An exhaustive study of a novel sulfur-linked adamantane tetrasubstituted zinc(II) phthalocyanine incorporated into liposomes

The lipophilic tetrasubstituted sensitizer 2,9(10),16(17),23(24)-tetrakis-(1-adamantylsulfanyl)phthalocyaninatozinc(II) (ZnPc) was incorporated into different liposomal formulations in order to evaluate its photophysical properties, as well as the size, incorporation efficiency, thermotropic properties and stability of liposomes during a time period. Liposomes were prepared by the thin-layer evaporation technique followed by hydratation with buffer at pH 7.4 and 0.15 M NaCl. Small unilamellar vesicles (SUV) were obtained after sonicating the mixture. Phthalocyanine was incorporated efficiently into all the liposomal formulations. The shape of ZnPc spectra depended on the environment. The S-PEG liposomal formulation showed the lowest aggregation value. The average diameter of liposomes with different lipid compositions varied from 49.70 ± 0.09 to 223.10 ± 0.36 nm, with significant differences between the various liposomal preparations. The inclusion of cholesterol (CHOL) and polyethylene glycol (PEG) on the lipid bilayer did not influence the size of the particles. The formulations with PEG increased the stability of liposomes for at least 9 months. After a long storage, the most stable formulations were those without CHOL. Singlet molecular oxygen values ranged between 0.10 and 0.26. These values were higher than other zinc(II) phthalocyanines incorporated into dimyristoyl phosphatidylcholine (DMPC) liposomes or Tween 80.

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► New lipophilic photosensitizer was incorporated into small unilamellar vesicles.
► The stability of liposomal formulations was improved by the addition of PEG.
► All liposomal formulations generated singlet molecular oxygen.
► The lowest aggregation value was obtained for S-PEG formulation.