Amino-acid recovery using ionic liquids: Partitioning in water + ionic liquid systems

The partition of a series of dinitrophenylated amino-acids is studied experimentally in two (Ionic Liquid + Sodium Phosphate Buffer) biphasic systems at 23 oC. The ionic liquids used in these experiments are 1-hexyl-3-methylimidazolium tetrafluoroborate, [C6mim][BF4], and 1-decyl-3-methylimidazolium tetrafluoroborate, [C10mim][BF4]. pH of the initial aqueous solution is fixed at 7.4 using a suitable sodium phosphate buffer. DNP-amino-acids distribute preferentially to the ionic liquid phase, and this partition increases with the length of the alkyl chain of amino-acid. The free energy of transfer for a methylene group is calculated from the partition coefficients of the solutes. This provides an effective measurement for the relative hydrophobicity of the conjugated phases, which is higher than in other biphasic systems used in biotechnology (e.g., polymer-polymer and polymer salt aqueous two-phase systems).