Applications of polyelectrolyte complexes for separation processes

Polyelectrolytes are polymers with potentially charged monomer units. Under the right conditions, oppositely charged polyelectrolytes in solution can interact and form polyelectrolyte complexes (PECs). These PECs have peculiar emergent properties. One of these properties is the ability to accumulate certain molecules in very high concentrations. A comparison can be made between PECs and membraneless-organelles (MLOs), which are droplet-like liquid-in-liquid phases present in our cells that aid the cell in organising its interior milieu through selective partitioning of specific molecules. Similar to PECs, MLOs are also composed op oppositely charged polyelectrolytes. In the case of MLOs, these are typically negatively charged RNA molecules and positively charged intrinsically disordered proteins. Taking inspiration from nature, in this dissertation we present the use of PECs for the partitioning of molecules. We investigated whether it was possible to use PECs to selectively extract a protein from a mixture. Followed by whether a PEC containing a protein could be used as a biocatalytic membrane. In chapters 2 – 4 we investigate various extraction procedures of small molecules and proteins using PECs. We find that various system parameters influence the degree of partitioning of these compounds. This culminates in chapter 4, where we were able to selectively extract lysozyme from lyophilised egg white by choosing a specific PEC composition as determined by the polycation:polyanion ratio. After extraction of lysozyme into the PEC phase and release back into a new aqueous phase, the lysozyme remained enzymatically active. In chapter 5 we produced a PEC membrane containing lysozyme via aqueous phase separation (APS). The resulting biocatalytic membrane gained the enzymatic activity of lysozyme without compromising on membrane properties. The membrane remained biocatalytically active for at least one week.