(501f) Solvation and Physical Properties of Lipid-Inspired Ionic Liquids

Recently, our group demonstrated that long chain n-alkyl-methyl imidazolium-based ionic liquids can be designed to remain room temperature liquids by incorporating cis-unsaturations into the alkyl chain. Typically, such ionic liquids with n-alkyl chains of 10 carbons or longer are room temperature solids. This increase in melting point relative to analogous ionic liquids with shorter n-alkyl chains is due to the longer n-alkyl chains aligning to form a continuous non-polar domain where enhanced dispersion force interactions lead to higher melting points.

In lipid-inspired ionic liquids, the ?kinked' structure caused by the unsaturations disrupts packing efficiency resulting in significantly lower melting points. Additionally, the melting point trends of these species mimics those of the fatty acids and phosoplipids containing analogous fatty acid chains. Many organisms utilize this phenomenon to regulate the fluidity of their cell membranes to compensate for temperature changes by incorporating saturated chains to decrease fluidity and unsaturated chains to increase fluidity.

The observed melting point decrease for ionic liquids with long unsaturated alkyl chains is significant and results in many of the species having melting points well below room temperature. This observation provided the opportunity to study the solvation properties of ionic liquids with long alkyl chains, which we anticipated would result in species with more non-polar-like properties. Initial studies indicated that non-polar molecules, such as cholesterol, have a significant solubility in these solvents and has prompted further investigation into their properties.

We have continued to study these as well as a new generation of structurally diverse and oxidatively stable lipid-inspired ionic liquids, characterizing their solvation and physical properties through melting point, solvatochromic and solubility measurements. Many of these ionic liquids have unusually high solubilities for non-polar compounds and offer the possibility of designing processes which take advantage of this solubility for reactions and separations.

In this work we present the new generation of these species as well as data describing their thermophysical properties as pure components and in mixtures.