The effect of photochromic 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene on liposome permeability

The main objective of this research is to develop a photosensitive supramolecular assembly by incorporating a photochromic compound into the lipid bilayer of a liposome. Photoinduced changes in the structure of this compound was expected to affect the membrane permeability of liposome to afford selective release of encapsulated compounds.;To study changes in membrane permeability, a fluorophore-quencher pair, 8-hydroxypyrene-1,3,6-trisulfonic acid and p-xylene-bis-pyridinium bromide (HPTS-DPX) was encapsulated inside large unilamellar vesicles (LUVs) composed of DPPC. Membrane permeability was correlated with an increase in the emission of HPTS as it diffuses from the interior of the liposome into bulk aqueous solution where it is relatively free from quenching. In these studies, DPPC containing 1 and HPTS with its controls at a mole ratio of 1:DPPC at 1:3 were prepared. The irradiation studies were performed by photocycling 1 between the opened (1o ) and closed (1c) ring isomers with exposure to ultraviolet (UVA) and visible (Vis) light. The net change in fluorescence intensity of HPTS due solely to isomerization of 1 in lipid bilayer was determined after a series of corrections and comparisons with the controls. In addition, the percentage release of HPTS was calculated based on the 100% release of encapsulated HPTS, which was determined by the addition of a lipid soluble surfactant Triton X-100 to lyse the liposome membrane. From these studies, an increase in the fluorescence intensity of HPTS was not observed. As a result, we conclude that the photoisomerization of 1 does not have a large effect on the membrane permeability of DPPC LUVs. In addition, the large standard deviations suggest that we are approaching the detection limits of our experimental setup. One possible reason for why significant increases in membrane permeability were not observed is that the size of 1 is relatively small compared to the thickness of bilayer. As well, without a complementary lipid structure, 1 may lack the well-defined organization within the span of bilayer that would lead to a larger disruption in the local lipid order. In addition, the change in molecular structure accompanying the isomerization of 1 is potentially not large enough to disrupt the packing of the lipids within the bilayer, which may be necessary for large changes in membrane permeability.;A photochromic compound, 1,2-bis(2-methyl-5-phenyl-3-thienyl) perfluorocyclopentene (1) was synthesized. The inclusion of 1 in a lipid bilayer of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and conservation of its photochromism were studied using differential scanning calorimetry (DSC) and absorption spectroscopy, respectively. From our DSC studies, a slight decrease of Tm and increase of DeltaT 1/2 were observed with increasing concentration of 1 in DPPC multilamellar vesicles (MLVs). Compared to MLVs of pure DPPC, a shift of the pretransition to lower temperature and its relative disappearance were observed for MLV samples containing 1. These results suggest that 1 is located in the C2-C8 methylene region of the lipid hydrocarbon chains.