Activating the Surface: A Study on Lipid Chirality, and Its Potential Function for Triggering Interfacial Interaction

Usually chiral species are obtained as racemic mixture upon their chemical synthesis. Not so in bio-synthesis: the ingredient molecules of the bio-machinery that were selected in biological evolution mostly consist of only one enantiomer, apparently depending on the functional role of the molecular unit. One abundant example is the lipid system, the major compound of all biomembranes. Its glycerol backbone with the fatty acid chains is in all L-α-form, turning the hydrophilic-hydrophobic membrane interface into a chiral interaction platform. The chirality of lipid was established as the origin of the liquid-condensed domains in monolayers, with their shapes varying upon the detailed composition, and their crystallographic symmetry being different for the enantiomers, their mixtures, and the racemic system. Adsorption at the interface is thus most probably sensitive to chirality and may have a significant biological impact for unspecific bilayer binding: the adsorption and insertion of a small chiral compound may vary depending on its symmetry. This effect may propagate into the chain region, changing the state there. Here we report on preliminary results involving membranes from mixtures of the enantiomers of DPPC as a test system. Studies include physico-chemical properties of the chiral lipid membrane, its structure, and its dynamics. Methods applied were calorimetry, Langmuir compression, neutron diffraction, and quasielastic neutron scattering. The results from the project shall provide fundamental insight on the chiral system as is, but also serve as a benchmark tools for future studies on chiral recognition at bilayer surfaces, namely the interaction of chiral drugs with biomembranes