Good's buffer ionic liquids as relevant phase-forming components of self-buffered aqueous biphasic systems

Abstract

BACKGROUND: Self-buffered aqueous biphasic systems (ABS) are prepared with ionic liquids (ILs) based on Good's buffers (GB-ILs) and used to purify proteins. RESULTS: A set of new GB-ILs based on the tetrabutylphosphonium cation ([P4444]+) was here synthesized and characterized. The self-buffering behaviour of the GB-ILs was asserted by measuring their protonation constants by potentiometry. These ionic liquids display self-buffering characteristics as well as a low toxicity towards the luminescent bacteria Vibrio fischeri. The ability of the GB-ILs to form ABS with the potassium citrate salt was investigated. These systems were then evaluated to extract and purify BSA from bovine serum samples. Extraction efficiencies of 100 ± 5% of BSA to the GB-IL-rich phase were obtained in a single step. In addition, good recovery yields (59.4 ± 0.8% to 80.1 ± 0.7%), and purity levels of BSA (75.0 ± 0.3% to 92 ± 1%) were also achieved. The BSA secondary structure in the aqueous IL-rich solutions was evaluated through infrared spectroscopic studies revealing the protein-friendly nature of the synthesized GB-ILs. Dynamic light scattering (DLS), ‘Conductor-like Screening Model for Real Solvents’ (COSMO-RS), and molecular docking studies were carried out to better understand the main driving forces of the extraction process. CONCLUSION: The results obtained show that GB-IL based ABS can be prepared and used for protein purifications, with the GB-ILs showing a stabilizing effect on the protein. © 2017 Society of Chemical Industry.