Structure and electronic properties of amino acid ionic liquids.

The interactions between eight amino acid based anions and four imidazolium-based cations have been investigated by density functional theory. The electronic and structural properties of the resulting amino acid ionic liquids (AAILs) have been unveiled by means of the atoms in molecules framework. The calculated interaction energy was found to increase in magnitude with decreasing alkyl chain length at imidazolium ring. Moreover, AAILs composed of an amino acid with some functional group such as aromatic ring had decreased interaction energy. Finally, several correlative relationships between glass transition temperature and interaction energy as well as density at bond critical point have been checked for 1-ethyl-3-methylimidazolium based ILs. Although the obtained correlations do not show excellent fits, a preliminary estimation of the glass transition temperature of different AAILs can be achieved by use of their electronic properties.