Phosphocholine (PC) lipid membranes exhibit polymorphic variances including the biologically relevant disordered fluid phase. The incorporation of cholesterol into such a fluid host membrane may readily induce a local ordered, named fluid-ordered, phase. Here, results are reported on the impact of a newly synthesized lipid consisting of a photo switchable molecule that was linked to a cholesterol base. An azobenzene derivative with cholesterol and ethylenediamine (AzCh) was synthesized according to established procedures , , with some slight modifications. The photosensitive AzCh switches its configuration between its cis and trans by absorption of UV and visible light (365nm / 440 nm). It was imbedded in a 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho¬choline (POPC) monolayer (ratio 6:1, POPC:AzCh) at the air/water interface of a Langmuir trough (Kibron Microtrough) for simultaneous compression and structure investigation. The trough was adopted to be mounted on the new liquid interfaces scattering apparatus (LISA) at the X-ray reflectivity beamline P08 (PETRA III, DESY, Hamburg, Germany). Reflectivity measurements (25 keV) were carried out under a flow of N2 and at an initial constant pressure of 20 mN/m. Measurements were done on the monolayer in the dark and during exposure to light. Preliminary results of the reflectivity curves give evidence of the structural details of the lipid monolayer. They indicate changes in the its organization by inoculation of the photosensitive molecules in the dark, and further structural modifications under illumination. In addition, the light induced changes are accompanied by related changes of the interfacial pressure.
switchable model membranes
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41st Danish Crystallographers Meeting & 4th DanScatt Meeting, 2011