Effect of salt-based adjuvant on partition behaviour of protein in aqueous two-phase systems composed of polypropylene glycol and cholinium glycinate

Structure of cholinium glycinate biocompatible ionic liquid at graphite electrode interface

We use constant potential molecular dynamics simulations to investigate the interfacial structure of the cholinium glycinate biocompatible ionic liquid (bio-IL) sandwiched between graphite electrodes with varying potential differences. Through number density profiles, we observe that the cation and anion densities oscillate up to ∼1.5 nm from the nearest electrode. The range of these oscillations does not change significantly with increasing electrode potential. However, the amplitudes of the cation (anion) density oscillations show a notable increase with increasing potential at the negative (positive) electrode. At higher potential differences, the bulkier N(CH₃)₃CH₂ group of cholinium cations ([Ch]⁺) overcomes the steric barrier and comes closer to the negative electrode as compared to oxygen atom (O_[Ch]⁺ ). We observe an increase in the interaction between O_[Ch]⁺ and the positive electrode with a decrease in the distance between them on increasing the potential difference. We also observe hydrogen bonding between the hydroxyl group of [Ch]⁺ cations and oxygens of glycinate anions through the simulated tangential radial distribution function. Orientational order parameter analysis shows that the cation (anion) prefers to align parallel to the negative (positive) electrode at higher applied potential differences. Charge density profiles show a positive charge density peak near the positive electrode at all the potential differences because of the presence of partially positive charged hydrogen atoms of cations and anions. The differential capacitance (C_d) of the bio-IL shows two constant regimes, one for each electrode. The magnitude of these C_d values clearly suggests potential application of such bio-ILs as promising battery electrolytes.

Salt-containing aqueous two-phase system shows predictable partition of proteins with surface amino acids residues

Aqueous two-phase system (ATPS) containing salts has been used for protein purification and enrichment. However, it is unclear how proteins are partitioned in the top or bottom phases of the system. In this study, we demonstrate that the partition of proteins in salt-containing ATPS (SATPS) depends only on the relation between the protein-surface amino acids and the type of salt using SATPS. The partition coefficients of four proteins changed depending on the kind of salt, according to the Hofmeister series. Interestingly, the partition coefficients of the proteins correlated to those of the combination of the amino acids in the surface of the protein with the correlation coefficients of >0.9. The results suggest that the interaction between the protein surface and aqueous ions plays an indispensable role for the partition of proteins in SATPS that can help in the design of protein partition in ATPS for purification and enrichment.

Purification of the Recombinant Green Fluorescent Protein Using Aqueous Two-Phase System Composed of Recyclable CO2-Based Alkyl Carbamate Ionic Liquid

The formation of aqueous two-phase system (ATPS) with the environmentally friendly and recyclable ionic liquid has been gaining popularity in the field of protein separation. In this study, the ATPSs comprising N,N-dimethylammonium N′,N′-dimethylcarbamate (DIMCARB) and thermo-responsive poly(propylene) glycol (PPG) were applied for the recovery of recombinant green fluorescent protein (GFP) derived from Escherichia coli. The partition behavior of GFP in the PPG + DIMCARB + water system was investigated systematically by varying the molecular weight of PPG and the total composition of ATPS. Overall, GFP was found to be preferentially partitioned to the hydrophilic DIMCARB-rich phase. An ATPS composed of 42% (w/w) PPG 1000 and 4.4% (w/w) DIMCARB gave the optimum performance in terms of GFP selectivity (1,237) and yield (98.8%). The optimal system was also successfully scaled up by 50 times without compromising the purification performance. The bottom phase containing GFP was subjected to rotary evaporation of DIMCARB. The stability of GFP was not affected by the distillation of DIMCARB, and the DIMCARB was successfully recycled in three successive rounds of GFP purification. The potential of PPG + DIMCARB + water system as a sustainable protein purification tool is promising.