LIPOSOMES CONTAINING PURINE AND PYRIMIDINE-BASES - STABLE UNILAMELLAR LIPOSOMES FROM PHOSPHATIDYL NUCLEOSIDES

With the aim of investigating the behavior of liposomes bearing nucleic acid bases in their double-layered spherical structure, 5'-(1-palmitoyl-2-oleoyl-sn-glycero(3)phospho)cytidine (1) and 5'-(1-palmitoyl-2-oleoyl-sn-glycero(3 )phospho)inosine (2) have been synthesized and unilamellar liposomes have been prepared by extrusion of a slightly alkaline aqueous lipid dispersion through polycarbonate membranes. The liposomes were characterized by electron microscopy, dynamic light scattering (LS), and circular dichroism (CD) spectroscopy. LS studies showed that the liposomes are monodisperse; those from 1 remained stable for over one week, the liposomes from 2 alone are less stable, whereas liposomes of equimolar mixtures of 1 and 2 are again characterized by a good stability. CD studies of liposomes of 1 showed a positive Cotton effect in the region of the cytidine absorption, and the significant differences with respect to the spectrum of cytidine monophosphate are seen as a result of the supramolecular structure of the liposomes. More in general, this study shows that it is possible to insert complementary purine and pyrimidine nucleosides into the spherical organization of liposomes.