Evaluation of Meta-tetra (Hydroxyphenil)chlorin incorporation into lipid bilayer

This work deals with the study of localization of photosensitizer meta-tetra (hydroxyphenil)chlorin (mTHPC) in structured lipid membranes. Unilamellar vesicles (ULV) of egg lecithin were used as a model to study the incorporation of mTHPC into lipid bilayer. Two types of ULV were prepared by sonication of phospholipids dispersion. The first contained mTHPC introducted into lipid before sonication and the second was added with mTHPC after sonication. Fluorescence quenching data obtained at 30 ºC by using KI as a membrane impermeable quencher of the porphyrin fluorescence were analyzed by the modified Stern-Volmer equation. According to the obtained results above 90% of mTHPC molecules embedded into lipid vesicles were inaccessible for the quencher. This finding confirms strongly the deep penetration of mTHPC into rigid hydrophobic regions of membrane bilayer. When mTHPC was introducted into suspension of ready ULV much more pigment molecules located on the membrane surface and were treated by quencher. Measurements of quenching characteristics in different intervals showed that in this case it took much time to reach equilibrium distribution of mTHPC in lipid vesicles.