Steady state and time-resolved spectroscopic studies on zinc(II) phthalocyanine in liposomes.
Zinc(II) phthalocyanine (ZnPc), a potential second-generation phototherapeutic agent for tumours, has been incorporated into small unilamellar vesicles (SUVs) (diameter, 52 nm) and large unilamellar vesicles (LUVs) (diameter, 84 nm) of dipalmitoyl-phosphatidylcholine (DPPC). Absorption spectroscopy, as well as steady state and time-resolved fluorescence emission studies, indicate that ZnPc is monomeric in SUVs at a stoichiometric concentration below 0.25 microM (corresponding to an actual endoliposomal concentration of about 0.5 mM), while in LUVs it is monomeric below 2 microM. The fluorescence lifetime of the monomer is 3-3.5 ns. Upon increasing the ZnPc concentration, aggregated derivatives are formed, which are characterized by shorter fluorescence lifetimes (1.2-1.5 ns; 0.4-0.6 ns). The possible implications of these observations for the phototherapeutic efficiency of ZnPc are briefly discussed.
Valduga
G
G
Department of Biology, University of Padova, Italy.
Reddi
E
E
Jori
G
G
Cubeddu
R
R
Taroni
P
P
Valentini
G
G
D015060:1,2-Dipalmitoylphosphatidylcholine; D007211:Indoles / Q000737:chemistry*; D054833:Isoindoles; D007700:Kinetics; D008081:Liposomes; D009942:Organometallic Compounds / Q000737:chemistry*; D013050:Spectrometry, Fluorescence / Q000379:methods; D013053:Spectrophotometry / Q000379:methods; D013997:Time Factors; D015032:Zinc / Q000737:chemistry*; D017967:Zinc Compounds
D007211:Indoles; D054833:Isoindoles; D008081:Liposomes; D009942:Organometallic Compounds; D017967:Zinc Compounds; C052159:Zn(II)-phthalocyanine; D015060:1,2-Dipalmitoylphosphatidylcholine; D015032:Zinc