Preparation of Giant Vesicles Exhibiting Visible-light-induced Morphological Changes

We describe the preparation of giant vesicles that incorporate a photoresponsive ruthenium complex having two alkyl chains. The vesicles exhibited morphological changes when exposed to visible light. The ruthenium complex proximal-[Ru(L1)(L2)OH₂](NO₃)₂, proximal-2 (L1 is 4'-decyloxy-2,2';6',2"-terpyridine, L2 is 2-(2'-(6'-decyloxy)-pyridyl)quinoline) was prepared by a thermal reaction of Ru(L1)Cl₃ and L2, followed by removal of a chloride ligand. In an aqueous solution and vesicle dispersions, proximal-2 was reversibly photoisomerized to the distal isomer. Giant vesicles containing proximal-2 were prepared by hydration of phospholipid films containing proximal-2 in the dark at 80 °C. Giant vesicles were frequently found in the dispersions prepared from DOPC/proximal-2 rather than from DPPC/proximal-2 (DOPC is 1,2-dioleoyl-sn-glycero-3-phosphocholine, DPPC is 1,2-dipalmitoyl -sn-glycero-3-phosphocholine). The ratio of proximal-2 and DOPC in the vesicle preparation was varied from 5:100 to 20:100. The light-induced morphological changes were observed for proximal-2/DOPC in the presence of Na₂SO₄. However, they were highly suppressed in the presence of NaOH. Incubation of light-exposed vesicles at 45 °C in the dark induced reverse morphological changes. Morphological changes were observed under fluorescence microscopy using 635 nm (red) light. Rhodamine-DOPC [rhodamine-DOPC: 1,2-dioleoyl-sn-glycero-3-phos-phoethanolamine-N-(lissamine rhodamine B sulfonyl)] was used to fluorescently label the vesicles.