consisting of a choline cation and an amino acid anion have been synthesized by R. Caminiti and A. Sferrazza, Dipartimento di Chimica, Università di Roma ‘La Sapienza’, Private Communication.

3 Alanine, ; valine, ; serine, ; cysteine, ; aspartic acid ; asparagine, ; phenylalanine ; histidine .

Additional information

Funding

A.B. acknowledges support from the European Commission under the Marie Curie Fellowship HYDRA [grant number 301463] and PSI-FELLOW [grant number 290605], with additional support provided by the School of Physics, University College Dublin, Ireland.