title: Effect of liposomal confinement on photothermal and photo-oximetric fluorescence lifetimes of photosensitizers with varying hydrophilicity.
abstract: The time-resolved fluorescence of photosensitizers (PSs) of varying hydrophobicities, di-and tetrasulfonated Al phthalocyanines (Al-2 and Al-4), and Photochlor (HPPH), was investigated in liposomes used as cell-mimetic models. Using frequency-and time-domain apparatus, the fluorescence lifetime, tau(fluo), was compared for PSs free in aqueous solution and in a liposome-associated state at varied temperatures (25 to 78 degrees C) and oxygen concentrations (0-190 microM). The analysis of tau(fluo) revealed different decay behaviors for the free-solution and liposome-confined PSs, most significantly for the lipophilic HPPH. Hydrophilic PS drugs (Al-4, Al-2) were less affected by the liposomal confinement, depending on the relative hydrophilicity of the compound and the consequent localization in liposomes. Changes in the emission decay due to confinement were detected as differences in the lifetime between the bulk solution and the liposome-localized PS in response to heating and deoxygenation. Specifically, hydrophilic Al-4 produced an identical lifetime trend as a function of temperature both in solu and in a liposome-confined state. Hydrophobic HPPH exhibited a fundamental transformation in its fluorescence decay kinetics, transitioning from a multiexponential (in free solution) to single-exponential (in liposome) decay. Deoxygenation resulted in a ubiquitous tau(fluo) increase for all PSs in free solution, while the opposite, a tau(fluo) decrease, occurred in all liposomal PSs.
authors.affiliation: National Optics Institute, Department of Biophotonics, 2740 Einstein St., Quebec, QC, Canada, G1P 4S4. ozzy.mermut@ino.ca
authors.forename: Ozzy
authors.initials: O
authors.lastname: Mermut
authors.forename: Isabelle
authors.initials: I
authors.lastname: Noiseux
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Bouchard
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Cormier
authors.forename: Patrice
authors.initials: P
authors.lastname: Desroches
authors.forename: Michel
authors.initials: M
authors.lastname: Fortin
authors.forename: Pascal
authors.initials: P
authors.lastname: Gallant
authors.forename: Sébastien
authors.initials: S
authors.lastname: Leclair
authors.forename: Marcia L
authors.initials: ML
authors.lastname: Vernon
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Diamond
authors.forename: Michael S
authors.initials: MS
authors.lastname: Patterson
mesh_terms: D004337:Drug Carriers / Q000737:chemistry*; D006358:Hot Temperature; D057927:Hydrophobic and Hydrophilic Interactions; D008027:Light; D008081:Liposomes / Q000737:chemistry*; D008422:Materials Testing; D010100:Oxygen / Q000737:chemistry*; D010777:Photochemistry / Q000379:methods; D017319:Photosensitizing Agents / Q000737:chemistry*; D012542:Scattering, Radiation
chemical_list: D004337:Drug Carriers; D008081:Liposomes; D017319:Photosensitizing Agents; D010100:Oxygen