No abstract

We consider the influence of the molecular structure of phospholipid membranes on their dielectric properties in the radio frequency range. Membranes have a stratified dielectric structure on the submolecular level, with the lipid chains forming a central hydrophobic layer enclosed by the polar headgroups (HGs) and bound water layers. In our numerical model, isotropic permittivities of 2.2 and 48.8 were assigned to the lipid chain and bound water layers, respectively. The HG region was assumed to possess an anisotropic static permittivity with 142.2 and 30.2 in the tangential and normal directions, respectively. The permittivities of the HG and bound water regions have been assumed to disperse at frequencies around 51 and 345 MHz to become 2.2 and 1.8, respectively, in both the normal and tangential directions. Electric field distribution and absorption were calculated for phospholipid vesicles with 75 nm radius as an example. Significant absorption has been obtained in the HG and bound water regions. Averaging the membrane absorption over the layers resulted in a decreased absorption below 1 GHz but a more than 10-fold increase above 1 GHz, compared to a model with a homogeneous membrane of averaged properties. We propose single particle dielectric spectroscopy by AC electrokinetics at low-bulk medium conductivities for an experimental verification of our model.

Nuclear magnetic resonance (NMR) spectroscopy and steady-state fluorescence anisotropy were used to study the behavior and interaction of 5-fluorouracil, both in a free form (5FU) and included in the polymer matrix of poly(butylcyanoacrylate) nanoparticles (5FUPBCN) with a phospholipid bilayer of large unilammellar vesicles composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), as a model system of biomembranes. The results confirm an interaction and penetration of 5FU into the phospholipid bilayer of DMPC liposomes. Different mechanisms of drug transfer from the aqueous environment into the model membrane environment, for the free drug and that incorporated into polymer nanoparticles, are suggested: (i) concentration-dependent reversible diffusion of the free 5FU and (ii) sustained 5FU release from nanoparticles adsorbed on the liposome surface resulting in continuous delivery of the drug into the phospholipid bilayers of the DMPC liposomes.