Amino acid ionic liquids have been shown to be an interesting subsection of ionic liquids. Amino acids are one of the most abundant biomaterials in nature and are readily available at reasonable cost, enabling ionic liquids based upon them to be prepared in large quantities, and in high purity. In addition, since an amino acid contains both an amino group and a carboxylic acid residue they may be used as either the anion or cation in a given ionic liquid. The physical and chemical properties of some these derivatives have been extensively investigated by Ohno, who detailed how the properties of the ionic liquids can vary depending on the amino acid side chain. Amino acid ionic liquids containing side chains with no functionality (i.e. they are simple alkyl tails) display a clear relationship between their ionic conductivity and glass transition temperature. Once the side chain is functionalised to some degree the nature of this relationship changes, implying the manifestation of intra- and/or inter-ion interactions.Neutron diffraction experiments were used to probe the structure of the ionic liquids [Emim][Gly], [Emim][Ala] and [Emim][Ser] as a means to further understand the behaviour of these different amino acid containing derivatives. Glycine represents the simplest of the amino acids (where the side chain, R, is hydrogen), alanine contains a small nonpolar alkyl side chain (R = Me), and serine which contains a polar alcohol functionality (R = CH2OH). Resolving the structure of this trio of ionic liquids not only provides a deeper understanding of the nature of these materials, but also serve to develop our understanding of the specific structural effects (and chemical influences) of the side chain functionality in these systems.

Using neutron diffraction to identify liquid interactions of amino acid ionic liquids

248th National Meeting (2014)

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