title: Planar Bilayer Measurements of Alamethicin and Gramicidin Reconstituted in Biomimetic Block Copolymers.
abstract: This work explores methods for forming and characterizing biomimetic planar membranes composed of amphiphilic block copolymers. The membranes are diblocks and triblocks with hydrophilic blocks of poly(2-methyl-2-oxazoline) (PMOXA) and hydrophobic blocks of poly(dimethylsiloxane) (PDMS). Experiments with the lipid diphytanoyl phosphocholine (DPhPC) serve as a basis for comparison with the polymeric membranes. Phase-contrast microscopy is used to study how membranes evolve over time after their formation. Capacitance measurements as a function of the thinned membrane area (prepared from two separate solvent systems) are performed to clarify the importance of the Plateau-Gibbs border in electrical measurements. Finally, functional reconstitution of the two ion channels, alamethicin and gramicidin, is investigated. Imaging in transmitted phase-contrast mode provides visualization of thinned regions that contain monolayers or bilayers (in the case of diblock copolymer). The specific capacitance measurements yield 0.28 μF/cm2with a corresponding thickness of 8.5 nm for PMOXA6-PDMS35-PMOXA6(blocks of 6 PMOXA and 35 PDMS repeat units) formed from a solution of ethanol-decane, 0.55 μF/cm2and 4.4 nm in chloroform-toluene, and 0.46 μF/cm2and 5.4 nm for the diblock PMOXA6-PDMS17in ethanol-decane. Alamethicin reconstitution in the block copolymers shows slower channel-forming kinetics with somewhat higher conductance values than found in DPhPC. Gramicidin in the block copolymer shows a slightly voltage-dependent conductance as a function of time, with little stochastic conductance state switching, in contrast to reconstitution in DPhPC where gramicidin switches states at ∼3 Hz.
authors.affiliation: Department of Chemical Engineering, University of Louisville , Louisville, Kentucky 40292, United States.
authors.forename: Michael
authors.identifier: 0000-0003-3395-3572
authors.initials: M
authors.lastname: Martin
authors.affiliation: Department of Chemical Engineering, University of Louisville , Louisville, Kentucky 40292, United States.
authors.forename: Timothy
authors.initials: T
authors.lastname: Dubbs
authors.affiliation: Department of Chemical Engineering, University of Louisville , Louisville, Kentucky 40292, United States.
authors.forename: J R
authors.initials: JR
authors.lastname: Fried