Abstract
Aqueous Two-Phase Extraction is known to be a gentle separation technique for biochemical molecules where product partitioning is fast. However, the reason for the high mass transfer rates has not been investigated, yet. Many researchers claim that the low interfacial tension facilitates the formation of very small droplets and with it a large interfacial area causing a fast partitioning. However, an experimental evidence for this hypothesis has not been published yet. In this study, the mass transfer coefficients of two proteins, namely lysozyme and bromelain, were determined by providing a defined interfacial area for partitioning. Compared to low molecular weight solutes the mass transfer coefficient for the proteins investigated was small proving for the first time that the large interfacial area and not fast diffusion seems to be the reason for fast protein partitioning.
Highlights
Aqueous Two-Phase Extraction (APTE) has been successfully applied as gentle unit operation for the purification of biomolecules such as therapeutic proteins[1,2,3], enzymes[4] and antibiotics[5,6]
Comparing the results with experiments obtained by Kruber et al where the transfer of hexan between heptane and methanol was determined in the same Nitsch-Cell used here, the equilibrium was reached faster and the k -value of 6.26 × 10−5 m s−1 21 was 17–18 times higher than the ones measured in this study
After comparing the physicochemical properties of the ionic liquid used in the study of Melgarejo-Torres, they differ in the viscosity of the Polyethylene glycol (PEG) phase and interfacial tension to that of the Aqueous Two-Phase Systems (ATPSs) used in this study and to that of the PEG8000/Dextran system
Summary
Aqueous Two-Phase Extraction (APTE) has been successfully applied as gentle unit operation for the purification of biomolecules such as therapeutic proteins[1,2,3], enzymes[4] and antibiotics[5,6]. Cunha et al briefly summarize, what Albertsson[9], Husted et al.[10] and Fauquex et al.[11] already explained: “The fast approach to equilibrium is owing to the low interfacial tension between the two phases, which enables the formation of very small droplets and a large interface for mass transfer with low energy input”[12]. This assumption is shared by many researchers[12,13,14,15,16,17,18,19]. By determining the mass transfer coefficient and comparing it to values of other systems one can decide, whether the mass transfer is high due to a high mass transfer coefficient or due to the ability of the ATPS to be and efficiently dispersed generating a large interface
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