Adsorption of haematoporphyrins on the planar bilayer membrane

Adsorption of haematoporphyrin derivatives with different hydrophobicity of peripheral groups on planar bilayer lipid membrane (BLM) was studied in dark and upon illumination by visible light. It was shown that haematoporphyrin molecules adsorb on BLM as anions. The adsorption changed the boundary potential at the membrane/water interface, in particular, it altered potential in the diffuse part of the double layer outside the membrane and increased an additional unscreenable potential drop inside of it. Illumination decreased an absolute value of the negative potential drop due probably to the appearence of positive charge in the haematoporphyrin macrocycle. The adsorption of haematoporphyrins affect the BLM conductivity induced by different ionophores, which can be explained by changing the membrane structure. Haematoporphyrin derivatives with higher hydrophobicity adsorbed more deeply inside the membrane, caused more remarkable changes in its structure and displayed stronger photodynamic effect.