A pH-Controllable Imprinted Composite Membrane for Selective Separation of Podophyllotoxin and Its Analog

A molecularly imprinted composite membrane (MICM) with pH-controllability and selectivity to podophyllotoxin (PPT) was prepared using a polyvinylidene fluoride (PVDF) microfiltration membrane as the support. The functional monomer is 1-phenyl-3-methyl-4-methacryloyl-5-pyrazolone (PMMP), which is a new beta-diketone compound with enol/ketol tautomerization. In this study, imprinting parameters, including the amounts of functional monomer and cross-linker, and immersion time of membrane in the imprinting solution, were optimized by equilibrium adsorption experiments. Pore structure and surface morphology of the optimal MICM (MICM2) was characterized. Finally, competitive permeability of PPT in the presence of its analog 4'-demethylpodophyllotoxin (DMEP) was measured under the drive of concentration difference. The results reveal that the surface morphology and pore structure of MICM2 are structurally different from those of the control nonimprinted membrane. As a result, MICM2 could efficiently recognize PPT in a complex system due to a better structural matching and the interaction between the functional groups of MICM2 and PPT. However, the most interesting finding is its pH-controllability. The membrane could switch the preference to either PPT or DMEP with the change of pH values in the sample solution. At pH values smaller than 8.4, it led to a faster transportation of PPT, while the situation reversed to DMEP at pH values greater than 8.4. This peculiar property would lead this imprinted membrane to have potential application in the separation and enrichment of PPT, and the new functional monomer PMMP exhibited an attractive application prospect in the functional material fields. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 128: 363-370, 2013