Selectively permeable biological membranes containing lipophilic barriers inspire the design of biomimetic carrier-mediated membranes for aqueous solute separation. The recovery of glucose, which can reversibly bind to boronic acid (BA) carriers, is examined in lipid pore-filled silica thin-film composite membranes with accessible mesopores. The successful incorporation of lipids (1,2-dipalmitoyl-sn-glycero-3-phosphocholine, DPPC) and BA carriers (4-((N-Boc-amino)methyl)phenylboronic acid, BAMP-BA) in the pores of mesoporous silica (∼10 nm pore diameter) through evaporation deposition is verified by confocal microscopy and differential scanning calorimetry. In the absence of BA carriers, lipids confined inside the pores of silica thin films (∼200 nm thick) provide a factor of 14 increase in diffusive transport resistance to glucose, relative to traditional supported lipid bilayers formed by vesicle fusion on the porous surface. The addition of lipid-immobilized BAMP-BA (59 mol % in DPPC) facilitates the transport of glucose through the membrane; glucose flux increases from 45 × 10 to 225 × 10 mol/m/s in the presence of BAMP-BA. Furthermore, the transport can be improved by environmental factors including pH gradient (to control the binding and release of glucose) and temperature (to adjust lipid bilayer fluidity). The successful development of biomimetic nanocomposite membranes demonstrated here is an important step toward the efficient dilute aqueous solute upgrading or separations, such as the processing of carbohydrates from lignocellulose hydrolysates, using engineered carrier/catalyst/support systems.
Redox probe transport through supported lipid bilayers and nanopore‐confined lipid assemblies on silica thin films is examined using electrochemical impedance spectroscopy (EIS). These supported lipid systems are emerging biomimetic separation and sensor platforms. The ability to quantify the accessibility of the pore structure of the mesoporous silica thin films is demonstrated, which is essential for the incorporation of carriers into the lipids for selective solute transport. Redox probe molecules with varying hydrophilicity are used to compare ion transport in supported lipid pore‐spanning bilayers (enveloped bilayers) and novel lipid filled pores of mesoporous silica thin films. The films feature orthogonally oriented 8–10 nm cylindrical nanopores formed by deposition of P123‐templated silica sols onto chemically modified fluorine‐doped tin oxide. Nanopore accessibility is confirmed by EIS with hydrophilic probe 1,1′‐ferrocenedimethanol (FDM). Filling the pores with lipid 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine results in a superior barrier (with roughly 1/9 the permeability) to transport of FDM compared to fragile enveloped lipid bilayers deposited by vesicle fusion. The pore‐confined lipids not only provide a better barrier to FDM, but also a better pathway for the transport across the films of a hydrophobic redox probe 1,1′‐dioctadecyl‐4,4′‐bipyridinium dibromide, with an ideal transport selectivity of 11 compared to FDM.
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