Plasma Membrane Associated Location of Sulfonated meso-Tetraphenyl-porphyrins of Different Hydrophilicity Probed by Total Internal Reflection Fluorescence Spectroscopy

Abstract Sulfonated meso-tetraphenylporphyrins of different hydrophilicity were microspectrofluorimetrically examined in endothelial cells using total internal reflection (TIR) illumination or epi-illumination. Since the penetration depth of the evanescent field during TIR illumination is limited to a few hundred nanometers, photosensitizers were almost selectively examined in close vicinity to the plasma membrane. Pronounced fluorescence signals during TIR illumination were observed for the hydrophilic compounds meso-tetraphenylporphyrin tetrasulfonate (TPPS4) and meso-tetraphenylporphyrin trisulfonate (TPPS3), whereas the more lipophilic compounds meso-tetraphenylporphyrin disulfonate (TPPS2a) and meso-tetraphenylporphyrin monosulfonate (TPPS1) could only be detected under epi-illumination. Irradiation of TPPS1 and TPPS2a in the Soret band led to an increase in fluorescence intensity and formation of a photoproduct with an emission maximum around 610 nm, which was limited to intracellular compartments. ...