B.-D. Lechner, H. Ebert, M. Prehm, S. Werner, A. Meister, G. Hause, A. Beerlink, K. Saalwächter, K. Bacia, C. Tschierske, A. Blume.
Temperature-Dependent In-Plane Structure Formation of an
X‑Shaped Bolapolyphile within Lipid Bilayers.
Langmuir 31, 2839-2850 (2015).
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.