Hydrophobicity, topography in membranes and photosensitization of silicon phthalocyanines with axial ligands of varying lengths.
Six amphiphilic silicon phthalocyanines (SiPc's) axially linked to a dimethylated amino alkyl group of varying length have been examined for their potential suitability as photosensitizers for photodynamic therapy (PDT). This group of molecules was chosen because the length of the axial ligand might place the chromophoric part of the molecule at different vertical depths in the membrane and possibly affect the extent of membrane localized damage caused by singlet oxygen. We tested the relative penetration depth of the SiPc groups in the membrane by the extent to which their fluorescence was quenched by external iodide ions. We also measured singlet oxygen quantum yields of the SiPc's in a liposome membrane, using the fluorescent target for singlet oxygen, 9,10-dimethylanthracene. The hydrophobicity parameters, LogP, were calculated and were also measured. Some correlation was found between them and Kb's, the binding constants for liposomes. The effect of the axial ligand's length is less striking than in similar cases with hematoporphyrins and protoporphyrins. We link this smaller effect with a bending of the linker chain that enables, sterically, a better positioning of the sensitizer molecules within the ordered lipid layer structure.
Sholto
Alan
A
Department of Physics and Nano Medicine Research Center, Institute of Nanotechnology and Advanced Materials, Bar Ilan University, Ramat Gan, Israel.
Ehrenberg
Benjamin
B
D000873:Anthracenes / Q000737:chemistry; D001665:Binding Sites; D001667:Binding, Competitive; D005453:Fluorescence; D057927:Hydrophobic and Hydrophilic Interactions; D007211:Indoles / Q000737:chemistry* / Q000528:radiation effects; D007454:Iodides / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D007700:Kinetics; D007834:Lasers; D008024:Ligands; D008081:Liposomes / Q000737:chemistry*; D015394:Molecular Structure; D017646:Organosilicon Compounds / Q000737:chemistry* / Q000528:radiation effects; D010100:Oxygen / Q000737:chemistry; D010777:Photochemistry; D017319:Photosensitizing Agents / Q000737:chemistry* / Q000528:radiation effects; D011789:Quantum Theory; D012680:Sensitivity and Specificity; D012995:Solubility; D013050:Spectrometry, Fluorescence / Q000379:methods; D013056:Spectrophotometry, Ultraviolet / Q000379:methods
D000873:Anthracenes; D007211:Indoles; D007454:Iodides; D007477:Ions; D008024:Ligands; D008081:Liposomes; D017646:Organosilicon Compounds; D017319:Photosensitizing Agents; C082854:silicon phthalocyanine; C029126:9,10-dimethylanthracene; D010100:Oxygen