Massimo Pizzichini

Non-isothermal potential of phospholipid bilayer films Influence of cholesterol and macrocyclic carrier effects

The effect of cholesterol on the ion selective behavior of phoshpolipid (phosphatidylcholine or phosphatidylethanolamine) bilayer films is studied through the measurement of the membrane non-isothermal potential. It is shown how the mixed phosphatidylcholine-cholesterol membrane can be either cation of anion permselective according to the film composition (cationic behavior is met in the 0--10% cholesterol composition range while anionic selectivity appears in the 20--50% range). On the contrary, mixed phosphatidylethanolamine-cholesterol membranes show the absence of ionic selectivity already met with pure phosphatidylethanolamine films. The presence of a cationic carrier as Dibenzo-18-crown-6 in the film transforms all the studied films (cationic, anionic and no selective bilayers) into ideally cationic selective membranes. These results are discussed on the basis of the current ideas on the charge distribution through the bilayer membranes. Moreover, the role of the permeating ions as potential determining species is stressed.

Performance of a hollow fibre membrane unit in oxygen-enriched air production

Abstract The performance of a pilot test for biogas upgrading has been tested under different process conditions to produce oxygen-enriched air for aqueous media application. The selectivity of the polysulfone hollow fibres for N 2 O 2 permeation allows the production of an oxygen-enriched air stream in the 30–50% range and an inert gas (nitrogen between 82–98%) by operating the pilot unit at different stage-cut values in a single pass mode. Membrane area requirements for a medium size plant of 100 Nm3 h−1 are discussed according to a simple perfect mixing model for gas permeation.

Cation and anion responses of zwitterion phospholipid bilayers

Abstract The electrochemical behavior of zwitterion phospholipid bilayers as determined with the help of membrane potential data, is examined. The synthetic DL-β,γ-dipalmitoyl-α-phosphatidylcoline bilayer shows at 30°C nernstian and sub-nernstian anion responses which depend on the cation present in the electrolytes (LiCl, NaCl, KCl, CsCl, CaCl2, CeCl3), and in some cases on the concentration of the solutions considered. On the other hand, nernstian cation responses have been observed in non-isothermal membrane-potential measurements performed on the same lipidic films. These experimental results are explained on the assumption that, from a potentiometric viewpoint the phospholipid membrane behaves as a neutral carrier membrane electrode. Accordingly, the form of the potential equations, and then the anion response of the bilayer, follows from the chemistry of the phospholipid molecules.

402 - Lecithin-cholesterol-cation interactions in mixed lipid cholesterol liposomes

Abstract Electrophoretic mobilities of mixed phosphatidylcholine-cholesterol liposomes formed in KCl solution show a ξ potential minimum at a lecithin-cholesterol 2 : 1 molar ratio. This minimum does not depend on the electrolyte concentration. Shielding of the lipidic negative charged phosphoric group with complexing cations (Ca2+, Ce3+) prevents the occurrence of the electrophoretic minimum. It is suggested that a specific 2 : 1 phospholipid-cholesterol association can be responsible for the observed behavior.

Recovery by Ultrafiltration of a Commercial Enzyme for Cellulose Hydrolysis

Abstract An enzymatic process of cellulose hydrolysis based mainly on the use of membrane techniques is under study. The proposed flow sheet assumes that during cellulose hydrolysis the enzyme is continuously separated from glucose and cellobiose and is recycled in the cellulose reaction vessel by membrane ultrafiltration. The ultrafiltration of Celluclast enzyme by Novo is performed in a DDS column module assembled with flat polysulfone membranes. Membrane polarization effects are studied in the 0.1–5% w/v enzyme concentration range under varying pressures up to 600 kPa. A partial loss of enzymatic activity is observed as a consequence of the ultrafiltration and membrane washing operations.

Temperature dependence of membrane potential and surface pressure of bilayers and monolayers of dipalmitoylphosphatidylcholine

Abstract The temperature effects on the membrane potential of bilayers made from synthetic dl -β-γ-di-palmitoyl-α-phosphatidylcholine in NaCl and CaCl2 solutions are measured and the membrane selectivity variation is discussed. An evaluation of the activation energies of the membrane-potential-determining process is performed and the calculated values are compared with data obtained from surface pressure measurements, at different temperatures, of monolayers of the same phospholipid formed on NaCl and CaCl2 solutions of variable concentrations (10−3 −2 M).