title: Temperature-dependent in-plane structure formation of an X-shaped bolapolyphile within lipid bilayers.
abstract: Polyphilic compound B12 is an X-shaped molecule with a stiff aromatic core, flexible aliphatic side chains, and hydrophilic end groups. Forming a thermotropic triangular honeycomb phase in the bulk between 177 and 182 °C but no lyotropic phases, it is designed to fit into DPPC or DMPC lipid bilayers, in which it phase separates at room temperature, as observed in giant unilamellar vesicles (GUVs) by fluorescence microscopy. TEM investigations of bilayer aggregates support the incorporation of B12 into intact membranes. The temperature-dependent behavior of the mixed samples was followed by differential scanning calorimetry (DSC), FT-IR spectroscopy, fluorescence spectroscopy, and X-ray scattering. DSC results support in-membrane phase separation, where a reduced main transition and new B12-related transitions indicate the incorporation of lipids into the B12-rich phase. The phase separation was confirmed by X-ray scattering, where two different lamellar repeat distances are visible over a wide temperature range. Polarized ATR-FTIR and fluorescence anisotropy experiments support the transmembrane orientation of B12, and FT-IR spectra further prove a stepwise "melting" of the lipid chains. The data suggest that in the B12-rich domains the DPPC chains are still rigid and the B12 molecules interact with each other via π-π interactions. All results obtained at temperatures above 75 °C confirm the formation of a single, homogeneously mixed phase with freely mobile B12 molecules.
authors.affiliation: Institut für Chemie - Physikalische Chemie and ‡Institut für Chemie - Organische Chemie, Martin-Luther-Universität Halle-Wittenberg , D-06120 Halle (Saale), Germany.
authors.forename: Bob-Dan
authors.initials: BD
authors.lastname: Lechner
authors.forename: Helgard
authors.initials: H
authors.lastname: Ebert
authors.forename: Marko
authors.initials: M
authors.lastname: Prehm
authors.forename: Stefan
authors.initials: S
authors.lastname: Werner
authors.forename: Annette
authors.initials: A
authors.lastname: Meister
authors.forename: Gerd
authors.initials: G
authors.lastname: Hause
authors.forename: André
authors.initials: A
authors.lastname: Beerlink
authors.forename: Kay
authors.initials: K
authors.lastname: Saalwächter
authors.forename: Kirsten
authors.initials: K
authors.lastname: Bacia
authors.forename: Carsten
authors.initials: C
authors.lastname: Tschierske
authors.forename: Alfred
authors.initials: A
authors.lastname: Blume
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D002462:Cell Membrane / Q000737:chemistry; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D008051:Lipid Bilayers / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D011108:Polymers / Q000737:chemistry*; D013696:Temperature
chemical_list: D008051:Lipid Bilayers; D011108:Polymers; D015060:1,2-Dipalmitoylphosphatidylcholine; C041325:polyphenylene sulfide; D004134:Dimyristoylphosphatidylcholine