Physicochemical properties of the soluble porphyrin tetrakis-(4-N-methylpyridyl)-porphine encapsulated in large unilamellar vesicles

Large unilamellar vesicles (LUV) formed by egg phosphatidylcholine (PC) and cholesterol (CL), and containing encapsulated soluble porphyrin H2TMpyP-4 were characterized and studied by light-scattering, freeze-fracture electron microscopy and fluorescence spectroscopy. The inclusion of CL produces a remarkable increase in LUV size (average size about 120 nm) and the number of porphyrin molecules entrapped by vesicles. Relaxation effects observed in porphyrin-loaded LUV have been attributed to the interaction between encapsulated H2TMpyP-4 molecules and the liposome membrane, a finding confirmed by fluorescence-emission spectroscopy. This technique also demonstrates the stability and integrity of LUV subjected to electrical discharges. Porphyrin-loaded LUV scatter light four times less than empty vesicles, a phenomenon attributed to a disturbance in lipid bilayer structure.