Porphyrin–phospholipid interaction and ring metallation depending on the phospholipid polar head type

The interaction between a hydrophobically modified 5,10,15,20-tetrakis(4-N-tetradecyl-pyridyl) porphyrin and three phospholipids: two negatively charged, DMPA (the sodium salt of dimyristoyl-sn-glycero-phosphatidyl acid) and DMPG (the sodium salt of 1,2-dimyristoyl-sn-glycero-3-[phospho-rac-(1-glycerol)]) and a zwitterionic DMPC (dimyristoyl-sn-glycero-phosphatidylcholine), were studied by means of surface pressure isotherms and spectroscopic methods. The interaction results in partial or total metallation of the porphyrin with zinc ions in the presence of negatively charged phospholipids, as attested by UV–vis and luminescence spectroscopy of the transferred films. In the presence of the zwitterionic phospholipid no insertion of zinc ion in the porphyrin ring is detected. These results are relevant for the understanding of photosensitizer-lipid-carrier binding for use in photodynamic therapy.

Graphical abstractMetallation of a hydrophobically modified 5,10,15,20-tetrakis(4-N-tetradecyl-pyridyl) porphyrin occurs in situ of Langmuir monolayers formed with DMPG; the metallation is partial with DMPA and does not occur for DMPC.Figure optionsDownload full-size imageDownload high-quality image (62 K)Download as PowerPoint slideResearch highlights► Mixed PyP/ phospholipids Langmuir monolayers ► Different phospholipids polar head ► Metallization of the porphyrinic ring takes place depending on the position of the negative charge at the phospholipid polar head and zinc ions accessibility