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

Abstract

The lipophilic tetrasubstituted sensitizer 2,9(10),16(17),23(24)-tetrakis-(1-adamantylsulfanyl)phthalocyaninatozinc(II) (ZnPc) was incorporated into different liposomal formulations in orderto evaluate its photophysical properties, as well as the size, incorporation efficiency, thermotropicproperties and stability of liposomes during a time period. Liposomes were prepared by the thin-layerevaporation technique followed by hydratation with buffer at pH 7.4 and 0.15 M NaCl. Small unilamellarvesicles (SUV) were obtained after sonicating the mixture. Phthalocyanine was incorporated efficientlyinto all the liposomal formulations. The shape of ZnPc spectra depended on the environment. The S-PEGliposomal formulation showed the lowest aggregation value. The average diameter of liposomes withdifferent lipid compositions varied from 49.70 ± 0.09 to 223.10 ± 0.36 nm, with significant differencesbetween 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 increasedthe stability of liposomes for at least 9 months. After a long storage, the most stable formulations werethose without CHOL. Singlet molecular oxygen values ranged between 0.10 and 0.26. These values werehigher than other zinc(II) phthalocyanines incorporated into dimyristoyl phosphatidylcholine (DMPC)liposomes or Tween 80