Synthesis of pH-responsive polymers forming recyclable aqueous two-phase systems and application to the extraction of demeclocycline

The application of aqueous two-phase systems (ATPS) to bioseparation and biocatalyst engineering has attracted interest. However, despite the distinct advantages of the technique, the scaling up of ATPS is limited by the cost of the system components. In this study, two novel recyclable pH-responsive polymers were synthesized and tested for the partition of demeclocycline. The recoveries of two recyclable pH.responsive polymers could reach over 95.0% by only adjusting the solution pH to the isoelectric points of the polymers. The control variate method was used to investigate the effects of polymerization conditions on polymer synthesis. Polymer P-ADB4.6 was firstly synthesized in 5001 reactor with two-stage heating method (25-40 degrees C and 40-62 degrees C), as the heating rate is an important factor in the scale-up process. The polymer characteristics (molecular weight, viscosity, surface tension, and zeta potential) were studied to understand their influences on the synthetic process. Furthermore, the phase formation mechanism was studied with low-field nuclear magnetic resonance (LF-NMR). The optimal partition coefficient and recovery of demeclocycline using the recyclable ATPS were 0.24 and 82.9% at pH 6.30 in presence of 20 mmol/L MgSO4.