Abstract
Aqueous two-phase systems (ATPS) occur by the mixture of two polymers or a polymer and an inorganic salt in water. It was shown that not only polymers but also ionic liquids in combination with inorganic cosmotrophic salts are able to build ATPS. Suitable for the formation of ionic liquid-based ATPS systems are hydrophilic water miscible ionic liquids. To understand the driving force for amino acid and peptide distribution in IL-ATPS at different pH values, the ionic liquid Ammoeng 110™ and K2HPO4 have been chosen as a test system. To quantify the concentration of amino acids and peptides in the different phases, liquid chromatography and mass spectrometry (LC–MS) technologies were used. Therefore the peptides and amino acids have been processed with EZ:faast™-Kit from Phenomenex for an easy and reliable quantification method even in complex sample matrices. Partitioning is a surface-dependent phenomenon, investigations were focused on surface-related amino acid respectively peptide properties such as charge and hydrophobicity. Only a very low dependence between the amino acids or peptides hydrophobicity and the partition coefficient was found. Nevertheless, the presented results show that electrostatic respectively ionic interactions between the ionic liquid and the amino acids or peptides have a strong impact on their partitioning behavior.
Highlights
During the past few decades ionic liquids have become an essential part in chemical and biochemical research (Wasserscheid and Welton 2008)
It is obvious that phenylalanine (Phe), glutamic acid (Glu) and histidine (His) are strongly enriched in the ionic liquids-containing upper phase of the Aqueous two-phase systems (ATPS) at both potential of hydrogen (pH) values
The results show that there has to be a interaction between the cation of Ammoeng 110TM (AE110, ionic liquid (IL)) and the negatively charged carboxyl groups of the amino acids (Fig. 2)
Summary
During the past few decades ionic liquids have become an essential part in chemical and biochemical research (Wasserscheid and Welton 2008). Ionic liquids are organic salts with unique physical properties, for example high thermal stability, low viscosity and a negligible vapor pressure. 100 °C, ionic liquids exist in a liquid state (Seddon 1997). Steric effects and charge delocalization of their ions hinder the formation of a stable crystal lattice (Kyte and Dolittle 1982). Already low thermal energy is sufficient to overcome the lattice energy and to break up the solid crystalline structure (Kyte and Dolittle 1982).
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