Use of Liposomes as a Dispersed Pseudo-Stationary Phase in Capillary Electrophoresis of Basic Proteins

The suitability of liposome capillary electrophoresis for separating basic proteins at different pH values in the acidic domain was evaluated preparing liposomes consisting of large unilamellar vesicles (LUV) of the phospholipid 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine (POPC), whose hydrodynamic diameter and size distribution were evaluated by dynamic light scattering measurements. The study was conducted evaluating different approaches of performing liposome capillary electrophoresis of proteins, using liposomes dispersed in the electrolyte solution of different composition and pH values ranging from pH 6.2 to pH 4.0. The liposomes were employed as a pseudo stationary phase dispersed in the electrolyte solution, which was introduced into the capillary as a plug of volume equivalent to that of the capillary tube, whereas liposome-free electrolyte solutions were contained into the electrolyte vessels during electrophoresis. The study was performed with either bare fused-silica capillaries or capillaries previously treated with POPC that was employed as a dynamic coating agent. Such treatment was performed rinsing the capillary tube with a proper volume of electrolyte solution containing POPC and resulted in a significant reduction of the electroosmotic flow, indicative of the adsorptive behavior of liposomes onto the internal surface of bare fused-silica capillaries. The usefulness of using liposome dynamically coated capillaries for separating basic proteins in absence of the dispersed liposome pseudo stationary phase filled into the capillary prior to injecting the protein sample was evaluated too. The results show that the presence of liposomes reduced drastically the untoward interactions between basic proteins and the capillary wall, also in capillary not subjected to the dynamic coating process with POPC. In addition, the use of liposomes as a pseudo stationary phase dispersed in the electrolyte solution enhanced the separation of basic proteins also in POPC dynamically coated capillaries.