Aquaporins are water channel proteins in cell membrane, highly specific for water molecules while restricting the passage of contaminants and small molecules, such as urea and boric acid. Cysteine functional groups were installed on aquaporin Z for covalent attachment to the polymer membrane matrix so that the proteins could be immobilized to the membranes and aligned in the direction of the flow. Depth profiling using x-ray photoelectron spectrometer (XPS) analysis showed the presence of functional groups corresponding to aquaporin Z modified with cysteine (Aqp-SH). Aqp-SH modified membranes showed a higher salt rejection as compared to unmodified membranes. For 2 M NaCl and CaCl2 solutions, the rejection obtained from Aqp-SH membranes was 49.3 ± 7.5% and 59.1 ± 5.1%. On the other hand, the rejections obtained for 2 M NaCl and CaCl2 solutions from unmodified membranes were 0.8 ± 0.4% and 1.3 ± 0.2% respectively. Furthermore, Aqp-SH membranes did not show a significant decrease in salt rejection with increasing feed concentrations, as was observed with other membranes. Through simulation studies, it was determined that there was approximately 24% capping of membrane pores by dispersed aquaporins.
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This material is based upon work supported by the National Science Foundation under Cooperative Agreement No.1355438, and by the NSF KY EPSCoR Program and in addition the author acknowledges Center of Membrane Sciences at University of Kentucky. Research reported in this publication, release was supported by the Maximizing Investigators’ Research Award (MIRA) (R35) from the National Institute of General Medical Sciences (NIGMS) of the National Institutes of Health (NIH) under grant number R35GM124977. We further acknowledge support from the American Chemical Society Petroleum Research Fund 58719-DN16. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1548562. In addition, the authors want to acknowledge the sources of funding, NSF 1308095 and USGS 104(b): Ohio Water Development Authority GRT00028988/60040357 for funding this project.
The following are available online at http://www.mdpi.com/2227-9717/7/2/76/s1, Figure S1: Flux linearity and permeability consistency for unmodified PBI and Aqp-SH modified PBI membranes. Figure S2: Diffusion cell assembly with 1000 ppm NaCl and DI water in two compartments separated by membrane. Table S1: Salt concentrations measured every day for all three membranes in diffusion cell assembly
Wagh, Priyesh Ashokrao; Zhang, Xinyi; Blood, Ryan; Kekenes-Huskey, Peter M.; Rajapaksha, Prasangi; Wei, Yinan; and Escobar, Isabel C., "Increasing Salt Rejection of Polybenzimidazole Nanofiltration Membranes via the Addition of Immobilized and Aligned Aquaporins" (2019). Chemical and Materials Engineering Faculty Publications. 72.